Imaging description

Focal fatty infiltration of the liver is usually easily recognized based on the characteristic findings of a focal lesion with a geographic shape adjacent to the porta hepatis or fissure for the ligamentum teres that may contain non-distorted traversing blood vessels [1]. Occasionally, focal fat is nodular and located in other locations in the liver. Such atypical nodular focal fatty infiltration may result in an appearance of echogenic lesions at ultrasound or hypodense lesions at CT that mimic metastases (Figures 18.1–18.2) [1–6].

Importance

Nodular focal fatty infiltration may mimic metastases, leading to patient anxiety and unnecessary investigations in pursuit of a non-existent primary site.

Typical clinical scenario

Nodular focal fatty infiltration is typically seen as an incidental finding in patients being imaged for unrelated reasons, but may occasionally be seen with patients with known causes of diffuse fatty infiltration such as diabetes or alcohol abuse (Figure 18.3).

Differential diagnosis

A target-like appearance with central echogenicity on ultrasound and central hyperdensity on contrast-enhanced CT has been described [2–4] but would not appear sufficiently distinctive to allow a confident diagnosis. MRI is often critical to the diagnosis by demonstrating signal loss on opposed phase imaging, and the absence of abnormal enhancement on post-contrast imaging that might suggest other focal hepatic lesions that may contain microscopic fat, such as focal nodular hyperplasia, adenoma, or hepatocellular carcinoma [1, 4]. With respect to these other focal lesions, it should be noted that fat occurs in 35 to 77% of adenomas, up to 35% of small hepatocellular carcinomas, and is extremely rare in focal nodular hyperplasia and usually patchy rather than uniform [7–10].