![hæmorrhages are said to be observed only in vertex presentations. The
more common supratentorial hæmorrhages—usually resulting from
difficult breech presentations—either remain more or less localized to a
certain region of the cortex, or become widely diffused over the surface
and base of the brain.
It is probable that Cushing is correct in his observations with
respect to the source of these supratentorial hæmorrhages. He states
that the blood is derived from one or more radicles of the superior
longitudinal sinus, especially from those veins which, in their upward
passage in the sulci of the brain, leave their cerebral beds for a short
and comparatively unprotected course, immediately previous to their
entry into the lacunæ laterales of the superior longitudinal sinus.
In addition, he points to the very important fact that the localized
hæmorrhages are commonly situated in relation to the mid-cerebral
cortex, close to the sinus, and on one or both sides of the falx cerebri.
In addition, therefore, to the symptoms of general cerebral compression,
certain definite localizing symptoms are to be observed, these being in
direct proportion to the size of the clot.
In an analysis of 74 autopsies on infants still-born or dying within
the first few days, Archibald[11] found ‘intrameningeal’ hæmorrhage in
32, in 19 of which it was of considerable extent: and in 5 others there
was extra-dural hæmorrhage. In only two or three was effused blood
found within the cerebral cortex. The importance of these facts from a
surgical point of view cannot be over-estimated.](https://image.slidesharecdn.com/5338-250412154154-46cb1862/85/AOP-in-NET-Practical-Aspect-Oriented-Programming-Matthew-D-Groves-38-320.jpg)
![Treatment.
transmitting its pedicle. On the other hand, the tumour may become separated
from the skin by bone; it would then project on the inner surface or between the
layers of the dura mater. If this view of the origin of dermoids be accepted, we
must modify our teaching and say that the depressions in which dermoids of the
cranium are lodged arise as imperfections in the developmental process, and are
not due to absorption induced by pressure; further, the fibrous connexion of such
dermoids with the dura mater is primary, not accidental.’[12]
When of inconsiderable size, and when intracranial
connexions are absent, of doubtful existence, or of slight extent, the
sooner the tumour is removed the better. The dura mater should not
be opened unless absolutely necessary, in which case it should be
carefully sewn up and the scalp-flap replaced without drainage.
When possessing deep and extensive connexions, careful
dissection may still allow of the complete removal of the dermoid. It
is impossible to foretell with certainty whether it is possible to
remove the tumour until its basal portion is exposed. The operation
may be a formidable one.
Some points in the differential diagnosis between
Cephaloceles, Dermoids, and Cephalhæmatomata
Cephaloceles (congenital). Dermoids. Cephalhæmatomata.
Present at birth. Present at birth. Usually appears after
birth.
In middle line, especially
over occiput and base
of nose.
In middle line, especially
over anterior fontanelle.
Always to one side of the
middle line, and usually
over the parietal bone.
Firm or fluctuating. Firm. Fluctuation over central
part only.
Perhaps translucent. Not translucent. Not translucent.
Perhaps pulsates. Does not pulsate. Does not pulsate.
Perhaps reducible, in
whole or in part.
Irreducible. Very slightly, if at all.
Perhaps swells up on
straining.
No alteration. Very slightly, if at all.
Perhaps associated with
cerebral symptoms.
No cerebral symptoms. No cerebral symptoms.](https://image.slidesharecdn.com/5338-250412154154-46cb1862/85/AOP-in-NET-Practical-Aspect-Oriented-Programming-Matthew-D-Groves-43-320.jpg)
![Congenital internal hydrocephalus.
Gap in skull felt. Depression in bone
common, actual gap
comparatively rare.
Deceptive raised margin,
no actual central
depression.
HYDROCEPHALUS
The conditions that lead up to internal hydrocephalus are
classified by Parkes Weber[13] in the following manner:—
1. ‘Cases secondary to and part of the phenomena of
tuberculous or any suppurative meningitis, comparable to pleural
effusions due to tuberculous or any septic invasions of the pleura.
2. Cases resulting from the presence of tumours, &c., analogous
to the pleuritic effusions accompanying tumours, &c., situated close
to or involving the pleura.
3. Ordinary infantile or congenital hydrocephalus, which is, in
some cases at least, due to intra-uterine meningitis.
4. Internal hydrocephalus supervening on the epidemic or
sporadic type of posterior basic non-suppurative meningitis.
6. Simple idiopathic internal hydrocephalus of adults or older
children due to serous ependymitis or ventricular meningitis.
7. Traumatic cases.’
This classification possibly includes all the various grades and
degrees of internal hydrocephalus, but for all practical purposes the
cases may be grouped into two classes, congenital and acquired,
both of which may be either acute or chronic.
The condition may be
recognized soon after the birth of the child, or the enlargement of
the head may only become apparent some weeks or months later.
The slow development and the insidious nature of the enlargement,
as observed in many cases, may lead to some confusion between
the late congenital and the early acquired varieties. However, the
absence of any symptoms pointing to meningeal inflammation
between the time of the birth of the child and the hydrocephalic
development usually allows of correct classification.
It is doubtful whether congenital internal hydrocephalus can be
ascribed to malformation of the inter-ventricular channels and](https://image.slidesharecdn.com/5338-250412154154-46cb1862/85/AOP-in-NET-Practical-Aspect-Oriented-Programming-Matthew-D-Groves-44-320.jpg)
![less obliterated, distinction between the white and grey matter may
be lost, the ventricular spaces are enormously dilated, and, in the
most marked cases, a mere shell of brain may intervene between
the ventricles and the surface of the brain.
This cerebral compression results in the development of two
main groups of symptoms, those referable to the general increase in
the intraventricular pressure and those due to regional compression.
The more general results are headache, vomiting, optic neuritis
and atrophy, slow pulse-rate, somnolence, and coma. The
temperature is variable, more commonly rising during the more
acute stages of the disease, and falling to normal or subnormal
during the quiescent periods.
Localizing features are to be found in squints, inequality of
pupils, retraction of the head and neck, dyspnœa, and dysphagia,
whilst compression of the cortical motor centres is evidenced by
twitchings, convulsions, and spasticity of the limbs. General
convulsions are by no means uncommon. Remissions and
intermissions of both local and general symptoms are frequently
observed, paralyses, for example, fluctuating in depth and character.
B. The bones comprising the vault of the skull become greatly
thinned and widely separated from one another, the fontanelles
enlarged, and the sutures unduly prominent. The head becomes
enlarged in all directions, and its increased weight renders the child
incapable of retaining postural control, the head being top-heavy
and falling about in all directions.
The bones of the base share in the deformity. The pressure
exerted on the orbital plates of the frontal bone force the globe in
the downward direction in such a manner that the infra-corneal
sclerotic is obscured by the lower lid, whilst the supra-corneal
portion is unduly prominent. The bony eminences in the region of
the sella turcica are diminished in size, the middle fossa of the skull
flattened from side to side, and the posterior fossa from before
backwards. In such cases the skull assumes an almost dolicocephalic
appearance. In any case, the disproportion between the enlarged
skull and diminutive face is a marked feature.[14]](https://image.slidesharecdn.com/5338-250412154154-46cb1862/85/AOP-in-NET-Practical-Aspect-Oriented-Programming-Matthew-D-Groves-46-320.jpg)
![Treatment. Indications for operation.
Lumbar puncture
Operation.
Ventricular puncture.
Through the anterior fontanelle.
The scalp becomes stretched, hairs are sparse and brittle, and
the veins dilated.
