- 6th Hillock - Inferior aspect of Helix and lobule
Describe the embryology of the External Auditory Canal?
i. 4th gestational week
a) Invagination of the 1st branchial arch groove over 4 weeks
b) Ectoderm invaginates to contact endoderm of 1st branchial pouch
ii. 28th gestational week - the epithelial core canalizes from medial to lateral to form the EAC
Describe the embryology of the tympanic membrane?
i) Trilaminar structure made up of a) endoderm (mucosa) b) mesoderm (radial and circular fibers) c) ectoderm (lateral epidermis) ii) Horizontal structure intially and becomes vertical by 3 years of age iii) Tympanic ring begins ossification at 3rd gestational month
Describe the embryology of the middle ear?
i) 4th month - tubotypanic recess (eustachian tube) formed by 1st branchial pouch
ii) 5-6th month - mesoderm between otic capsule & branchial cleft form ossicles
iii) 5-8th month - endoderm around ossicles go from slit-like opening to open to create middle ear space
iv) Late in fetal life and present at birth - pneumatized mastoid cavity
What are the four embryological sacs of the middle ear (between the 12th and 28th weeks)?
Saccus Anticus - extends anterosuperiorly to tensor tympani and forms the anterior pouch of Von Troltsch
Saccus Medius - Anterior pouch forms attic, Middle pouch forms incudal recess, Posterior forms mastoid air cells
Saccus Superior - Posterior pouch of Von Troltch extending posterosuperiorly entering into antrum and mastoid cavity
Saccus Posticus - Courses in hypotympanum & includes: OW, RW & s. tympani