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Pop-Off Mechanism in Posterior Urethral Valve

Diary A. Rahman, Maher A. Ghazala, Mamoun Al Marzouqi, A.R. Mustafawi,

Department of Paediatric Surgery

Al Wasl Hospital, Dubai, United Arab Emirates.

 

Correspondence

Diary A. Rahman; Al Wasl Hospital, P.O. BOX: 9115,
Dubai, United Arab Emirates.
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Tel: (009714) 2193545; Fax: (009714) 3113068


Abstract

Aim: To report Al Wasl Hospital experience with diagnosis and management of patients with “pop-off” mechanism in posterior urethral valves.

Materials and Methods: From January 2000 through January 2005, the records of 17 patients with posterior urethral valve (PUV) were evaluated retrospectively in the department of paediatric surgery, Al Wasl Hospital, Dubai, United Arab Emirates. Radiological studies were reviewed, eight patients with “pop-off” mechanism were abstracted.

Results: All patients had PUV with urinary diverticulum in one patient, three patients presented with urinary ascites, bilateral urinoma in the first two patients and left peri-renal urinoma in the third patient. MCUG showed left VUR and bilateral VUR in the last two patients respectively. In the remaining four patients, the “pop-off” mechanism presented as left VUR with poor functioning left kidney in all of them ranging from 0-14% function. One patient also had right vesico-ureteric junction obstruction. All patients were operated as valve ablation, one patient had urinary diverticulectomy, one patient had left ureterostomy, vesicostomy in two patients. Two patients had left nephro-ureterectomy with histological changes of dysplasia. In one patient, right ureteric DJ stent was inserted to overcome right VUJ obstruction. Postoperatively all except one have excellent renal function.

Conclusion: The presence of a pressure “pop-off” mechanism in PUV is a favourable prognostic sign.

Key words: Posterior Urethral Valve, pop-off mechanism, renal function

 

Introduction

The most common obstructive abnormality in male children affecting both kidneys is Posterior Urethral Valve (PUV) [1]. Certain protective factors, which provided a “pop-off” mechanism that resulted in preservation of renal function, were identified[2].

In theory, they could serve to buffer the affected system from the deleterious effects of the elevated intra-vesical pressures that occur with outlet obstruction[3].

Materials and methods:

The records of 17 patients with posterior urethral valves were evaluated retrospectively from January 2000 through January 2005 in Department of Paediatric Surgery, Al Wasl Hospital, Dubai, United Arab Emirates. Radiological studies were reviewed with particular attention to the type of pressure “pop-off”. Eight patients with bladder diverticulum, urinomas/ urinary ascites and unilateral VUR were abstracted. Results:

Case 1

Thirteen hours old male child was referred because of antenatal diagnosis of bilateral hydronephrosis and hydroureters with distended bladder. Postnatal ultrasound scan and MCUG confirmed the diagnosis of PUV with bladder diverticulum. No VUR was visible. Initial serum creatinine was 1.2mg/dL. The child had valve ablation with subsequent urinary diverticulectomy. Last time was seen at the age of four years with normal urea & electrolytes, good function of both kidneys on renal isotope scan. MCUG showed almost normal posterior urethra and bladder. (Fig. 1)

eArt37-1a eArt37-1b eArt37-1c
Figure 1.A. MCUG shows dilated posterior urethra due to PUV Figure 1.B. MCUG shows bladder diverticulum Figure 1.C. MCUG shows almost normal posterior urethra after valve ablation and diverticulectomy

Cases 2,3 & 4:

Three patients were referred at the age of 3 hours, 20 days and 6 months mainly because of abdominal distension with antenatal hydro-ureteronephrosis bilaterally in case no. 2. Postnatal ultrasound scan showed bilateral hydronephrosis, hydroureter and small, trabeculated, thick wall bladder with urinary ascites, bilateral peri-renal urinoma in cases 2 and 3, and left sided peri-renal urinoma in case 4 (Fig. 2). MCUG shows PUV in all cases with left sided VUR in case 3 and bilateral VUR in case 4. Initial serum creatinine was 1.1mg/dL, 10.7mg/dL and 10mg/dL respectively while after urinary catheterisation and valve ablation with left ureterostomy in case no. 4 serum creatinine drops to 0.6mg/dL, 0.5mg/dL and 0.7mg/dL respectively. (Table 1) Follow up with blood biochemistry, renal USS, DTPA and MCUG shows progressive improvement.

eArt37-2
Figure 2.A. Plain Abdominal x-ray shows urinary ascites.

Figure 2.B & 2.C: Renal USS shows perirenal urinoma of the left kidney.

Figure 2.D: Renal USS of same patient after valve ablation shows normal left kidney.

Case

Age

Cause of
referral

Postnatal USS

Initial
s. creat
mg/dL

Last
s. creat
mg/dL

MCUG

Isotope scan

Tratament

2

3H

Abdominal
distension.
Antenatal
USS.

