Frequency and etiology of unexplained bilateral hydronephrosis in patients with breast cancer: results of a longitudinal CT study.

We retrospectively reviewed the records of 153 patients with breast cancer undergoing serial abdominal computed tomography (CT). During a median follow-up of 40 months, 2 (1.4%) of 153 patients developed bilateral hydronephrosis in the absence of radiologically visible obstructing pathology. Surgery confirmed malignant infiltration of the ureters by metastatic lobular carcinoma in both patients, suggesting that new unexplained bilateral hydronephrosis on serial CT in patients with breast cancer is likely to reflect infiltrative retroperitoneal involvement of the ureters by metastatic lobular carcinoma.