[Large cystic neurinoma: a case report]

We report a case of large cystic acoustic neurinoma. A 52-year-old male was admitted to hospital with a history of progressive dysphagia, gait disturbance and diplopia for 2 months. On admission, neurological examinations revealed Bruns' type nystagmus to the left side, hypesthesia in the distribution of the second and third divisions of the left trigeminal nerve, and partial paresis of cranial nerves IX, X, and XII on the left side, and truncal ataxia. A pure-tone threshold audiogram indicated the presence of 32 dB hearing loss in the left ear. Speech discrimination was 80%. Caloric vestibular responses were absent on the left side. Skull radiographs with polytomographs of the internal auditory canal (IAC) were normal. Bony changes in the IAC were not found by high-resolution bone-window computed tomography (CT) scan. A plain CT scan revealed a large low-attenuated cystic mass in the left cerebellopontine angle (CPA), which was associated with displacement of the fourth ventricle. An enhanced CT scan demonstrated a thin rim-enhancement in the cyst wall. Magnetic resonance imaging (MRI) scans disclosed a large rim-enhanced cystic mass extending superiorly into the tentorial incisura and inferiorly into the foramen magnum. At surgery via a left suboccipital approach, a large cystic mass was found at the left CPA arising from the VIIIth nerve, and compressing the Vth, VIth, VIIth and lower cranial nerves. The cyst was filled with a xanthochromic fluid and was firmly attached to the internal auditory meatus (IAM). However no tumor extension into the IAM was confirmed. The tumor was excised completely. The postoperative course was uneventful, except for impairment of the VIIth and VIIIth nerves. At 6 months after the first operation, the facial nerve had improved up to grade III (Hause-Brackmann stage). Histological examinations revealed a typical benign acoustic neurinoma with predominant representation of Antoni B tissues. The cyst wall contained numerous abnormal sinusoid and telangiectasia-like vessels which showed occasional thromboses. The vessel walls displayed endothelial proliferations and were frequently hyalinized. Hemosiderin deposits and hemosiderin-containing phagocytes were also found near these vessels. Myxoid degeneration and necrosis were evident in vast areas. These degenerative changes appeared to be the principal causes of the large cystic formation. 16 cases including our case have been reported. The broad characteristics of the clinical symptoms and radiological findings of these tumors are discussed.