Further Reading

graphic findings consistent with urinary tract obstruction improves renal outcome.

–Signs of infection within the obstructed system warrant urgent intervention because infection with hydronephrosis may progress rapidly to sepsis.

–Bilateral Hydronephrosis with or without hydroureter and hydronephrosis in a solitary kidney calls for early evaluation and possible surgical intervention.

–Urethral catheterization is important to help rule out a lower urinary tract cause for hydronephrosis and hydroureter.

–Difficulty in passing a Foley catheter may suggest urethral stricture or bladder neck contracture.

–A percutaneous nephrostomy tube:

•This is useful in confirming and locating the site of obstruction.

•It is also useful in draining the obstructed kidney and reliving the pressure on the renal parenchyma.

•It is also a useful measure to drain the kidney and buy time for the infant to grow in preparation for surgical intervention.

•Add to this the fact that the ureter in those patients with pelviureteric junction obstruction is small which makes it difficult to reconstruct the PUJ.

Further Reading

1. Chung S, Majd M, Rushton HG, Belman AB. Diuretic renography in the evaluation of neonatal hydronephrosis: is it reliable? J Urol. 1993;150(2 Pt 2):765–8.

2.Coplen DE. Prenatal intervention for hydronephrosis. J Urol. 1997;157(6):2270–7.

3. Estrada CR, Peters CA, Retik AB, Nguyen HT. Vesicoureteral reflux and urinary tract infection in children with a history of prenatal hydronephrosis – should voiding cystourethrography be performed in cases of postnatally persistent grade II hydronephrosis? J Urol. 2009;181(2):801–6.

4. Gordon I. Diuretic renography in infants with prenatal unilateral hydronephrosis: an explanation for the controversy about poor drainage. BJU Int. 2001;87(6):551–5.

5. Gordon I, Dhillon HK, Gatanash H, Peters AM. Antenatal diagnosis of pelvic hydronephrosis: assessment of renal function and drainage as a guide to management. J Nucl Med. 1991;32(9):1649–54.

6. Grattan-Smith JD, Little SB, Jones RA. MR urography evaluation of obstructive uropathy. Pediatr Radiol. 2008;38 Suppl 1:S49–69.

7.Josephson S. Antenatally detected pelvi-ureteric junction obstruction: concerns about conservative management. BJU Int. 2000;85(7):973.

8. Koff SA. Postnatal management of antenatal hydronephrosis using an observational approach. Urology. 2000;55(5):609–11.

9. Mamì C, Paolata A, Palmara A, et al. Outcome and management of isolated moderate renal pelvis dilatation detected at postnatal screening. Pediatr Nephrol. 2009;24(10):2005–8.

10. Sidhu G, Beyene J, Rosenblum ND. Outcome of isolated antenatal hydronephrosis: a systematic review and meta-analysis. Pediatr Nephrol. 2006;21:218–24.

11. Taylor Jr A, Clark S, Ball T. Comparison of Tc-99 m MAG3 and Tc-99 m DTPA scintigraphy in neonates. Clin Nucl Med. 1994;19(7):575–80.

12. Ulman I, Jayanthi VR, Koff SA. The long-term fol- low-up of newborns with severe unilateral hydronephrosis initially treated nonoperatively. J Urol. 2000;164(3 Suppl 1):787–9.

13.Woodward M, Frank D. Postnatal management of antenatal hydronephrosis. BJU Int. 2002;89(2): 149–56.

3.1Introduction

•Pelviuureteric junction (PUJ) obstruction is a partial or complete blockage of the flow of urine from the renal pelvis into the ureter (Fig. 3.1).

•This results in accumulation of the urine in the renal pelvis leading to its dilatation and back pressure on the renal parenchyma leading to progressive renal damage and deterioration.

•PUJ obstruction is the most common cause of antenatally detected hydronephrosis and the most common cause of pediatric hydronephrosis.

•Ultrasonography reveals fetal upper urinary tract dilatation in approximately 1 in 100 pregnancies; however, only 1 in 500 are later diagnosed with significant urologic problems.

•PUJ obstruction is found in approximately 50 % of patients diagnosed with antenatal hydronephrosis.

•The reported incidence of PUJ obstruction is 1 in 500 live births. Others report the estimated incidence of PUJ obstruction as 1 per 1,000–2,000 live newborns.

•The widespread use of antenatal ultrasonography has contributed to an increase in the number and earlier diagnosis of hydronephrosis.

•PUJ obstruction is commonly seen in infants and children and less commonly in adults.

•PUJ obstruction is found more commonly in boys than in girls. The male-to-female ratio of UPJ obstruction is 3–4:1.

•PUJ obstruction occurs more on the left side than on the right. The left kidney is affected in 67% of cases and the right kidney in 33% of the cases.

•Bilateral PUJ obstruction is seen in about 10 % of the cases. Bilateral PUJ obstruction (synchronous and asynchronous) is seen in 10–40 % of infants <6 months.

•Less than 5 % of patients with bilateral PUJ require bilateral repair because of spontaneous resolution in a significant number of cases.

