Abstract / Summary
Rationale: Primary pulmonary lymphoma (PPL) is an extremely rare malignant lung tumor that is frequently misdiagnosed as pneumonia or lung cancer due to its atypical radiological and clinical presentation. The rationale of this report is to elucidate the diagnostic value of combining computed tomography (CT) and 18 F-fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F-FDG PET/CT) in evaluating a rare presentation of PPL. Patient concerns: A 44-year-old male was admitted after an incidental lung lesion was discovered during routine screening. He was completely asymptomatic, lacking respiratory or systemic “B symptoms.” Diagnoses: A baseline chest CT identified a 3.9 × 3.5 cm soft-tissue mass in the right hilar region that compressed the right upper lobe bronchus, leading to secondary post-obstructive consolidation that lacked the characteristic air bronchogram sign. The CT also revealed an incidental 2.6 × 2.6 cm anterior mediastinal nodule. Subsequent whole-body 18 F-FDG PET/CT demonstrated intense tracer uptake in the right hilar mass with a maximum standardized uptake value of 7.1 and mild-to-moderate uptake in an adjacent regional lymph node (maximum standardized uptake value of 3.2). The scan showed completely absent uptake in the anterior mediastinal nodule and the post-obstructive consolidation, arguing against metabolically active malignancy in those areas. Histopathological and immunohistochemical analysis from a bronchoscopic transbronchial lung biopsy confirmed primary pulmonary mucosa-associated lymphoid tissue lymphoma. Interventions: The patient underwent localized radiotherapy targeting the right hilar mass and the FDG-avid regional hilar/posterior mediastinal lymph node. A total dose of 66 Gy was delivered in 18 fractions over the course of 3 weeks. Outcomes: At the 2-month post-discharge follow-up, a repeat chest CT revealed a marked reduction in the size of both the hilar lesion and the regional lymph nodes. The patient remained completely asymptomatic, and his laboratory parameters normalized. Lessons: Differentiating PPL from central lung cancer and coexisting benign mediastinal abnormalities presents a significant clinical challenge, particularly when atypical radiological features mimic aggressive carcinomas. Whole-body 18 F-FDG PET/CT serves as an invaluable, noninvasive modality for metabolic characterization, accurate loco-regional staging, and preventing clinical overstaging by effectively differentiating metabolically active lymphoma from concurrent benign lesions.