Cystic acoustic neurinomas: studies of 14 cases.

Cystic acoustic neurinomas (ANs) are less frequent and are different from solid ANs in clinical and radiological features. We had 14 cystic ANs (13.5% of 104 cases) in the last 17 years. Computerized tomographic or magnetic resonance images allowed for the classification of these cystic ANs into three types: Type A being large single cysts with a thin tumourous wall (7 cases); type B single cysts with a thick tumourous wall (3 cases); type C multicystic (4 cases). Half of the cystic ANs were not accompanied by enlargement of the internal auditory canal, despite the largeness of the cysts. The mean size of the tumours was 29 mm in diameter. Type A cysts had a shorter clinical history than types B and C. One patient had intact hearing. In five cases, an atypical initial symptom such as facial pain, dysgeusia, facial palsy, unsteadiness or vertigo presented. The trigeminal nerve was involved in 12 cases, the facial nerve in nine. The characteristic features of cystic ANs are largeness of the tumour, a short clinical history, an atypical initial symptom, facial nerve involvement, and/or no enlargement of the internal auditory canal. In addition, the histological features are a lobular growth pattern, high nuclear atypia, and numerous macro phages.