(1)
Pediatric Surgery, AlSadik Hospital, Qatif, Saudi Arabia
7.1 Introduction
The term megaureter refers to an enlarged dilated ureter (Fig. 7.1).
Fig. 7.1
Intravenous urography showing a right megaureter. Note the markedly dilated ureter causing back pressure on the kidney
In children, any ureter greater than 7 mm in diameter is considered a megaureter.
The megaureter is divided into two main groups depending on etiology:
Primary megaureter:
This results from a functional or anatomical abnormality involving the ureterovesical junction (Fig. 7.2).
Fig. 7.2
A clinical intraoperative photograph showing a primary megaureter. Note the small narrowed distal ureteric segment which is aperistalitic
Secondary megaureter:
This results from abnormalities that involve the bladder or urethra including:
Myelomeningocele/neurogenic bladder
Severe urethral stricture
Posterior urethral valves
Primary megaureter is further sub classified according to the presence or absence of reflux and obstruction.
Megaureter is divided into four types:
Refluxing megaureter
Obstructed megaureter
Refluxing/obstructed megaureter
Non-refluxing/ non-obstructed megureter
Each of these types is further subdivided into primary or secondary:
This is based on either intrinsic or extrinsic causes for their appearance.
Bilateral involvement is present in about 20 % of patients with primary obstructed megaureter.
The left side is more commonly affected than the right (1.6–4.5 times).
Primary obstructed megaureter is more common in males with male-to-female ration of about 4:1.
Congenital primary megaureter is an idiopathic condition in which the bladder and bladder outlet are normal but the ureter is dilated.
Primary megaureter is the second most common cause of neonatal hydronephrosis.
The majority of cases are non-refluxing and unobstructed.
The incidence of obstructed megaureter is 1 in 10,000 live newborns.
Most primary megaureter in neonates is non-refluxing and unobstructed.
The etiology of this is unknown
It may be due to high fetal urine outflow
It may be caused by changes in the ureter pre- and postnatal or transient anatomical obstructions that improve with postnatal development, such as ureteral folds.
In unilateral primary megaureter the contra-lateral kidney is absent or dysplastic in 10–15 % of patients.
About 50 % of primary megaureter cases are asymptomatic and are discovered on routine antenatal ultrasound.
Most asymptomatic patients have unobstructed primary megaureter.
Symptomatic primary megaureter present with:
Urinary tract infections
Hydronephrosis
Fever
Abdominal and flank pain
Microscopic hematuria is frequent and may occur without infection.
The presence of microscopic hematuria may indicate calculus formation.
These patients rarely present with signs of renal failure.
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
Causes of secondary megaureter include (Figs. 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 7.10, 7.11, 7.12, 7.13, and 7.14):
Figs. 7.3 and 7.4
Micturating cystourethrograms showing posterior urethral valves and associated vesicoureteral reflux
Figs. 7.5, 7.6, and 7.7
CT-urography showing duplex system and bilateral hydroureteronephrosis. Note the dilated megaureters
Figs. 7.8, 7.9, and 7.10
Pelvic ultrasound and intraoperative photograph showing uretrocele. Note the markedly dilated ureter
Fig. 7.11
Micturating cystourethrogram showing massively dilated ureter
Figs. 7.12, 7.13, and 7.14
Micturating cystourethrogram showing severe bilateral reflux and megaureters. Note the absence of posterior urethral valve
Posterior urethral valve: This is often associated with bilateral hydroureter/hydronephrosis
Ureteral diverticulum
Urolithiasis
Urotrocele
Duplex collecting system with reflux into lower pole moiety
Myelomeningocele/neurogenic bladder
Severe urethral stricture
Primary megaureter is a common cause of obstructive uropathy among neonates and young children.
It is estimated that vesico-ureteric junction obstruction account for 23 % of neonates diagnosed with obstructive uropathy.
Children presenting before 1 year old are more likely to have bilateral Primary megaureter than are older patients.
The condition is not known to be hereditary, but families with more than one member with PM have been described.
7.2 Classification
The term ‘megaureter’ could be applied to any dilated (mega) ureter.
In general use, the term megaureter is not applied to a hydroureter caused by overt neuropathic bladder or typical bladder neck obstruction.
Megaureter is usually reserved for conditions in which the bladder and bladder outlet are normal but the ureter is dilated.
