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Ureteropelvic Junction (UPJ Obstruction)
Review literature: (Tan and Smith, 2004)
Definition of UPJ Obstruction
The ureteropelvic junction (UPJ) is the junction between the proximal ureter and renal pelvis. Congenital malformations with obstruction of the ureteropelvic junction are a common cause for hydronephrosis [fig. UPJ obstruction].
Schematic drawing of a UPJ obstruction caused by a lower pole renal artery (left). After surgical correction (technique by Anderson-Hynes), the vessel is transposed dorsally of the ureteral anastomosis (right).
Epidemiology of UPJ Obstruction
Up to 48% of fetal hydronephrosis are caused by a ureteropelvic obstruction.
Incidence of UPJ obstruction is 1:1500. 60% on the left side, 10–40% of cases involve both kidneys. Male to female ratio is 2:1 in the neonatal age group.
Etiology of UPJ obstruction
Insufficient tubularisation of the proximal ureteral segment in the 10th to 12th week of pregnancy causes obstruction of the UPJ, probably caused by a lack of innervation and/or imbalance of growth factors. This leads to a disturbed structure of the smooth muscles within the ureteral wall and insufficient peristalsis of the proximal ureteral segment. Rare intrinsic causes: ureteral valves or polyps.
- Compression of the ureter by a lower pole renal artery (15–40%) [fig. intraoperative findings of a UPJ obstruction].
- Common associated malformations: pelvic kidney, horseshoe kidney, renal malrotation, double renal systems.
- Fibrotic strands
Intraoperative findings of a UPJ obstruction (1) with lower pole renal vessels (2). See also figure retrograde pyelography of a UPJ obstruction from the same patient. With kind permission of Dr. R. Gumpinger, Kempten.
Secondary UPJ obstruction:
In 10% of patients with severe vesicoureteral reflux, UPJ obstruction exists (or develops).
Pathophysiology of UPJ obstruction
Increased resistance of the urinary flow:
The obstruction leads to a chronic increase of the pressure in the renal pelvis. This leads to smooth muscle hypertrophy, dilatation of the renal pelvis and to an increased renal intratubular pressure.
Activation of inflammatory mediators and the RAAS:
The increased renal pressure leads to a decrease in renal blood flow (RBF) and glomerular filtration rate (GFR). The reduced urine production normalizes the pressure within the renal pelvis, which remains dilated. A uncorrected UPJ obstruction may lead to a functionless hydronephrosis. An activated RAAS-system seems to be the main mediator of the pathophysiological effects (reduction of RBF and GFR). The administration of ACE inhibitors has a protective effect on renal function.
Signs and Symptoms of a UPJ Obstruction
Newborns and infants:
Abdominal tumor, failure to thrive and urosepsis are the classic presentation. Nowadays, many (more) children are diagnosed via prenatal ultrasound imaging and a large proportion of them is asymptomatic.
In children and adults:
Flank pain or upper abdominal pain, often with nausea and vomiting, particularly after fluid intake. Further symptoms are pyelonephritis and hematuria.
Diagnosis of UPJ Obstruction
With renal ultrasound, differentiation between physiologic dilation and significant hydronephrosis is not possible. The anteroposterior diameter of the renal pelvis is used as a parameter for the extent of obstruction of the UPJ obstruction.
With an anteroposterior diameter of the renal pelvis of 12 mm three months after birth, renal scintigraphy should be initiated. The ap diameter three months after birth is also a risk factor for future necessary operation: 75% of children with an anteroposterior diameter of the renal pelvis of more than 21 mm will need an operation. Doppler ultrasound may reveal an increased resistive index (RI, usually about 0.7) in the affected kidney.
- Dilatation of the renal pelvis and calyceal system with a stenotic ureteropelvic segment.
- Delayed drainage of contrast media from the from the renal pelvis.
- Intravenous urography is often not used in children, since better alternatives (e.g. MR urography) are available.