The results obtained by
operation for internal hydrocephalus are not sufficiently encouraging
to enable the surgeon to urge immediate operative treatment.[15]
Still, it is perfectly clear that he cannot possibly carry out surgical
treatment with benefit to the patient if the ventricular distension is
allowed to progress to such a degree that marked cortical flattening
and degeneration occurs. No fixed probationary period can be laid
down as a guide, each case must be judged on its own merits.
Special attention should be paid, however, to the disks and lower
extremities. Any suggestion of optic neuritis or spasticity should be
regarded as urgently demanding operative interference.
cannot be expected to confer other than
temporary benefit even under the most favourable circumstances,
whilst, in the event of interference in the normal communication
between the ventricular and cerebro-spinal spaces, no relief can be
anticipated. Connal recommends that lumbar puncture should be
carried out daily, or twice daily, over extended periods of time. This
operation, however, is by no means devoid of danger, and the results
obtained by such treatment are not at all satisfactory.
Operations are carried out (a) with the object of
withdrawing fluid from the distended ventricular cavities (ventricular
puncture), and (b) to establish a communication, or short-circuit,
between the ventricular space and other spaces (ventricular
drainage).
This operation may be carried out through
the anterior fontanelle, through the frontal bone, or over the
descending cornu of the lateral ventricle.
The region of the fontanelle is
shaved and cleansed in the usual manner, after which the
surrounding parts are cut off from the field of operation by a large
sheet of gauze or lint, in which a hole is cut sufficing to allow of
exposure of the site of election for puncture.
The patient should be in the recumbent position, the head well
towards the end of the table. The operation is performed without an](https://image.slidesharecdn.com/5338-250412154154-46cb1862/85/AOP-in-NET-Practical-Aspect-Oriented-Programming-Matthew-D-Groves-47-320.jpg)
AOP in NET Practical Aspect Oriented Programming Matthew D. Groves
- 1. AOP in NET Practical Aspect Oriented Programming Matthew D. Groves pdf download https://ebookfinal.com/download/aop-in-net-practical-aspect- oriented-programming-matthew-d-groves/ Explore and download more ebooks or textbooks at ebookfinal.com
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- 5. AOP in NET Practical Aspect Oriented Programming Matthew D. Groves Digital Instant Download Author(s): MatthewD. Groves ISBN(s): 9781617291142, 1617291145 Edition: Pap/Psc File Details: PDF, 9.47 MB Year: 2013 Language: english
- 6. M A N N I N G Matthew D. Groves FOREWORD BY Phil Haack Practical Aspect-Oriented Programming
- 7. AOP in .NET
- 9. AOP in .NET PRACTICAL ASPECT-ORIENTED PROGRAMMING MATTHEW D. GROVES M A N N I N G SHELTER ISLAND
- 10. For online information and ordering of this and other Manning books, please visit www.manning.com. The publisher offers discounts on this book when ordered in quantity. For more information, please contact Special Sales Department Manning Publications Co. 20 Baldwin Road PO Box 261 Shelter Island, NY 11964 Email: orders@manning.com ©2013 by Manning Publications Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in the book, and Manning Publications was aware of a trademark claim, the designations have been printed in initial caps or all caps. Recognizing the importance of preserving what has been written, it is Manning’s policy to have the books we publish printed on acid-free paper, and we exert our best efforts to that end. Recognizing also our responsibility to conserve the resources of our planet, Manning books are printed on paper that is at least 15 percent recycled and processed without the use of elemental chlorine. Manning Publications Co. Development editors: Frank Pohlmann, Cynthia Kane 20 Baldwin Road Technical proofreader: Javier Lozano PO Box 261 Copyeditor: Nancy Kotary Shelter Island, NY 11964 Proofreader: Elizabeth Martin Typesetter: Dottie Marsico Cover designer: Marija Tudor ISBN 9781617291142 Printed in the United States of America 1 2 3 4 5 6 7 8 9 10 – MAL – 18 17 16 15 14 13
- 11. To my children Matthew and Emma I will never grow tired of your yelling, “Daddy, Daddy!” and tackling me when you hear the creak of my office door.
- 13. vii brief contents PART 1 GETTING STARTED WITH AOP.......................................1 1 ■ Introducing AOP 3 2 ■ Acme Car Rental 21 PART 2 THE FUNDAMENTALSOF AOP ......................................53 3 ■ Call this instead: intercepting methods 55 4 ■ Before and after: boundary aspects 79 5 ■ Get this instead: intercepting locations 115 6 ■ Unit testing aspects 141 PART 3 ADVANCED AOP CONCEPTS .......................................169 7 ■ AOP implementation types 171 8 ■ Using AOP as an architectural tool 191 9 ■ Aspect composition: example and execution 213
- 15. ix contents foreword xiii preface xv acknowledgments xvii about this book xix PART 1 GETTING STARTED WITH AOP .......................... 1 1 Introducing AOP 3 1.1 What is AOP? 4 Features 4 ■ Benefits 8 ■ AOP in your daily life 13 1.2 Hello, World 14 1.3 Summary 19 2 Acme Car Rental 21 2.1 Start a new project 22 Business requirements 23 ■ Necessary nonfunctional requirements 24 2.2 Life without AOP 24 Write the business logic 25 ■ Testing the business logic 28 Add logging 29 ■ Introducing defensive programming 31 Working with transactions and retries 32 ■ Handling exceptions 35 ■ Refactor without AOP 38
- 16. CONTENTS x 2.3 The cost of change 43 Requirements will change 43 ■ Small versus large projects 43 Signature changes 44 ■ Working on a team 45 2.4 Refactor with AOP 45 Start simple and isolate the logging 45 ■ Refactor defensive programming 47 ■ Creating an aspect for transactions and retries 49 ■ Put exception handling into its own class 50 2.5 Summary 52 PART 2 THE FUNDAMENTALSOF AOP.......................... 53 3 Call this instead: intercepting methods 55 3.1 Method interception 56 PostSharp method interception 57 ■ Castle DynamicProxy method interception 60 3.2 Real-world example: data transactions 63 Ensuring data integrity with begin and commit 63 When transactions go bad: rollback 67 ■ When all else fails, retry 67 3.3 Real-world example: threading 70 The basics of .NET threading 70 ■ UI threads and worker threads 71 ■ Declarative threading with AOP 74 3.4 Summary 77 4 Before and after: boundary aspects 79 4.1 Boundary aspects 80 PostSharp method bounding 80 ■ Method boundaries versus method interception 83 ■ ASP.NET HttpModule bounding 88 4.2 Real-world example: detecting mobile users 92 Offer a link to an application 93 ■ Don’t be a pest 99 4.3 Real-world example: caching 100 ASP.NET Cache 102 ■ An application that could benefit from caching 103 ■ Caching a result 108 ■ Retrieving from the cache 110 ■ A more robust cache key 113 4.4 Summary 114
- 17. CONTENTS xi 5 Get this instead: intercepting locations 115 5.1 Location interception 116 Fields and properties in .NET 116 ■ PostSharp location interception 118 5.2 Real-world example: lazy loading 119 Lazy loading approaches in .NET 120 ■ Implementing lazy loading with AOP 121 ■ What about lazy-loading fields? 124 5.3 Real-world example: INotifyPropertyChanged 128 Using INotifyPropertyChanged in a desktop application 128 Problems and constraints with INotifyPropertyChanged 132 Reducing boilerplate with AOP 134 5.4 Summary 138 6 Unit testing aspects 141 6.1 Writing tests with NUnit 142 Writing and running NUnit tests 142 ■ Testing strategies for aspects 145 6.2 Castle DynamicProxy testing 147 Testing an interceptor 147 ■ Injecting dependencies 149 6.3 PostSharp testing 156 Unit testing a PostSharp aspect 157 ■ Injecting dependencies 158 ■ Problems with PostSharp and testing 162 6.4 Summary 168 PART 3 ADVANCED AOP CONCEPTS .......................... 169 7 AOP implementation types 171 7.1 How does AOP work? 172 7.2 Runtime weaving 172 Proxy pattern revisited 173 ■ Dynamic proxies 176 7.3 Compile-time weaving 183 Postcompiling 184 ■ Before and after 184 7.4 Runtime versus compile-time weaving 188 Pros of runtime weaving 189 ■ Pros of compile-time weaving 189 7.5 Summary 190
