Intracranial Mesenchymal Tumor With FET::CREB Fusion Involving Lateral Ventricle: A Case Report With Review of Literature.

Intracranial mesenchymal tumor, FET::CREB fusion-positive is a provisional tumor type in the 2021 World Health Organization (WHO) classification of central nervous system tumors, typically seen in children and young adults. Herein, we describe a patient with intracranial mesenchymal tumor, FET::CREB fusion-positive arising at a rare site, that is, lateral ventricle in a young girl with complaints of headache and diplopia. The mass was excised and sent for histopathological examination wherein, a possibility of intracranial myxoid mesenchymal tumor with FET::CREB fusion was suggested. Subsequently, the diagnosis was confirmed on demonstration of EWSR1 gene rearrangement by break apart fluorescence in situ hybridization (FISH). Owing to its rarity, there are very few published reports in the literature and hence their clinical course is not well known. On review of the world literature, it is documented to be a locally aggressive tumor with a high recurrence rate. It is imperative that pathologists are aware of the full clinicopathologic spectrum of this rare entity, as the differential diagnosis can be challenging.