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1
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- S. Oljeski MD, B. Huang MD, T. Marino MD, & M. Castillo MD
- University of North Carolina Hospitals
- Department of Radiology
- Chapel Hill, NC
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2
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- To become familiar with the normal anatomy of the inner ear & of the
8th cranial nerve.
- To understand the embryology of the inner ear as it relates to
congenital hearing loss.
- To review examples of various causes of congenital hearing loss
emphasizing MRI findings particularly as seen on CISS images.
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3
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4
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5
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6
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- Three primary phases of development:
- Development- weeks 4-8 of life
- Growth- weeks 8-16 of life
- Ossification- weeks 16-24 of life
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7
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- Otic placode develops during weeks 4-8 of life, beginning as a plaque
of neural ectoderm lying between 1st branchial groove & hindbrain.
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8
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- Otic placode invaginates to form the otic pit.
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9
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- Enlargement & invagination separates otic pit from overlying tissues
to form otocyst.
- Otocyst divides into a dorsal pouch (becomes utricle & semicircular
canals) & a ventral pouch (becomes cochlear duct & saccule).
- Endolymphatic duct arises separately.
- At end of week 8, membranous labyrinth & cochlea are complete.
- Cartilagenous condensation & ossification begins at this time as
well.
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10
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- Occurs between weeks 8-16 of life.
- Otic capsule recruits vascular channels via the fissula ante fenestrum.
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11
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- Cartilagenous condensation continues.
- Ossification occurs via 14 separate ossification centers (no growth
plates).
- Complete by 24 weeks; fetus is then capable of hearing.
- Ossification complete as endochondral bone.
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12
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13
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- Arrest of development in the 5th week.
- Unusual lesion, representing 3% of cochlear malformations.
- Absent cochlea with remnants of vestibule & semi-circular canals.
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14
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15
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16
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- Most common inner ear malformation (55%):
- Incomplete partition of cochlea.
- Classic example is Mondini deformity:
- Insult during 7th week of life.
- Cochlea develops only 1.5 turns, lacking spiral lamina &
interscalar septum.
- Apical & middle turns are confluent, basal turn is preserved.
- Associated anomalies of vestibule, semicircular canals &
endolymphatic in 20% of patients.
- Development of organ of Corti & auditory nerves is variable.
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17
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18
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19
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- Most common imaging abnormality in pediatric congenital hearing loss.
- Insult during 4-8 weeks.
- Vestibular aqueduct is large when >1.5 mm at midpoint.
- Size of dilated endolymphatic sac has no correlation with size of duct.
- Often presents as decremental hearing loss.
- Cochlear dysplasia always present.
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20
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21
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22
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23
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- Deformity results from insult during 4-5 weeks of life between formation
of otocyst & differentiation into primordia of inner ear structures.
- Entity represents 25% of cochlear malformations.
- Size of cyst usually < than 1 cm.
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24
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25
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26
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- Inflammatory disease of membranous labyrinth associated with hearing
loss & vertigo.
- Classified by agent: meningogenic (bacterial,viral) or etiology (serous,
suppurative).
- Begins with inflammation, proceeds to fibrous stage, and may culminate
in ossifying labyrinthitis over months to years.
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27
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28
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29
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30
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31
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- Knowledge of inner ear anatomy and embryology are fundamental to a basic
understanding of causes of congenital hearing loss.
- As many of the causes of congenital hearing loss present with similar
clinical findings, familiarity with imaging findings is critical in
making the correct diagnosis.
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32
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- Harnsberger, H. et al. Diagnostic Imaging: Head and Neck. 3rd
Ed. New York: Elsevier, 2004.
- Som, P. and Curtin, H. Head and Neck Imaging. 4th Ed. NY:
Mosby: 2003.
- Swartz, J. and Harnsberger, H. Imaging of the Temporal Bone. 3rd
Ed. NY: Thieme, 1998.
- www.med.unc.edu/inner-ear
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Notes
