Megaureter
CHRISTOPHER J. LONG
J. CHRISTOPHER AUSTIN
DOUGLAS A. CANNING
Megaureter is a relatively rare congenital anomaly of the urinary tract. We define a megaureter as having a diameter that is 8 mm or greater. The upper limit width for a normal ureter in a full-term newborn is 7 mm. Megaureter is a broad term and is further subdivided into four categories: (a) refluxing; (b) obstructed; (c) both refluxing and obstructed; and (d) nonobstructed, nonrefluxing megaureter. The Pfister-Hendren classification stratifies the ureter based on appearance: in type I, dilation is limited to the distal ureter with no pelvic dilation; type II involves dilation of both the ureter and the pelvis; and type III has severe dilation of the ureter and pelvis with tortuosity of the ureter. Further, megaureters can be either primary or secondary; secondary causes of megaureter include posterior urethral valves, high-volume vesicoureteral reflux, neuropathic bladder resulting in higher detrusor pressure, or less commonly an acquired condition such as external compression of the ureter from a mass lesion or retroperitoneal fibrosis. Primary megaureters, in contrast, are isolated physical abnormalities of the ureter or ureterovesical junction resulting in a dilated ureter.
Prior to the widespread use of screening prenatal ultrasonography, most children with megaureters presented with urinary tract infection, flank pain, urolithiasis, abdominal mass, or hematuria. Most cases today are detected in asymptomatic infants with hydroureteronephrosis in utero. This earlier presentation has led to changes in the approach to management.
The pathophysiology of obstructive megaureters lies not within the dilated segment of the ureter but in the distal, nondilated segment. This segment of ureter is characterized by a deficiency in muscle fiber cross-linking and increased collagen deposition, although this segment is not usually narrowed compared with the normal ureter. These changes compromise the ureter’s ability to effectively propagate the urine bolus as it descends toward the bladder. When the bolus of urine encounters the aperistaltic segment, only a portion of the urine passes into the bladder; the remainder ascends back up the ureter in a yo-yo fashion. This process constantly repeats itself and results in the characteristic appearance of fusiform dilation in which the distal ureter is more severely affected. Proximal dilation and hydronephrosis may develop when the amount and force of the bolus are sufficiently large that it dilates the entire ureter and reaches the renal pelvis.
DIAGNOSIS
The primary goal when evaluating a megaureter is to distinguish an obstructed megaureter from the nonobstructed entities. These ureters demonstrate a spectrum of severity rather than separate conditions. The diagnostic workup depends on the presenting signs and symptoms and may vary from patient to patient. For the child with prenatal hydroureter (width 8 mm or above), the usual evaluation includes a renal/bladder ultrasound, a voiding cystourethrogram (VCUG), and a renal scintigram (renal scan) depending on the degree of dilation. Hydroureteronephrosis is identified with the renal ultrasound. Severe hydronephrosis warrants antibiotic prophylaxis upon initial diagnosis and should be continued for at least 6 to 12 months if no surgical intervention occurs. The dilated ureter is usually visible in the pelvis and is posterolateral to the bladder. If the ureter is dilated inferior to the level of the trigone, an ectopic ureter may be present rather than a primary megaureter with a pseudoureterocele visualized in the bladder. The VCUG separates children with refluxing megaureters from those without reflux and will identify a ureterocele if present. The renal scan in the newborn should be performed with mercaptoacetyl triglycine (MAG-3) with diuretic washout. The scan will estimate the relative function of each kidney and measure the effectiveness of renal clearance of radiotracer from the collecting system. In the past, the t1/2 (time required for half of the radiotracer to clear from the renal pelvis) had been used as an indicator of obstruction. However, in practice, the use of the t1/2 alone to estimate obstruction is not always reliable and can be delayed simply by the presence of a dilated ureter or pelvis. Because the clearance is variable based on the patient’s prestudy hydration level, age, renal function, and response to the diuretic, we prefer to follow trends in the relative renal function, reserving surgery for those with increasing t1/2 or decreasing relative renal function. A differential renal function of <40% or a change in split function >10% should be considered clinically significant.