- 18. CONTENTS xii 8 Using AOP as an architectural tool 191 8.1 Compile-time initialization and validation 192 Initializing at compile time 193 ■ Validating the correct use of an aspect 195 ■ Real-world example: Threading revisited 197 8.2 Architectural constraints 199 Enforcing architecture 200 ■ Real-world example: NHibernate and virtual 203 8.3 Multicasting 205 At the class level 206 ■ At the assembly level 210 8.4 Summary 211 9 Aspect composition: example and execution 213 9.1 Using multiple aspects 214 9.2 Aspect roles with PostSharp 215 PostSharp aspect roles 217 ■ Role dependencies 217 9.3 Composing aspects with DynamicProxy 219 Ordering aspects 219 ■ Reducing repetition with custom conventions 222 9.4 Real-world example: caching and authorization 224 Application architecture 225 ■ PostSharp 232 Castle DynamicProxy 236 9.5 Summary 241 appendix A Ecosystem of .NET AOP tools 243 appendix B NuGet basics 257 index 265
- 19. xiii foreword Like many great advances in our industry, the explicit concept of aspect-oriented pro- gramming (AOP) was developed at what is now known as PARC, a Xerox Company. Soon after, in 2001, the AspectJ extensions brought AOP to Java. Aspects have enjoyed a long history in the Java community, but for many .NET developers, aspects are still considered new and exotic. Even so, many .NET developers have been using them without knowing it. Aspects provide a means of separating cross-cutting concerns from your core implementation code into separate modules. Rather than having every method con- tain logging code, for example, a logging aspect can be applied to methods external to the method implementation. It’s a powerful technique to help employ the princi- ple of separation of concerns within code. In AOP in .NET, Matthew D. Groves deftly shines a light on the many ways develop- ers can take advantage of aspects in .NET. He begins with an approachable introduc- tion to AOP and builds on that with an example of an application written without aspects, which is then cleaned up with aspects. Subsequent chapters dig deeper into the various types of aspects and how to apply them using PostSharp and Castle DynamicProxy. Each chapter builds on the previous one in a distinct, understandable style, each with sample code that clarifies the concepts covered in the chapter. Great care was obviously put into the code samples. One example in particular shows how aspects are not limited to intermediate lan- guage (IL) rewriting and method interception. He challenges this implicit assump- tion by showing an aspect that wraps an HTTP request boundary in ASP.NET through
- 20. FOREWORD xiv a custom HttpModule implementation. It’s an example that might not, at first glance, be thought of as an aspect. But on reflection, it obviously meets the definition. Aspects are not limited to compile-time interception. This drives home the point that many developers have been using aspects of one form or another for a long time without realizing it. One subject near and dear to me is unit testing and this book contains an entire chapter covering the implications of unit testing and how to unit test aspects. It’s clear this book is not just meant to educate the reader on a subject, but to help the reader integrate the techniques and technologies with real-world practices. AOP in .NET is a great resource for those interested in learning how aspects can help maintain separation of concerns in a code base. I encourage you to take a look. PHIL HAACK DEVELOPER, GITHUB
- 21. xv preface A few years ago I was working on a team of consultants embedded in an organization (that shall remain unnamed). Our job was to create a system that would help increase a key source of revenue. This organization’s IT department had many problems: political, technical, organizational, and financial. As consultants, we, naturally, wanted to overhaul everything immediately to solve these problems, but the reality of consulting is that we had to take very slow, very small steps toward the goal. In the meantime, we had to work around the technical and organizational problems in order to help solve the financial ones, and that’s how I first learned about aspect-ori- ented programming (AOP). We were creating a website for the public to submit registration information and pay fees. One of the constraints we faced when writing this system was the enterprise database. We had to access the enterprise data via an unreliable and error-prone ser- vice that was meant to act as this organization’s SOA (service-oriented architecture). There were some good ideas in this service, but the implementation was poor: some- times as many as half the requests to this system would result in an exception, seem- ingly at random. After considerable testing and tinkering, we discovered that simply retrying the identical request once or twice would result in a successful request. Because of this, we didn’t want to use this buggy, unproven SOA service, but at that point we didn’t have a choice. We needed to create a reliable website that would be able to function with an unre- liable layer of data persistence and enterprise services. What we built was a piece of code that would begin a transaction, try a request, catch exceptions of a certain type, and retry the request until it succeeded, or roll it back if it didn’t. If it didn’t succeed,
- 22. PREFACE xvi it would log the exception type, the exception message, and some related information about the request. With this log, we hoped to first, build evidence that we could use to prove how unreliable this SOA service was, and second, be able to match exceptions with any customer-reported technical issues. What we built was a critical transaction helper class that was used over and over every time we needed to use the SOA service. This leads me to one of the organizational problems: the QA department was responsible for testing our application, but QA was notorious for being overworked and/or unreliable. This meant that they might not get around to reporting a bug that they found in our project until possibly two weeks later, or more. If one of us on the team accidentally forgot to use our transaction helper class when accessing the SOA service (or when someone new to the team was unaware of this helper class), then we might not find out for weeks, even if QA was (un)lucky enough to get one of the ran- dom exceptions. I was pulling my hair out: surely there was a way to refactor this nonfunctional requirement so we didn’t have to worry about forgetting it. Plus, it was getting tangled up with the rest of our code, making it harder to read and maintain. By chance, I was attending a .NET conference in Ohio, and Michael Kramer, an acquaintance of mine, was giving an introductory talk on AOP using PostSharp. He showed basic 101-level examples, similar to the ones you’ll see early in this book. The idea of being able to write a piece of code that would be in class A yet run somewhere else (say, before and after the methods in class B) was astounding to me, and I men- tally checked out of the rest of the conference and immediately started thinking of ways to apply AOP to the transaction helper class problem. Fast-forward to now, and I’m still using AOP to solve similar problems (although I left that organization and the consulting business altogether). I started speaking at software conferences about AOP, started blogging about AOP, and became something of a community advocate for AOP. I was often asked if I could recommend a book on the topic for .NET developers, and I really couldn’t. I eventually decided that this book had to be written. So that’s what you have here, a book on a topic about which I am very passionate—not only because it’s a powerful and useful tool when used properly, but because it helped me out in a very tough situation.
