The cochlear cleft

Abstract

Background and purpose: Recent advances in the display of medical images permit the routine study of temporal bone CT images at high magnification. We noted an unfamiliar structure, which we now call the "cochlear cleft," in the otic capsule. To our knowledge, this report represents the first description of this structure in the medical imaging literature.

Methods: Temporal bone CT performed in 100 pediatric patients without sensorineural hearing loss were examined for the presence of cochlear clefts. Incidence of cochlear clefts as well as the relationship between age and incidence was examined.

Results: Cochlear clefts were present in 41% of the subjects. Incidence decreased with age.

Conclusion: We describe a cleft in the otic capsule that is frequently seen on magnified images of temporal bone CT studies in children. The cleft may be the fissula ante fenestram.

Fig 1.

Large cochlear cleft in a 2-year-old child. A. Axial CT. The cleft (arrowhead) measures 1.3 high and 0.3 mm wide. B. Coronal CT. The cleft (arrowheads) is 3.4 mm high and 0.2–0.4 mm wide.

Fig 2.

Large cochlear cleft in a 7-year-old child. A. Axial CT. The cleft (arrowhead) is in the otic capsule lateral to the middle turn of the cochlea. It measures 0.8 high and 0.4 mm wide. B. Coronal CT. The cleft (arrowheads) is in the lateral part of the cochlear otic capsule. It measures 5.0 mm high and 0.2–0.3 mm wide

Fig 3.

Small cochlear cleft in an 8-year-old child. A. Axial CT. The cleft (arrowhead) measures 0.9 mm high and 0.2 mm wide. B. Coronal CT. The cleft (arrowheads) is 3.7 mm high and 0.2–0.4 mm wide.

Fig 4.

Plot of cochlear cleft occurrence versus age. The occurrence rate decreases from 62% in the youngest age group to 19% in the oldest.

Fig 5.

Illustration of the perilymphatic labyrinthine space, the fissula ante fenestram (label underlined) and fossula post fenestram (adapted from [8], permission pending). The endolymphatic spaces within the semicircular canals and cochlear duct are drawn as grooves in the perilymphatic surface. The outer surface of the perilymphatic space conforms to the bony labyrinth. The fissula ante fenestram arises from the lateral wall of the vestibule and nearby scala vestibulae, and it continues parallel to the adjacent cochlear turn.

Fig 6.

Temporal bone photomicrographs showing temporal bone structures in an axial plane. (Courtesy of Dr. Barbara A. Bohne at the Washington University in St. Louis School of Medicine) A, A nonosseous cleft is in the lateral part of the cochlear otic capsule (arrow). Ear structures visible are the carotid artery (CA), cochlea (CO), eustachian tube (ET), facial nerve (FN), foot plate of the stapes (FP), internal auditory canal (IAC), tympanic membrane (TM), tensor tympani muscle (TT), and vestibule (VE). B, Enlarged view of the cochlea. The cochlear cleft (CC) is in the middle layer of the otic capsule. The base turn (BT) and middle turn (MT) of the cochlea are adjacent to the cleft.