Drainage characteristics and differential function of the horseshoe kidney: What is typical?

Purpose: To describe the drainage and differential function of the horseshoe kidney. Patients and Methods: A retrospective review of mercaptoacetyltriglycine (MAG3) nuclear renograms from 1991 to 2007 was performed. Nineteen patients with horseshoe kidney who had not undergone previous renal surgery were identified. All studies were reviewed, and patient information was gathered. Drainage characteristics and differential function were determined. Results: Nineteen primary MAG3 studies were found, representing 38 evaluable renal units. For these units altogether, the median t1/2 was 11 minutes. A t1/2 of 10 minutes or less was found in 18 units (47%), while 12 units (32%) showed a t1/2 longer than 20 minutes. The relative function difference mean was 24.6%. The number of patients with a relative function difference greater than 10% was 11 (57%), and those with a relative function difference greater than 20% was 7 (37%). Conclusion: Horseshoe kidney is associated with fairly high rates of poor renal drainage and elevated differential function.