- 23. xvii acknowledgments There are so many people who have influenced my career and experience, and thus this book. Everyone on Twitter whom I follow, everyone I’ve worked with, all the attendees and speakers that I meet at user groups and conferences. Even if it’s a small thing like teaching me a keyboard shortcut, I owe you a debt of gratitude. I’d like to specifically acknowledge: Nick Chase, Frank Pohlmann, Cynthia Kane, Michael Stephens, Bert Bates, Eliza- beth Martin, Mary Piergies, and everyone else at Manning. Thank you for your guid- ance and help, and for getting this ship into the water. Seth Petry-Johnson, Jonathan Hammond, Jesse Riley, David Giard, Charles Huse- mann, Brady Gaster, Chris Farrell, Jim Christopher, Steve Horn, H. Alan Stevens, Jason Follas, Brian Watson, Richard Dudley, Jay Harris, James Bender, Steve Fischer, John Dages, Brian Prince. I could fill a book with all the great people I’ve met on my career’s journey. If I forgot to include you, I’m sorry; I owe you lunch. Dan Allen, for giving me my first programming job. Michael Kramer, for that fateful day when he unwittingly unleashed AOP into my life. Everyone I’ve worked with at OSU, Quick Solutions, and Telligent. Xiaoran Wang, for the tremendous diagrams (explaining tangling, scattering, and weaving) that he was kind enough to let me use in this book. Vince Fabro, for being an inspiring, patient leader in tough times, and Jonathan Mitchem for making our time in the foxholes more educational and entertaining than I ever expected. Jason Gilmore, for your guidance and all you do for the developer community.
- 24. ACKNOWLEDGMENTS xviii Ben Maddox, whose honesty and integrity are like gold. Mark Greenway, for being an amazingly smart and helpful guy, and naming the guy on the book cover the “Archduke of Programmerland.” Gael Fraiteur and Britt King, for working so hard on your product and for encour- aging and supporting me. Donald Belcham, Dustin Davis, Joe Kuemerle, Chad Eng- land, the rest of the PostSharp MVPs, and all community advocates for aspect-oriented programming. Craig McKeachie, for giving me really good advice. Bill Sempf, for being an inspiration and a mentor. Phil Haack, for being gracious enough to write the foreword, not to mention his long list of incredible contributions to the .NET community. Jim Holmes, a selfless (albeit poorly dressed) legend who spreads joy and awesome- ness wherever he treads. Jon Plante, for playing video games with me during a terribly difficult time in my life. I have been, and always shall be, your friend. Javier Lozano, for his careful technical review of the final manuscript and source code shortly before the start of production. My reviewers, who read the manuscript several times during its development and provided invaluable feedback: Aaron Colcord, Heather Campbell, Jeremy Baker, Jona- than Clark, Koen Handekyn, Maarten Balliauw, Margriet Bruggeman, Mark Bell- house, Mark Greenway, Mick Wilson, Nikander Bruggeman, Paul Stack, Phil Haack, Pim Van Oerle, Stuart Grassie, and Toby Moore. My entire family, specifically, my parents Kevin and Mary, for always encouraging me, even when my greatest aspiration as a seven-year-old was to be a garbage collector (ironic, considering that I now write managed code). If you don’t make it through the first chapter without being bored to tears, I completely understand, and I love you anyway. And Dad, thanks for teaching me BASIC on a TRS-80 all those years ago. And of course, my wife Ali, who encourages me, puts my needs above her own, and has given me the gifts that keep on giving: our children. I love you.
- 25. xix about this book Aspect-oriented programming (AOP) is a concept that is too often surrounded by dense language and academic terminology, which can make it difficult for a working developer—who is already short on time and struggling to meet deadlines—to under- stand, apply, and get value from AOP quickly. It’s unfortunate, because at its core, AOP is much less difficult than it sounds and can provide immediate benefits to real-world projects. My goal has been to write the book that I wish I had read years ago and to show that AOP is much easier done than said. To that end, this book is somewhat informal in tone and short on theory, and it contains lots of code samples, with which I hope you follow along. As much as I want this book to take a generalized approach to AOP, in order to show you real aspects I have to use real tools. I have chosen PostSharp (specifically, the free version, PostSharp Express edition) as the primary framework that I will be using most often. Castle DynamicProxy examples are also used frequently. I also discuss some of the advanced features of the paid version of PostSharp, and other tools and frame- works will be used and discussed in the course of the book, as well as in appendix A. Roadmap Chapter 1 introduces AOP. It covers some of the features and terms that are used in AOP. You will also write a “Hello, World” aspect. Chapter 2 is a complete project tutorial. You will start a new project, implement fea- tures, add cross-cutting concerns, and then refactor it using AOP.
- 26. Discovering Diverse Content Through Random Scribd Documents
- 27. Treatment. general convulsions, preceded by symptoms of brain irritation or compression. Three courses are available in the treatment of this condition:— 1. Expectant treatment, combined with the application of pressure. 2. Aspiration and puncture. 3. Free exposure and further treatment according to the conditions found. In the majority of cases the local conditions preclude any attempt at radical cure—the gap in the skull is large, the margins of the deficiency are thinned and everted, and the brain enters largely into the formation of the projecting mass. Furthermore, the dura mater is torn and in a tag-like condition. Only in the most favourable cases—when the tumour is small and the gap narrow—can radical treatment be advocated. The application of pressure—without previous aspiration—exercises but little effect on the size of the tumour and, under such treatment, the danger of brain-compression is always present. Aspiration with the object of removing the fluid constituents of the tumour, and thus of reducing its size, has occasionally been followed by disastrous results. Still, many cases were so treated in the pre-aseptic days, and the modern methods of cleanliness should allow of better results. One or more aspirations may be carried out, this treatment to be followed by the application of steady and uniform pressure, preferably with the aid of elastic bandages, the degree of compression depending on the size and constituents of the tumour. The patient must be watched most carefully, in order to guard against the development of symptoms pointing to cerebral compression. Irritating injections should never be used. One must acknowledge that this mode of treatment has—except in a few isolated cases—not produced very satisfactory results. Still, since an open operation is usually out of the question, no other course remains. The after-history of these cases is not very encouraging. In one of Weinlecher’s cases the child was living 5 years later, but pulsation was still present. In Lucas’s case the patient died 21 months later from meningitis. In Sir T. Smith’s case, pulsation was present 3 years after the accident, and in Silcock’s there was no marked change for the better
- 28. after 11 years. On the other hand, a case reported by Golding Bird steadily improved, and a second case reported by the same writer gave every promise of a permanent cure. The two following cases have come under my own observation:— 1. A female child, 11 months old, was knocked down by a van, and, on admission, a large hæmatoma was seen situated over the right temporo-parietal region. The child was semi-comatose, but recovered consciousness next day. The hæmatoma softening, a gap in the bone was felt, one-third of an inch wide, and extending from the occipital bone upwards and inwards to the middle line. The swelling increased in size when the child cried. Pulsation was present and translucency was obtained. The tumour increased in size for some days, but no untoward symptoms developed. For over one month pressure was applied, but without much benefit, though the general condition of the child was good. The edges of the gap became thickened. The child was then removed from the hospital. 2. A male child fell 19 feet on to his head. He was concussed, and, on admission, presented a hæmatoma over the right fronto-parietal region, and subconjunctival hæmorrhage in the left orbit. Four days later he was apathetic and there was some paresis of the left arm and leg. As the hæmatoma became softer, pulsation was noticed over a small area, and, in this situation, the swelling increased in size on straining. A fracture was detected later, one-third of an inch in diameter, and extending across the left frontal bone to the right temporal region. Pressure was applied, the tumour steadily decreased in size, and eventually the gap was completely closed. Synopsis of 38 cases of traumatic cephalocele. Sex. Males, 16. Females, 13. Sex not stated, 9. Age at time of accident. 2 cases at birth. 9 in the first 6 months. 9 in the second 6 months. 14 between 1 and 2 years of age. 1 between 3 and 10. 1 between 10 and 15. 1 between 15 and 20. 1 between 20 and 30. Region affected. Right parietal, 17 cases. Left parietal, 4 cases. Other bones, right and left, 8 cases. Parietal with others, 9 cases. Parietal bone involved in 30 out of 38 cases.
