Hydronephrosis

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Hydronephrosis: dilation of the renal pelvis (pelviectasis) and calyces (caliectasis) due to excess urine in the collecting system of the kidney
  • Hydroureteronephrosis: dilation of the renal collecting system and the ureter to the level of the bladder
  • The presentation can be acute or chronic, unilateral or bilateral. Often, children who have hydronephrosis have the condition from birth (antenatal or fetal or prenatal). Severity ranges from mild to severe.

EPIDEMIOLOGY

  • 10–30% of fetuses with hydronephrosis are due to ureteropelvic junction obstruction.
  • Posterior urethral valves and triad syndrome account for 1–2% of cases.

ETIOLOGY

  • In most cases (64–95%), fetal hydronephrosis is transient/physiologic and resolves with time; however, congenital anomalies of the kidney and urinary tract (e.g., obstruction, reflux) can present with fetal hydronephrosis and can lead to renal injury.
  • Ureteropelvic junction obstruction
    • Partial/intermittent or complete obstruction at the region where the renal pelvis drains into the ureter
    • Can be congenital or acquired
    • Congenital ureteropelvic junction obstruction is more common in children, commonly due to abnormal muscle development of proximal ureter and rarely due to abnormal crossing vessel, or a polyp
  • Vesicoureteral reflux
    • Abnormal backflow of urine from the bladder to one or both ureters
    • In primary reflux (grades I to V depending on the severity), it is due to an insufficient flap valve–type mechanism at the ureterovesical junction that allows urine to flow retrograde from the bladder up into the ureters.
    • Hydroureteronephrosis is usually seen only with higher grades of reflux (grades III to V) or secondary reflux (reflux in the presence of an abnormal bladder, in which the reflux is often due to high storage or voiding pressures within the bladder). Secondary reflux is not graded.
  • Megaureter
    • Abnormally wide or large ureter
    • Primary megaureter is due to abnormal muscle development (anatomical) or aperistaltic segment (functional) of the distal ureter next to the ureterovesical junction.
    • Secondary megaureter can be due to abnormal bladder or urethra (neurogenic bladder, posterior urethral valves).
  • Ureterocele
    • Hydroureteronephrosis secondary to obstruction of the ureter from a cystic dilation of the intravesical portion of the distal ureter
    • Most often associated with the upper pole ureter in duplicated collecting system; less frequently associated with a single system
    • Ureterocele is further classified as intravesical (contained completely within the bladder) or ectopic (extending down the bladder neck and often into the urethra).
  • Duplicated collecting system
    • Due to duplication of ureteric bud
    • Can be complete or partial
    • In complete duplication, the kidney has two separate pelvicalyceal systems and two ureters.
    • Partial duplication is more common, with two pelvicalyceal systems with either a single or two ureters that unite prior to insertion into the bladder.
  • Ectopic ureter
    • A ureter that drains into an abnormal location outside of the bladder
    • The hydroureteronephrosis can be the upper pole ureter of a duplicated collecting system or a single system.
    • Ectopic ureters can drain at various sites along the lower urinary tract depending on the sex of the child. In boys, they can drain into the bladder neck, prostatic urethra, vas deferens, seminal vesicle, or epididymis. In girls, they can drain into the bladder neck, urethra, introitus, and vagina.
    • The ectopic locations often require passage through the bladder neck or urogenital diaphragm, which produces obstruction of the distal ureter.
  • Urolithiasis
    • Obstructing calculi often produce dilation of the urinary tract proximal to its location.
    • Stone disease is rare in infancy except in preterm infants who receive furosemide.
    • Hydronephrosis is usually associated with renal colic.
  • Posterior urethral valves
    • Hydroureteronephrosis: usually bilateral, produced by outflow obstruction of the bladder from an obstructing membrane in the prostatic urethra
    • Many patients have bilateral renal dysplasia, ongoing renal injury due to bladder dysfunction or infection, which increases the risk of chronic kidney disease and eventual progression to end-stage renal disease.
  • Prune-belly syndrome
    • Also known as triad or Eagle-Barrett syndrome
    • The exact etiology is unknown. Congenital defect predominantly affects males.
    • Affected infants have a triad of hypoplastic abdominal wall musculature (leading to a prune-like appearance), bilateral undescended testes, and a dilated urinary tract.
    • Pulmonary hypoplasia is a significant complication due to oligohydramnios. There is a significant risk of renal insufficiency and bladder dysfunction.

There's more to see -- the rest of this topic is available only to subscribers.