Ureteropelvic junction obstruction

Imaging description A nine-year-old boy presented with intermittent episodic left flank pain consistent with Dietl’s crisis (=sudden attack of acute lumbar and abdominal pain accompanied by nausea and vomiting, caused by distension of the renal pelvis due to kinking of the ureter or other obstruction of urine flow from the kidney to the ureter). An initial ultrasound showed moderate left renal pelvocaliectasis (Fig. 65.1a). A follow-up study one month later showed mild dilatation of the left renal pelvis (Fig. 65.1b) and a follow-up ultrasound six months later when the child was again acutely symptomatic showed moderate hydronephrosis with marked dilatation of the renal pelvis (Fig. 65.1c). A review of serial ultrasounds of the kidneys revealed fluctuating mild to moderate hydronephrosis of the left kidney over several years. The imaging appearance was strongly suggestive of intermittent ureteropelvic junction (UPJ) obstruction. Importance. UPJ obstruction is the most common cause of hydronephrosis in children and accounts for approximately 64% of cases. It is defined as a partial or total obstruction at the point where the renal pelvis narrows to form the ureter. It is found more commonly in boys and frequently involves the left kidney. It can be bilateral in 10–40% of cases. Ipsilateral vesicoureteral reflux is seen in about 10% of patients with UPJ obstruction. Various congenital renal anomalies may be associated with UPJ obstruction, including contralateral multicystic dysplastic kidney (MCDK), renal agenesis, duplicated renal collecting system, horseshoe kidney (Fig. 65.2), and ectopic kidney. Other associated congenital anomalies include imperforate anus, congenital heart disease, esophageal atresia, and VATER syndrome.