Peripheral vestibular system in Down syndrome: Quantitative assessment of vestibular histopathology

Objective. To evaluate the maturity of the peripheral vestibular system in Down syndrome by examining the number of Scarpa's ganglion cells and the density of vestibular hair cells. Study Design. Case-control study using human temporal bones. Setting. Tertiary academic center, otopathology laboratory. Subjects and Methods. Sixteen temporal bones from 8 patients with Down syndrome and 15 control temporal bones from 8 individuals with no history of otologic disease were selected. Hypoplasia of the lateral semicircular canal (LSC) and vestibule was investigated by measuring the dimensions of the structures. Scarpa's ganglion cells were counted under light microscopy. The vestibular hair cells were counted in the LSC crista and the utricular and saccular maculae under differential interference contrast (Nomarski) microscopy and expressed as density. Results. The patients with Down syndrome were divided into 2 groups: with and without LSC hypoplasia. The number of Scarpa's ganglion cells and the density of vestibular hair cells were significantly smaller in both groups of patients with Down syndrome than in the control group. There was no significant difference in the number of Scarpa's ganglion cells or the density of vestibular hair cells between the groups with and without LSC hypoplasia. Conclusion. The peripheral vestibular system, including Scarpa's ganglion cells and vestibular hair cells, is hypoplastic irrespective of the vestibular malformation in Down syndrome.