Pictorial essay: PET/CT in tuberculosis

Abstract

In routine practice, oncologic workup is responsible for the majority of referrals for whole-body FDG-PET/CT. The indications in oncology include staging, restaging, assessment of therapy response, and detection of recurrence. In spite of the great success achieved by FDG-PET imaging in the evaluation of malignant disorders, the modality is not specific for the diagnosis of cancer.[1] It has been noted that processes such as infection and inflammation, and particularly granulomatous diseases, also cause increased FDG uptake in the affected tissues.[2–6] Tuberculosis (TB) is a chronic granulomatous inflammation caused by Mycobacterium tuberculosis. India accounts for nearly a third of the global burden of tuberculosis, with approximately 1.8 million new cases of tuberculosis reported every year.[7] Although it involves the thorax most frequently, any organ system in the body can be infected. The clinical and radiological features of tuberculosis are known to mimic those of many other diseases. The role of FDG PET and PET/CT in TB and other inflammatory diseases is evolving and is not as yet clearly defined. At the same time, there is a considerable increase in PET/CT referrals for patients with fever of unknown origin (FUO), generalized lymph node (LN) enlargement, and mediastinal or abdominal lymphadenopathy, especially when other investigations are inconclusive. The aim of such referrals is generally to rule out an underlying malignant disease or to detect an inflammatory pathology. Infections remain the most frequent cause of FUO, followed by neoplasms and noninfectious inflammatory diseases.[8,9] In India, TB is known to be the commonest infection to present as FUO.[10] ′The high sensitivity of FDG PET in detecting malignant lesions, infections, and other inflammatory processes alike, makes it an important tool that has the potential to play a role in the diagnostic protocol and management of patients with FUO.′[11,12] While performing FDG PET/CT for oncologic workup, we found TB to be a common cancer mimic, producing uptake patterns that are indistinguishable from that of cancer. Many studies have documented increased FDG uptake in active TB in diverse anatomical locations, mimicking malignant processes.[5,6,13–17] Though a high standardized uptake value (SUV), greater than 2.5, is attributed to malignant lesions,[18] we have encountered high values of peak SUV, upto 21.0 (range 2.2-21.0), in tuberculous lesions Figures [​[11–7]. Figure 1 (A-E) Mediastinal lymphadenopathy in a patient of carcinoma colon who, post-hemicolectomy and post-chemotherapy was detected to have raised tumor marker (CEA) levels. Coronal plain CT (A), PET (B), PET/CT (C) with axial plain CT (D), and PET/CT (E) images of ... Figure 7 (A-D) Disseminated TB with multifocal hepatic and diffuse splenic uptake. Coronal plain CT (A) and PET (B) with axial PET/CT (C, D) images in a patient with FUO show diffuse increased FDG uptake in an enlarged spleen and multifocal uptake in the liver, mediastinal ... Figure 6 (A-D) Repeat axial CT (A), PET/CT (B) images of the thorax, and axial (C) and coronal (D) PET/CT abdomen images of the same patient described in Figure 5 show complete resolution of the liver lesion and a considerable reduction in the size of the left hilar ...