Visualization of small acoustic neurinomas by CT scan

Thirty patients with histologically verified acoustic neurinomas were examined by means of the CT scan (HITACHI CT-H, 256 x 256 Matrix), from January, 1976, to December, 1979. The CT findings of these 30 cases were then analyzed and compared with those of conventional radiological examinations. The purpose of this report is to evaluate the capability of the CT scan to detect small acoustic neurinomas. (1) Twenty-seven (90%) out of these 30 cases showed positive contrast enhancement following an iodinated contrast infusion (I.C.I.) scan. The tumors of all but one of these 27 cases were over 2 cm in diameter. In the one exceptional case where the diameter was less than 2 cm (1.5 cm), overlapping scanning was useful for delineation. (2) The tumors of the 3 cases showing no contrast enhancement were all less than 2 cm in diameter. These were all positive in metrizamide CT cisternography. Among these 3 tumors, 2 were 1 cm in diameter and showed only 8th cranial nerve symptoms. On the basis of our experience and the previous literature, the I.C.I. scan is considered to be almost always able to show acoustic neurinomas over 2 cm without false negative scans. Metrizamide CT cisternography is very helpful for the detection of smallest tumors with a negative I.C.I. scan, as is indicated in this study in which 2 tumors of 1-cm diameter were demonstrated. In the near future, metrizamide CT cisternography with the further developed scanners will gradually replace iophendylate cisternography. (author)