Malformations

Fig. 11.6

a Diagram showing a sagittal section through the bladder and male reproductive tract.

■ Malformations

Duplication Anomalies

Duplex Kidney

Duplex Ureter

Bifid Ureter

The renal collecting ducts, renal pelvis, and ureter are formed by the differentiation of the cranial end of the ureteral bud in the fourth to fifth week of gestation. The ureteral bud itself forms posteriorly and medially from the primary ureter, the wolffian duct, before it opens into the urogenital sinus. The presence of a second, separate ureteral bud gives rise to a complete ureteral duplication, while division of the ureteral bud at the later stage results in

a partial duplication. When two ureters are present, the Weigert–Meyer rule states that the upper-pole ureter inserts closer to the bladder neck, frequently at an ectopic site, owing to the medial and caudal rotation of the wolffian duct that occurs during embryonic development. Meanwhile the lower-pole ureter inserts closer to the bladder roof. This accounts for the tendency for reflux to occur in the lower-pole

system whereas the upper system is more susceptible to obstruction.

A ureterocele is another relatively common anomaly resulting from abnormal development of the initially higher ureteral bud, which drains the upper-pole system but opens in the bladder floor due to caudal rotation. This leads to frequent dysplasia with megaureter formation and hydronephrosis of the upper system.

Fig. 11.7 Duplex kidney: normal renal size (9.6 cm), complete parenchymal band with a notch in the renal outline (cystic renal cell carcinoma was diagnosed 5 years later; see Fig. 9.57a contralateral kidney and Fig. 11.23).

Fig. 11.8 Bifid ureter, therefore also duplex kidney. The duplicated upper ureters (U) are joined inferior to the level of the ureteropelvic junction. Urinary obstruction (for the cause, see Fig. 11.14a).

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Urinary Tract

Duplex Ureter

Bifid Ureter

Bifid ureter is a partial ureteral duplication in which the ureters arise from separate renal pelvises and unite between the pelvis and bladder to form a single ureter (Fig.11.8, Fig.11.9).

Fig. 11.9 Bifid ureter: both ureters (U) are obstructed.

a Oblique upper abdominal scan through the left kidney (P = renal pelvis).

Dilatations and Stenoses

b Oblique midabdominal scan on the left side, showing the site where the ureters join together.

c Oblique lower abdominal scan on the left side. Cause of the ureteral obstruction: metastatic tumor (T) of the left ovary.

Urinary Tract

Malformations Duplication Anomalies

Dilatations and Stenoses

Dilated Renal Pelvis and Ureter Renal Pelvic Mass, Ureteral Mass Changes in Bladder Size or Shape Intracavitary Mass

Wall Changes

Caliceal and Ureteral Diverticula

Megacalicosis

Ureteropelvic Junction Obstruction

Ureterovesical Junction Obstruction (Megaureter)

Fig. 11.10 Caliceal diverticulum (12-year-old boy). a Oval, echo-free area of caliectasis. N = kidney.

b A stone (ST; arrow = acoustic shadow) is visible in the distended calix of a child with colicky episodes. It is likely that the caliectasis is primary and that the stone formed secondarily. SS = shadowing.

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Malformations

Fig. 11.12a and b Hydronephrotic sac. Dilated proximal ureter (U). Cause: severe ureteropelvic junction obstruction (surgery)? P, K = massive pyelocaliectasis.

Fig. 11.13 Differential diagnosis: ureteropelvic junction stone (arrow, acoustic shadow S). Severe dilatation of the pelvis. Scans should always include the ureteropelvic junction to aid the differential diagnosis. N = kidney; P = pelvis.

Classification of Megaureter

(Ureterovesical Function Obstruction)

●Obstructive megaureter

–Primary, idiopathic

–Secondary (e. g., to neurogenic bladder, subvesical obstruction)

●Refluxing megaureter

–Primary due to reflux

–Secondary to neurogenic bladder, subvesical obstruction

●Nonobstructive, nonrefluxive megaureter