Pediatrics: UPJO & Megaureter

Ureteropelvic Junction Obstruction (UJPO)

See Management of Upper Urinary Tract Obstruction Chapter Notes
Hydronephrosis in children, defined by an anteroposterior intrarenal pelvis diameter of 12 mm, differs from that seen later in life and is not necessarily synonymous with true obstruction
Classified in children as congenital/primary vs. acquired/secondary
- Congenital/primary UPJO
  - Typically due to either:
    - Intrinsic narrowing
      - The ureteral segment has an interruption in the development of the circular musculature of the UPJ and an alteration in collagen fibers in and around the muscular cells. This results in a narrowed segment of the UPJ with functional discontinuity of the muscular contractions and ultimately to insufficient emptying of the renal pelvis
      - UPJO in newborns and infants is most often caused by an intrinsic narrowing
    - Extrinsic obstruction
      - Seen in association with a lower pole vessel (aberrant, accessory, or early branching) that passes anteriorly to the UPJ or proximal ureter and contributes to mechanical obstruction
      - UPJO in childhood and adolescence is often extrinsic narrowing caused by an accessory vessel to the lower pole of the kidney giving rise to flank pain, nausea, and vomiting.
- Acquired/secondary UPJO
  - High-grade vesicoureteral reflux (VUR) with a tortuous dilated ureter can result in kinking or narrowing of the UPJ
Congenital renal malformations commonly associated with UPJO (8):
1. Contralateral UPJO (most common anomaly)
2. Renal dysplasia
3. Multicystic dysplastic kidneys
4. Renal agenesis
5. Horseshoe kidneys
6. VUR
7. Ectopic kidney (Chapter 130)
8. Duplex kidney (Chapter 134)
Intermittent UPJO
- Dietl's crisis is intermittent abdominal pain associated with nausea and vomiting following an episode of high fluid intake.
- Although a renal scan with Lasix is used in an attempt to prompt the crisis, it may on occasion be falsely negative.
- In these patients, it is best to repeat a renal ultrasound at the time of pain and compare this to a baseline renal ultrasound taken when the patient was asymptomatic. If increased hydronephrosis at the time of symptoms is present, it is diagnostic and the pyeloplasty will be curative.
Management
- Only ≈1/3 of affected children will need surgical intervention
- Indications for surgery (4):
  1. Symptoms
  2. Infections while on prophylactic antibiotics
  3. Increasing hydronephrosis
  4. Low or decreasing differential renal function
- Options: pyeloplasty vs. endoscopic
  - Pyeloplasty
    - Dismembered Pyeloplasty
      - Improved outcomes over non-dismemembered approach in the repair of a UPJO
        Anderson-Hynes dismembered pyeloplasty is the preferred technique
        
        Advantages of dismembering the UPJ (3):
        A vessel crossing the lower pole can be preserved
        
        The adynamic part of the ureter excised
        
        Redundant pelvic tissue reduced
        
        Main steps of the Anderson-Hynes dismembered pyeloplasty:
        After opening the Gerota fascia, the anterior or posterior aspect of the UPJ is dissected (depending on the access used). The lower pole of the kidney is freed to avoid overlooking an accessory vessel. Electrocautery should be used with caution to minimize damage to the blood supply of both the pelvis and the ureter, with preference given to bipolar diathermy.
        
        A stay suture is placed in the pelvis proximal to the anticipated line of dismemberment; another stay suture can be placed in the ureter at the level of the stenosis.
        
        The UPJ is dismembered, and the pelvis reduced if indicated. A tensely dilated pelvis should be decompressed with a 21-gauge needle before dismembering, to avoid excessive pelvic reduction.
        
        The ureter is then spatulated along its lateral border, well beyond the dysplastic stenotic segment and carried through adequately into healthy ureteral tissue. At this stage, the stenotic part of the ureter should not be removed, because it can serve as a handle that minimizes ureteral tissue manipulation while performing the anastomosis, reducing the risk for mucosal edema.
        
