Multicystic Dysplasia

Clinical
Fetal kidney nephrons form from fetal metanephric blastema surrounding the ureteral bud. This fetal blastema normally matures during gestation, but occasionally some persists after birth as nephrogenic rests. These nephrogenic
rests are associated with an increased risk of multicystic dysplasia, multilocular cystic nephroma, and Wilms’ tumors. They are more common in several syndromes, such as Beckwith-Wiedemann syndrome (discussed in a later section), hemihypertrophy, and sporadic aniridia; children with these syndromes should be screened for Wilms’ tumors.
Complete multicystic dysplasia (also called ulticystic kidney, renal dysplasia, and renal dysgenesis) is found only unilaterally— complete bilateral involvement is incompatible with life. Depending on the extent of involvement, dysplasia is limited to the infundibula, renal pelvis, and proximal ureter, or it involves a kidney to the point that dilated calyces appear as intrarenal cysts. Segmental multicystic dysplasia occurs in a setting of a duplex collecting system. At times a hypoplastic renal artery is identified.
Most often multicystic dysplasia is detected as an abdominal tumor in infancy. Some older patients present with ureteropelvic junction obstruction. The condition is discovered in an occasional adult as an incidental finding. A variant of multicystic dysplasia includes an associated hydronephrosis, with renal cysts communicating with the renal pelvis. This condition presumably develops from incomplete ureteral obstruction. Often some renal function is evident.
Among term neonates and infants with unilateral multicystic dysplastic kidneys, in those with no vesicoureteral reflux the contralateral kidney was more than 1 standard deviation longer than the mean for age in 54%. Contralateral vesicoureteral reflux is detected in 15% to 25% of children with a newly diagnosed multicystic kidney, and these refluxing kidneys are significantly shorter than nonrefluxing ones. Other anomalies include ectopic ureters, ureterocele, bladder diverticula, and urethral duplication. An association exists among renal dysplasia, Gartner’s duct cyst, and ipsilateral
müllerian duct obstruction. An investigation for lower urinary tract abnormalities is thus in order in these infants. Extraurinary anomalies include bowel malrotation and congenital cardiomyopathy.
Renal malignancy is rare in multicystic dysplasia, and current opinion is that this condition is not premalignant, although the kidney appears prone to nodular renal blastema and reports suggest that renal cell carcinoma, Wilms’tumor, and even mesothelioma appear to be more common than by chance alone. Complicating the issue is that occasionally other lesions, including tumors are misdiagnosed as multicystic dysplasia.
The current trend is to follow segmental multicystic kidneys nonoperatively because these cysts tend to involute and the kidney decreases in size. With age, some patients develop extensive calcifications. At times by adulthood only a cystic remnant with a calcified rim is apparent.
Imaging
A voiding cystourethrogram and renal US appear appropriate in newborns with suspected multicystic kidney disease to confirm the diagnosis and detect any associated anomalies. The grape-like intrarenal cysts do not communicate with the ureter. Little normal renal parenchyma is detected in the involved kidney. A characteristic finding is a club-like deformity of a rudimentary ureter. A small dysplastic kidney is more echogenic than a normal kidney; the US differential diagnosis also includes hydronephrosis due to other etiologies. Occasionally during renal scintigraphy a multicystic dysplastic kidney accumulates a radiopharmaceutical agent; such uptake correlates with the presence of mature renal cortical tissue in the diseased kidney. Tc-99m-DMSA renal uptake is decreased in the contralateral kidney in a majority of patients with a multicystic kidney, reflecting tubular and glomerular damage.
image
Radiology images of right multicystic dysplastic kidney. Noncontrast computed tomography (CT) identifies a small, irregular right kidney (arrow).
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