LATERAL EXTENT OF INTERNAL AUDITORY-CANAL INVOLVEMENT BY ACOUSTIC NEUROMAS - A SURGICAL-RADIOLOGIC CORRELATION

The sensitivity of gadolinium-enhanced magnetic resonance imaging (MRI ) is such that inflamed areas of individual nerves can be visualized. Given this, might the lateral extent of an acoustic neuroma in the int ernal auditory canal be inaccurately depicted by MRI with gadolinium c ontrast due to variable enhancement in inflamed neural tissues? The au thors studied the correlation between preoperative MRI and intraoperat ive observation of the lateral extent of tumor in the internal auditor y canal (IAC) of 82 patients with acoustic neuromas. The surgeon made a visual determination of tumor extent when the lateral-most aspect of the tumor was exposed. The radiologist, blind to surgical findings, n oted the degree of extension into the IAC based on the MRI. The majori ty (83%) of the tumors involved the lateral third and fundus of the IA C. Agreement between scans and surgical findings was excellent for tum ors extending into the lateral third of the IAC, with a test sensitivi ty of 94 percent and a positive predictive value of 98.5 percent. Know ledge of the accuracy of MRI in demonstrating extent of tumor in the I AC is important in making decisions regarding surgical approach.