LAUSR

A 22-year-old male presented with left hydrothorax, left shoulder pain and weight loss over the past 3 months. Initial positron emission tomography–computed tomography (PET–CT) imaging (Fig. 1A) showed a left scapular region mass with high 18F-fluorodeoxyglucose (FDG) uptake and a standardized uptake value (SUV) of 8.38. Pleural thickening (SUV = 7.37) was observed on the left side, suggesting tumor growth. No obvious 18F-FDG uptake was observed in the right thoracic wall, which was collapsed on computed tomography (CT). CT-guided core needle aspiration biopsy of the scapular lesion confirmed the diagnosis of diffuse large B-cell lymphoma, and thus, standard R-CHOP chemotherapy was administered. The patient’s symptoms improved immediately after just one cycle, but reappeared before the third cycle. Pulmonary CT showed pleural thickening with bilateral pleural effusions. PET–CT showed bright armor signs wrapping around the pleural space (SUV = 7.77). The left scapular lesion SUV was reduced to 2.02 (Fig. 1B–E). The patient’s pleural lesions were initially considered as tumor progression, and thus, the third cycle of R-CHOP was started promptly. Nevertheless, the patient’s symptoms persisted and he also developed night sweats and low-grade fever. Pleural biopsy was performed to confirm the diagnosis, and pathology revealed acid-fast positive necrotic granulomatosis with Mycobacteria tuberculosis DNA detected by quantitative polymerase chain reaction. Thereafter, HRE (isoniazid, rifampicin, and ethambutol) anti-tuberculosis therapy was initiated, and the patient’s symptoms improved. Moreover, CT after 1 month of anti-tuberculosis therapy showed that the pleural effusion had been absorbed. After that, chemotherapy was continued concomitantly with antituberculosis treatment. After 8 cycles of chemotherapy, PET–CT showed no signs of tumor or infection in previously involved areas (Fig. 1F). The pleural “armor” sign on PET–CT is a very rare manifestation of active pleural tuberculosis. Although PET–CT visualizes glucose metabolism and has been regarded as useful for differentiating between benign and malignant diseases, inflammatory disorders such as pulmonary tuberculosis can also induce significant 18F-FDG uptake in active lesions. Similar to the “armored heart” pattern caused by tuberculous constrictive pericarditis, widespread pleural inflammation will lead to diffuse 18F-FDG uptake and give the appearance of armor on PET. However, solid tumors such as mesothelioma often grow in a nodular pattern, so that advanced disease may appear as irregular and nodular pleural thickening with pleural effusion. This is also the case with metastatic cancer. In patients with concurrent lymphoma, both imaging findings and symptoms of tuberculous pleurisy may be neglected and empirically regarded as lymphoma infiltration. This tangled relationship between tuberculosis and lymphoma has made differential diagnosis difficult, even in the era of PET–CT. During the treatment of hematological malignancies, hematologists and radiologists should always be aware of the possibility of certain infections, such as tuberculosis.