The mistaken or indeterminate CT diagnosis of hepatic metastases: the value of sonography.

Small liver cysts may be mistakenly diagnosed as metastatic disease on screening CT of the abdomen in patients with known carcinoma. These cysts can appear solid as a result of volume averaging. On retrospective review of 122 patients with known extrahepatic malignancies and liver lesions on CT, 77 had metastases, three had large cysts, and two had cavernous hemangiomas. The other 40 were found to have single or multiple, small (less than 2-cm), low-density lesions. In 33 patients these were proven to be benign hepatic cysts by sonography, follow-up CT, or clinical course. The initial CT interpretations in these patients had been metastatic disease in seven (21%), benign cysts in five (15%), and indeterminate in 21 (64%). Since the distinction between cysts and metastases has important clinical implications, sonography should be used whenever the true nature of these lesions cannot be determined by CT.