Pyogenic Hepatic Abscess: MRI Findings

Hepatic abscess is defined as a localized collection of pus in the liver from any infectious process, with resultant destruction of the hepatic parenchyma and stroma. Abscesses can be classified into pyogenic, amebic, or fungal. Signs and symptoms include fever +/- RUQ pain, tenderness w/ hepatomegaly. This may be associated with chills, malaise and may have weight loss, anorexia and occasionally mental status changes. There has been drastic improvement in the diagnosis of liver abscess with the advent of cross sectional imaging. Compared to conventional sonography, CT and MRI offer greater contrast resolution of the abscess. Abscesses usually appear as thick-walled lesions with homogeneous low attenuation at CT, low signal intensity on T1-weighted, and high signal intensity on T2-weighted MR images. While on contrast enhanced CT or MRI, the multiloculated or uniloculated mass frequently shows a peripheral rim or capsule. Characteristic “double target" sign is seen when there is peripheral rim enhancement which is related to the capillary permeability or edema around the surrounding liver parenchyma. Perifocal or perilesional hyperemia is also seen in primary or secondary hepatic malignancy. But this type of segmental enhancement surrounding the abscesses and no enhancement of cystic structure readily differentiate liver abscess from other benign and malignant cystic lesions . On contrast enhanced MRI, intense mural enhancement on early gadolinium-enhanced images is seen which may persists with negligible change in thickness and intensity on later post-gadolinium images. These MRI features may help to distinguish abscesses from other focal liver lesions. Apart from clinical correlation and laboratory work up, imaging diagnosis of liver abscess is essential not only in characterization but also in follow ups to see serial changes in their morphology and enhancement while on treatment. Delayed diagnosis of hepatic abscess may cause a high mortality rate, therefore requires prompt recognition and adequate treatment. Most pyogenic abscesses require drainage and/or treatment of biliary obstruction, if present apart from antibiotics. Amebic and fungal abscesses are treated with metronidazole and amphotericin B and the drainage is however not required. Fine needle aspiration cytology performed in this case was consistent with pyogenic abscess