Focal liver lesions. Evaluation of simple and complex cysts.

Ultrasound is often the first imaging study used to determine the nature of focal liver lesions. Although simple cysts often need no treatment, those large enough to compress or to irritate adjacent structures should be surgically unroofed and drained. Complex liver cysts may be caused by bacteria, amebae, or tapeworms (Echinococcus granulosus). Rarely, neoplasms present as cystic lesions and need further study for definitive diagnosis.