Retinoid-induced ear malformations.

Treatment of pregnant Sprague-Dawley rats with retinoic acid or etretinate pregnancy day 8.5 to 9.0 resulted in craniofacial defects in 100% of the embryos. A morphologic investigation of the malformations occurring in the ear was performed. Outer ears were missing, microtic, low-placed, and dorsally situated. External acoustic meatus was short or absent. Middle ear structures were delayed in differentiation, middle ear ossicle primordia were hypoplastic and malformed, the stapedial artery and facial nerve were hypoplastic, and their relation to the stapes was variable. In the inner ear, the otic capsule was thick, the cochlea had fewer turns and the semicircular ducts showed poor differentiation.