Dimensions of the cochlear nerve canal: a radioanatomic investigation.

The purpose of this study was to determine the normal variations of cochlear nerve canal dimensions, which is useful information to have when assessing congenital malformations, i.e. during the preoperative evaluation of cochlear implant candidates. The length and diameter of the cochlear nerve canal were measured in 117 casts from randomly selected temporal bone specimens obtained from the Uppsala Temporal Bone Laboratory. In 16 of the casts the dimensions were correlated with those obtained from CT scans of the same temporal bone. Measurements were also made from CT examinations of the temporal bone of 50 patients referred for evaluation of cholesteatoma or chronic otitis media. The mean length and diameter in the axiopetrosal plane measured in casts were 1.17 and 2.58 mm, respectively. The mean diameter in the axial plane was 2.59 mm. The mean length and diameter determined from CT scans of the specimens were 1.19 and 1.98 mm, respectively. The mean length and diameter determined from CT examinations of patients were 1.08 and 1.91 mm, respectively. In conclusion, the cochlear nerve canal is short, with a circular cross-section. If the diameter of the canal is < 1.4 mm then the possibility of cochlear nerve abnormality should be considered; if it is > 3.0 mm then other anomalies may coexist.