We present one example of this occurrence and its uncharacteristic features. A term newborn female was transferred immediately after birth from an outside facility under care of general surgery because of prenatal imaging documenting a large abdominal cyst (>7 cm in largest Cilengitide mw dimension). The

child was stable clinically with good urine output and stooling. She had no issues with feeding or respiratory effort in the first days of life. Physical examination revealed an easily palpable abdominal mass on the left side from the costal margin to the pelvic brim that did not cross midline. A complete abdominal ultrasound was performed on day of life 2 (Fig. 1), and the findings were interpreted as a cystic mass with no solid areas or septations but with a slightly thickened

wall. It was medial to the left kidney but without identifiable communication to the kidney or bladder and measuring 10.4 × 4.1 cm. The left kidney had moderate hydronephrosis without hydroureter. The differential diagnoses were a gastrointestinal duplication cyst, an ovarian cyst, or a mesenteric lymphatic malformation. With these considerations, the general surgery team took the child to the operating room for exploration. The cyst was easily identified and discovered to be intimately associated with a healthy appearing left kidney (Figure 2 and Figure 3). The urology team was called for consultation, and the cyst was confirmed to be a severely dilated left renal pelvis. The renal pelvis was opened revealing mild calyceal dilation, and the ureter was easily cannulated with a 5F catheter Vemurafenib mouse with no evidence of intrinsic obstruction or presence of obstructive crossing vessels. Owing to lack of evidence of obstruction, a renal pelvis

reduction was performed without intervention at the ureteropelvic junction (UPJ) and no stenting or renal drainage. At 1 month postoperatively, a renal ultrasound revealed mild left hydronephrosis improved from the preoperative study without evidence of a dilated renal pelvis. Voiding cysto-urethrogram did not old show vesicoureteral reflux. A MAG-3 renal scan showed no evidence of obstruction (T1/2 of 4 minutes; 93% emptying) with 51.4% differential uptake of the left kidney. An extrarenal collecting system presenting as a cystic abdominal mass has been reported although infrequently in the published literature.1, 2 and 3 All previous reports have assumed or demonstrated UPJ obstruction in association with the dilated renal pelvis as would seem logical. These patients underwent a pyeloplasty with reconstruction of the UPJ. This case is unique in that no UPJ obstruction was observed or demonstrated during or after surgery without reconstruction of the UPJ. The etiology for this massively dilated extrarenal pelvis is, therefore, unclear but would suggest a developmental malformation. The child will continue to have monitoring with periodic renal ultrasound to assure stability of this left system.