Intracranial myeloid sarcoma

A 41-year-old female presented with a 2 d history of ‘refusing to talk’ and a 1 d history of ‘decreased movement’. She had a recent history of being treated for otitis media, but no history of malignancy. On admission, a full blood count and differential white cell count were normal. Magnetic resonance imaging revealed a 6 cm contrast-enhancing left-sided middle cranial fossa mass with extension inferiorly into the subtemporal fossa and parapharyngeal space (top left). The radiologist’s differential diagnosis included meningeal sarcoma, atypical meningioma, undifferentiated sinonasal cancer and lymphoma. A needle core biopsy was performed, but was non-diagnostic. Due to concerns about herniation and the lack of diagnostic tissue, the patient underwent a craniotomy. The cytospin and touch preparations from the tissue biopsy demonstrated a monomorphic population of atypical mononuclear cells with high nuclear:cytoplasmic ratios, vacuolated cytoplasm and prominent nucleoli (top right). Histological sections showed a diffuse infiltrate of large cells with large nuclei, irregular nuclear contours, prominent nucleoli and open chromatin (bottom left). The cells were positive for myeloperoxidase by immunohistochemistry. Flow cytometry detected myeloid blasts, which were CD34+, CD13+, CD33+, CD117+, CD20− and CD10−. There was aberrant expression of CD19 and partial expression of CD56 (bottom right). Cytogenetic analysis demonstrated 45,X,-X, t(8;21;12)(q22;q22;q21). There was no evidence of bone marrow involvement by morphology or flow cytometry. The patient’s mental status improved dramatically after four cycles of cytarabine. She was lost to follow-up after 7 months. Myeloid sarcoma is an uncommon neoplasm and intracranial involvement comprises approximately 3% of all cases. Most are manifestations of previous or concurrent acute myeloid leukaemia although some may precede it. Intracranial myeloid sarcomas present as extra-axial masses and are believed to arise from the bone marrow of the skull. Histological differentiation between myeloid sarcoma and a large cell lymphoma can be difficult, if not impossible, without immunohistochemistry or flow cytometric analysis. Diagnosis can be especially problematic because these tumours can express B-cell antigens (e.g. CD19, CD79a), thus leading to the misdiagnosis of B-cell lymphoma.