Appearance of hypoplastic cochleae in CT and MRI: a new subclassification

Hypoplastic cochleae are among the inner ear malformations more frequently encountered by radiologists; little detailed information is available on these, however. We present the first large series of hypoplastic cochleae and document imaging findings to better characterize this anomaly radiologically. We used our electronic database to search for inner ear malformations described between 1995 and 2009 and extracted 81 ears (of 47 patients) with hypoplastic cochleae out of 289 patients with inner ear malformations. Two neuroradiologists evaluated the available CT and MRI data. Measurements of all inner ear structures were performed. Accompanying findings were listed. Cochlear hypoplasia (58 ears, 32 patients) often involves not only the apical turn being reduced in size but also the basal turn being smaller in length. Additionally, 11 ears (eight patients) of hypoplastic cochleae with only a basal turn and five ears (four patients) of cochleae with only a small bud were identified. Non-classifiable hypoplastic cochleae (seven ears, five patients) were those with either a rudimentary or an absent basal turn or a dwarf appearance with no further partition. The term hypoplastic cochlea is very general; a further division into severe and less severe forms based on the length and existence of cochlea turns is possible and can help enhance the comparison of CI outcome data. Measurements can help the less experienced radiologist to detect them more easily.