A histologic study on the temporal bone of guinea pigs.

OBJECTIVES We examined histopathologic and anatomical features of the guinea pig temporal bone and evaluated the differences and similarities with respect to the human ear. STUDY DESIGN Seventeen adult guinea pigs were deeply anesthetized with pentobarbital and then decapitated. Each temporal bone was removed and fixed in 10% formaldehyde for a week, then decalcified in 10% formic acid for three weeks. Paraffin-embedded specimens were serially and horizontally sectioned at 7-micron thickness. One of every five sections was stained with hematoxylin and eosin and studied under light microscopy. RESULTS The temporal bone consisted of a mastoid-like process, a tympanic bulla, a tympanic ring, a petrosal segment, and a poorly developed squamosal bone. The tympanic bulla was a semispherical cavity surrounded by the tympanic ring. The head of the malleus and the body of the incus were fused, forming a malleoincudal complex. The diameters of the tympanic sulcus and the tympanic membrane were much greater than that of the tympanic ring, resulting in protrusion of the external ear-canal into the bulla. The Eustachian tube was J-shaped, lying in a bony hiatus at the anteromedial aspect of the bulla. The inner ear consisted of the cochlea, semicircular canals, and the vestibule. The cochlea made 3.5 turns and projected into the bulla. No internal auditory meatus was observed. CONCLUSION The guinea pig temporal bone was found to have histological similarities to that of humans, making it a good model for selected experimental studies in otology.