Megaureter

Megaureter

Description

Hydroureter or dilated ureter is associated with a lower obstructive lesion in over 90% of cases and frequently associated with other malformations including double ureter, ectopic ureter, ureterocele, dysplastic kidneys, ureterovesical strictures or single kidney. In simple megaureter the kidneys and bladder are normal and no anatomic obstruction is found. Elongation and kinking are usually present and the lower end of the ureter may form a bulb-like dilatation with the intramural portion of normal calibre. In some cases the narrowing is located a short distance above the bladder. Megaureter may or may not be associated with reflux. The metanephros (primitive kidney) appears in week 5 of development and develops from the metanephric diverticulum (ureteric bud) and the metanephric blastema. The ureteral bud normally increases in length undergoing multiple divisions to form the ureters, renal pelvis and related structures. Hydroureter from obstruction leads to dilatation of the ureter, elongation, kinking, and tortuosity. First an obstructed ureter may hypertrophy followed by gradual failure leading to urinary reflux in advanced stages. One possible explanation for simple megaureter is an abnormally long persistence of the ureteric membrane. Hydroureter is often unilateral and shows a preponderance in males.

Diagnosis

Hydroureter or megaureter is diagnosed by tracing hypoechogenic tubular (often tortuous) structures to the fetal renal pelvis or the fetal bladder. The normal ureter is not usually visualised as a tubular structure in the fetus. It is important to try to differentiate primary” megaureter from “secondary” obstructive megaureter since the prognosis and treatment are affected by the aetiology. An enlarged bladder often implies a lower obstructive lesion but megacystis and hydroureters (with or without vesicoureteral reflux) have been seen in its absence. Oligohydramnios in the presence of an enlarged bladder is a strong indicator of obstruction, however, normal amniotic fluid volume or even polyhydramnios does not rule it out. It can also be seen in the presence of other fetal malformations such as gastrointestinal obstruction. In “primary” megaureter the renal pelvis is often normal or minimally dilated, the ureter is usually less tortuous and the amniotic fluid volume is normal. More severe hydronephrosis is likely to imply an obstructive lesion. An attempt should be made to identify other genitourinary malformations as well as retroperitoneal masses i.e. hydrocolopos, intrapelvic sacrococcygeal teratoma, or other pelvic masses extrinsic to the urinary tract which may result in ureteral obstruction.”

Differential Diagnosis

Mesenteric and adnexal cystic masses are usually round, not tubular. Dilated loops of bowel may demonstrate peristalsis and particulate matter in the lumen. Colour flow Doppler can be used to identify blood vessels in the area of the ureters.

Sonographic Features

Dilated ureter(s) – tubular, tortuous

Peristalsis possible in dilated ureter(s)

If unilateral, amniotic fluid usually normal

If bilateral, there can be oligohydramnios

Pyelectasis, hydronephrosis , megacystis may also be present

Duplication of kidneys, renal pelves and ureters may be associated

Ureterocele may be present

Associated Syndromes

  • Bladder exstrophy
  • Congenital hydronephrosis
  • DOOR
  • MMIHS (megaureter megacystis intestinal hyperperistalsis syndrome
  • Ochoa
  • Posterior urethral valves
  • Prune Belly
  • Schinzel-Gierdion
  • Triploidy
  • Vesico-ureteral reflux

References

Romero R, Pilu G, Jeanty P, Ghidini A, Hobbins J In: Prenatal Diagnosis of Congenital Anomalies Appleton & Lange: Norwalk, p278-280


Warkany J In: Congenital Malformations, Notes & Comments Mosby Year Book: Chicago, p1670-1071


Crawfurd MdA In:The Genetics of Renal Tract Disorders Oxford U Press: Oxford/New York, p561-563