- 29. Fractures of the skull resulting from injuries received at or shortly after birth. (a) Depressed fractures. Right side involved in 27 out of 38 cases. Date of appearance of tumour. 7 cases in the first week. 11 cases in the second week. 4 cases in the third week. 4 cases between 2 and 18 months. In the remainder, date uncertain. In the consideration of injuries to the skull and brain in babies the following points should be noted:— 1. The bones of the skull are elastic and pliable, and consequently a blow may lead to a ‘bending-in’, either temporary or permanent. Slight depressions may exist without any associated fracture, but all major depressions are accompanied by a fracture of the bone, especially evident on examination of the internal table. 2. The fibrous tissue intervening between the component parts of the vault tends to cause a limitation of the fracture to the particular bone affected. Downward extension to the base is of infrequent occurrence, but, when that region is involved, the fracture usually follows the transbasic lines described in the section dealing with fracture of the base of the skull (p. 82). 3. The dura is said to be more adherent to the inner table of the skull than in adults. The relative infrequency in the young of extra-dural hæmorrhage has been ascribed to this peculiarity. It would appear, however, more probable that the rarity of such hæmorrhages results from the bending-in, without splintering, of the bone. 4. The brain of the infant is equally—if not more—liable to bruising and laceration, but the results are far less definite than in adults. There can be no question that extensive cerebral injury may exist in the child without leading to the development of any definite localizing symptoms. FRACTURES OF THE VAULT Depressed fractures either result from injury received during the birth of the child—whether from forceps delivery or from the pressure exerted on the head by a contracted pelvis —or from blows received shortly after birth.
- 30. Course and treatment. Fig. 23. A Depressed Birth-fracture. The depression, varying greatly in depth and extent, may be situated over any part of the skull, but commonly involves the fronto- parietal region. It is often obscured in the early stages by the presence of an overlying hæmatoma, the condition perhaps only being discovered after the absorption of the blood-clot. In many cases no symptoms result, partly owing to the shallowness of the depression and partly due to the situation of the lesion over one of the so-called ‘silent’ areas of the brain. Under other circumstances the child may evidence the general increase in the intracranial pressure by cyanosis, difficulty in respiration, unconsciousness, and slow pulse. The anterior fontanelle will be tense, and pulsation will be absent or greatly diminished—a feature of the greatest diagnostic value. Localizing symptoms ensue when an extensive depression is situated over the motor area, the extremities of the opposite side being flaccid, or evidencing irritation by twitchings and convulsions. The ready response of the infant to cortical irritation frequently results in the early transformation of local twitchings into general convulsions.
- 31. It is often stated that these depressed fractures remedy themselves in the course of time, the development of the underlying cortex curing the depression by the outward leverage exerted. In the minor degrees of depression there may be some chance of such spontaneous cure. I am, however, entirely opposed to the view that spontaneous cure is the rule, and there can be no question that the more severe types of depression remain as permanent defects unless surgical remedies are adopted. Furthermore, even if the deformity should cure itself in time, the intermediate dangers are not to be disregarded, for, during the process of spontaneous cure, there is a decided liability for the depressed cortex to lag behind in the process of development, or to undergo degenerative changes as the result of the pressure exerted—with disastrous results on the parts supplied by the region compressed. Mental deficiency, paralyses, and contractures will result, and there is every reason to believe that some cases of infantile paralysis are dependent on this lesion. The following case, recently under my care, adds further proof to the statement that spontaneous cure is usually out of the question:— The child, 10 weeks old, was admitted with a depressed fracture over the parieto- frontal region, oval in shape, and about 31⁄2 inches in its long antero-posterior diameter. The centre of the depression lay about 11⁄2 inches below a normal surface. The injury was produced at birth (contracted pelvis), and frequent convulsions were observed during the first few days of life. The fits then ceased, but the depression became, if anything, more marked day by day. The child was then brought up to see me. The depression was exposed by a suitable scalp-flap and a small trephine hole made immediately posterior to the depression. The dura mater was stripped away from the under surface of the bone and every effort made to remedy the depression. No impression was thus made on the defect. The whole depressed area was then cut out with a pair of scissors, the segment removed, wrapped up in a piece of gauze, and forcibly manipulated in the hope that the depression could be overcome and the segment placed back in the normal position. This attempt was also greeted with failure. The segment was then placed back in the inverted position, the dural surface external and vice versa. The segment required some trimming with the scissors before it fitted accurately in position. The scalp-flap was then replaced. The child suffered but very slightly from the operation, firm union was present in two weeks, and, six months later, examination of the skull showed that the two sides were absolutely symmetrical. It should be noted that, although the child was only 10 weeks old, and in spite of the fact that the depression was fully exposed, it was quite impossible to lever up the depressed bone. This hardly coincides with the views of those who maintain that birth- depressions undergo spontaneous cure.