        The anastomosis can be completed with interrupted or continuous suturing. Suture size depends on the prevailing anatomy, but most often a 6-0 or 5-0 resorbable monofilament suture on a round needle is used. Care should be taken at the tip of the V of the anastomosis, which has to be assembled precisely and in a tension-free manner. Placing inadvertent excessive tension on the stay sutures while aligning the anastomosis should be avoided because it can lead to kinking of the ureter once tension is relieved.
        
        Just before completing the anastomosis, the stenotic part of the ureter is removed and the pelvis is irrigated with saline to avoid blood clots obstructing the ureter.
        
        Stenting the anastomosis is a matter of choice
        
        The kidney is brought back to its native position, and the anastomosis can be covered with perinephric fat if available.
        
        Usually the use of external drainage in the form of a Penrose is not indicated
    - Non-dismembered Pyeloplasty
      - Techniques: Heineke-Mikulicz, Foley Y-V plasty
    - Laparoscopic vs. open pyeloplasties
      - Laparoscopic pyeloplasties provide excellent visualization of the anatomy, enhance cosmesis, and duplicate the results of open pyeloplasties with short-term follow-up.
        During laparoscopy monopolar cautery increases the risk of unrecognized lesions to intra-abdominal organs, particularly the bowel.
        
        The technical challenges of this approach have been facilitated by the use of a robotic-assisted procedure that improves the anastomotic repair
        
        Trocars should not be removed before the intra-abdominal pressure is close to normal. Lowering the pressure before removing the trocars will reveal that the hemostasis is under control and prevents intra-abdominal (bowel, omentum) content from entering the port holes.
        
        The peritoneal lining mirrors the light from the telescope, giving the transperitoneal approach better visibility than in the retroperitoneal route.
        
        Horseshoe kidneys are a relative contraindication to the retroperitoneal approach as access to the UPJ from the posterior aspect is extremely difficult
        
        Hypothermia during laparoscopy in all infants is caused by insufflation of a large amount of CO2 due to port leakage.
        
        Bladeless optical trocars or open access for the camera port might be helpful for pediatric minimally invasive surgery in obese patients
      - Newborns may be more suitable for open pyeloplasty since access to the ureteropelvic junction (UPJ) requires only a very small incision.
    - Complications (3):
      1. Prolonged urinary drainage postoperatively
      2. Lack of improvement in renal function or improvement in washout
      3. Occasionally, worsening hydronephrosis and diminished renal function post-operatively
        Such a situation may lend itself to a repair using endoscopic procedures or a repeat dismembered pyeloplasty
  - Endoscopic
    - Preoperative screening for accessory vessels is required by CT, MRI, or transluminal US, so as to avoid vascular injury
    - Endopyelotomy may have a place in the management of failed primary open or laparoscopic procedures followed by the placement of a double-pigtail catheter for 6 weeks. A repeat pyeloplasty, either open or laparoscopically, is the best choice in most cases.

Megaureter

Definition of megaureter: dilatation of the ureter irrespective of cause
Classified as primary vs. secondary
- Primary obstructed megaureters (POM)
  - A condition intrinsic to the ureter itself; obstruction results from the presence of an abnormal adynamic segment at the terminal end of the ureter near or at the ureterovesical junction (UVJ)
    - Insufficient peristalsis at the UVJ leads to obstruction and upstream dilatation
- Secondary to bladder pathologic processes, such as neurogenic bladder dysfunction, bladder outlet obstruction, and/or infection
Subclassified based on cause (4):
1. Obstructed
2. Refluxing
3. Non-obstructed non-refluxing
4. Refluxing with obstruction
Management
- The goal is to prevent renal functional deterioration with either conservative or surgical treatment
- Conservative
  - > 90% of antenatally detected non-refluxing, non-obstructing megaureters will improve with conservative management within the first few years of life
  - Patients with ureteral diameters > 10 mm were more prone to complications
- Surgery
  - Indications for surgery of POM (5):
    1. Symptoms
    2. Infections (recurring UTIs)
    3. Increasing hydronephrosis/hydroureter
    4. < 40% differential renal function
    5. ≥ 5% decrease in differential renal function of on sequential “comparable” nuclear functional studies
      - The T 1/2, or Lasix washout time, especially in neonatal megaureters is not a reliable indicator of obstruction
        Washout curves in neonates and infants can be affected by many factors other than restriction of flow.
        
