FALSE-POSITIVE MAGNETIC-RESONANCE-IMAGING OF SMALL INTERNAL AUDITORY-CANAL TUMORS - A CLINICAL, RADIOLOGIC, AND PATHOLOGICAL CORRELATION STUDY

Magnetic resonance imaging with gadolinium facilitates the early diagn osis of internal auditory canal tumors at a small enough stage to perm it increasing application of hearing preservation surgical techniques. Surgeons report successful removal of tumors as small as 3 mm, which are diagnosed with enhanced magnetic resonance imaging. A retrospectiv e study was performed to determine the risk of false-positive ''tumor' ' diagnosis with enhanced magnetic resonance imaging. We reviewed the imaging records, office notes, and surgical records of 112 consecutive ''tumors'' involving the internal auditory canal treated by the Wilfo rd Hall USAF Medical Center Neurotology Service between July 1991 and July 1994. Two categories of false-positive magnetic resonance imaging were identified: (1) surgically confirmed absence of internal auditor y canal neoplasm and (2) spontaneous resolution of the internal audito ry canal lesions on subsequent, enhanced magnetic resonance images. Ov erall, eight false-positive scans were identified. Three were surgical ly confirmed as false-positive, and five resolved on subsequent imagin g studies. All cases were smaller than 6 mm and involved the distal in ternal auditory canal (fundus). The surgically confirmed cases were ap proached through a middle fossa technique with successful hearing pres ervation. The overall rate of surgical false-positive results was 3.5% (3 cases in 86 surgeries). However, the overall false-positive rate f or intracanalicular ''tumors'' was 32% (8 cases in 25 intracanalicular lesions). Although hearing preservation is more likely in small lesio ns, the surgeon must consider the possibility that an internal auditor y canal lesion smaller than 6 mm may actually represent a nonneoplasti c process. Enhancing lesions limited to the internal auditory canal fu ndus may be treated by reimaging the patient in 6 months after the fir st image rather than by prompt surgical exploration.