Acute myeloid leukemia presenting as an isolated orbital mass in an adult.

Purpose: Myeloid sarcoma (MS) is an extramedullary-based hematolymphoid tumor that presents in 2-9 % of cases of acute myeloid leukemia (AML). Observations: A 61-year-old man presented with several weeks of unilateral eye pain, proptosis, and diplopia. Examination demonstrated 4 mm of proptosis with limitation of supraduction and abduction. Presenting visual acuity was 20/50 with no signs of optic neuropathy. Imaging revealed an infiltrative, retrobulbar soft tissue density involving the extraocular muscles and optic nerve. Laboratory workup for inflammatory and infectious etiologies was negative. The patient initially responded well to a high-dose oral steroid taper but developed recurrent symptoms. Biopsy was pursued and histopathology was consistent with MS, conferring a diagnosis of AML. Oncologic workup demonstrated central nervous system involvement. After orbital radiation and chemotherapy, no further blasts were detectable in the cerebral spinal fluid. At one year follow-up the patient had complete clinical tumor regression, with stable visual acuity and resolved right exophthalmos. Conclusions and importance: In adults, MS presents rarely as an isolated finding in the orbit. Biopsy is indicated when an orbital mass recurs or does not fully respond to anti-inflammatory treatment. Establishing a diagnosis of MS can be a histopathological challenge. Genetic testing to evaluate for CEBPA mutations in the bZIP domain can predict a good prognosis.