In segment IVa of the liver, there is a large hypodense mass with an FDG-avid rim (SUV_max 4.2).

Hepatic abscess. A culture grew Streptococcus milleri (anginosus).

Most liver abscesses are pyogenic, resulting from a bacterial infection elsewhere. Organisms may reach the liver by: the portal vein, arterial supply, ascending infection in the biliary tract, direct invasion, or a penetrating injury. Immunosuppressed patients (eg old age with debilitating disease, immunosuppression, chemotherapy with marrow failure) may develop liver abscesses in the absence of infection elsewhere. Clinically, liver abscesses may be associated with fever, right upper quadrant pain and tender hepatomegaly. Jaundice may occur if there is extrahepatic biliary obstruction. Whilst antibiotic therapy can be used for small abscesses, surgical drainage is often required for larger abscesses. Delayed diagnosis may occur due to frequent coexistent disease. The mortality rate for large liver abscesses is therefore high, ranging from 30% to 90%. FDG-PET/CT significantly contributes to establishing a final diagnosis in patients with prolonged fever. Conversely, benign lesions such as due to infection or inflammation, are frequent causes (up to 25%) of false positive interpretation in PET/CT scans performed for proven or suspected malignancy. The CT component helps in morphologic characterization of lesions, and thereby increases the specificity of PET/CT, particularly for lesions with moderate or marked FDG uptake.