Duplicated Renal Collecting System. In this anatomical anomaly, the upper and lower poles of the kidney-called moieties-are each drained b) a separate ureter (Fig. 10-42). Duplication is found in approximately 1 in 4000 pregnancies, is more common in females, and is bilateral in 15 to 20 percent of cases (James, 1998; Vergani, 1998; Whitten, 2001). Sonographically, an intervening tissue band separates two distinct renal pelves. Development of hydronephrosis or ureteral dilatation may occur due to abnormal implantation of one or both ureters within the bladder-a relationship that reflects the anatomical Weigert-Meyer rule. The upper pole ureter may develop obstruction from a ureterocele within the bladder, whereas the lower pole ureter has a shortened intravesical segment that predisposes to vesicoureteral reflux (see Fig. 10-42B). Thus, both moieties may become dilated from diferent etiologies, and both are at risk for loss of function.
The prevalence of bilateral renal agenesis is approximately in 8000 births, whereas that of unilateral renal agenesis is 1 in
FIGURE 10-42 Duplicated renal collecting system. The upper and lower moieties of the kidney are each drained by a separate ureter.
A. Renal pelvis dilatation is visible in both the upper (U) and lower (L) pole moieties, which are separated by an intervening band of renal tissue (arrowhead). B.The bladder, encircled by the highlighted umbilical arteries, contains a ureterocele (arrowhead).
1000 births (Cragan, 2009; Dolk, 2010; Sheih, 1989; Wiesel, 2005). When a kidney is absent, color Doppler imaging of the descending aorta demonstrates absence of the ipsilateral renal artery (Fig. 10-43). In addition, the ipsilateral adrenal gland typically enlarges to ill the renal fossa, termed the ying down adrenal sin (Hofman, 1992). As with other fetal anomalies, amniocentesis for chromosomal microarray analysis should be considered.
If renal agenesis is bilateral, no urine is produced, and the resulting anhydramnios leads to pulmonary hypoplasia, limb contractures, and a distinctively compressed face. When this combination results from renal agenesis, it is called Poter syndrome, after Dr. Edith Potter, who described it in 1946. When these abnormalities result from severely decreased amnionic luid volume from another etiology, such as bilateral multicystic dysplastic kidney or autosomal recessive polycystic kidney disease, it is called Poter sequence. he prognosis for these abnormalities is extremely poor.
This severe form of renal dysplasia results in a nonfunctioning kidney. The nephrons and collecting ducts do not form normally, such that primitive ducts are surrounded by ibromuscular tissue, and the ureter is atretic (Hains, 2009). Sonographically, the kidney contains numerous smooth-walled cysts of varying size that do not communicate with the renal pelvis and are surrounded by echogenic cortex (Fig. 10-44).