Objective: The objective of this histologic study of archival temporal bone sections was to describe the morphology of human cochleae found with three turns, a previously unreported anomaly, found in three pairs of temporal bones.
Methods: The authors conducted histopathologic processing and measurement of basilar membrane length. Basilar membrane length was compared with that found in six normal control bones.
Results: Cochleae with three complete turns, rather than the usual two and a half turns, are described for the first time. All had longer than normal basilar membranes, with a mean length of 40.6 mm compared with a mean of 33.8 mm in the normal bones.
Conclusions: Human cochleae with three turns exist as an unreported anomaly. This is a new category of anomaly, not likely based on interruption of development.