Renal scintigraphy after administration of a radionuclide (MAG3) assesses renal function separate for each kidney and measures the drainage from the renal pelvis to the bladder after stimulation with furosemide. Poor drainage from the renal pelvis means a washout of tracer of less than 50% tracer activity within 20 minutes after furosemide stimulation. A tracer half time of less than 10 minutes after furosemide stimulation is considered normal. A half time between 10–20 min is considered uncertain in relation to relevant obstruction. Indications for surgery are relevant obstruction, especially with symptoms or decreasing fractional renal function.
Vesicoureteral reflux is associated in 10% of cases with UPJ obstruction. Voiding cystourethrogram is necessary for dilated ureters.
Retrograde pyelography and ureteroscopy are necessary for unclear proximal ureteral stenoses. Furthermore, retrograde pyelography is done if insertion of a ureteral stent is done for the relieve of symptoms or before surgery [figure retrograde pyelography of UPJ obstruction in a duplex system and retrograde pyelography of UPJ obstruction].
Retrograde pyelography of a duplex renal system with UPJ obstruction due to the lower pole renal artery. See also fig. intraoperative findings of a UPJ obstruction of the same patient. With kind permission of Dr. R. Gumpinger, Kempten.
Retrograde pyelography of a UPJ obstruction of the left kidney with a lower pole renal artery, see also section laparoscopic pyeloplasty with intraoperative figures of the same patient. With kind permission of Dr. R. Gumpinger, Kempten.
Spiral CT or MRI angiography:
Imaging technique for adults for the identification of a lower pole renal artery, if endopyelotomy is planned or to image complex anatomy of kidney malformations.
The Whitaker test in an invasive measurement of the renal pelvis pressure during infusion through a percutaneous nephrostomy with 10 ml/min. The pressure of bladder is subtracted from the renal pelvis pressure, the difference should be lower than 20 cm water column. Due to the invasiveness of the test, it is seldom used in practice.
Differential diagnosis of UPJ Obstruction
Functional UPJ obstruction (lack of obstruction despite a typical morphology), megacalycosis, megaureter, vesicoureteral reflux.
Treatment of UPJ Obstruction
Indications for Surgery:
- Progressive loss of renal function with evidence of obstruction in renal scintigraphy.
- Flank pain or recurrent pyelonephritis with proven obstruction in renal scintigraphy.
Conservative management with regular renal scintigraphy is indicated in the absence of symptoms and with good renal function on the affected side.
The most popular technique of pyeloplasty is the dismembered Anderson-Hynes technique, which can be done via a open lumbar, open subcostal, laparoscopic, retroperitoneoscopic or robotic-assisted approach (Munver et al, 2004). The Anderson-Hynes technique consists of the transection and reduction of the renal pelvis, excision of the narrow ureteropelvic junction, spatulation of the proximal ureter and reanastomosis of the proximal ureter to the renal pelvis (end-to-side). If a lower pole renal vessel is present, the ureter is repositioned after transection and anastomosis is done anterior to the vessel. For surgical technique and complications see sections open surgical technique of pyeloplasty and laparoscopic technique of pyeloplasty.
Antegrade or Retrograde Endopyelotomy:
Retrograde access (ureteroscopy) or antegrade access to the ureteropelvic junction and endoscopic incision of the narrow segment (posterior position to avoid any lower pole vessel) with the cold knife, with a laser fiber or with special cutting devices. Endopyelotomy is an option if a lower pole renal vessel has been excluded and after failed pyeloplasty. Larger series have reported success rates around 75–90%. The endopyelotomy is seldom used in children. Disadvantages of endopyelotomy are the use of fluoroscopy, 2–3 anesthetics and the lower success rates compared to pyeloplasty.
UPJ obstruction with poor renal function (less than 15–20% on the affected side) should be treated with (laparoscopic) nephrectomy.
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- Munver u.a. 2004 MUNVER, R. ; SOSA, R. E. ; PIZZO, J. J. del:
- Laparoscopic pyeloplasty: history, evolution, and future.
In: J Endourol
18 (2004), Nr. 8, S. 748–55
- Tan und Smith 2004 TAN, B. J. ; SMITH, A. D.:
- Ureteropelvic junction obstruction repair: when, how, what?
In: Curr Opin Urol
14 (2004), Nr. 2, S. 55–9
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