FDG PET/CT in Primary Extranodal Non-Hodgkin’s Lymphoma: Imaging Spectrum and Diagnostic Challenges in the Abdomen and Musculoskeletal System

Primary extranodal non-Hodgkin lymphomas (eNHL) are clinically and radiologically diverse. The clinical and imaging presentation is heterogenous and often mimicking primary malignancies, infection, or inflammatory diseases. FDG PET/CT although provides whole-body metabolic assessment but presents unique challenges. To illustrate the diverse manifestations of primary eNHL and highlight imaging patterns, pitfalls, and clinically differentials, in abdominal and musculoskeletal involvement. Histopathologically confirmed cases of primary eNHL evaluated with FDG PET/CT were retrospectively reviewed. Cases were purposively selected to represent common and uncommon sites. Imaging findings were correlated with CT morphology, histopathology, immunohistochemistry, and treatment response. In eNHL, FDG PET/CT demonstrated a wide spectrum of involvement, including liver, spleen, stomach, bowel, adrenals, kidney, skin, and bone. Recognition of characteristic various patterns, such as bulky lesions with preserved tissue architecture, aneurysmal bowel dilatation, vascular encasement without narrowing, and permeative osseous involvement, helped distinguish eNHL from common mimics. PET/CT also identified occult disease, multifocal involvement and extent of disease and allows assessment of treatment response. Inflammation and variable FDG avidity in indolent lymphomas remained important pitfalls. FDG PET/CT is a valuable tool for staging, detection of occult extranodal disease, and treatment-response assessment in eNHL. Awareness of site-specific imaging patterns and mimics, integrated with contrast-enhanced CT and histopathological correlation, is essential for optimal clinical management.