7.3 Etiology and Pathophysiology

capacity of the ureter by peristalsis or as the result of ureteral atony that accompany a gram-negative urinary tract infection.

•Primary refluxing obstructed megureter:

–This occurs in the presence of an incompetent VUJ that allows reflux through an adynamic distal segment.

7.3Etiology

and Pathophysiology

•Primary obstructive megaureter:

–It is a common cause of obstructive uropathy in children.

–There is a general agreement that there is no true narrowing at the VUJ.

in which the dilated ureters may be caused by reflux or VUJ obstruction, or maybe not refluxing and unobstructed, and categorized according to these characteristics.

–A dysgenetic distal ureteric segment that not only fails to cope within the intramural tunnel but also has ineffective peristalsis is implicated in its pathogenesis.

•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.

–Most primary megaureter in neonates fall into this category.

–There is neither reflux nor stenosis of the juxtavesical ureter, but the ureter is dilated beginning at a point just above the bladder.

–The cause of this phenomenon is unknown.

–Several theories were proposed:

•Fetal urine production is four to six times greater before than after delivery. This is because of differences in renal vascular resistance, GFR and concentrating ability.

•This high outflow might contribute to ureteric dilatation in the absence of functionally significant obstruction, as is occasionally seen with diabetes insipidus.

•Another contributing factor appears to be increased compliance of the fetal ureter because of differences in the deposition of type III collagen, elastin and other extracellular matrix proteins.

•Partial or transient anatomical or functional obstructions that spontaneously improve with postnatal development could contribute to proximal ureteric dilatation.

•Persistent fetal ureteric folds or delays in the development of normal ureteric peristalsis may be responsible for such transient obstructions.

•Primary megaureter is not known to be hereditary, but families with more than one affected member have been described.

•Primary megaureter may be associated with renal agenesis, megacalycosis and urolithiasis.

7.4Clinical Presentation

•The widespread use of obstetrical US with concomitant fetal screening resulted in an increase in the prenatal diagnosis of congenital uropathies, including megaureter.

•Currently, about half of the cases of congenital megaureter are asymptomatic and discovered on prenatal US.

•Symptomatic patients commonly present with UTI, fever and abdominal pain.

•Microscopic hematuria is frequent and may occur in the absence of urinary tract infection. This is presumably caused by the disruption of mucosal vessels of the ureter secondary to ureteric distension.

•Hematuria may also be a sign of calculus formation secondary to urinary stasis.

•It is not unusual for the dilated asymptomatic ureter to be noted at the time of abdominal surgery for other reasons.

•Rarely, these patients present late with signs of renal failure.

7.5Investigations and Diagnosis

•The diagnosis of megaureter is based on clinical presentation and ultrasound before and after birth.

•The antenatal diagnosis of megaureter is based on ultrasound showing hydronephrosis.

•The diagnosis is confirmed by postnatal ultrasound.

•Grey-scale ultrasound:

–Grey-scale ultrasound is the initial study obtained in any child in whom a urinary abnormality is suspected.

–It provides useful anatomical detail of the renal parenchyma, collecting system, ureter and bladder.

–Ultrasound offers a baseline of the degree of hydroureteronephrosis that can be used in serial follow-up.

•The finding of a ureter more than 7 mm in diameter confirm the diagnosis of a megaureter.

Fig. 7.18 A micturating cystourethrogram of the same patient showing no vesicoureteral reflux

•In obstructive primary megaureter (Figs. 7.15, 7.16, 7.17, and 7.18):

–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.

–There is associated hydronephrosis.

–Active peristaltic waves can be seen on ultrasound.

•The primary nature of megaureter must be confirmed and the secondary causes of megaureter must be excluded.

•Causes of secondary megaureter include:

–Polyuria (diabetes insipidus)

–Infection

–Bladder outlet obstruction

–Neuropathic bladder

–Non-neurogenic voiding dysfunction

–Infravesical obstruction or extrinsic lesions such as posterior urethral valve and severe urethral stricture.

•Doppler ultrasonography:

–Doppler ultrasonography with a measurement of renal resistive index (RI) was recently introduced as a noninvasive method of diagnosing obstructive uropathy.

–It has been shown that the RI is agedependent and is commonly >0.70 in healthy children in the first year of life.

–A normal RI exclude obstruction in the presence of a dilated collecting system.

–An RI threshold of 0.70 gave a sensitivity of 82 %, a specificity of 63 % and an overall accuracy of 76 % in children with obstructive uropathy.

–Several methods have been used to increase the diagnostic accuracy of RI.

–The infusion of normal saline and administration of frusemide significantly decreased the RI of unobstructed kidneys and increased the RI of obstructed units.

–The calculation of the difference between the RI of obstructed and unobstructed kidneys ( RI) strengthens the diagnosis.

– Values of RI of >0.06–0.10 are diagnostic of obstruction.

–Recent reports showed a good correlation between the RI and DR. Therefore, the RI could be used for monitoring the dilated collecting systems under observation, obviating the need for frequent radioisotope scanning.

•The diagnosis is confirmed by intravenous urography (IVU) and radioisotope renography.

•Intravenous urography (IVU) (Figs. 7.19 and 7.20):

–The anatomical detail provided by IVU is useful when the level of obstruction cannot be defined.

–IVU usually shows the pathognomonic configuration of a dilated distal ureteric spindle, a less dilated proximal ureter and a dilated or relatively normal-appearing renal pelvis.

–Caliectasis is either absent or mild.

–IVU is currently rarely used as an initial step in the diagnosis of primary megaureter.

–This is especially in neonates because of renal immaturity and bowel gas.

–IVU should not be used before the age of 3–4 weeks and images taken 1 and 2 h after injection with contrast medium should be obtained.

•Radioisotope renography (Figs. 7.21 and 7.22):

–A renogram provides anatomical information together with objective reproducible variables of both function and obstruction.