A congenital (primary) megaureter is a 'basket-term' to encompass causes of an enlarged ureter which are intrinsic to the ureter, rather than as a result of a more distal abnormality; e.g. bladder, urethra (see secondary megaureter). It encompasses:
- obstructed primary megaureter
- refluxing primary megaureter (although vesico-ureteric reflux (VUR) is a cause of primary congenital megaureter it is usually considered separately)
- non-refluxing unobstructed primary megaureter
In all three types of megaureter, patients are often asymptomatic, with symptoms referable not to the dilated ureter per se, but rather complications urinary stasis (e.g. urinary sepsis and nephrolithiasis) and, if present, reflux.
Congenital primary megaureter is sometimes associated with:
- congenital megacalyces 3
- ipsilateral renal dysplasia 4
Obstructive primary megaureter
Obstructive primary megaureter is related to a distal adynamic segment with proximal dilatation, and is a common cause of obstructive uropathy in children 1. It is analogous to oesophageal achalasia or colonic Hirschsprung disease although lack of ganglion cells within the wall of the ureter has not been proven to be the cause 2.
Refluxing primary megaureter
Refluxing primary megaureter is a result of an abnormal vesico-ureteric junction, which impedes the normal anti-reflux mechanisms. This can be due to a short vertical intramural segment, congenital paraureteric diverticulum, ureterocoele with or without associated duplicated collecting system etc..
It is relatively common and usually considered separately (see vesico-ureteric reflux (VUR) )
Non-refluxing unobstructed primary megaureter
This is thought to be the most common cause of primary megaureter in neonates, and even though the vesicoureteric junction is normal, with no evidence of reflux or obstruction the ureter is enlarged. The cause for this is unknown.
In all three types the ureter is enlarged ( >7 mm ) 2 sometimes markedly so. On all modalities able to visualise the ureter (CT, US, MRI, IVP) it appears as a tubular structure usually posterior to the bladder 4.
In obstructive primary megaureter the ureter tapers to a short segment of normal caliber or narrowed distal ureter, usually just above the vesicoureteric junction (VUJ). The distal ureter above this narrowed segment is most dilated (similar to achalasia). There is associated hydronephrosis, and active peristaltic waves can be seen on ultrasound.
In refluxing primary megaureter, vesicoureteric reflux is demonstrated (see vesico-ureteric reflux (VUR) )
In non-refluxing unobstructed primary megaureter there is absent or only a minor degree of hydronephrosis. Although rare, congenital megaureter may co-exist with congenital megacalyces 1, making assessment of hydronephrosis more difficult.
Treatment and prognosis
Usually asymptomatic and requiring no treatment. If complications occur or the degree of obstruction is marked then re-implantation following resection of the aganglionic segment may be performed.
Differential diagnostic considerations include:
- vesicoureteric reflux disease (VUR): although actually a cause of primary congenital megaureter it is usually considered separately as prognosis and treatment, depending on degree of reflux, is different
- secondary megaureter
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