- 32. Taking all these facts into consideration, it would appear advisable to adopt the following course:—slight depressions, situated in the region of ‘silent’ areas of the brain, may be left for one or two weeks, and, in the event of failure at spontaneous cure, the depression must be elevated. In all the more serious cases, whether associated with symptoms of brain-pressure or not, surgical interference is imperative. A
- 33. Operation. B Fig. 24. A Case of Depressed Birth-fracture. a, Before operation; b, After operation. (For further description, see text.) The baby would be well wrapped up and, after shaving and cleansing of the scalp, the scalp-tourniquet applied. Babies stand these operations exceedingly well so long as hæmorrhage is but slight. A scalp-flap is turned down and a small trephine (1 ⁄2-inch diameter) applied immediately to one side of the depression, the trephine circle including the outer margin of the depressed area. The dura is stripped away and a flat periosteal elevator introduced so that its apex corresponds to the apex of the depression. An attempt is then made to lever the depressed area in the outward direction. If that result be attained, well and good. The flap is replaced and dressings applied. In many cases, however, the elevated region promptly assumes its original depressed position as soon as the elevator is removed, and, in other cases, all attempts at rectification of the deformity are of no avail. Under
- 34. (b) Fissured fractures. these circumstances, it is advisable to carry out the method advocated by Nicholl—adopted in the case described above—the whole of the depressed area being cut out with blunt-pointed scissors, reduced to a more normal curvature by manipulation between layers of gauze, and replaced in the inverted position, the original dural surface becoming now external. This inversion is requisite, as it is usually quite impossible —even under considerable pressure—to reduce the depression to a permanently satisfactory degree. Nicholl reports on 23 cases, the ages of the patients varying from 3 weeks to 8 years. The first 13 cases were treated by elevation. The results obtained were most unsatisfactory, complete reduction of the deformity seldom being attained, whilst recurrence, of a greater or lesser degree, was the rule. In the last 10 cases the inversion method was carried out, with, in all cases, satisfactory results. Bony union was present in 10 days. Four cases of depressed birth-fractures have come under my own care. In two cases the depression was elevated—in both cases with considerable difficulty—whilst in the other two cases, after failure of leverage, Nicholl’s method was carried out, in both cases with eminently satisfactory results. Fissured fractures are especially prone to involve the parietal bone, and, in their direction, to follow the lines of ossification. Thus, in the case of the parietal bone, the fissures will radiate from the parietal prominence. There is also a certain tendency for the fracture to remain limited to the particular bone affected. The presence and extent of the fracture is commonly obscured by the overlying hæmatoma, which is either subpericranial or subaponeurotic. On the other hand, the hæmatoma may, from its size and shape, supply evidence as to the nature of the underlying lesion. Thus, when confined to the parietal bone, it may be inferred that the fracture is also limited to that region. Again, when linear, the presumption is that the fracture is of a similar nature. A definite diagnosis may be impossible without aspiration or till after absorption of the hæmatoma. The fissure will then be found to vary in extent from a mere crack in the bone to a wide gap as broad or broader than the width of the finger. In a case recently under my care the fissure, over
- 35. Symptoms. Treatment. half an inch in breadth, extended from the vertex to the base, whilst throughout the whole extent of the gap pulsation was readily obtained. Fissured fractures in the very young possess another point of interest in that the cleft often tends to increase, this being notably the case when the fracture is associated with injury to underlying dura and brain. The local and general increase of intracranial pressure not only widens the gap, but also leads to thinning and eversion of the margins of the deficiency with possible herniation of brain-matter—traumatic cephalocele. In many cases—in spite of the severity of the lesion— there are no symptoms, the child appearing but little the worse for the accident. In most cases, however, the child evidences symptoms of brain-concussion, irritation, or compression, for which conditions reference should be made to the sections dealing with those subjects. It should be noted, however, that the anterior fontanelle supplies evidence as to increase or decrease of intracranial pressure. In concussion the fontanelle is depressed, in compression it is tense and pulsation is absent or diminished. Irritation of the brain is evidenced by irritability and general convulsions. In the absence of symptoms, or when the fracture is associated with concussion or irritation, operative measures are contra- indicated, the patient being treated after the general principles laid down for those conditions. When associated with symptoms of brain-compression, exploration is almost always advisable, the scalp-tourniquet being applied and the injured region exposed by a suitable scalp-flap. Depressed bone is elevated, or the trephine applied so as to fully expose the underlying dura mater. A bulging, non-pulsatile, and plum-coloured membrane points to the existence of a subdural hæmatoma. The membrane is then incised and the clot evacuated. Whenever possible the dura mater should be sewn up and the scalp-flap replaced without drainage. Operative measures are also indicated when a linear fracture gapes widely—especially when the gap shows a tendency to increase in width. The steps of such an operation are as follows:— 1. Expose the fracture throughout its whole length. 2. Cut away all pericranium or fibrous tissue that intervenes between the margins of the cleft.
- 36. Extracranial hæmorrhages. Subaponeurotic hæmatomata. Subpericranial hæmatomata. 3. Separate the dura mater from the bone on either side of the cleft for a distance of about 1 ⁄2 inch, at the same time sewing up any rents in the membrane. 4. Bore a few holes through the skull—using an ordinary bradawl— on either side of the cleft, the holes being placed about 1 ⁄2 inch apart. 5. Approximate and lace the margins of the cleft by means of fine silver wire or strong catgut. 6. Sew up the flap without drainage. BIRTH-HÆMORRHAGES As the result of injury sustained during protracted labour, hæmatomata may develop beneath the aponeurosis of the occipito-frontalis or underneath the pericranium, the latter being the more common situation. The right side of the head is the more frequently involved, and the parietal region is the part usually affected. Occasionally these hæmatomata are bilateral and symmetrical. The two varieties of cephalhæmatoma—subaponeurotic and subpericranial—possess certain peculiarities that aid materially in their differential diagnosis. The blood, though spreading widely throughout the subaponeurotic space, tends to gravitate towards the lower confines of that space, and, from the position assumed by the patient, is most evident in the occipital region. The presence of the blood is evidenced by œdema, doughiness, and ecchymosis. The blood is confined to the region of the particular bone affected, usually the right parietal bone. This is due to the fact that the pericranium blends at the margins of the bone with the tissue intervening between that bone and the neighbouring parts of the skull. Subpericranial hæmatomata present further peculiarities. The tumour is usually more or less circular in outline, and fluctuates freely. It may arise immediately after the birth of the child, but, more commonly, some two or three days elapse before attention is drawn to its existence. Within a few days clotting occurs at the periphery of the hæmatoma with the formation of a circumferential ridge. The central portion of the clot remains soft but tense, so much so that firm pressure is required before the examining finger is enabled to feel the underlying bone.
- 37. Treatment. Intracranial birth-hæmorrhages. These cephalhæmatomata are not infrequently mistaken for depressed fractures, but no difficulty should be experienced if the existence of the circumferential ridge be appreciated and if the underlying bone can be felt at the centre of the tumour. In cases of doubt the blood should be drawn off by aspiration and the swelling again examined. For differential diagnosis, see p. 57. The less extensive hæmatomata require no active surgical treatment, the absorption of the clot being aided by protection of the part and by cooling lotions. Similar expectant treatment is generally advised with regard to the extensive subpericranial hæmatomata, but as infection of the clot may take place, and as its resolution invariably requires a considerable period of time—often many weeks—more active measures can be adopted. The region of the hæmatoma is carefully shaved and cleansed, and, under local anæsthesia, a small incision made through the scalp, the clot squeezed out, and firm pressure applied. Under this form of treatment the patient is well within a few days. Attention was first drawn to the question of intracranial birth-hæmorrhages by Little, who showed that a history of difficult labour could be obtained in a large percentage of cases in which children in after-life suffered from uni- or bilateral spastic paraplegia; hence the name, ‘Little’s disease’ or birth palsy. Further information was supplied by Sarah MacNutt, and the whole question was fully investigated by Harvey Cushing. In all cases a history of difficult and protracted labour can be obtained, with considerable post-partum respiratory difficulties, the child being described as ‘blue in the face’ for some hours after birth. The stress and strain which the advancing head undergoes, and the consequent moulding and overlapping of the various segments of the skull, exposes the brain to great alterations of pressure, and throws considerable tension on the intracranial veins. It is, in fact, rather surprising that birth-hæmorrhages are not more common. The hæmorrhages may be wholly within the meshes of the pia- arachnoid system, but, in the great majority of cases, the lesion is more serious, and the extravasation comes to lie within the subdural space. Occasionally the bleeding takes place beneath the tentorium cerebelli, the blood-clot lying in relation to the pons and medulla. Such
- 38. hæmorrhages are said to be observed only in vertex presentations. The more common supratentorial hæmorrhages—usually resulting from difficult breech presentations—either remain more or less localized to a certain region of the cortex, or become widely diffused over the surface and base of the brain. It is probable that Cushing is correct in his observations with respect to the source of these supratentorial hæmorrhages. He states that the blood is derived from one or more radicles of the superior longitudinal sinus, especially from those veins which, in their upward passage in the sulci of the brain, leave their cerebral beds for a short and comparatively unprotected course, immediately previous to their entry into the lacunæ laterales of the superior longitudinal sinus. In addition, he points to the very important fact that the localized hæmorrhages are commonly situated in relation to the mid-cerebral cortex, close to the sinus, and on one or both sides of the falx cerebri. In addition, therefore, to the symptoms of general cerebral compression, certain definite localizing symptoms are to be observed, these being in direct proportion to the size of the clot. In an analysis of 74 autopsies on infants still-born or dying within the first few days, Archibald[11] found ‘intrameningeal’ hæmorrhage in 32, in 19 of which it was of considerable extent: and in 5 others there was extra-dural hæmorrhage. In only two or three was effused blood found within the cerebral cortex. The importance of these facts from a surgical point of view cannot be over-estimated.
