Primary pulmonary lymphoma (PPL) is an uncommon malignant lung neoplasm that often presents with nonspecific clinical and radiological features, leading to misdiagnosis as pneumonia or primary lung carcinoma. This case report illustrates the complementary role of chest CT and whole-body 18F-FDG PET/CT in characterizing an atypical presentation of PPL and in distinguishing metabolically active lymphoma from concurrent benign mediastinal findings.
A 44-year-old man underwent routine screening imaging that revealed a lung lesion. He was asymptomatic, without respiratory complaints or systemic "B symptoms." Laboratory data at presentation were not reported in detail in the abstract. The patient was evaluated further with diagnostic imaging and tissue sampling to establish the nature of the lesion.
Baseline chest computed tomography identified a soft-tissue mass in the right hilar region measuring 3.9 × 3.5 cm. The mass compressed the right upper lobe bronchus and produced secondary post-obstructive consolidation. Notably, the consolidation lacked the typical air bronchogram sign often seen in certain pulmonary pathologies. In addition to the hilar lesion, CT detected an incidental anterior mediastinal nodule measuring 2.6 × 2.6 cm.
Whole-body 18F-FDG PET/CT was performed for metabolic characterization and staging. The right hilar mass showed intense FDG uptake with a maximum standardized uptake value (SUVmax) of 7.1. An adjacent regional lymph node demonstrated mild-to-moderate FDG avidity (SUVmax 3.2). By contrast, the anterior mediastinal nodule and the post-obstructive consolidation demonstrated absent FDG uptake on PET/CT, findings that argued against metabolically active malignancy in those areas and supported a focal process confined to the FDG-avid hilar mass and nearby node.
Tissue diagnosis was obtained via bronchoscopic transbronchial lung biopsy. Histopathological examination with immunohistochemical analysis confirmed the diagnosis of primary pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma, a marginal zone B-cell lymphoma subtype that can present as a pulmonary mass.
Given the localized, FDG-avid disease, the patient received targeted radiotherapy to the right hilar mass and the FDG-avid regional hilar/posterior mediastinal lymph node. The delivered dose was 66 Gy, administered in 18 fractions over a 3-week period. Details regarding systemic therapy, if considered or offered, were not reported in the abstract.
At the 2-month follow-up after discharge, repeat chest CT demonstrated a marked reduction in the size of the hilar lesion and involved regional lymph nodes. The patient remained completely asymptomatic, and laboratory parameters had normalized by the time of follow-up reporting.
This case highlights several diagnostic and management points:
Presentation: PPL can present as a central hilar mass and may be clinically silent, discovered incidentally on screening imaging.
Radiological mimicry: Central PPL may mimic aggressive primary lung carcinoma on morphologic imaging, especially when lesions cause bronchial compression and post-obstructive changes without classic signs such as air bronchograms.
Value of PET/CT: Whole-body 18F-FDG PET/CT provided metabolic discrimination between the FDG-avid lymphoma and coexisting nonavid lesions (the anterior mediastinal nodule and post-obstructive consolidation). PET/CT contributed to accurate loco-regional staging and helped prevent clinical overstaging by identifying which lesions were metabolically active.
Management and response: Localized radiotherapy directed to the FDG-avid sites produced a marked radiographic response within 2 months, with clinical and laboratory improvement.
Diagnostic confirmation: Definitive diagnosis requires histopathology and immunohistochemistry; imaging alone cannot reliably distinguish PPL from other central lung malignancies.
These observations support the role of combined anatomic and metabolic imaging in the evaluation of suspected PPL and emphasize the importance of tissue diagnosis for treatment planning.
The authors declared no conflicts of interest. This case report was published in Medicine (Baltimore). Identifiers reported in the source include PMID 42826325 and DOI 10.1097/MD.0000000000051002.