Case 579 -- A 16-year-old male with a cerebellar mass

Contributed by Gabrielle A. Yeaney, MD1, Siobhan M. O'Connor, MD1, Brian T. Jankowitz, MD2, Ronald L. Hamilton, MD1
     1 Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA
     2 Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, PA


A 16-year-old right-handed male presented to an emergency room after suffering mild head trauma from a fall onto his head while intoxicated with alcohol. Physical examination revealed a healthy, inebriated male with no focal neurological deficit. The mother reported that her son had experienced excessive fatigue over the last three months. The patient's past medical, surgical and family history were all noncontributory.

MRI revealed a 3.1 x 3.9 x 3.4 cm solid, heterogeneous, midline posterior fossa lesion with a 2.6 x 4 x 4.5 cm posterior cystic component (Figure 1). The solid lesion extended into the proximal portion of the right foramina of Luschka and appeared isointense on T1 and T2 imaging, while the cystic component remained hypointense and hyperintense on T1 and T2, respectively (Figure 2). The solid component showed moderate, heterogeneous enhancement (Figures 3, 4). The cyst wall did not enhance. There was minimal signal on the FLAIR sequence in the surrounding tissue (Figure 5). MRI of the total spine revealed no evidence of metastatic disease.

A suboccipital craniotomy revealed a large cyst filled with clear yellow fluid surrounded by a translucent membrane. The solid component was grey and gelatinous with ill defined margins and was adherent to the floor of the fourth ventricle. There were numerous vascular pedicles feeding the lesion that caused significant bleeding. A gross total resection was obtained.


Cytologic preparation of the intraoperative material showed abundant plump pleomorphic cells and inter-mixed small lymphocytes (Figure 6). The pleomorphic population had ample glassy eosinophilic cytoplasm and showed occasional multinucleation (Figure 7). Cytoplasmic processes were suggested but were not a prominent feature. Nuclei were hyperchromatic, and some showed intranuclear inclusions secondary to cytoplasmic invagination (Figure 8). On H&E stained permanent sections, the large bizarre tumor cells were arranged in compact sheets punctuated by small lymphocytes (Figures 9, 10, 11). An infiltrating component resembling diffuse astrocytoma could be found in areas (Figure 12, 13). Rosenthal fibers were particularly abundant in the areas of infiltrating glioma (Figure 14). Only a scarce mitotic figure was found. Necrosis was absent. Intratumoral vessels were thin walled without proliferation of endothelium, and some showed perivascular CD3-positive T cells (Figure 15). Reticulin fibers between individual cells were focally abundant (Figure 16). Glial fibrillary acidic protein (GFAP; figure 17) and vimentin (Figure 18) were strongly expressed in many cells, while synaptophysin and neurofilament protein were not. Ki-67 showed a very low proliferation index (Figure 19).


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