Pleural-Based Diffuse Large B-Cell Lymphoma with Extensive Chest-Wall and Neural Foraminal Extension Mimicking Aggressive Sarcoma on 18F-FDG PET/CT

Abstract

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma; however, primary pleural involvement with extensive contiguous invasion of the chest wall and neural structures is exceedingly rare and may closely mimic aggressive nonhematologic malignancies. We report a 31-year-old man who presented with a progressively enlarging left thoracic mass initially suspected to be a sarcoma. Baseline 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) demonstrated an intensely hypermetabolic pleural-based subpleural soft-tissue mass with continuous infiltrative extension into the chest wall, ribs, paravertebral soft tissues, and neural foramen. Initial histopathologic evaluation was inconclusive, but subsequent immunohistochemical analysis confirmed DLBCL. Disease progression resulted in acute neurologic deterioration due to spinal canal stenosis and spinal cord compression, which was clearly delineated by PET/CT and magnetic resonance imaging correlation. Systemic chemoimmunotherapy with R-CHOP was promptly initiated. Interim 18F-FDG PET/CT after four cycles revealed marked reduction in lesion size and metabolic activity, consistent with a partial metabolic response (Deauville score 3), accompanied by significant clinical and neurologic improvement. This case illustrates an uncommon 18F-FDG PET/CT phenotype of pleural-based extranodal DLBCL with continuous pleura-to-foraminal spread, emphasizing the pivotal role of PET/CT in defining disease extent, guiding urgent clinical management, and monitoring therapeutic response in rare and diagnostically challenging extranodal presentations.