Cystic trigeminal schwannoma with fluid-fluid levels

A 53-year-old man presented with a 2-year history of progressive decreased vision and proptosis involving the right eye. Opthalmological examination showed right optic disc atrophy. Neurological examination revealed hypoesthesia in the distribution of the second branch of the right trigeminal nerve. Computed tomography (CT) and magnetic resonance (MR) scans revealed a large extra-axial lobulated mass in the right middle cranial fossa (Fig. 1a,b). Non-infiltrative smooth margins of the mass and bone remodeling of adjacent bone were present, suggesting a longterm, benign growth of the lesion (Fig. 1a). In addition, multiple cysts of variable size and fluid-fluid levels were present within the lesion (Fig. 1a,b). At surgery, a multilobulated cystic mass involving the second branch of the right trigeminal nerve was identified and resected, and a relatively hard, dark red hematoma was found in the tumor and evacuated. Histological examination revealed an irregular distribution of hypercellular Antoni-A and hypocellular Antoni-B tissues, and neural tumor tissue was surrounded by multiple, irregularly shaped, cystic and hemorrhagic areas (Fig. 2). These findings were consistent with fifth nerve schwannoma. About 25–45% of benign schwannomas arise in the head and neck region [1]. In some cases, intracranial and extracranial schwannomas undergo cystic changes, intermixed with cellular portions [1]. Several pathophysiological mechanisms in the formation of cysts accompanying schwannomas have been postulated: intratumoral bleeding, ischemic central necrosis and degenerative changes, specially in schwannomas in which Antoni-B areas prevail [1, 2]. For some authors, confluence of mucinous and microcystic areas in Antoni-B tissue accounts for most of the large cysts produced in schwannoma [2]. In our case, most of the cystic areas were found to be composed of blood products, suggesting repeated episodes of intratumoral bleeding, resulting in cyst formation. Other rarely reported causes of cystic spaces within schwannomas are the formation of an associated arachnoid cyst and the presence of glandular or pseudoglandular elements in the tumor [2]. Fluid-fluid levels may occur whenever substances of differing density or composition are contained within a cyst. In hemorrhagic cysts, the physical formation of the fluid level is due to the setting of the relatively denser cellular components [1, 2]. The hypointense signal of the Eur Radiol (2004) 14:1941–1943 DOI 10.1007/s00330-004-2286-4 L E T T E R T O T H E E D I T O R