PATH-20. A case report of gliosarcoma in a pathologically confirmed tumefactive demyelinating lesion

BACKGROUND Tumefactive demyelinating lesions (TDLs) and intracranial neoplasm can be challenging to differentiate due to their similar clinical and radiographic features. The coexistence of brain tumors and demyelination has rarely been reported. Herein, we present a rare case of gliosarcoma arising in the prior excised region of a TDL. Case report: A 37-year-old man presented after a first-time seizure with an MRI showing a heterogeneously enhancing mass in the right temporal lobe. He underwent stereotactic biopsy and pathological examination showed inflammatory demyelination. He was treated with steroids. Two months later, he developed confusion and aphasia. Imaging showed enlargement of the mass with increased vasogenic edema. He was treated with steroids and plasma exchange (PLEX) without radiographic improvement. Brain lesion resection was performed and confirmed the diagnosis of TDL. At the follow-up, he developed a new ring-enhancing nodule at the resection margin on MRI and was started on rituximab. Seven months after his initial visit, he returned with severe headache, emesis, and aphasia with an MRI demonstrating a large enhancing mass replacing the previous resection cavity. He underwent tumor resection and pathology was consistent with gliosarcoma, IDH wild type (WHO Grade 4). Subsequently, concurrent chemoradiotherapy with Temozolomide was initiated. CONCLUSIONS This case report is the first to show gliosarcoma arising from a TDL. It is unclear whether the coexistence of malignancy and TDL is a consequence of glial cell transformation in the demyelinating lesions or a coincidence. Clinicians should be aware of the possibility of coexisting intracranial neoplasms and TDLs and understand the disease course of both conditions. Atypical characteristics of TDLs (such as recurrence in the same location and minimal response to steroids and PLEX) should raise concerns for possible mimics or coexistence with brain tumors. Re-examination with pathological studies should be considered in such cases.