A Case of an Enigmatic Pulmonary Infiltrate

The differential diagnosis of a pulmonary mass in an immunosuppressed host with a history of cancer is broad and includes malignant, infectious and inflammatory etiologies. Mycobacterium avium complex (MAC) is a rare cause of opportunistic infection in susceptible individuals that can present as either localized or disseminated disease. On radiologic studies, the pulmonary disease can manifest as heterogeneous linear or nodular densities, a mass-like lesion, or thin-walled cavitary lesions. We present the case of pulmonary MAC in a patient with a history of lung cancer requiring lobectomy, and splenic lymphoma being treated with chemotherapy, presenting with extreme fatigue and a fludeoxyglucose (FDG)-avid mass on positron emission tomography–computed tomography (PET-CT). The patient had a CT-guided biopsy of the mass that demonstrated non-caseating granulomas followed by a right middle lobe transbronchial biopsy that upon histologic examination revealed mild acute and chronic inflammation, and necrotizing caseating granulomas. The acid-fast culture of bronchoalveolar lavage showed the growth of acid-fast bacilli that were identified by deoxyribonucleic acid (DNA) probe as Mycobacterium avium complex. We discuss the typical radiological manifestations of MAC as well as the role of immunosuppression and B cell-depleting therapy from the predisposition to infection.