Four variations of the Mondini inner ear malformations as seen in microdissections.

Four variations and degrees of severity of the Mondini malformation were found in the temporal bones from two neonates, one with congenital heart disease and the other with trisomy D, and from one teenager with leukemia: 1) short cochlea and normal vestibular organs; 2) short cochlea and persistent horizontal canal anlage; 3) markedly shortened cochlea with no modiolus, wide internal auditory meatus, and persistent horizontal canal anlage; 4) same as variation 3, but with persistent anlagen in all semicircular canals. Variations 3 and 4 were from the case of trisomy D, in which the left cochlea had a normal hair cell population but few nerve fibers, and the intraganglionic spiral bundle was displaced from Rosenthal's canal to the osseous spiral lamina. The right ear had no cochlear nerve fibers; the organ of Corti was present, but hair cells were unusually small. In the case of trisomy D, both ears showed subtotal loss of vestibular nerve fibers. Although the rudimentary cristae of the right ear had numerous hair cells, the macular hair cells were fewer and malformed. No hydrops was present.