•With the current routine use of antenatal ultrasound, most cases of congenital pelviureteric junction obstruction are diagnosed antenatally.

•PUJ obstruction may be diagnosed at any age.

–Some of these cases may be asymptomatic discovered incidentally during evaluation of some other unrelated problem.

–PUJ may be identified during the investigation of intermittent flank or abdominal pain, urinary tract infection, hematuria.

–Symptomatic cases may present with intermittent flank or abdominal pain that is made worse by drinking large amounts of fluids or they may present with an abdominal or flank swelling.

•The cause is usually a congenital abnormality in the pelviureteric junction leading to its narrowing.

•Other causes of intrinsic PUJ obstruction include:

–Valvular mucosal folds

–Persistent fetal ureteral convolutions

–Ureteral polyps

•In about 10 % of children with PUJ obstruction, an aberrant or accessory renal artery or arterial branch may cross the lower pole of the kidney, resulting in compression of the PUJ and blockage of urinary flow.

•In some cases, the obstruction may be acquired following injury to the pelviureteric junction leading to its narrowing. This is usually secondary to inflammation related to a stone stuck at the junction.

•PUJ obstruction is known to be associated with other urological anomalies and these include:

–Renal dysplasia

–Contralateral multicystic dysplastic kidney

–Contralateral renal agenesis

–Duplicated renal collecting system, in which case the lower pole system is usually the obstructed segment

–Horseshoe kidney

–Ectopic kidney

–Vesicoureteral reflux (up to 40 %)

•The degree of obstruction is variable ranging from mild to severe.

•Mild degrees of PUJ obstruction do not require any surgical treatment, and these patients can be followed up hoping for complete spontaneous relive of obstruction.

•Symptomatic patients and those with impaired renal function require surgical intervention to preserve the remaining function of the kidney.

•The first reconstruction of an obstructed kidney was made in the late 1800s by Trendelenburg.

•In 1936, Foley described the YV-plasty to repair PUJ.

•In 1946, Anderson and Hynes described their operation to treat PUJ obstruction. This is now the standard operation used to repair PUJ obstruction and bear their name (The Anderson-Hynes dismembered pyeloplasty).

3.2Embryology

•The ureter develops from the ureteral bud.

•It extends upward towards the developing kidney.

•Induction of the metanephric blastema has been thought to be mediated by the ureteral bud through several factors including:

–Transcription factors such a Pax-2

–Growth factors such as c-ret, kdn-1, and wt1

–Transforming growth factor β (TGFβ).

•Embryologically, the pelvi-ureteric junction forms usually around the fifth week of intrauterine life.

•At around the 10th–12th weeks of intrauterine life, the initial solid tubular lumen of the ureter becomes reanalyzed.

•It has been suggested that the ureteropelvic and ureterovesical portions of the ureter are the last to canalize.

•Failure of canalization or partial canalization is thought to be the main embryological explanation of a PUJ obstruction.

•Another theory suggests arrest of ureteral wall musculature development leading to the persistence of an aperistaltic segment at the PUJ level leading to partial obstruction.

•Another theory suggests improper innervation with diminished synaptic vesicles at the PUJ which may play a role in the development of PUJ obstruction. This was supported by the findings of decreased amounts of the several factors in the resected specimens of PUJ. These include:

–Protein gene product (PGP) 9.5 (a general neuronal marker)

–S-100 protein (a nerve supporting cell marker)

–Synaptophysin (a synapse vesical marker)

–Nerve growth factor receptor

•Early in the embryological development, the proximal ureter is folded on itself and persistence of the unfolding may contribute to the kinked appearance of the proximal ureter.

•The most attractive theory is that the PUJ obstruction is secondary to muscular discontinuity. This disrupts the coordinated smooth

muscles movement and disrupt peristalsis propagation across the PUJ. The end result is a narrow but structurally patent lumen at the PUJ which in the presence of high urine volume cannot efficiently empty. This is supported by the followings:

–The findings of rearrangement and widely separated smooth muscle cells

–The findings of excessive collagen fibers

–The findings of increased elastin in the adventitia

–The findings of diminution of nerve terminals and nerves at the stenotic portion.

3.3Pathophysiology

•The drainage of urine from the renal pelvis to the ureter depends on several factors.

–Pressure within the renal pelvis is determined by the volume of urine produced

–The internal diameter of the PUJ and collecting system

–The compliance of renal pelvis

–The peristaltic activity of the ureter

•In response to the increased urinary volume and pressure, the renal pelvis dilates.

•The effect of this on the renal parenchyma may be quite variable.

•Sometimes and despite of massive dilation of the renal pelvis, preservation of renal function may occur.

•A pressure-dependent flow:

–This is seen in those with intrinsic obstruction where at low urinary flow rates, no obstruction exists; but as the urinary flow rate increases, urinary stasis will develop leading to dilatation of the renal pelvis.

•A volume-dependent flow:

–This is seen in those with extrinsic obstruction usually caused by aberrant vessels. There is a normal urine flow which is impeded only after a definite amount of urine is collected in the renal pelvis.

–Patients with extrinsic obstructions tend to present late in childhood, with intermittent abdominal or flank pain.