Imaging description

Focal fatty sparing is usually geographic in shape and located near the gallbladder fossa and porta hepatis [1]. Occasionally, focal sparing is nodular and located elsewhere in the liver. Such atypical nodular focal fatty sparing may result in lesions that are hypoechoic at ultrasound and hyperdense at CT and may be mistaken for metastases or other tumors (Figures 19.1 and 19.2) [2–4]. MRI can be very helpful in establishing the diagnosis of nodular focal fatty sparing [2].

Importance

Failure to recognize the characteristic MR findings of nodular fatty sparing could lead to a misdiagnosis of hepatic tumor and inappropriate biopsy.

Typical clinical scenario

By definition, fatty sparing occurs in patients with diffuse fatty infiltration of the liver, which may be idiopathic or secondary to obesity, starvation, parenteral nutrition, steroid therapy, diabetes mellitus, alcohol, and hepatitis.

Differential diagnosis

Nodular or mass-like lesions in a diffusely fatty liver that are only well seen on out of phase gradient-echo MR imaging, when visualized during an MR study that includes T2-weighted and dynamic gadolinium-enhanced sequences, should suggest focal fatty sparing.It is possible that true primary or secondary tumors in a diffusely fatty liver could also be better seen on opposed phase imaging, but such lesions would almost certainly demonstrate increased T2 signal intensity or altered vascularity relative to the liver parenchyma on dynamic gadolinium-enhanced images.