Intracranial myxoid mesenchymal tumour: a novel diagnostic entity in WHO 5th edition

• Main Authors: Jasmine Kueh Wui Thing, Kueh, Chelvam Rajesvaran, Rajesvaran, Bryan Pei Chun Sia, Pei, Ahmad Tirmizi, Jobli
• Format: Article
• Language: English
• Published: College of Pathologists, Academy of Medicine Malaysia. 2022
• Subjects: RB Pathology; RZ Other systems of medicine
• Online Access: http://ir.unimas.my/id/eprint/39588/3/19th%20Annual%20Scientific%20Meeting%20-%20Copy.pdf; http://ir.unimas.my/id/eprint/39588/; http://www.mjpath.org.my/
• Institution: Universiti Malaysia Sarawak

Introduction: Primary mesenchymal tumours of the central nervous system (CNS) are rare. In the recent WHO 5th edition, a new diagnostic entity of non-meningothelial tumours of uncertain differentiation known as intracranial mesenchymal tumour, FET-CREB fusion-positive has been described. It has uncertain histogenesis with variable morphology and characterised by presence of FET-CREB fusion gene. Case report: A 61year-old-lady with underlying invasive breast carcinoma diagnosed 17 years ago and treated with chemoradiation, mastectomy and tamoxifen, recently presented with forgetfulness, headache, and right sided weakness for 6 months. MRI showed a multiloculated, multiseptated lesion at the left parieto-temporooccipital lobe. Craniotomy and tumour excision was done, showing an intraaxial brain tumour with no dural attachment. Initial microscopic examination was reported as chordoid meningioma. The case was reviewed back after meningioma stains were negative. Histologically, the tumour showed neoplastic spindle cells within a bluish myxoid background. Only vimentin and ER reactivity were seen after an exhaustive panels of immunostaining were done. EWSR1 gene rearrangement was negative. Discussion: The differentials for this case are wide including chordoid meningioma, metastatic breast carcinoma as well as metastatic and primary intracranial sarcoma. After exclusion using immunostains and limited molecular study, intracranial mesenchymal tumour FET-CREB fusion-positive was suspected. However, further molecular testing needed for confirmation was not available locally, with prohibitive cost to send overseas. Further development of national molecular services are needed to keep abreast of newer diagnostic CNS entities.