Case 561 -- A recurrent cerebellar lesion in a young boy

Contributed by Gregory T. Ray, MD, PhD1, Shanti S. Agarwal, MD2, Roger E. McLendon, MD1
1Department of Pathology, Duke University Medical Center, Durham, North Carolina
2Department of Pathology, Palms West Hospital, Loxahatchee, Florida


A 7 year old boy originally presented with a cerebellar lesion. The MRI demonstrated a complex posterior fossa mass with predominantly T1 darkness and a nidus of enhancement (Fig 1). The mass was impinging upon the posterior aspect of the fourth ventricle. This original resection was followed by a second resection approximately 2 years later and a third resection approximately 4 years after the first resection.


In the original resection specimen (Fig 2), this neoplasm is characterized by a monomorphic population of small round cells with dispersed chromatin. There are many acellular neuropil-rich formations. Mitotic figures, microvascular proliferation, and necrosis are not seen. Rosenthal fibers, eosinophilic granular bodies, and a biphasic appearance are not identified. The tumor cells are positive for synaptophysin (Fig 3) and negative for glial fibrillary acidic protein (GFAP, Fig 4). In the most recent resection specimen, the tumor has similar morphology (Fig 5) and the tumor cells are positive for synaptophysin (Fig 6) and S-100 but negative for Neu-N, neurofilament protein, epithelial membrane antigen, chromogranin, and GFAP (Fig 7). The Ki67 labeling index is 1%.


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