Orbital myeloid sarcoma presenting as massive proptosis

A 10-year-old boy presented with right proptosis for 8 months. The eyeball was grossly pushed down, with diffuse corneal haze and non-reactive pupil. Systemic examination was normal. Previous investigations in another centre included a computerized tomography scan, which showed a well-defined enhancing retro-bulbar mass, a non-contributory fine needle aspiration cytology and a biopsy showing fibrocollagenous tissue with moderate lympho-monocytic infiltrate suggestive of non-specific inflammation. PET-CT scan revealed the presence of enlarged fluoro-deoxyglucose-avid cervical and mesenteric lymph nodes. Biopsy of the retro-bulbar mass was repeated in our centre. It showed fibrocollagenous and skeletal muscle tissue infiltrated by lymphoid follicles, dispersely lying lymphocytes and plasma cells, and admixed large atypical cells with vesicular nuclei, prominent nucleoli and scanty cytoplasm, strongly positive for myeloperoxidase, CD43 and CD99 immunohistochemistry. Hemogram was normal. Bone marrow aspiration/biopsy and CSF showed no evidence of acute myeloid leukemia. The child received chemotherapy in another centre and is in complete remission 6 months after completion.