Chapter 175. Congenital Malformations of The Vestibulocochlear System - Review of Medical Embryology Book

Malformations of the vestibulocochlear system can be classified into 3 different groups, corresponding to the specific embryologic characteristics of each of the ear's 3 parts

Rubella in the second month of pregnancy is often a cause of lesions here since this is when the internal ear differentiates

The epithelium of the cochlea and vestibule is altered, but the organ of Corti has some intact regions, so that children affected do perceive some deep frequencies

The semicircular canals: few malformations are known, although some have been seen with the use of thalidomide

After an infection, the mesenchymal plate separating the ossicles may become sclerotic, impede movement, and may result in total deafness
Congenital fixation of the stapes results in severe congenital conductive deafness, although the remainder of the ear is normal. The stapes is fixed to the bony labyrinth

May be due to a failure of differentiation of the annular ligament of the stapes

Defects of the malleus and stapes are often associated with abnormalities of branchial arch I, , in hypoplasia of the mandible as seen in micrognathia

May result from the absence or nonunion of the primordial tubercles
Major variations of the auricle have been associated with serious internal abnormalities, such as kidney malformations
Abnormal position of the ear: usually associated with abnormal mandibular development, such as agnathia or micrognathia

Instead of moving to the sides of the head, the ears develop at the site of the primordia namely, at the level of the first branchial groov Thus, at birth, the ears are seen at the angle of the missing jaw (otocephalus)

Auricular appendages or tags are common and due to accessory auricular hillocks
Absence and hypoplasia of the auricles are rare and are associated with arch I syndrome where there is a failure of the auricular hillocks to develop (anotia) or they are suppressed in their development (microtia)
Auricular sinus and fistulas: sinuses are usually preauricular and fistulas connect the exterior with the tympanic cavity
Atresia of the external auditory meatus: failure of the meatal plug to canalize

An abnormal development of the membranous and bony labyrinths
Malformations of the eardrum and ossicles
In extreme cases, the tympanic cavity and the external auditory meatus are completely absent

Rubella virus, affecting the embryo in weeks 7 and 8 of development, can cause severe damage to the organ of Corti; diabetes; erythroblastosis fetalis; hypothyroidism; toxoplasmosis; and x-radiation

MAJOR VARIATIONS OF THE AURICLE have been associated with serious internal abnormalities, such as seen with kidney malformations