Arachnoiditis simulating acoustic neuroma on air-CT cisternography.

Routine thin-sect ion CT after contrast enhancement may fail to demonstrate smal l acoustic neuromas, usually those smaller than 10 mm [1, 2]. Metrizamide CT cisternography has demonstrated such small acoustic neuromas, but cannot demonstrate an intracanalicular tumor accurately [3]. Pantopaque c isternography can demonstrate an intracanalicular mass, but has a high percentage of inconclusive examinations and a risk of inducing arachnoiditis [4-6]. The newest procedure, air-CT cisternography (air-CTC), has been reported to be more sensitive in demonstrating the small intracanalicu lar tumor [7, 8]. We describe a case of nonfilling of the acoustic canal on air-CTC caused by arachnoiditis simulating an acoustic neuroma.