Contributors of Campbell-Walsh-Wein, 12th edition
Brian A. VanderBrink, Pramod P. Reddy, John C. Pope IV, Craig A. Peters, Kirstan K. Meldrum, Irina Stanasel, L. Henning Olsen, and Yazan F.H. Rawashdeh
Congenital renal anomalies
Renal agenesis
Renal agenesis (RA) represents congenital absence of one or both kidneys, caused by developmental failures of the ureteral bud and metanephric mesenchyme. Bilateral RA is fatal due to oligohydramnios and pulmonary hypoplasia. Unilateral RA is frequently associated with contralateral ureteral abnormalities, including ureteropelvic junction (UPJ) obstruction (11%), ureterovesical junction (UVJ) obstruction (7%), and vesicoureteral reflux (VUR) (30%). In unilateral RA, consider voiding cystourethrogram (VCUG) because of the high coincidence of VUR, particularly if hydronephrosis or hydroureter is present in the solitary kidney.
Ipsilateral genital duct abnormalities are present in 10%–15% of boys and 25%–50% of girls with unilateral RA. Boys may have ipsilateral vasal agenesis. Girls may have a unicornuate or bicornuate uterus with absent or underdeveloped ipsilateral uterine horn and fallopian tube. Zinner syndrome in boys and obstructed hemivagina ipsilateral renal agenesis syndrome in girls are analogous conditions in which an ectopic ureteral insertion into the genital duct system results in ipsilateral renal agenesis ( Fig. 7.1 ).
Horseshoe kidney
Horseshoe kidney is the most common renal fusion anomaly with an estimated incidence of 1 in 400 births. Anatomically, horseshoe kidneys have a parenchymatous isthmus connecting the right and left renal moieties, typically at the L3–L4 level, and crossed by the inferior mesenteric artery. Calyces point posteriorly and the ureter inserts in a relatively nondependent and lateral location on the renal pelvis. Approximately 30% of patients with horseshoe kidney have other congenital anomalies, notably Turner syndrome, hypospadias or undescended testis (5%), mullerian abnormalities (5%), VUR (50%), and UPJ obstruction (UPJO). Unobstructed dilation caused by nondependent ureteral insertion is common. Because of relative stasis, children with horseshoe kidney are at increased risk for stones and upper tract infection.
Cross-fused ectopic kidney
Crossed ectopia refers to a kidney positioned contralateral to its ureteral insertion in the bladder. Ninety percent of crossed ectopic kidneys are fused to the opposite renal moiety. Most commonly, the ectopic kidney crosses from left to right, and the ectopic moiety is positioned inferior to the normal moiety. In all types, ureteral orifices are normal and orthotopic. Crossed ectopic kidneys are usually asymptomatic and discovered incidentally, but a minority of patients present with urinary tract infections (UTIs), stones, or hematuria ( Fig. 7.2 ).
Renal duplication anomalies
Branching of a single ureteral bud results in incomplete pyeloureteral duplication, characterized by a single ipsilateral orifice and bifid renal pelvis or Y-shaped ureter. Incomplete duplication is seldom associated with clinical pathology. By contrast, takeoff of two separate ureteral buds from the same mesonephric duct results in complete ureteral duplication, wherein a relatively cephalad and laterally positioned orifice drains the lower moiety (LM) and a more caudal and medial orifice drains the upper moiety (UM). The UM ureter is more prone to distal obstruction and may be associated with a ureterocele or ectopic ureteral insertion. The LM ureter is more prone to vesicoureteral reflux via a shortened intramural tunnel length.
Renal obstruction: Key principles
Congenital obstructive uropathy (COU) is distinct from postnatal acquired obstruction in that it alters the growth and differentiation of the developing kidney. Pathophysiological mechanisms remain to be precisely defined but likely reflect alterations of key developmental pathways. Key pathological patterns include fibrosis and altered morphogenesis and ultimately dysplasia in severe cases. Postnatal correction of obstruction does not usually permit normalization but may limit progression. Progression may, however, continue because of altered function and ongoing pathophysiological processes. This can be seen in bilateral obstruction or in solitary obstructed kidneys. Biopsy studies have shown that even with normal uptake on nuclear imaging, affected kidneys may have significant histologic. It has also been shown that early insults to normal kidney development are associated with later progression to renal insufficiency. Few useful biomarkers of obstructive uropathy are currently available to define the need for intervention.
