Utility of 18F‐FDG PET/CT in identifying terminal ileal myeloid sarcoma in an asymptomatic patient
Authors: Elaine Yuen Phin Lee, Anskar Yu‐Hung Leung, Marina‐Portia Anthony, Florence Loong, Pek‐Lan Khong
Journal: American Journal of Hematology (2011)

A 63-year-old man was presented with bone pain and was found to be anemic and thrombocytopenic. There were circulating myeloblasts with dysplastic neutrophils. Repeated bone marrow aspirations showed marrow necrosis but no histological features to support the diagnosis of acute myeloid leukemia. In the absence of a definitive diagnosis at the time, a combined 18-F fluoro-deoxyglucose positron emission tomography and computed tomography (18F-FDG PET/CT) was requested to look for extramedullary neoplasms that might be associated with marrow necrosis (Images1 and2). 18F-FDG PET in maximum intensity projection, demonstrating hypermetabolic activity at the right iliac fossa (solid black arrow). In addition, there was diffuse skeletal marrow uptake due to the marrow necrosis and pathological fracture at the right anterior first rib (dotted black arrow). PET (A), PET/CT fusion (B), axial (C), and coronal (D) contrasted 64-slice MDCT reformatted images: Hypermetabolic activity (solid white arrow) was seen at the terminal ileum with SUVmaxlbm 5.0 (Reference liver parenchyma SUVmaxlbm 1.9). [SUVmaxlbm: maximum standard uptake value based on lean body mass]. The contrasted CT component showed asymmetrical nodular mucosal thickening at the terminal ileum and small adjacent loco-regional ileo-colic lymph nodes. The differential diagnosis of this appearance included tuberculosis, which has high prevalence in this region of the world. Studies and case reports have demonstrated the usefulness of 18F-FDG PET in detection, assessment, and follow up of myeloid sarcoma [1-4]. 18F-FDG PET is a useful tool in detecting early MS, in early relapse, before other cross-sectional imaging modalities are able to detect any morphological change or effects of its metabolic activity after treatment. The 18F-FDG uptake of MS is wide, ranging from SUVmax 2.6–9.7 (Images3 and 4) [2]. Corresponding axial CT presented on “bone window” to illustrate the pathological fracture through the right anterior first rib (white arrow) which gave the hypermetabolic activity as seen on the MIP image in Image 1. A: (H&E ×10) showed the intestinal villous was expanded by myeloblasts and eosinophil precursors, which were stained positive by myeloperoxidase immunohistochemically (B; ×10). Cases of MS involving the gastrointestinal tract are uncommon, comprising only 7% in a biopsy-proven series [5]. Although most cases of MS are clinically undetectable, gastrointestinal MS commonly presents symptomatically as small bowel obstruction, bleeding, perforation, or intussusceptions [6-8]. This patient was completely asymptomatic in the gastrointestinal tract. The 18F-FDG PET/CT finding, however, prompted a colonoscopy, which identified a solitary ulcer with an erythematous base just inside the terminal ileum. A biopsy of this ulcer showed an infiltration of atypical mononuclear cells consistent with blasts and myeloid precursors with eosinophilic granules. An immunohistochemical stain was positive for the myeloid marker, myeloperoxidase; therefore, the findings were compatible with a diagnosis of myeloid sarcoma. As bone marrow necrosis is a rare presentation of acute myeloid leukemia, the diagnosis was immediately confirmed and consolidated. The patient was subsequently offered aggressive induction chemotherapy. A bone marrow examination was repeated on day 21 after induction chemotherapy; it showed marrow fibrosis with an absence of necrosis. The patient's hemoglobin and platelet count had improved. This case report underscores the importance of a PET/CT scan in the detection of myeloid sarcoma.