Magnetic resonance urography and angiography in the evaluation of a horseshoe kidney with ureteropelvic junction obstruction

A 42-year-old man presented with gross hematuria, which prompted a urologic workup. Intravenous urogram (IVU) demonstrated a horseshoe kidney with fight-sided hydronephrosis. Furosemide renal scan confirmed an incomplete right ureteropelvic junction (UPJ) obstruction. Horseshoe kidney is the most common fusion anomaly, with an incidence of approximately i in 400 births and a predominance in men. It presents great variability in morphology, position, and vascular supply, making therapeutic approaches very challenging. Associated anomalies occur in at least one third of patients. These include UPJ obstruction, ureteral duplication, and reflux. To better evaluate the UPJ, a retrograde pyelogram was performed (Fig. 1). In this study, a gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) enhanced magnetic resonance urography (MRU) 1 was performed as an alternative to the invasive retrograde pyelogram (Fig. 2). A comparison of the IVU and the Gd-enhanced MRU is demonstrated in Figure 3. Lastly, a second bolus of Gd (30-mL Gd-DTPA) was administered to the patient for magnetic resonance angiography (MRA), which demonstrated multiple aberrant vascular supplies to the kidney (Fig. 4). This information is important to the surgeon in order that he may more accurately decide between the endourologic and open surgical approaches. A delayed MRU obtained after this second bolus provides superior imaging quality, allowing better delineation of the anatomy of the horseshoe kidney (Fig. 5). This case demonstrates the advantages of using MRU and MRA in the primary evaluation of renal obstruction. The technique offers superior imaging