Hepatic abscess appearance on US CT and MRI
General: Hepatic abscesses can develop from (1) biliary, (2) portal venous, (3) arterial, (4) local extension, and (5) traumatic etiologic factors.
US: A hepatic abscess appears as a complex fluid collection, typically with septations, an irregular wall, and internal debris or air. Air is seen as a focal area of echogenicity with posterior shadowing. An abscess can also appear as a simple fluid collection, similar to a cyst.
MDCT: CT is the most sensitive imaging modality; however, the CT findings vary with the size and age of the abscess. Generally, an abscess is a well-defined, low-attenuating uni- or multilocular mass with a well-defined enhancing wall that may contain internal septations. Air bubbles within the abscess cavity, although present in a minority of cases, are the most specific sign for an abscess.
MRI: An abscess appears as a well-defined homogeneous or heterogeneous lesion with decreased T1-w and increased T2-w signal. The cavity may contain septations and is surrounded by a low-signal enhancing capsule. Other complex cystic lesions, such as necrotic or hemorrhagic neoplasms, may have a similar appearance.
