Liver MRI

1 Abscesses – Pyogenic Type (p. 2)

Hepatic abscesses result from an infectious process of bacterial origin associated with destruction of the hepatic parenchyma and stroma in 0.006–2.2% of hospital admissions. Gram-negative bacteria of colonic origin (E. coli, Klebsiella, and Enterobacter) can often be isolated from such abscesses. Pyogenic liver abscesses may result from obstruction of the biliary tract with stasis of bile and bacterial overgrowth, or as a complication of direct biliary tract infection. Hematogenous spread and bacterial seeding of the liver may occur via the portal vein secondary to abdominal infection. Other less common routes are hematogenous and direct perihepatic spread.

MR Imaging Findings

Hepatic abscess presents as a relatively complicated fluid collection, which is composed of central areas with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Particularly, on T2-weighted images the central cavity may show septa and debris. A central fluid-containing cavity is often surrounded by a few millimeters (in most cases: 1–5 mm, in some cases: >,5 mm) of thick inflamed liver parenchyma (wall of the abscess), which most likely contains microabscesses. Perilesional (wedge-shaped) edema may be present. Most abscesses show early persistent enhancement of the wall (Figs. 1.1–1.3A, B). Although in most patients the diagnosis and follow-up is carried out on computed tomography (CT), magnetic resonance (MR) imaging is increasingly being performed on acutely ill patients, therefore, it is important for radiologists to understand the appearance of hepatic abscesses at MR imaging.

Differential Diagnosis

In ambiguous cases, the differential diagnosis may include: (1) metastases (the ring enhancement progresses in a centripetal fashion with a decrease in intensity on delayed images), (2) infected metastases (difficult to differentiate, thicker andmore irregular wall, clinical history important), (3) hepatosplenic candidiasis (multiple lesions <,10 mm in diameter), (4) hydatid cysts (internal septa), (5) echinococcus abscesses (thicker septa and daughter cysts) (Fig. 1.3C, D).

Management

Management options include: (1) percutaneous drainage, (2) open surgical drainage, and (3) antibiotic therapy. Single dominant hepatic abscesswith a large fluid cavity can be treatedwith percutaneous drainage. Treatment should be tailored to each patient.

Literature

1. Mendez RJ, Schiebler ML, Outwater EK, Kressel HY (1994) Hepatic abscesses: MR imaging findings. Radiology 190:431–436
2. Balci CN, Semelka RC, Noone TC, et al. (1999) Pyogenic hepatic abscesses: MRI findings on T1- and T2-weighted and serial gadolinium-enhanced gradient-echo images. J Magn Reson Imaging 9:285–290
3. Perez JAA, Gonzalez JJ, Baldonedo RF, et al. (2001) Clinical course, treatment, and multivariate analysis of risk factors for pyogenic liver abscess. Am J Surg 181:177–186