Mucinous cystic tumor of the retroperitoneum. A report of two cases.

Two cases of retroperitoneal mucinous cystic tumors and some diagnostic problems on aspiration cytology are presented. The first was a mixed benign, borderline and malignant mucinous tumor, and the second was a mixed benign and borderline mucinous tumor. Our knowledge of the cytology of ovarian mucinous cystic tumors was not helpful in making a correct diagnosis in these cases. Based on our experience, we emphasize the following. First, consider methods of collecting enough cells to make a diagnosis. Second, consider the possibility of mixed histologic features. Direct aspiration, if possible, from papillary lesions inside the cyst will probably lead to an accurate diagnosis. Measurement of carcinoembryonic antigen levels in the cystic fluid is useful in checking for underdiagnosis of such tumors.