Intracranial extraosseous dural-based Ewing's sarcoma with fluid-haematocrit levels: imaging findings of a rare tumour.

Extraosseous dural-based primary Ewing's sarcoma of the central nervous system is a rare tumour posing a diagnostic challenge. On cross-sectional radiological imaging, the lesion has an extra-axial location with heterogeneous appearance. These lesions are usually multicystic with internal haemorrhage causing fluid-haematocrit levels. It mimics conditions like an aneurysmal bone cyst, microcystic meningioma, telangiectatic osteosarcoma or cystic metastasis. Exclusion of primary Ewing's sarcoma or malignancy elsewhere in the body is required to rule out a secondary. Surgery along with adjuvant chemotherapy and focal radiotherapy is the preferred mode of treatment. Due to the presence of non-specific small round blue cells on H&E stain, these tumours are also confused with lymphoma, osteosarcoma, rhabdomyosarcoma, Merkel cell carcinoma, ependymoblastoma and neuroendocrine carcinoma. Immunohistochemistry provides a definitive diagnosis. A high degree of suspicion in the preoperative scans is crucial for prognostication and early management of this aggressive tumour leading to improved patient survival.