An Incidental Cavitary Pulmonary Lesion Unveiling Diffuse Large B-cell Lymphoma in an Undiagnosed HIV Patient.

Diffuse large B-cell lymphoma (DLBCL) rarely presents with pulmonary involvement, and cavitary lung lesions as the initial manifestation are exceptionally uncommon. We report the case of a 65-year-old man who presented to the emergency department after a mechanical fall, during which imaging revealed an incidental thin-walled cavitary lesion in the left lung apex. The patient was asymptomatic and was lost to follow-up. Six months later, he presented again with a new right axillary mass. Imaging demonstrated a persistent cavitary lesion with bilateral axillary lymphadenopathy and a new solid lung nodule in the left lower lobe. Biopsies confirmed DLBCL in both the lung and lymph node. He was also diagnosed with a previously unrecognized HIV infection, with a CD4 count of 84 cells/mm³. The patient was started on antiretroviral therapy and R-CHOP chemotherapy. This case highlights the importance of maintaining a broad differential diagnosis for cavitary lung lesions, pursuing tissue diagnosis even in asymptomatic patients, and ensuring robust follow-up of incidental findings to avoid delays in diagnosis and treatment.