UPJ obstruction
Definition
Ureteropelvic junction is the most common form of pediatric upper urinary tract obstruction and is seen in a spectrum of severity with both symptomatic and asymptomatic presentation. The underlying etiology is variable, and spontaneous resolution in many infants is common. Some obstructions are caused by intrinsically abnormal proximal ureteral development and in others extrinsic obstruction is a common cause presenting with flank pain and hydronephrosis. This extrinsic obstruction is often caused by a lower pole vessel of the kidney that creates a kinking of the ureter.
Presentation
Clinical presentation of UPJ obstruction is most commonly through prenatal detection of hydronephrosis but also with symptomatic presentation of abdominal or flank pain. At 20 weeks’ gestation, an anatomic screening ultrasound is generally performed. If hydronephrosis is detected, the anteroposterior (AP) diameter of the dilation is followed with serial ultrasonography. Postnatal follow-up is warranted when AP diameter of the dilated pelvis is ≥ 7 mm during the third trimester.
Later presentation with abdominal or flank pain may be mistaken for gastroenterologic problems, and in some children, the appropriate diagnosis is missed for long periods of time. Abrupt onset of severe pain, frequently with nausea and vomiting that is colicky in nature, is the typical pattern and is termed Deitl’s crisis. These episodes can last several hours but then typically clear completely with no residual discomfort. They may be often confused for cyclic vomiting syndrome or abdominal migraine. If the child is not having symptoms, imaging may not reveal significant hydronephrosis, but imaging during the acute phase will usually show increased dilation from a baseline study. Providing the family with a standing order for an immediate ultrasound during an episode of pain may provide for a definitive diagnosis. Symptoms may be triggered during a diuretic renogram, although this is inconsistent. There can be a delayed nephrogram for up to 48 hours after an episode of pain on a MAG-3 renal scan.
Following prenatal detection, postnatal evaluation with ultrasonography and selection of further functional imaging in the first weeks of life is typical. Controversy remains over the indications for functional imaging as well as the interpretation of diuretic renography. It is also controversial whether to obtain a VCUG, and some recent reports suggest deferring this unless there is associated ureteral dilation, a duplication anomaly, or a dysmorphic kidney. There will still be an incidence, albeit low, of significant reflux that may be missed.
Evaluation
Key factors to be evaluated using diuretic renography (MAG-3 scan) include the relative function of the affected kidney compared with the contralateral as well as the washout time following Lasix administration. Traditional thresholds for obstruction include washout half-time > 20 minutes, but this is not universally agreed upon in pediatric practice. The actual definition of obstruction remains controversial, with some practitioners considering a system to be significantly obstructed only when there is documented decline in relative renal function over time. For others, reduced function at presentation with a delayed drainage curve suggests the need for surgical intervention.
Management
There are no universally agreed-upon criteria for surgery with congenital hydronephrosis. Most series demonstrate that approximately 25% of children with significant unilateral dilation ultimately undergo operative repair because of decreasing relative renal function or increasing hydronephrosis.
Conservative management.
A practical observation plan would include follow-up ultrasonography every 3 months during the first year of life and then increased to every 6–12 months going forward depending on the severity of the hydronephrosis. Periodic repeat of the nuclear medicine studies to assess function can be performed every 6–12 months or if increasing hydronephrosis is detected. Parental preferences need to be incorporated into the management plan because continued testing can be burdensome.
Clear indications for surgery include markedly increased hydronephrosis, > 10% decrease in relative uptake on renography, and symptoms such as pain or UTI. Persistence of hydronephrosis with no improvement over time may also be an indication for intervention.
Surgical management.
The gold standard for correcting UPJ obstruction is a dismembered pyeloplasty. This can be performed at any age. Retrograde pyelography prior to incision is optional and may be combined with stent placement. The standard approach is a subcostal extraperitoneal incision with mobilization of the renal pelvis and excision of the UPJ segment and part of the renal pelvis. The ureter is spatulated laterally, and an anastomosis with fine absorbable suture is performed. A dorsal lumbotomy approach is another option in children. With open surgery, stenting is optional, as well as wound drain.
