Contrast-enhanced ultrasonography evaluation of hepatocellular carcinoma with peritumoral fat-spared area: a case report.

Peritumoral fat-spared area (PTFSA), a focal spared area surrounding hepatic tumors, is a specific finding of liver tumors in fatty livers. PTFSA mimics a liver tumor, making it difficult to recognize the tumor boundary. We report a case of a 56-year-old man with fatty liver who was diagnosed with a liver tumor. Ultrasonography (US) revealed a nearly homogeneous hyperechoic liver tumor measuring 40 mm in the left lobe. A thick hypoechoic area was observed around the tumor that spread more widely than an ordinary halo. Histological examination revealed that the hypoechoic area comprised a thin fibrous capsule and normal liver parenchyma without fat, which is PTFSA. Contrast-enhanced US (CEUS) indicated corona enhancement only at the inner part of the PTFSA. The inner part showed the same pattern as that of an ordinary halo and was a part of hepatocellular carcinoma, whereas the outer part showed the same pattern as that of the other liver parenchyma. CEUS was an effective modality for distinguishing the difference. Thus, CEUS was useful in defining the tumor boundary. Before initiating treatment, tumors should be evaluated using various modalities to detect their accurate boundary. CEUS may be a useful modality for detecting the boundary and making a diagnosis.