Many classifications were proposed for megaureter.
The international classification of Smith et al. is the most comprehensive classification.
Obstructed
Refluxing
Unobstructed
None refluxing
Each of these categories is subdivided into a primary and secondary group.
In primary megaureter the cause is idiopathic.
Secondary megaureter may be caused by:
Urethral obstruction
Bladder outlet obstruction
Neurogenic bladder
Polyuria
Infection
A more practical classification of megaureter was given by King as:
Refluxing
Obstructed
Not refluxing
Not obstructed
Refluxing and obstructed
Primary megaureter usually includes:
Obstructed primary megaureter
Unobstructed primary megaureter
Secondary megaureter is caused by a variety of urological disorders.
Primary obstructed megaureter:
This is most commonly caused by an adynamic juxtavesical segment of the ureter that fails to effectively propagate urine from the ureter into the urinary bladder.
Secondary obstructed megaureter:
This occurs usually when ureteral dilatation is the result of a functional ureteral obstruction associated with elevated bladder pressures secondary to PUV or a neurogenic bladder that impedes ureteral emptying.
Classification of Megaureter
The international classification of Smith et al. is the most comprehensive classification.
Obstructed
Refluxing
Unobstructed
None refluxing
Each of these categories is subdivided into a primary and secondary group.
Primary obstructed megaureter
Secondary obstructed megaureter
Primary refluxing megaureter
Secondary refluxing megaureter
Primary nonrefluxing/nonobstructing megaureter
Secondary nonrefluxing/nonobstructing megaureter
Primary refluxing/obstructed megaureter
Primary refluxing megaureter:
This is associated with severe VUR that alters the uretero-vesical junction leading to dilatation of the ureter.
The megaureter-megacystis syndrome is an extreme form of primary refluxing megaureters.
Secondary refluxing megaureter:
This occurs secondary to posterior urethral valve and neurogenic bladder.
Elevated urinary bladder pressure causes decompensation of the one-way valve at the uretero-vesical junction.
Class
Primary
Secondary
Obstructed
Intrinsic ureteric obstruction (an adynamic juxtavesical segment of the ureter)
Infravesical obstruction (elevated bladder pressure secondary to PUV or a neurogenic bladder that impedes ureteral emptying)
Refluxing
Reflux is the only abnormality (severe VUR that alters the uretero-vesical junction)
Associated with bladder outlet obstruction or neurogenic bladder (Elevated urinary bladder pressure causes decompensation of the uretero-vesical junction
Non-refluxing/unobstructed
Idiopathic ureteric dilatation (No obstruction or reflux)
Polyuria (diabetes insipidus) or gram – ve UTI
Primary nonrefluxing/nonobstructed megaureter:
This is diagnosed when no evidence of obstruction or reflux can be demonstrated.
Secondary nonrefluxing/nonobstructed megaureter:
This occurs secondary to diabetes insipidus, in which high urinary flow rates may overwhelm the maximum transport 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.
7.3 Etiology 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.
This is a functional obstruction secondary to a distal adynamic juxtavesical segment 0.5–4 cm long that is unable to transport urine at acceptable rates.
This leads to proximal ureteric dilatation.
The exact etiology of this aperistatic segment is not known.
Several etiological theories have been proposed including:
Excessive collagen deposition.
Increased matrix deposition alters cell-to-cell junctions and disrupts myoelectrical propagation and peristalsis.
Segmental changes of ureter muscle cells, where there is atrophy of the inner longitudinal layer that conducts the peristaltic waves and hypertrophy of the outer circular layer that causes obstruction.
Thick circumferential periureteral tissues devoid of muscle.
A bulky peri-ureteric sheath
A thick sleeve of muscle forming a continuous layer surrounding the muscle bundles of the terminal ureter. The muscle forming this outer layer is distinct in its histological appearance and arrangement from the muscle bundles which form the ureteric muscle of the VUJ. Furthermore, this muscle layer is very densely innervated by nonadrenergic (immunoreactive to dopamine beta-hydroxylase) nerves when compared with the smooth muscle coat of the ureter. This dense nonadrenergic innervation of this muscle collar might cause it to constrict inappropriately, impeding urinary flow, and ultimately lead to the development of megaureter.
The altered peristalsis prevents the free outflow of urine and functional obstruction results.Related posts:
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