The cochlear nuclear complex: MR location and abnormalities.

PURPOSE To determine the usefulness of MR imaging in locating known structural landmarks of the cochlear nuclear complex (CNC), and to determine the frequency of CNC abnormalities, based on these landmarks, in patients referred for MR evaluation of unilateral sensorineural hearing loss.

SUBJECTS AND METHODS We studied 12 consecutive months of temporal bone/posterior fossa MR images retrospectively to find four known structural landmarks of the CNC: the vestibulocochlear nerve root entry zone; the cerebellar flocculus; the curvilinear choroid plexus along and protruding from the foramen of Luschka; and the bulge of the CNC into the lateral recess of the fourth ventricle and the foramen of Luschka. We tabulated the number of landmarks located per CNC and the number and type of CNC MR abnormalities. Medical records were then reviewed to tabulate clinical indication for MR imaging, type of hearing deficit, and etiology of the hearing deficit and clinical-pathologic proof.

RESULTS 175 patients (ages 15-75 years) provided 350 CNCs for study. All 350 CNCs showed at least three of the four landmarks. Thirteen of the 175 patients (7.4%) had focal CNC MR abnormalities; 136 of these 175 patients had been referred for MR evaluation of unilateral sensorineural hearing loss. In 10 of these 136 patients (7.4%), the CNC abnormalities shown on MR proved to be the cause of the sensorineural hearing loss.

CONCLUSIONS MR reliably delineates the CNC. Over 1 year, approximately 7% of patients referred for MR evaluation of unilateral sensorineural hearing loss had MR-determined focal CNC abnormalities that caused the sensorineural hearing loss.