In children who are symptomatic, the presenting symptom(s) determines the subsequent workup. Hematuria, rarely noted in children with megaureter, is normally evaluated initially with a renal/bladder ultrasound. The finding of hydroureteronephrosis should be followed by a renal scan or intravenous pyelogram. If there is suspicion of renal or ureteral stone, a noncontrast computerized tomography scan should be performed. The renal scan may be required to provide a baseline estimate of relative renal function. If the anatomy is unclear, magnetic resonance urography (MRU) can identify both aberrant anatomy and differential function and can help distinguish between an obstructed megaureter and an ectopic ureter.
If there is impaired function of the affected kidney and the child is undergoing surgical correction, cystoscopy should be performed at the beginning of the reconstructive procedure to evaluate the position of the ureteral orifice. The orifice is normally positioned in an obstructed megaureter, whereas an ectopic ureter will distort the trigone and an ectopic orifice can often be visualized in the urethra.
INDICATIONS FOR SURGERY
Relative indications to proceed with surgical repair include poor initial relative function (<40% of differential renal function by renal scan), progressive hydronephrosis, decreasing function (>10%) in serial renal scans, persistent severe hydroureteronephrosis, bilateral megaureters, or failure of conservative management (the development of symptoms such as pain localized to the side of the megaureter or febrile urinary tract infection). In older children with megaureter, we tend to operate on those who present with symptoms of intermittent flank pain or urinary tract infection.
In infants with indications for intervention, we consider alternative approaches given the infant’s small, thin-walled bladder and the technical difficulties of reimplanting a large, hydronephrotic ureter into the small infant bladder. Options in these patients include endoscopic stenting, a staged reconstructive approach with temporary diversion to an end-cutaneous ureterostomy, and construction of a refluxing ureteral reimplantation, or, rarely, diverting pyelostomy should be given consideration instead of primary surgical repair (1,2).
Prior to surgery, we evaluate the child for voiding dysfunction. Rarely, children develop a secondary megaureter from high-pressure bladder storage that is transmitted to the ureter and renal pelvis. Ureteral dilation can be detected in association with neuropathic bladder dysfunction, posterior urethral valves, or severe voiding dysfunction. Appropriate treatment of the posterior urethral valves or the bladder dysfunction may result in improvement or resolution of ureteral dilation. Dysfunctional bowel elimination can have a significant impact on bladder emptying and should be assessed in every patient evaluated for dysfunctional voiding. Failure to recognize bladder and bowel dysfunction before surgical intervention increases complication rates including persistent obstruction or vesicoureteral reflux.
ALTERNATIVE THERAPY
Because most patients are asymptomatic and identified on prenatal ultrasound, the great majority of children with primary megaureters do not require surgical correction. Ureteral dilation does not always indicate obstruction. Dilation in some boys and girls may represent the residuum of in utero obstruction that has resolved. The long-term experience at the Children’s Hospital of Philadelphia (CHOP) has been that the majority of children with megaureter maintain renal function and ureteral dilation often improves with time, albeit with close observation for renal function preservation. In a series of 27 children with megaureters treated conservatively with a mean followup of 6.8 years, hydronephrosis completely resolved in 53% and was improved or stable in the rest. Only 10% of patients required surgical correction, while 90% were followed with serial radiologic studies. A single patient from this cohort developed progression of hydronephrosis and diminished function at age 14 (3). Likewise, in a series of 53 patients with 67 megaureters, only 17% required surgery for poor initial function or progressive loss of function; in addition, the dilation completely resolved by ultrasound in 34% (4). These two series are concordant with additional literature on primary ureter management and suggest that the majority can be managed conservatively. Because of the rare risk of late progression of obstruction, we recommend that all children with persistent hydronephrosis have extended follow-up.
