Brain Pathology Case of the Month - December 2007

Contributed by Lisa Browning1, John Leach2, Christopher Watts3, Wilhelm Kuker3, Richard Stacey2
1 Department of Neuropathology, 2Department of Neurosurgery, 3Department of Neuroradiology, Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE


A 51 year-old right-handed female presented with a two-month history of double vision and numbness around her left ear. Her walking became unsteady and she progressively developed left facial and tongue numbness, left-sided hearing loss and a left facial droop. In the two weeks prior to presentation she complained of headaches with associated nausea and vomiting.

On examination she was alert and orientated with a Glasgow Coma score of 15/15. Cranial nerve examination revealed: an internuclear ophthalmoplegia; left masseter muscle wasting, abnormal left facial and tongue sensation and an absent left corneal reflex; left facial nerve palsy; reduced hearing on the left side; symmetrical palatal movement and an intact gag reflex. There were mild left sided cerebellar signs.


The T2 weighted axial image through the posterior fossa (figure 1) showed an area of high signal intensity in the left cerebellar hemisphere and brain stem with displacement of the fourth ventricle. Within the left cerebellar hemisphere, a nodular lesion with low signal intensity was noted compressing the ventricle (arrow). There was a second, crescent shaped area of low signal intensity (double arrow) suggestive of calcification as well as volume loss of the left cerebellar hemisphere, best appreciated on the coronal FLAIR images (figure 2). The contrast-enhanced T1-weighted axial image (figure 3) showed avid enhancement in the previously low signal nodular lesion adjacent to the ventricle. There was no contrast uptake in the rest of the cerebellum. These features were suggestive of two lesions; one non-contrast-enhancing high-signal area in the cerebellum with associated calcification, and a second contrast-enhancing low signal area in association with the fourth ventricle. In addition, the cerebellar atrophy may point to a more chronic process. There are, however, no features of Lhermitte-Duclos.


At craniotomy there were apparently two components to the tumor: the first was a firm, pale, fibrous mass arising from the left cerebellar hemisphere. On dissection of this tumor a distinct soft gray-purple mass was encountered filling the fourth ventricle. A subtotal excision was performed as the tumor was densely adherent to the adjacent cerebellar peduncle and medulla.


The histopathological features were those of a low-grade, focally calcified tumor comprising atypical ganglion and glial cells (low power H&E, figure 4). Many of the ganglion cells were binucleate, with occasional trinucleate forms (high power H&E figure 5). The glial component comprised spindle-shaped cells with interspersed Rosenthal fibres. Mitotic figures were not seen, and there was no necrosis. A mild infiltrate of small reactive lymphocytes was noted interspersed among the neoplastic cells. Immunohistochemistry revealed expression of synaptophysin by many of the dysplastic ganglion cells (figure 6), with some co-expressing neurofilament protein and occasionally glial fibrillary acidic protein (GFAP) (figure 7). Several of the dysplastic ganglion cells also expressed CD34. Immunostains for GFAP highlighted the glial cell population. Ki-67 (MIB-1) activity was not noted among the neoplastic populations - the few positive nuclei in these areas were those of interspersed reactive CD3 positive T lymphocytes.

While the low grade tumor described above was the predominant component of the biopsies received, at the edge of one of the biopsies (on the left of figure 4) was a dense infiltrate of mitotically-active large atypical lymphocytes (high power H&E figure 8). Immunohistochemistry revealed that this was a population of neoplastic CD20 positive B lymphocytes (figure 9), and here the Ki-67 (MIB-1) labelling index reached 80%. The small reactive lymphocytes interspersed among the lymphoma cells and within the ganglioglioma are CD 20 negative T cells.


International Society of Neuropathology