        A normal creatinine and symmetric renal function support initial observation in a child
  - Options (3):
    1. Decompression
      - Indications for prompt decompression:
        Neonate with a megaureter and sepsis
        
        Ipsilateral reduced function (< 35% in a neonate)
        
        Marked or increasing hydroureteronephrosis
      - Options (2):
        Distal cutaneous ureterostomy (preferred)
        
        Nephrostomy tube
        Nephrostomy tubes are difficult to keep in place
    2. Endoscopic
      - Endoscopic dilatation and stenting of the UVJ in POM is an alternative that is less invasive than formal open or laparoscopic surgical intervention, with short- to medium-term success rates ≈70%
    3. Surgical repair
      - Excision and tapered re-implant
        The stenotic distal part of the ureter is excised
        
        The megaureter is straightened and then tapered to facilitate reimplantation in a nonrefluxing fashion with adequate ratio of length to diameter of 5:1 to improve coaptation of the ureteral lumen, whereby effective peristalsis and urine transportation are achieved
        Ureteral tailoring is usually necessary to achieve the proper length-to-diameter ratio required of successful reimplants. Especially in small children, the reimplant can be otherwise impossible.
        
        Folding techniques for ureteral tailoring are not applicable in ureters >1.75 cm in diameter.
        
        The most serious complication to ureteral tailoring is compromise of the distal vasculature of the ureter with subsequent fibrosis.
        Fibrosis can lead to recurrent obstruction and require a redo. However, when performed with care, the risk of vascular compromise should be minimal
        
        Most surgeons advocate temporary postoperative stenting
      - Complications: obstruction, vesicoureteric reflux, and persistent dilatation
      - A concomitant reimplantation and dismembered pyeloplasty should be discouraged, as the ureteral blood supply may be compromised.

Congenital ureteral strictures

Rare anomalies causing hydroureteronephrosis
Management entails excision of the stenotic ureteral segment and reanastomosis by ureteroureterostomy
Excised segments range in length from 1-3 cm and histologically are characterized by increased collagen deposition and muscular hypertrophy

Ureteral Polyps

Rare anomaly that may lead to obstruction and dilatation
Most often found in the proximal third of the ureter.
Management options include dismembered pyeloplasty with resection of the afflicted part of the ureter when polyps are near the UPJ or ureteral resection and ureteroureterostomy by open and even laparoscopic surgery. In cases of smaller polyps, ureteroscopic excision might be a feasible alternative

Questions

List congenital renal malformations common seen with UPJO. Which is most common?
What are indications for surgical intervention of UPJO?
What is the natural history of antenatally detected megaureter?
What are indications for surgery of primary obstructive megaureter?

Answers

List congenital renal malformations common seen with UPJO. Which is most common?
1. Contralateral UPJO (most common anomalyv)
2. Renal dysplasia
3. Multicystic dysplastic kidneys
4. Renal agenesis
5. Horseshoe kidneys
6. VUR
7. Ectopic kidney
8. Duplex kidney
What are indications for surgical intervention of UPJO?
1. Symptoms
2. Infections while on prophylactic antibiotics
3. Increasing hydronephrosis
4. Low or decreasing differential renal function
What is the natural history of antenatally detected megaureter?
- > 90% of antenatally detected megaureters will improve with conservative management within the first few years of life
What are indications for surgery of primary obstructive megaureter?
1. Symptoms
2. Infections
3. Increasing hydronephrosis/hydroureter
4. < 40% differential renal function
5. ≥ 5% decrease in differential renal function of on sequential “comparable” nuclear functional studies

References

Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 133