Diffuse Large B-cell Lymphoma Presenting as a Hypermetabolic Mesenteric Root Mass Without Preoperative Imaging...

Diffuse large B-cell lymphoma (DLBCL) may occasionally present as an intra-abdominal mass, but a dominant mesenteric root presentation can closely mimic other aggressive abdominal malignancies. Markedly elevated fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) suggests high tumor metabolic activity but is not histologically specific. A 72-year-old male presented with a two-week history of abdominal pain and was found to have a retroperitoneal mass on imaging. On physical examination, a hard, ill-defined, mobile mass was palpable above the umbilicus on deep palpation, without tenderness. Contrast-enhanced CT and FDG PET/CT demonstrated a dominant soft-tissue mass closely associated with adjacent bowel loops and mesenteric vascular structures. PET/CT showed intense FDG uptake, with a maximum standardized uptake value (SUVmax) of 35.5 on standard imaging and approximately 40.0 on delayed imaging. Preoperative imaging favored an aggressive abdominal malignancy rather than lymphoma. Because percutaneous biopsy was considered high risk due to the lesion's location, the patient underwent surgical exploration. Intraoperative frozen-section analysis suggested a hematolymphoid malignancy, prompting the surgical team to avoid extensive bowel or mesenteric vascular resection and to limit the procedure to diagnostic tissue acquisition. Final pathology confirmed DLBCL, non-germinal center B-cell type, with a high proliferative index. This case highlights that very high FDG uptake in an abdominal mass should be interpreted as evidence of aggressive tumor biology rather than as a marker of a specific histologic diagnosis. When lymphoma is not suspected preoperatively and image-guided biopsy is unsafe, intraoperative frozen-section assessment can be critical in redirecting surgical management and avoiding non-therapeutic radical resection.