Limitations of computed tomography in the investigation of acoustic neuromas.

Seventy percent of 80 surgically proven acoustic neuromas were visualized on preoperative computed tomography (CT) scans. Many more tumors were seen on contrast enhanced scans than on unenhanced scans (55 vs 25). No intracanalicular tumors and only one of 15 tumors less than 2 cm in size were visualized on CT scan. Most medium size tumors (2.0-3.0 cm) and all large tumors (greater than 3.0 cm) were visualized on CT scan when optimal technique was used. Positive CT scans often replace more invasive diagnostic studies in the investigation of acoustic neuromas. Negative scans do not rule out tumors as intracanalicular, and small tumors are usually not visualized with current techniques. If there is clinical suspicion of an acoustic neuroma, positive contrast posterior fossa cisternography should be done when the CT scan is negative.