Ultrasound demonstrates an abnormal right kidney which contains multiple cysts of varying sizes that do not communicate. The small amount of renal parenchyma visible between the cysts is echogenic and
MCDK results from atresia of the renal pelvis and ureter during embryonic development of the kidney. The result is a disorganized, dysplastic kidney with essentially no function. The MCDK can be distinguished from hydronephrosis by observing that the fluid filled cysts do not communicate, whereas in hydronephrosis the fluid filled, dilated calyces can be seen to communicate with the renal pelvis and infundibula. The MCDK is typically unilateral (bilateral MCDK would result in stillbirth or fetal demise). However, the contralateral kidney has an increased risk of vesicoureteral reflux, ureteropelvic junction obstruction, and lower urinary tract abnormalities. Voiding cystourethrogram should be performed to rule out vesicoureteral reflux on the contralateral side, to prevent progressive damage to the functioning kidney.
Most multicystic dysplastic kidneys are followed by ultrasound, which often demonstrates slow involution of the kidney. Occasionally it will involute completely. Surgical resection is unnecessary unless complications, such as mass effect by an enlarged MCDK or hypertension, occur.
It is important to note that MCDK is a developmental abnormality unrelated to polycystic kidney disease and other hereditary forms of cystic renal dysplasia.