THE COCHLEAR NUCLEAR-COMPLEX - MR LOCATION AND ABNORMALITIES

PURPOSE: To determine the usefulness of MR imaging in locating known s tructural landmarks of the cochlear nuclear complex (CNC), and to dete rmine the frequency of CNC abnormalities, based on these landmarks, in patients referred for MR evaluation of unilateral sensorineural heari ng loss. SUBJECTS AND METHODS: We studied 12 consecutive months of tem poral bone/posterior fossa MR images retrospectively to find four know n structural landmarks of the CNC: the vestibulocochlear nerve root en try zone; the cerebellar flocculus; the curvilinear choroid plexus alo ng and protruding from the foramen of Luschka; and the bulge of the CN C into the lateral recess of the fourth ventricle and the foramen of L uschka. We tabulated the number of landmarks located per CNC and the n umber and type of CNC MR abnormalities. Medical records were then revi ewed to tabulate clinical indication for MR imaging, type of hearing d eficit, and etiology of the hearing deficit and clinical-pathologic pr oof. RESULTS: 175 patients (ages 15-75 years) provided 350 CNCs for st udy. All 350 CNCs showed at least three of the four landmarks. Thirtee n of the 175 patients (7.4%) had focal CNC MR abnormalities; 136 of th ese 175 patients had been referred for MR evaluation of unilateral sen sorineural hearing loss. In 10 of these 136 patients (7.4%), the CNC a bnormalities shown on MR proved to be the cause of the sensorineural h earing 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.