Anomalies of renal and ureteral position and structure

Anomalies of renal position and fusion

Normally, during embryogenesis, the kidneys ascend in a cranial direction. Disruption of this process leads to ectopia. The kidney may remain in the pelvis, iliac fossa, cross the midline, or, in rare cases, herniate into the thoracic cavity (thoracic kidney). When two pelvic kidneys fuse, a pancake kidney (pancake kidney) is formed.

Horseshoe kidney (horseshoe kidney) Results from the fusion of metanephroi. The lower poles of the kidneys fuse medially via an isthmus (isthmus), causing rotation of the organs' axes. The ascent of such a kidney stops when the isthmus abuts against the inferior mesenteric artery. The isthmus lies anterior to the aorta and inferior vena cava. Complications: ureteropelvic junction (UPJ) obstruction, nephrolithiasis (in 10–30% of cases), increased risk of infections and Wilms' tumor development.

Crossed fused ectopia (crossed fused ectopia) One kidney is displaced to the opposite side and fuses with the contralateral one. Both kidneys lie on the same side of the spine, yet the ureters insert orthotopically into the urinary bladder.

Duplication of the collecting system

The renal parenchyma may be divided by a column of Bertin (septum of Bertin). Duplication can be complete or incomplete.

• Incomplete duplication (bifid renal pelvis): two renal pelves or ureters merge proximal to the UPJ or distal to it (Y-shaped configuration). It is asymptomatic but may cause ureteroureteral reflux (yo-yo reflux), where urine refluxes from one segment into the other, causing dilatation and infections.
• Complete duplication (complete duplication): follows the Weigert-Meyer rule. The ureter draining the upper moiety of the kidney (upper moiety) inserts ectopically—medially and inferiorly to normal (sometimes extravesically). It is frequently associated with ureterocele and obstruction. The lower moiety ureter inserts in the typical location, but is predisposed to vesicoureteral reflux (VUR).

Ureteral anomalies

Ureteral malformations include variations in number, course, diameter, and structure.

Strictures and megaureter Ureteral strictures are the most common congenital anomaly, typically localized in the UPJ area due to prenatal ischemia and fibrosis. Megaureter (megaureter) is defined as ureteral dilatation exceeding 7 mm. Primary megaureter is divided into three forms: obstructed, refluxing, and non-obstructive non-refluxing. In 75% of cases, the pathology is unilateral and more common in males.

Ectopia and ureterocele An ectopic ureter is often narrowed in its distal segment, causing local dilatation known as a ureterocele. It contains layers of bladder and ureteral epithelium. On intravenous urography (IVU), a ureterocele presents as the "cobra head" sign (cobra neck appearance). Extravesical ectopia (into the urethra or vagina) manifests differently between sexes. In males, the orifice remains above the external sphincter, whereas in females, 50% of patients experience continuous urinary leakage despite normal micturition.

Ureteral deviations Ureteral displacements are often caused by external factors:

• Medial deviation: retrocaval ureter, retroperitoneal fibrosis (periaortitis), pelvic lipomatosis (produces the radiological pear-shaped bladder sign).
• Lateral deviation: psoas muscle hypertrophy (psoas), lymphadenopathy, aortic aneurysms.

Class and exam questions

What else to study on this topic

• Classification of vesicoureteral reflux (VUR grades I-V)
• Whitaker test in the differential diagnosis of residual UPJ obstruction
• Diagnostic criteria and complications of pelvic lipomatosis
• Radioisotope renography with 99mTc-DMSA in evaluating the function of ectopic kidneys

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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