Overview Snapshot A 2-year-old boy is referred by his pediatrician to a nephrologist for recurrent urinary tract infections. He was born at 39 weeks and appeared healthy at birth; however, he has developed significantly more urinary tract infections than expected for a child of his age. Physical exam reveals increased fullness in the abdomen and an MRI scan is obtained. Urine cultures are obtained and empirical antibiotics are started pending culture results. Introduction Clinical definition congenital malformation of the renal system resulting in fused kidneys Epidemiology common malformation found in 1/400 live births twice as common in males Pathogenesis fusion of the lower poles of the kidneys (most common) trapping of the fused kidneys under the inferior mesenteric artery arrest of the normal retroperitoneal ascent of the kidneys Associated conditions Turner syndrome trisomy 18 (Edwards syndrome) Prognosis typically very good most patients remain asymptomatic Presentation Symptoms asymptomatic (most common) increased rate of urinary tract infections hydronephrosis due to ureteropelvic junction obstruction renal stones Physical exam abdominal fullness upon palpation Imaging Kidney ultrasound indications initial evaluation of symptomatic patients Voiding cysturethrogram indications further evaluation of abnormal anatomy findings fusion of kidney poles trapped under the inferior mesenteric artery Intravenous pyelogram indications for evaluation of symptomatic kidney stones findings filling defect at the level of the obstruction Differential Unilateral renal agenesis Posterior urethral valves Multicystic dysplastic kidney Duplex collecting system Treatment Conservative no treatment for asymptomatic patients Medical antibiotics indication urinary tract infections outcomes very good Complications Postrenal kidney failure due to kidney stones rare since most cases are asymptomatic treatment removal of kidney stones Hydronephrosis if obstruction is left untreated Anomalous original of multiple renal arteries may complicate surgery