FDG PET/CT in evaluation of pyrexia of unknown origin.

Pyrexia of unknown origin (PUO) is defined as fever above 38.5°C lasting for 3 weeks, of which at least 1 week has been spent in thorough investigation without a conclusive cause. Tuberculosis remains an important cause of PUO, particularly with the rising incidence of human immunodeficiency virus infection. It may strike virtually any organ in the body and can even mimic metastases especially in a known treated case of carcinoma. Bacterial infections, human immunodeficiency virus, hidden malignancy, sarcoidosis, and autoimmune disorders are some other important causes of PUO. Initial investigations include examination of blood, urine, stool, blood biochemistry, culture, etc. Typical radiologic investigations include chest radiography, computed tomography, and magnetic resonance imaging. Presented here is an atlas of cases where these investigations had been inconclusive but fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography demonstrated the site of pathology and directed histologic diagnosis.