CT in Diagnosis of Acoustic Neuromas 645

A detailed analysis of the CT findings in 75 cases of acoustic neuroma is presented. The method of examination included plain and enhanced CT, metrizamide CT cisternography (M-CTC), and gas CT cisternography (gas-CTC). The common CT appearances of acoustic neuromas were as follows: 93.6% appeared as isodense or hypodense on precontrast scan; homogeneous enhancement was observed in 53.8% on postcontrast scan; the tumor center, mostly located at the level of the internal acoustic canal, was spherical in shape with an acute angle between the lateral tumor border and petrous bone; and there was widening of the internal acoustic canal or destruction of petrous bone. However, the presence of an acoustic neuroma could not be excluded if widening of the internal acoustic canal was absent. It was not certain whether contrast filling of the internal acoustic canal occurred at M-CTC in the four cases so examined. One case of intracanalicular neuroma was diagnosed by gas-CTC, which is the most sensitive and reliable technique for detecting and excluding small tumors. The significance of various CT appearances, early diagnosis, and differential diagnosis of acoustic neuroma from other cerebellopontine-angle tumors, particularly meningioma, are discussed.