A case of a hemorrhagic hepatic cyst with a contrast-enhancing mural nodule for which it was possible to retrospectively examine the process from a simple cyst

Hepatic intracystic hemorrhage is a rare complication of congenital cysts. The imaging findings are often nonspecific and complicated, so it is difficult to differentiate from hepatic cystic tumors. Hemorrhagic hepatic cysts show an internal heterogeneous echo level, intracystic mass-like structure, and septum-like structure on ultrasonography (US), but they are difficult to detect on computed tomography (CT) because the clot has a CT value equivalent to that of the fluid in the cyst, so it is characterized by a discrepancy between the US and CT findings. On the other hand, hepatic cystic tumors have mural nodules that can also be recognized on CT, and various contrast studies show contrast enhancement of mural nodules and septa. We herein report a case with a hemorrhagic hepatic cyst that was suspected at first glance to be a hepatic cystic tumor because CT showed an enhanced mural nodule. A comprehensive evaluation with various modalities is necessary to differentiate cystic lesions of the liver, and contrast-enhanced US (CEUS) in particular may be effective. In the post-vascular phase of CEUS, hepatic cystic tumors were reported to have a contrast effect, which hepatic hematomas due to intracystic hemorrhage were reported not to have, suggesting that this may be a key finding for differentiation. Furthermore, we were able to retrospectively examine the process from a simple cyst by investigating the past imaging studies. It was an interesting change in imaging findings as it showed the natural history from a simple cyst to a hemorrhagic cyst.