Isolated Hepatic Actinomycosis Mimicking Cholangiocarcinoma: a case report and literature review

Isolated hepatic actinomycosis (IHA) is a rare infectious disease, which presents as a space-occupying lesion. We present a case of pathologically proven liver actinomycosis. Ultrasonography and computed tomography scan revealed a large solitary liver mass. The mild heterogeneously enhancing mass appeared as a hypointense area on a T1-weighted image and as a hyperintense area on a T2-weighted image, with a peripherally enhancing rim, and mimicked the appearance of a peripheral cholangiocarcinoma (PCC) on magnetic resonance imaging (MRI). However, the mean apparent diffusion coefficient (ADC) value (0.78 × 10–3 s/mm2) of the mass obtained from diffusion-weighted MRI (DW-MRI) was significantly lower than that of PCCs. IHA is characterized by extension of the mass to the abdominal wall and the presence of numerous honeycomb-like septa within the mass. IHA generally responds well to antibiotic therapy but is easily misdiagnosed. Knowledge of the radiological features of IHA is essential for avoiding delayed treatment and unnecessary surgery. Correspondence Author to: Kwo-Whei Lee Department of Radiology, Changhua Christian Hospital, Changhua, Taiwan No. 135, Nan-Xiao Street, Changhua 500, Taiwan J Radiol Sci 2012; 37: 29-33 Isolated hepatic actinomycosis mimicking liver cancer 30 J Radiol Sci March 2012 Vol.37 No.1 mass in the right hepatic lobe (S5/8), without significant blood flow. Imaging with a multidetector computed tomography (CT) scanner (LightSpeed 16; GE Healthcare) showed a mild heterogeneously enhancing mass in the arterial phase, which was surrounded by a low-density peripheral rim and contained with laminated septa extending to the right anterior abdominal wall (Fig. 1a). In the delayed venous phase, progressive and persistent enhancements were observed in the peripheral rim and in the numerous fine septa of the mass (Fig. 1b). MRI (1.5-T MR system; Magnetom Verio, Siemens) showed a large liver mass that had extended to the anterior abdominal wall. The mass appeared as a heterogeneous hypointense area on a T1-weighted image and as a slightly hyperintense area on a T2-weighted image (Fig. 2). With 3 different b values set at 100, 500, and 1000 s/mm2, the results from axial DW MRI and the ADC map showed water restriction of the mass(Fig. 3). The mean ADC value (0.78 × 10–3 mm2/s2) was measured as follows: (1) The axial image with the largest diameter was selected. (2) A circular regionof-interest (ROI) was made by placing a maximal circle entirely inside the mass, but not exceeding the mass margin so as to avoid inclusion of the peripheral wall of the mass. Dynamic contrast-enhanced fat-saturated T1-weighted MRI showed a mild heterogeneously enhancing mass in the arterial phase and numerous fine septa within the mass