Hepatic S4 cyst represents a cyst in the left inner lobe of the liver. The liver is divided into eight segments according to the distribution of the hepatic venous system and portal system within the liver. Each liver has a separate inflow and outflow vascular system as well as a biliary system, of which segment S1 is the caudate lobe, segment S2 is the upper left outer lobe, segment S3 is the lower left outer lobe, and segment S4 is the left inner lobe; segment S5 is the lower right anterior lobe of the liver, segment S6 is the lower right posterior lobe of the liver, segment S7 is the upper right posterior lobe of the liver, and segment S8 is the upper right anterior lobe of the liver. Hepatic cysts are common benign lesions of the liver that are filled with fluid. In general, small (<5cm in diameter) single congenital liver cysts do not require treatment and can be followed up regularly, while larger, symptomatic or fast-growing ones require surgery.