Pathologic quiz case: A cystic mass in the cerebellopontine angle.

Abstract

43-year-old white man sought medical attention because of right-sided facial numbness and recurrent bouts of headaches during the previous 1‰ years; these symptoms had worsened during the preceding 3 months. The patient reported no significant weight loss or decreased appetite. He was a chronic smoker of 33 packyears and had an elevated cholesterol level during the last 2 years. Apart from the hemifacial hypoesthesia, no other neurological deficit was elicited, and the remainder of the findings from the physical examination were unremarkable. Magnetic resonance imaging revealed a 3-cm mass lesion located in the right cerebellopontine cistern; this mass exhibited low intensity with T1-weighted imaging and high intensity with T2-weighted imaging and did not enhance with contrast media (Figure 1, arrow). Transtemporal craniotomy and resection of the mass with decompression through retrosigmoid approach was performed. At surgery, the mass was noted to be cystic, thin-walled, and filled with mucuslike material. It was significantly adherent to several cranial nerves, including V, VII, VIII, IX, X, and XI, as well as to the basilar and both vertebral arteries. The content of the cyst was gutted out, and the capsule was stripped completely from the nerves and arteries. Several thin fragments of white to light brown soft tissue and soft flakelike brown material admixed with mucus with an aggregate measurement of 1.9 3 0.9 3 0.3 cm were received for pathologic examination. On microscopic examination, the lining of the cyst was composed of single to pseudostratified layers of tall columnar epithelium with foci of transition to nonkeratinized stratified squamous cells that rested on a thin collagenous basement membrane (Figure 2). The columnar cells displayed prominent apical ciliation with clear cytoplasm and basally situated regular nuclei (Figure 3). Neither cellular atypia nor mitosis was demonstrated. What is your diagnosis?