- 39. Symptoms. Fig. 25. Diagram to illustrate the Effects and Position of a Birth-hæmorrhage. sc., Scalp; b., Bone; d.m., Dura mater; br., Brain; s.l.s., Superior longitudinal sinus; c.v.1, The protected part of a superficial cerebral vein; c.v.2, The unprotected part of a superficial cerebral vein; c., The subdural clot, exercising pressure on (1) the cortical leg arm, (2) the arm area, and (3) the face area. Besides the history of protracted labour and the ‘blue’ asphyxiated appearance of the baby, other evidence is to hand with respect to both general and local increase of brain-pressure. The general increase is evidenced first and foremost by the bulging and non-pulsatile anterior fontanelle. The fontanelle may be regarded as an index of intracranial pressure. The margins of the fontanelle are outlined with some difficulty, and, owing to the free communication between the intra- and extra-cranial venous systems, the scalp-veins are unduly prominent. The general condition of the child varies according to rise of intracranial pressure. In the more serious cases it may be impossible to arouse the patient: in the
- 40. Treatment. slighter hæmorrhages the child may appear but little the worse, with the exception, perhaps, of being rather more irritable than usual. The effect of the pressure on the medullary centres is shown by respiratory difficulties—irregularities of rhythm, &c.—some retardation in pulse-rate, and increase in blood-pressure. The reflexes are increased and the child is readily thrown into general convulsions. The effect of the localized pressure on the upper Rolandic centres seldom becomes evident till after the lapse of a few days— and often after a longer period—when muscular weakness, twitchings, rigidity, or paralysis—more especially of the contralateral lower extremity—becomes apparent. The mother often draws attention to the fact that the child does not move one of its legs properly. When the extravasation is extensive, spreading downwards over other motor areas, the upper extremities and even the face may be involved. When a small hæmorrhage is present, situated on either side of the falx cerebri, both lower extremities suffer and diplegia results. In some cases, chemosis of the conjunction, œdema of the lids, and proptosis have been observed. In any case an ophthalmoscopic examination should be carried out. Frequently some fullness of the retinal veins and diminution in the calibre of the arteries supply confirmatory evidence. In the event of doubt in diagnosis, lumbar puncture should be carried out. It should be noted, however, that although the positive evidence of free blood corpuscles points to subdural hæmorrhage, yet that absence of blood in the fluid withdrawn does not exclude the possibility of a localized and more or less encapsulated hæmorrhage. In the event of failure at recognition of the serious lesion present, disastrous results will ensue—monoplegia, diplegia, hemiplegia, epilepsy, and idiocy. The age of the patient must not be allowed to weigh in the balance against operative treatment, for, if due precautions be taken, the new-born child stands operation well. Cushing points out that ‘the possibilities of surgical relief are limited
- 41. to the first week or two after the hæmorrhage has occurred, for old cortical scars can neither be helped by medicine nor by the scalpel’. The clot can be exposed by craniectomy or by craniotomy. The latter operation results in a more complete exposure, but the shock is undoubtedly more severe. Exposure by craniotomy is advocated by Cushing, and carried out in the following manner: ‘An omega- shaped incision just within the outer margin of the parietal bone is carried down to the bone through the scalp and pericranium, and the latter is scraped away so as to expose the thin serrated edge of the parietal bone. Under this a blunt dissector is passed, so that the edge of the bone is tilted up, and then, with a proper cutting instrument (strong blunt-pointed scissors suffice), the bone is incised in a line conforming with the skin incision 1 centimetre or more within the parietal margin. The parietal bone is then broken across at its base. The dura is opened by a curved incision some distance within the bony margin, and the superficial clot broken away or lifted off in fragments, or irrigated away with a gentle stream of warm saline solution. The dura should be accurately sutured, the bone replaced, and the skin closed with suture.’ He reports on 9 cases so treated, with 4 recoveries, apparently complete and permanent. The fatal cases were all associated with extensive extravasation over the entire hemisphere. In 3 cases bilateral exposure was necessitated. Taking, however, the question into more general consideration, it would appear that equally satisfactory results can be obtained, with a lesser degree of operative danger, by carrying out craniectomy in the manner described in the treatment of ‘traumatic subdural hæmorrhage’ (see p. 156). DERMOIDS Dermoids, in this region of the body, are almost invariably situated in the middle line between nasion and inion, though cases have been described in which congenital tumours, dermoid-like in nature, were situated over the mastoid process and in other regions.
- 42. They occur with the greatest frequency over the anterior fontanelle and in the region of the external occipital protuberance. In the latter situation they are specially prone to possess those deep attachments to the dura mater which are further alluded to below. In the great majority of cases careful examination will show that the tumour occupies a depression in the bone, saucer-like in nature, in which the tumour rests. They are seldom freely movable, and are often markedly fixed, being either attached to the pericranium or to deeper structures. They are not attached to the overlying skin. The tumour is irreducible, and pulsation is absent except in those rare cases where, in the presence of a wide gap in the skull, transmitted pulsation may be obtained. On careful dissection it may be found that the tumour communicates, by means of a small hole in the skull, with the underlying membranes. In more exceptional cases a wide gap in the skull may be found by means of which the dermoid obtains extensive connexion with the dura mater and even with the brain. In rare cases the dermoid may be pedunculated. Bland Sutton drew attention to this frequent connexion between the dermoid and the membranes of the brain, showing further that the entire tumour may lie on the inner side of the occipital bone. The following account affords further information as to the nature and origin of cephalic dermoids. ‘Morphologically considered, the bony framework of the skull is an additional element to the primitive cranium which is represented by the dura mater, and the term extra-cranial should be applied to all tissues outside the dura mater. Early in embryological life the dura mater and skin are in contact; gradually the base and portions of the side wall of the membranous cranium chondrify, thus separating the skin from the dura mater. In the vault of the skull, bone developes between the dura mater and its cutaneous cap, but the skin and dura mater remain in contact along the various sutures even for a year or more after birth. This relation persists longest in the region of the anterior fontanelle and the neighbourhood of the inion. Should the skin be imperfectly separated, or a portion remain persistently adherent to the dura mater, it would act precisely as a tumour germ and give rise to a dermoid. Such a tumour may retain its original attachment to the dura mater, and its pedicle become surrounded by bone; the dermoid would lie outside the bone but be lodged in a depression on the surface, with an aperture
- 43. Treatment. transmitting its pedicle. On the other hand, the tumour may become separated from the skin by bone; it would then project on the inner surface or between the layers of the dura mater. If this view of the origin of dermoids be accepted, we must modify our teaching and say that the depressions in which dermoids of the cranium are lodged arise as imperfections in the developmental process, and are not due to absorption induced by pressure; further, the fibrous connexion of such dermoids with the dura mater is primary, not accidental.’[12] When of inconsiderable size, and when intracranial connexions are absent, of doubtful existence, or of slight extent, the sooner the tumour is removed the better. The dura mater should not be opened unless absolutely necessary, in which case it should be carefully sewn up and the scalp-flap replaced without drainage. When possessing deep and extensive connexions, careful dissection may still allow of the complete removal of the dermoid. It is impossible to foretell with certainty whether it is possible to remove the tumour until its basal portion is exposed. The operation may be a formidable one. Some points in the differential diagnosis between Cephaloceles, Dermoids, and Cephalhæmatomata Cephaloceles (congenital). Dermoids. Cephalhæmatomata. Present at birth. Present at birth. Usually appears after birth. In middle line, especially over occiput and base of nose. In middle line, especially over anterior fontanelle. Always to one side of the middle line, and usually over the parietal bone. Firm or fluctuating. Firm. Fluctuation over central part only. Perhaps translucent. Not translucent. Not translucent. Perhaps pulsates. Does not pulsate. Does not pulsate. Perhaps reducible, in whole or in part. Irreducible. Very slightly, if at all. Perhaps swells up on straining. No alteration. Very slightly, if at all. Perhaps associated with cerebral symptoms. No cerebral symptoms. No cerebral symptoms.
