Embryology of Ear and Malformations MCQs

The tympanic membrane develops from all three germinal layers. The outer epithelial layer is formed by the ectoderm The inner mucosal layer of the endoderm The middle fibrous layer is formed by the mesoderm. Explanation of other options: External auditory canal (Option B): The External auditory canal develops from the ectodermal layer. Stapes (Option C): The Stapes develop from the endodermal layer. Vestibular labyrinth (Option D): Forms from the otic placode (ectoderm) and surrounding mesoderm, but does not involve endoderm. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8th Edition, Page Number: 15

Scheibe dysplasia Most common inner ear anomaly. Dysplasia of cochlea and saccule; hence also called cochleosaccular dysplasia.(Pars Inferior) Bony labyrinth is normal. Superior part of membranous labyrinth(utricle and semicircular ducts) is normal.(Pars Superior) Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 135.

Mondini dysplasia may be seen in Pendred, Waardenburg, branchio-oto-renal, Treacher-Collins and Wildervanck syndromes along with other anamolies. Mondini dysplasia: Inner ear malformation Only basal coil is present or cochlea is 1.5 turns. There is incomplete partition between the scalae due to absence of osseous spiral lamina. Condition is unilateral or bilateral Can be treated by a cochlear implant. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 135.

During embryonic development, the saccule, one of the two otolith organs in the inner ear, develops from the pars inferior to the otocyst . The saccule is responsible for detecting linear acceleration and head position. Other options: Sacculus anterior This is a small sac that is located in the utricle of the inner ear. It is not involved in the development of the saccule. Pars superior: This is the superior portion of the otic vesicle. It gives rise to the utricle and the semicircular canals.

Mild intracochlear ossification is not a contraindication for cochlear implant. Option a - Michel aplasia - Complete absence of bony and membranous labyrinth. No hearing aids or cochlear implantation can be used. Option b - Cochlear implant works by stimulating the auditory nerve. So absence of cochlear nerve is a contraindication for its use. Option d - Persistent otitis media and mastoiditis without eradication of the disease - Bone Anchored Hearing Aids should be considered. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 135, 146.

Indications of ABI include: Neurofibroma type 2 - Bilateral vestibular schwannoma Congenital aplasia of VIII nerve Cochlear aplasia(Michel Aplasia) The prerequisite for cochlear implant surgery is presence of normal VIII nerve. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 147.

Mondini dysplasia of cochlea refers to the condition when there are one and half turns of cochlea rather than two and half. There is absence of the apical modiolus and interscalar septum, resulting in an incomplete partitioning of the cochlea together with an enlarged vestibular aqueduct(EVA) and dilated vestibule. This is not a contraindication of cochlear implantation. Reference : Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8th Edition, Chapter name: Rehabilitation of the Hearing Impaired, Page number: 145