Myeloid sarcoma of appendix mimicking acute appendicitis.

CONTEXT: Myeloid sarcoma is a neoplasm of immature myeloid cells involving an extramedullary anatomic site that is usually, although not always, associated with acute myeloid leukemia. Any extramedullary site can be involved by myeloid sarcoma, but involvement of the cecal appendix is uncommon, and symptoms mimicking acute appendicitis as a result of appendiceal involvement are rare.
OBJECTIVE: To describe the clinicopathologic features of 2 patients with myeloid sarcoma involving the appendix who presented with right lower quadrant pain suggestive of acute appendicitis and prompting appendectomy.
DESIGN: Clinical information for both patients was obtained from the medical record. Routine hematoxylin-eosin-stained slides, naphthol-ASD-chloroacetate stain, and immunohistochemical stains for myeloid, B-cell, and T-cell antigens were prepared.
RESULTS: Peripheral blood and bone marrow were infiltrated by coexistent acute myeloid leukemia in case 1 but were negative for leukemia in case 2. In case 2, the patient had a history of acute myeloid leukemia that had been treated by an allogenic bone marrow transplant 7 months earlier. Histologic examination of the appendix revealed poorly differentiated myeloid sarcoma in both cases. Each neoplasm was positive for chloroacetate esterase, myeloperoxidase, lysozyme, and CD43 and was negative for CD3 and CD20.
CONCLUSIONS: Myeloid sarcoma involving the appendix can rarely cause pain or other symptoms mimicking acute appendicitis. A high index of suspicion combined with the use of cytochemical and immunohistochemical studies are helpful in establishing the diagnosis.