Case of an Intramedullary Ancient Schwannoma of the Brainstem Mimicking Astrocytoma: A Rare Clinical Presentation with a Diagnostic Dilemma

Schwannomas are common benign tumours arising from the myelin sheath of peripheral nerves. These tumours are usually located in the intradural and extramedullary regions. The common sites are cervical (58%) and thoracic region (32%), followed by the lumbar region (10%). Intramedullary location is rare and if present, is usually associated with neurofibromatosis 1 and 2 (NF-1 and 2). Intramedullary brainstem schwannomas without NF are uncommon, and to the best of the authors' knowledge, only 19 cases have been reported to date. It was first described by James Watson Kernohan, an Irish-American pathologist, in 1931. The rarity of these tumours in this location is due to the absence of Schwann cells in this area. There are several hypotheses postulating the presence of these tumours in this location. The exact cause is not yet known. The authors here present a case of intramedullary brainstem ancient schwannoma with an unusual clinicoradiological presentation, which raised suspicion of Glioma with the possibility of Astrocytoma. The patient presented with right-sided neck stiffness and shoulder pain for a period of four months. Total excision of the tumour was performed, and the postoperative period was uneventful with clinical improvement in the patient. Histomorphology raised the suspicion of a tumour of glial origin with the possibility of Astrocytoma; Immunohistochemistry (IHC) helped in reaching the definitive diagnosis of Ancient Schwannoma. Thus, a combined approach of clinicoradiological, as well as histomorphology and IHC, is essential for a definitive diagnosis of these tumours. Future multicentric studies are required to elucidate the pathogenesis of the location of these tumours.