Case 584 -- Posterior fossa tumor in a 12 year-old boy

Contributed by Evriviadis Mpairamidis1, MD, George A Alexiou1 , MD, Kalliopi Stefanaki 2, MD, PhD,
     Manolakos Ilias1 , MD, Sfakianos George1, MD, PhD and Prodromou Neofytos1, MD, PhD
1Department of Neurosurgery, 2 Department of Pathology, Children's Hospital ''Agia Sofia'', Athens, Greece.


CLINICAL HISTORY

A 12-year-old male was admitted to our hospital complaining of right upper limb tremor, loss of the normal capacity to modulate fine voluntary movements with his right hand and headache, lasting for over a month. On neurological examination dysdiadochokinesia and intention tremor of the right upper limb was noted. A computed tomography (CT) scan was performed and revealed a large lesion expanding in the right cerebellar hemisphere, compressing the fourth ventricle which was occluded. Magnetic resonance imaging (MRI) of the brain demonstrated the same space-occupying lesion in the fourth ventricle measuring approximately 4 3.8 4 cm. It was hypointense on T1-weighted images (Fig.1), medium intense on T2 and FLAIR sequences, and heterogeneously enhanced after gadolinium administration (Fig. 2). The lesion was surrounded by edema and caused displacement of the cerebellar vermis and pons. A suboccipital midline craniotomy was performed, the cerebellar vermis was split and the lesion was totally excised.

GROSS AND MICROSCOPIC PATHOLOGY

Macroscopically, the resected tumor had a varied appearance with evidence of old and recent hemorrhage, necrosis and areas of firm tissue. Histological examination revealed extensive infiltration of cerebellar tissue by a cellular malignant tumor (Fig. 3) composed of round and spindle cells with eosinophilic cytoplasm, moderate-severe nuclear atypia and brisk mitotic activity (Fig. 4). Characteristic features were: a) the presence of numerous giant mononuclear and multinuclear neoplastic cells, b) the presence of geographic necrosis (necrosis with palisading) (Fig. 5), c) glomeruloid microvascular hyperplasia, and d) the infiltrating pattern of invasion into the adjacent parenchyma. Immunohistochemistry showed rare GFAP expression in the neoplastic cells, while there was no expression of synaptophysin, neurofilament, Neu-N (a marker of neurons) and Epithelial Membrane antigen (EMA). The INI-1 protein retained nuclear expression in the tumor component. The Ki-67/MIB-1 proliferative index was detected in >70% of the nuclei (Fig. 6) and p53 protein in 90% of them. No EGFR expression was observed.

FINAL DIAGNOSIS


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