HIS 125 Congenital Deafness and Medical Problems
3 likes798 views
The document discusses congenital hearing loss, including that it exists at birth or within the first six to twelve months. Congenital hearing loss creates lifelong disabilities if not detected early. The embryology of the inner ear is reviewed, starting as an auditory placode that develops into otocysts and eventually the mature inner ear structures. Early intervention is important for children with congenital deafness. Causes of congenital deafness include genetic factors, elimination of rubella, and cytomegalovirus.
HIS 125 Congenital Deafness and Medical Problems
- 1. Congenital means “existing at birth”. However, with hearing loss, congenital includes an onset prior to speech/language development– usually within the first six to twelve months (post-natal).
- 2. Congenital hearing loss creates a lifelong disability. When detected late in early childhood development, it can create delays in language development which may never be corrected to normal.
- 3. It is important to recognize congenital conductive hearing loss, because amplification often leads to normal levels of hearing.
- 4. Children with corrected congenital conductive hearing loss, have the potential for normal speech/language development.
- 5. Let’s review the embryology of the inner ear.
- 6. First Appearances/otocysts The inner ear first appears as a thickening of ectoderm—the auditory placode. In the twenty-fourth day of embryo formation hollow cysts have formed-- otocysts (auditory vesicles)
- 7. First Appearances/otocysts The otocysts soon become detached from the ectoderm from which they arose. At that point where the otocyst has detached from the ectoderm, the endolymphatic sac begins to extend in the medial direction.
- 8. First Appearances/Cochlear Duct It continues to dilate; and this slender medial endolymphatic sac becomes the cochlear duct. The dorsal portion begins to show indications of developing the semicircular canals (for balance).
- 9. First Appearance/Cochlea By the end of the seventh week, the otocyst has been modeled roughly into the membranous labyrinth with its semicircular canals and a cochlea with one turn.
- 10. First Appearance/Cochlear Duct In the eighth week, the endolymphatic duct with the three semicircular canal are well defined and utricle and saccule have been divided. The cochlear duct has begun to coil into its familiar snail shell shape.
- 11. First Appearance/Cochlear Duct By the third month, the adult form of the inner ear has been nearly completed. Its further development results in complete separation of the utricle and saccule which remains attached to the endolymphatic duct by a short slender canal.
- 12. First Appearance/Tectorial Membrane With the development of the membranous labyrinth, the spiral organ divides into an inner and outer ridge. Both ridges become covered with an increasingly prominent tectorial membrane.
- 13. First Appearance/Hair Cells In the area between these two ridges the epithelial cells begin to form the sensory hair cells.
- 14. First Appearance/Bony Labyrinth The mesoderm surrounding the membranous (epithelial) labyrinth becomes differentiated into a fibrous membrane and later into cartilage.
- 15. First Appearance/Perilymph At about the tenth week, the cartilage immediately surrounding the membranous labyrinth undergoes a peculiar reversal of development. It returns to a precartilaginous condition in which the cells lose their boundaries.
- 16. First Appearance/Perilymph This loose network of cells becomes the perilymphatic space surrounding the membranous labyrinth. When this has taken place, the membranous labyrinth becomes suspended in the fluid of the perilymphatic spaces.
- 17. First Appearance/Perilymph The perilymphatic spaces continue to develop above and below the cochlear duct creating the upper (scala vestibuli area) and the lower (scala tympani area).
- 18. First Appearance/Bony Labyrinth By the fifth month, the cartilage surrounding the membranous labyrinth has become the bony labyrinth (the hardest bone in the human body). Thus, by the middle of fetal life, the inner ear has attained its full adult size.
- 19. Now that we are aware of how the inner ear is formed inside the womb, we can become more aware of how the mother’s health conditions may affect the development of the fetus’s inner ear.
- 20. Embryology Summary The human embryo has three primitive tissue layers from which all organs of the body are formed. They are: 1. The ectoderm 2. The entoderm 3. The mesoderm
- 21. Embryology Summary During the formation of the embryo, an abnormal formation of one organ will many times indicate the abnormal formation of another.
- 22. Embryology Summary For example, a congenital anomaly of the eye involves the ectoderm, as does the endolymphatic portion of the inner ear. Therefore, a congenital anomaly of the eye suggests the infant may also have a congenital inner ear abnormality.
- 23. Embryology Summary Timing of the embryonic insult will also determine which organs may possess abnormal formation. Examples of embryonic insult include: X-rays, viruses, drugs, and environmental toxins.
- 24. Embryology Summary For example, the timing of embryonic exposure to maternal rubella within the first trimester may cause cardiac defects, cataracts, mental retardation, and hearing loss. However, if exposure occurs within the second or third trimester, only hearing loss may result.
- 25. While there continues to be controversy about the best way to habilitate a hearing impaired child, it is generally accepted that early intervention is extremely important!
- 26. Because of the importance of early intervention for children with congenital deafness, several approaches have been tried over the years.
- 27. Over the past few decades, identifying congenitally deaf children through the use of a high- risk register (HRR) has become a common method. The HRR is based on birth factors often associated with childhood deafness.
- 28. The infants identified as having factors on the high-risk register (HHR), are to be screened by three months and placed into a habilitation program by six months of age. New testing technology supports the HHR through objective assessment (ABR and EOAE).
- 29. In 1994, the Joint Committee on Infant Hearing recommended universal hearing screening upon all infants prior to three months of age using either auditory brainstem response (ABR) or evoked otoacoustic emissions (EOAE).
- 30. Let’s review some HHR indicators in Northern page #192.
- 31. The management of the hearing impaired child involves several members of the hearing health care team. The pediatric audiologist must accurately measure the hearing loss. The otologist must rule out treatable disease . The speech pathologist must assess the child’s communication skills.
- 32. Three factors have influenced the prevalence of congenital deafness in the United States. 1. Genetic factor 2. New vaccine factor 3. Cytomegalovirus (CMV) factor
- 33. Genetic Factor If one excludes the environmental causes of hearing loss, over fifty percent are felt to have a genetic etiology.
- 34. New Vaccine Factor Maternal rubella has essentially been eliminated. On the other hand, small premature infants are surviving and many of them are at an increased risk for hearing loss.
- 35. Cytomegalovirus (CMV) factor Many genetists believe that this is one of the leading causes of congenital hearing loss previously described as “unknown etiology”.
- 36. Most congenital hearing loss is nonsyndromic or not associated with any other abnormalities of the ear. Genetic deafness is very difficult to recognize when the family history is negative.
- 37. Let’s review Northern page #194 for described etiology of severe to profound congenital hearing loss.
- 38. Let’s review Northern pages #194—195 for a list of syndromes commonly associated with hearing loss.
- 39. As stated earlier, congenital hearing loss is often associated with other medical problems. For example, a steeply sloping high frequency hearing loss is suggestive of perinatal etiology.
- 40. With this revealed precipitous HL and twelve months post-natal, an MRI may reveal periventricular leukomalacia. Children with this “signature audiogram” may have an increased risk of cerebral palsy, mental retardation, attention-deficit disorder, and seizures.
- 41. Today, the most common cause of post-natal severe to profound deafness is bacterial meningitis.
- 42. NOTE: The deaf population are rarely concerned about having a deaf child. They have their own language and culture which contributes to little concern regarding the birth of a hearing impaired child.
- 43. In contrast, a deaf child born into a family not familiar with the communication challenges of deafness; may require that family to learn the “language of the deaf” for adequate communication development of the child.