MEGAURETER

Megaureter may be seen alone or in association with dilatation of the renal pelvis and calyces.

ETIOLOGY

• Distal ureteral obstruction (ureteral stenosis, fibrosis, abnormal muscularis, or compression by a tumor).
• Vesicoureteric reflux (functional problem or bladder outlet obstruction).
• Idiopathic (nonobstructive, nonrefluxing).

CLASSIFICATION

• Primary megaureter is due to an intrinsic ureteral defect (usually stenosis above the ureterovesical junction).

Primary megaureter or megaloureter is an uncommon cause of severe hydronephrosis (1). It includes all cases of megaureter associated with idiopathic congenital abnormality at the UVJ. The exact etiology of these is unknown.

Belman (2) defined 3 types of primary megaureter:

· Obstructed:

o The obstructed variety is really caused by a functional obstruction theoretically of similar etiology to the UPJ obstruction but at the distal end of the ureter (ie, deficiency of ureteral smooth muscle fibers leading to limited peristalsis).

o It usually involves the distal 2 cm (0.5–4 cm) of ureter.

o The abnormal ureter is of normal calibre.

o More proximal ureter, usually the distal third, but at times the entire ureter and even the pelvis are dilated.

o The ureteral orifice and the submucosal tunnel are normal

· Refluxing - may be caused by a short or absent intravesicle ureter or a paraureteric diverticulum.

· Nonrefluxing unobstructed. - The nonobstructing nonrefluxing megaureter is caused neither by reflux or stenosis and is the most common type of magaureter in neonates. Further imaging information is necessary to exclude secondary causes of megaureter such as posterior urethral valves, urethral stricture, ureterocele, or neurogenic bladder. Voiding cystourethrography (VCU) will exclude reflux.

• Secondary megaureter refers to a ureter dilated by vesicoureteric reflux secondary to lower urinary tract obstruction.

ULTRASOUND

• Dilated, tortuous ureter.
• Runs from the kidney to the bladder and must be differentiated from retroperitoneal fluid filled bowel loops.
• Visible and often exaggerated peristaltic waves may be present.
• Pyelectasis or caliectasis may / may not be present.
• Ectopic ureterocele may be present if it is associated with a duplex collecting system.

ASSOCIATIONS

• Contralateral renal agenesis.
• Multicystic renal dysplasia.
• Complete or incomplete duplication of various components.
• Hirschprung's disease.

REFERENCES

1. V. Gylys-Morin, E. Minevich, L. Tackett et al., Magnetic resonance imaging of the dysplastic renal moiety and ectopic ureter. J Urol 164 (2000), pp. 2034–2039.
2. B.A. Belman, A perspective on vesicoureteral reflux. Urol Clin North Am 22 (1995), pp. 139–150.