More recently laparoscopic and robotic techniques have been employed with equal success rates. These are typically done with a transperitoneal exposure utilizing a running sutured anastomosis. Frequently, a ureteral stent is left in place. This can be done with an extraction string to avoid a later cystoscopy. Wound drains are not typically used.
If an extrinsic obstruction is present, the ureter is dismembered and is transposed anteriorly to the vessel, and a typical spatulated anastomosis is performed. A vascular hitch procedure has been described to fix the renal pelvis inferior to the vessel without any ureteral dismemberment; however, the results with this technique have been inconsistent.
Typical postoperative evaluation includes a renal ultrasound 4–8 weeks after surgery. Continued monitoring is reasonable. Some groups perform a diuretic renogram at 3 months and if this drains well, discontinue further follow-up. However, ongoing monitoring of hydronephrosis for 2–5 years is prudent.
Surgical success rates are typically very high, well above 95% in most series. Complications include urinary leakage, and development of a urinoma may require drainage. Postoperative infection is common, and prophylactic antibiotics may be appropriate. Persisting obstruction, although uncommon, is possible and may require replacement of a ureteral stent, balloon dilation, or reoperative pyeloplasty ( Figs. 7.3 and 7.4 ).
Ureterovesical junction obstruction
Definition
Ureterovesical junction obstruction (UVJO), also referred to as primary obstructed megaureter, results from a narrow, a peristaltic segment of intramural ureter, causing a variable degree of upper tract obstruction.
The term “megaureter” is used to describe hydroureter of ≥ 7 mm, regardless of etiology. A megaureter may be associated with UVJO, reflux, or both. Ureteral dilation can be nonpathologic, representing a balanced state of stable dilation.
Presentation
UVJO is most commonly recognized prenatally. Infants or children may present with febrile UTI, sepsis, pain, stones, or microscopic hematuria. UVJO is more common in boys and more common on the left. The natural history of UVJO tend strongly toward spontaneous resolution in the first years of life.
Evaluation
Prenatally detected hydroureteronephrosis generally prompts ultrasonography and VCUG as initial studies. Patients with UVJO often have significant hydroureteronephrosis without VUR. MAG-3 renogram is obtained around 6 weeks of age to evaluate function and drainage. Washout curves and half times are often considerably delayed but generally do not guide management. Endoscopic evaluation or magnetic resonance urography (MRU) is occasionally needed to differentiate UVJO from ectopic ureter.
Management
Conservative management.
Even in the setting of delayed excretion on renogram, observation is the preferred management approach for children with UVJO who have no infections or functional loss. Infants are typically placed on antibiotic prophylaxis given concern for UTI within a relatively static, dilated system. Serial ultrasounds are obtained frequently during year 1 and every 6–12 months thereafter. A renogram may be repeated less often to confirm functional stability and improved drainage.
Temporizing management.
Infants with UVJO and profound dilation, functional loss, or sepsis may require temporizing diversion as a bridge to definitive reconstruction. Options include end or loop cutaneous ureterostomy or refluxing anastomosis of the pelvic ureter to the lateral wall of the bladder.
Definitive management.
Indications for definitive reconstruction include recurrent or severe infection, ipsilateral function under 40%, and significant or sequential functional decline. Stone formation, pain, or progressive, unremitting dilation may prompt surgery in some patients. UVJO is repaired via excision of the narrow adynamic segment and ureteral reimplantation. Intravesical or extravesical approaches may be utilized. Ureteral tailoring, either by plication or excisional tapering, is usually required ( Fig. 7.5 ).
Related posts:
Lower urinary tract dysfunction and anomalies in children
Principles of endourology and fundamentals of laparoscopic and robotic urologic surgery
Principles of urologic surgery: Perioperative management
Urologic evaluation of the child
Evaluation of the urologic patient: History, physical examination, laboratory tests, imaging, and hematuria workup
Urinary tract infections and vesicoureteral reflux
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