FINAL DIAGNOSIS: INTRACEREBRAL BENIGN NERVE SHEATH TUMOR (SCHWANNOMA)
Intracranial schwannomas constitute 5% of all intracranial tumors (1) and a majority of them arise from the vestibular portion of the vestibulo-cochlear nerve and less frequently from other cranial nerves with the exception of optic nerves. Intraparenchymal schwannomas are extremely uncommon and generally amount to case reports only. However, Sharma et al. and Casadei et al. have reported 2 series comprising of 8 and 9 cases respectively (2,3). The most common sites are intracerebral followed by cerebellum, brainstem, sella and fourth ventricle. Review of the literature as well as our own series of eight cases (2) revealed a male preponderance and early onset of symptoms. Imaging generally revealed mixed density to enhancing mass lesions. Interestingly, cyst with mural nodule is an extremely uncommon radiological feature. In a series of 9 cases reported by Casadei et al (3), 2 showed cyst with enhancing mural nodule mimicking a pilocytic astrocytoma.
Therefore, in an intracerebral cyst with mural nodule, in addition to the differential diagnoses of pilocytic astrocytoma, pleomorphic xanthoastrocytoma, ganglioglioma and hemangioblastoma, the possibility of an intraparenchymal benign nerve sheath tumor (shwannoma) should be considered. Microscopically, other differential diagnoses considered in this case were of a pilocytic astrocytoma and fibroblastic meningioma (4). However, histopathological features, reticulin abundance, positivity for S-100 protein and GFAP and negativity for EMA rule out these conditions. Further, presence of basal lamina and absence of intercellular junctions on electron microscopic examination confirmed the diagnosis.
Contributed by C Sarkar, MC Sharma, R Arora, S Gaikwad, VS Mehta