ENDOSCOPIC TECHNIQUES
One option that deserves consideration is double-J stent insertion with or without dilation of the diseased segment via either endoscopic balloon dilation or laser incision. Cystoscopy is performed to evaluate the appearance of the ureteral orifice. Retrograde pyelogram is performed to assess the area of narrowing and the proximal ureter. If balloon dilation is performed, the ureter is intubated with a 14Fr endoscopic balloon and inflated to 14 atmospheres for 3 minutes. For narrowing that extends beyond 2 cm, a ureteroscope can be inserted to perform laser incision of the ureter at the 12 o’clock position, followed by balloon dilation of the ureter. A double-J stent is left in place for 2 months postoperatively. One additional option is double stenting of the ureter, with the theory that the constant sliding of the stents against one another allows the ureter to heal at a wider caliber.
The endoscopic approach has several advantages. It can be performed as an outpatient procedure and if failure occurs, a formal reimplant remains an option although some groups have reported inflammation and subsequent ureteral scarring after stent placement. Its use in infants younger than 1 year of age has increased, acting to temporarily relieve the obstruction until bladder growth allows for a more definitive formal reimplant.
SURGICAL TECHNIQUE
The surgical correction is similar for refluxing and obstructed megaureters. Obstructed megaureters have a distal ureteral segment of variable length with a normal or narrowed caliber that does not contract normally and should be excised. Refluxing megaureters are dilated to the level of the ureterovesical junction. Distal segment excision is not always required.
The child is positioned supine on the operating room table. In boys, the lower abdomen and genitalia are fully prepped and draped. Females are placed in a mild frog-legged position with gel bolsters under the knees to permit intraoperative access to the urethra if needed. The bladder may be left full during the initial surgical exposure. A Pfannenstiel incision is made in the abdominal skin crease. The rectus fascia is opened transversely along the course of the incision and the flaps of fascia are elevated off the muscle superiorly to just below the umbilicus and inferiorly to the pubis. The rectus muscles are separated in the midline. The space of Retzius is entered, exposing the bladder.
Intravesical Approach
At this point, depending upon the surgeon’s preference, the dissection of the ureter begins either intravesically or through an extravesical exposure. It has been our preference to begin intravesically. The bladder is opened via a midline cystotomy. The bladder dome is packed with damp sponges and a Dennis-Brown retractor is placed to provide exposure of the trigone. A 5Fr feeding tube is passed up the ureter and secured at the orifice with a 4-0 suture. The urothelium surrounding the orifice is divided using electrocautery. With the mucosa divided circumferentially, the ureteral catheter is gently pulled to expose the medial and inferior attachments of the trigonal musculature. These attachments are divided with electrocautery. At this point, the dissection proceeds to carefully divide the
muscular attachments of the ureter through the plane of Waldeyer sheath. This dissection will free the distal ureter, which should have a normal or narrowed caliber. The surgeon should recognize the blood supply of the ureter, as shown in Figure 89.1. As the dissection proceeds more proximally, the blood supply of the ureter originates from medial branches of the hypogastric (male) or cervical (female) arteries. These vessels should be preserved, as should the longitudinal blood supply, by taking care to prevent dissection too close to the ureteral wall. When the ureter is free from its intramural attachments, the mobilization should proceed extravesically. The ureter at this point can be passed through the bladder wall, and the dissection proceeds more proximally. When the dilated region of the ureter is reached, dissection should continue until an adequate length for reimplantation has been mobilized, again paying attention to preserving the blood supply. An ischemic distal ureter may lead to fibrosis and obstruction.
muscular attachments of the ureter through the plane of Waldeyer sheath. This dissection will free the distal ureter, which should have a normal or narrowed caliber. The surgeon should recognize the blood supply of the ureter, as shown in Figure 89.1. As the dissection proceeds more proximally, the blood supply of the ureter originates from medial branches of the hypogastric (male) or cervical (female) arteries. These vessels should be preserved, as should the longitudinal blood supply, by taking care to prevent dissection too close to the ureteral wall. When the ureter is free from its intramural attachments, the mobilization should proceed extravesically. The ureter at this point can be passed through the bladder wall, and the dissection proceeds more proximally. When the dilated region of the ureter is reached, dissection should continue until an adequate length for reimplantation has been mobilized, again paying attention to preserving the blood supply. An ischemic distal ureter may lead to fibrosis and obstruction.
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