Case 1014 - A 25-Year-Old Gentleman with a Posterior Fossa Mass

Contributed by Aravind Sekar, MD1, Kirti Gupta, MD1, Ashish Aggarwal, DNB, M Ch2, Pravin Salunke MS, MCh2
Departments of Histopathology1 and Neurosurgery2, Postgraduate Institute of Medical Education and Research, Chandigarh. India


A 25-year-old gentleman presented with short history of headache and gait disturbances. Radiology revealed a heterogeneously enhancing mass in the fourth ventricle extending from midbrain to pons. CT scan showed a hyperdense mass in the 4th ventricle. There was no calcification or cysts seen within the lesion. MRI showed a well defined mass in the fourth ventricle. The lesion was isointense on T1, hyperintense on T2 (Fig. 1A) and enhanced heterogeneously on contrast administration (Fig. 1B). The contrast images showed tumor infiltration into brain stem suggesting a poor plane of cleavage, better appreciated on sagittal MRI (Fig. 1C). FLAIR MRI showed slightly hyperintense lesion suggesting a cellular tumor (Fig. 1D). Though the lesion showed no calcifications or cysts or areas of bleed, the enhancement pattern and infiltration in the fourth ventricular floor suggested a radiological diagnosis of ependymoma. The lesion was operated through a midline suboccipital craniotomy. The lesion was yellow grey, not very vascular and was attached to the brain stem. A thin sliver of tumor adherent to the brain stem was left. Near total resection could be achieved.


The histopathological examination revealed characteristic features of a tumor, which was defined by perivascular pseudorosettes, elongated round to oval uniform nuclei, present in a fibrillary background (Fig. 1E). Amidst these areas, interestingly, there were numerous islands composed of pale central nuclear-free neuropil-rich zones (Figs. 1F, 1G). These on the periphery were bordered by similar tumor cells (Fig. 1H). The transition between these islands and tumor cells was abrupt. On a low magnification, these islands were strikingly similar to pseudo-palisading necrosis of high-grade gliomas. Tumor cells were immunoreactive for glial fibrillary acidic protein (GFAP) with perivascular accentuation (Fig. 1I). Epithelial membrane antigen (EMA) revealed distinct dot-like positivity within the tumor cells (Fig. 1J). The pale neuropil-like islands were intensely positive with synaptophysin (Fig. 1K). No immunostaining for Neu N was observed. Mitotic activity was brisk with intermediate to high Ki-67 labelling index. Necrosis and vascular proliferation was absent What is your diagnosis?


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