44‐YEAR‐OLD MAN WITH ABNORMAL GAIT

CLINICAL HISTORY

A 44‐year‐old man was hospitalized with an acute onset of giddiness, drunken gait and tendency to fall. He was apparently well until 1 week prior to presentation. He experienced these symptoms after drinking heavily at a party. There was no history of trauma, headache, vomiting or seizures.

On neurological examination, there was no motor or sensory deficit. Finger‐to‐nose testing revealed mildly abnormal coordination. The patient tended to sway and fall sideways on heel‐to‐toe walking. Romberg's test was mildly positive. Meningeal signs were absent.

Computed tomography (CT) scan revealed a large hyperdense calcified lesion in the fourth ventricle. Magnetic resonance imaging scans showed a fourth ventricular space‐occupying lesion with mild hydrocephalus. Craniectomy with endoscopic fourth ventriculostomy was performed. A reddish brown tumor mass was encountered measuring 30 mm × 20 mm attached to the floor of the fourth ventricle. The tumor was almost entirely resected.

PATHOLOGY

Histopathological examination revealed a moderately cellular tumor with large areas of calcification (1, 2). The tumor cells were arranged in groups and cords as well as showing papillary formation in many areas. The tumor cells were generally large and contained brightly eosinophilic granular cytoplasm with central nuclei (Figure 3). There was only mild nuclear pleomorphism and mitoses were rare.

Figure 1.

Figure 2.

Figure 3.

Immunohistochemical staining showed that many of the neoplastic cells had strong positive reaction for S‐100 protein (Figure 4). Some of these cells were also positive for cytokeratin, epithelial membrane antigen and glial fibrillary acidic protein (GFAP) (not shown).

Figure 4.

FINAL DIAGNOSIS

Oncocytic variant of choroid plexus papilloma (CPP).

DISCUSSION

CPP is an uncommon, slowly growing, usually benign intracranial neoplasm that is commonly located in the ventricular system. It may demonstrate various types of metaplastic changes. The stroma may exhibit focal metaplastic changes such as xanthomatous change, calcification and rarely ossification. The epithelial component may show mucinous metaplasia, pigmentation with presence of neuromelanin, ependymal differentiation or oncocytic transformation. The oncocytic variant of CPP is rare and has been reported in seven cases to date in the international literature, to the best of our knowledge 1, 2, 4, 8, 10.

The term “oncocyte” was introduced by Hamperl in 1931 (5) to describe epithelial cells that appear large with abundant eosinophilic granular cytoplasm. Oncocytic transformation has been observed in various pathologic and non‐pathologic conditions possibly as a consequence of compensatory mitochondrial hyperplasia caused by the defects of oxidative metabolism (9). Although oncocytic transformation may occur in almost all tumors, it is more commonly seen in renal, thyroid, parathyroid and salivary gland tumors. On electron microscopic examination all oncocytes have in common a large number of mitochondria.

Oncocytic transformation is rare in intracranial tumors with the exception of pituitary adenomas. However, a few cases of oncocytic meningioma have been described in the literature (3). Kepes (6) reported oncocytic transformation of choroid plexus epithelium in all the cerebral ventricles in a 27‐year‐old woman who suffered from adult form of Leigh's disease and expired.

CPP is an uncommon tumor in the brain. It is most common in children and usually is in the lateral ventricles, whereas in adults it typically arises in the fourth ventricle. The oncocytic variant of CPP is extremely rare and a report published by Stefanko in 1985 (10) appears to be the first one describing the occurrence of oncocytic transformation in CPP. Since then only seven cases have been reported in the literature. The oncocytic variant has been found to occur more often in older individuals and the fourth ventricle has been the most common site among these cases.

Focal positivity for GFAP has been observed in CPPs and choroid plexus carcinomas in 35%–40% of cases (1). It has been suggested that focal GFAP positivity indicates glial or possibly ependymal differentiation in the choroid plexus epithelium. GFAP‐positive cells are normally not seen in choroid plexus epithelium.

CPP is usually a benign World Health Organization grade I tumor with low or absent mitoses and without invasion of the adjacent brain (7). Tumors with increased mitotic activity are likely to behave in an aggressive manner. As only a few cases have been reported in literature the biological behavior of oncocytic variant is unclear. Malignant transformation of an oncocytic CPP has been reported by Diengdoh and Shaw (4). Additional cases may help to ascertain the biological behavior of this tumor.

ABSTRACT

We present a case of an oncocytic choroid plexus papilloma (CPP) of the fourth ventricle in a 44‐year‐old man. Histopathological examination revealed a CPP composed of large cells with abundant granular eosinophilic cytoplasm. Oncocytic transformation is rare in intracranial tumors with the exception of pituitary adenomas. The oncocytic variant of CPP is even more rare. Only seven cases have been reported in the international literature, and the biological behavior of the oncocytic variant of CPPs is not clear.