- 44. Congenital internal hydrocephalus. Gap in skull felt. Depression in bone common, actual gap comparatively rare. Deceptive raised margin, no actual central depression. HYDROCEPHALUS The conditions that lead up to internal hydrocephalus are classified by Parkes Weber[13] in the following manner:— 1. ‘Cases secondary to and part of the phenomena of tuberculous or any suppurative meningitis, comparable to pleural effusions due to tuberculous or any septic invasions of the pleura. 2. Cases resulting from the presence of tumours, &c., analogous to the pleuritic effusions accompanying tumours, &c., situated close to or involving the pleura. 3. Ordinary infantile or congenital hydrocephalus, which is, in some cases at least, due to intra-uterine meningitis. 4. Internal hydrocephalus supervening on the epidemic or sporadic type of posterior basic non-suppurative meningitis. 6. Simple idiopathic internal hydrocephalus of adults or older children due to serous ependymitis or ventricular meningitis. 7. Traumatic cases.’ This classification possibly includes all the various grades and degrees of internal hydrocephalus, but for all practical purposes the cases may be grouped into two classes, congenital and acquired, both of which may be either acute or chronic. The condition may be recognized soon after the birth of the child, or the enlargement of the head may only become apparent some weeks or months later. The slow development and the insidious nature of the enlargement, as observed in many cases, may lead to some confusion between the late congenital and the early acquired varieties. However, the absence of any symptoms pointing to meningeal inflammation between the time of the birth of the child and the hydrocephalic development usually allows of correct classification. It is doubtful whether congenital internal hydrocephalus can be ascribed to malformation of the inter-ventricular channels and
- 45. Acquired hydrocephalus. Progress of the case. occlusion of the passages by means of which the cerebro-spinal fluid escapes into the cerebral subarachnoid space, or whether the development is dependent on hypersecretion from the ependyma and choroid plexuses. Virchow showed that occasionally there was an actual formation of small grey-red masses, about the size of a hemp-seed or cherry, in the walls of the ventricles, but other authorities deny the existence of such changes, and consider that the hydrocephalic condition is entirely dependent on congenital malformation. It would, however, seem more probable that we have to deal with two distinct varieties of congenital internal hydrocephalus, one resulting from intra-uterine ependymal inflammation (? syphilitic), the other dependent on congenital malformations, especially in the region of the fourth ventricle, where the foramina of Majendie, Key, and Retzius are regarded as permitting the outward escape of the fluid secreted from the lining membrane and choroid plexuses of the ventricles. Acquired hydrocephalus, whether acute or chronic, presents certain antecedents or associations which enable us to have a more clear idea as to the pathological conditions present. In the majority of cases it is secondary to basic meningitis which, whether tuberculous or not, results in matting of membranes and in the development of adhesions. The normal flow of cerebro- spinal fluid from the ventricular to the cerebral subarachnoid spaces is thus impeded. Similar interference to the flow of cerebro-spinal fluid may be caused by the growth of a tumour, especially those which originate in the subtentorial region. Whether the progress of the case be acute or chronic, the ultimate results are much the same. The fluid in the ventricular spaces may be increased up to 1,000 c.c. or more, pressure effects being exerted on the surrounding parts, with the following results:— A. The soft cerebral substance is slowly but surely compressed, with the result that the sulci on the surface of the brain are more or
- 46. less obliterated, distinction between the white and grey matter may be lost, the ventricular spaces are enormously dilated, and, in the most marked cases, a mere shell of brain may intervene between the ventricles and the surface of the brain. This cerebral compression results in the development of two main groups of symptoms, those referable to the general increase in the intraventricular pressure and those due to regional compression. The more general results are headache, vomiting, optic neuritis and atrophy, slow pulse-rate, somnolence, and coma. The temperature is variable, more commonly rising during the more acute stages of the disease, and falling to normal or subnormal during the quiescent periods. Localizing features are to be found in squints, inequality of pupils, retraction of the head and neck, dyspnœa, and dysphagia, whilst compression of the cortical motor centres is evidenced by twitchings, convulsions, and spasticity of the limbs. General convulsions are by no means uncommon. Remissions and intermissions of both local and general symptoms are frequently observed, paralyses, for example, fluctuating in depth and character. B. The bones comprising the vault of the skull become greatly thinned and widely separated from one another, the fontanelles enlarged, and the sutures unduly prominent. The head becomes enlarged in all directions, and its increased weight renders the child incapable of retaining postural control, the head being top-heavy and falling about in all directions. The bones of the base share in the deformity. The pressure exerted on the orbital plates of the frontal bone force the globe in the downward direction in such a manner that the infra-corneal sclerotic is obscured by the lower lid, whilst the supra-corneal portion is unduly prominent. The bony eminences in the region of the sella turcica are diminished in size, the middle fossa of the skull flattened from side to side, and the posterior fossa from before backwards. In such cases the skull assumes an almost dolicocephalic appearance. In any case, the disproportion between the enlarged skull and diminutive face is a marked feature.[14]
- 47. Treatment. Indications for operation. Lumbar puncture Operation. Ventricular puncture. Through the anterior fontanelle. The scalp becomes stretched, hairs are sparse and brittle, and the veins dilated. The results obtained by operation for internal hydrocephalus are not sufficiently encouraging to enable the surgeon to urge immediate operative treatment.[15] Still, it is perfectly clear that he cannot possibly carry out surgical treatment with benefit to the patient if the ventricular distension is allowed to progress to such a degree that marked cortical flattening and degeneration occurs. No fixed probationary period can be laid down as a guide, each case must be judged on its own merits. Special attention should be paid, however, to the disks and lower extremities. Any suggestion of optic neuritis or spasticity should be regarded as urgently demanding operative interference. cannot be expected to confer other than temporary benefit even under the most favourable circumstances, whilst, in the event of interference in the normal communication between the ventricular and cerebro-spinal spaces, no relief can be anticipated. Connal recommends that lumbar puncture should be carried out daily, or twice daily, over extended periods of time. This operation, however, is by no means devoid of danger, and the results obtained by such treatment are not at all satisfactory. Operations are carried out (a) with the object of withdrawing fluid from the distended ventricular cavities (ventricular puncture), and (b) to establish a communication, or short-circuit, between the ventricular space and other spaces (ventricular drainage). This operation may be carried out through the anterior fontanelle, through the frontal bone, or over the descending cornu of the lateral ventricle. The region of the fontanelle is shaved and cleansed in the usual manner, after which the surrounding parts are cut off from the field of operation by a large sheet of gauze or lint, in which a hole is cut sufficing to allow of exposure of the site of election for puncture. The patient should be in the recumbent position, the head well towards the end of the table. The operation is performed without an
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