Bilateral hydrouretero-nephrosis, thick
wall
bladder

with
bilateral
urinoma
&
urinary ascites

1.1

0.6

PUV

Good
function
bilaterally

Valve ablation

3

20D

Abdominal
distension

Bilateral hydrouretero-ne
phrosis,  thick wall bladder
with bilateral urinoma &
urinary ascites

10

0.5

PUV
+
left
VUR

Good
function
bilaterally

Valve ablation

4

6M

Abdominal
distension

Bilateral hydrouretero-ne-
phrosis, thick wall bladder
with left peri-renal urinoma
& urinary ascites

10

0.7

PUV
+bilat.
VUR

Rt. Kidney
– good  
function
Lt. Kidney
poor
function

Valve
ablation+
Left
ureterestomy


 

Case

Age

Cause of referral

Initial

s.creat

mg/dL

Last

s. creat

mg/dL

MCUG

Isotope renal scan

Treatment

5

4M

Fever FTT

3

0.7

PUV &

Left VUR

Poor function left kidney

Valve ablation + Left nephro-

ureterectomy

6

3D

Antenatal USS

4.1

1.2

PUV &

Left VUR

Non-functioning left

kidney.

Right VUJ obstruction

Valve ablation + vesicostomy +

Left nephoureterectomy

Right DJ stent

7

3D

Antenatal USS

2.2

0.2

PUV &

Left VUR

Poor function

Left kidney

Valve ablation

8

2D

Antenatal USS

1.5

0..5

PUV &

Left VUR

Poor function

Left kidney

Valve ablation +

Vesicostomy


Cases 5, 6, 7 & 8:

Case 5 was referred at the age of four months because of fever and failure to thrive. All other three patients were sent to us after birth because of antenatal hydronephrosis and hydroureters with distended bladder and suspicion of PUV. Postnatal USS shows bilateral hydroureteruonephrosis with thick wall bladder in all four cases. MCUG was diagnostic for PUV with left sided VUR. (Fig. 3)

Initial creatinine was 3mg/dL, 4.1mg/dL, 2.2mg/dL and 1.5mg/dL respectively. Last serum creatinine on follow up was 0.7mg/dL, 1.2mg/dL, 0.2mg/dL and 0.5mg/dL respectively. Renal isotope shows non-functioning to poor functioning left kidney ranging from 0–14%. (Table 2)

Valve ablation was done in all cases with vesicostomy incases 6 & 8, left nephro-ureterectomy in cases 5 & 6 and in addition DJ stent insertion in right ureter in case 6. Postoperatively all are doing well except one with repeated attacks of urinary tract infection and serum creatinine always above 1mg/dL as in case No. 6 with right vesico-ureteric junction obstruction and he is receiving nephrologist care. .

eArt37-3 

Figure 3. MCUG showing PUV with dilated posterior urethra, small capacity bladder and left sided VUR.

Discussion:

Posterior urethral valves result in variable degrees of renal impairment and bladder dysfunction. The anomaly severely affects some boys but is virtually innocuous in others for reasons that remain unclear[3]. Three anatomical variables have been described in PUV, which might provide a “pop-off” mechanism: [2, 3, 4, 5, 6].

1. PUV associated with large congenital diverticulae.

2. Urinoma/ urinary ascites presenting in the newborn period as abdominal distension or respiratory distress.

3. The syndrome of posterior urethral valves, unilateral vesico-ureteric reflux and renal dysplasia (VURD syndrome).

Bladder diverticulae may be congenital or acquired. Acquired diverticulae are usually associated with the functional or anatomical out flow obstruction. They are multiple and small with bladder trabeculation. While congenital diverticulae are not associated with bladder outlet obstruction[2].

Johnston[7], recognized the “Safety valve action” of large diverticulae associated with obstruction, and usually the bladder is of normal size with no trabeculation as in case no. 1, and he cautioned that diverticulectomy without simultaneous relief of obstruction may be followed by progressive hydro-ureteronephrosis. Our patient did well and there was no urinary tract infection especially after diverticulectomy, with normal urea & electrolytes. Urinary extravasation resulting in either urinary ascites or an isolated urinoma has been described primarily in the neonatal period and presumably result from increased pressure within an obstructed foetal urinary system[8, 9, 10].

Urinoma formation may be seen in 3 – 17% of neonates with PUV [5], in our study it was seen in 3 out of 17 patients like others. Extravasation results from increased pressure within the obstructed fetal urinary tract, with subsequent drainage to the peritoneal cavity, resulting in ascites. Urinary leak early in gestation at early stages of renal development could result in a lesser degree of renal dysplasia and atrophy[2].

Adzick et al. [11] pointed that, accumulation into a localized urinoma often provided less adequate decompression and had a variable effect on renal preservation while Rittenberg et al. [5], reported well preserved renal function in three cases with localized urinomas.

However in our study, three patients had urinary ascites, bilateral urinomas in two patients and left perirenal urinoma in one patient. In one patient (case no. 3) with bilateral urinoma he had left VUR while bilateral VUR with poor functioning left kidney was the finding of the patient with left urinoma (case no.4)

So a patient can have more than one “pop-off” mechanism but the beneficial effect of either could not be determined separately and it would appear that any factor that provides a release of intra-renal pressure would contribute to preservation of renal function[2]. Vesicoureteral reflux frequently is present initially in about half of patients with posterior urethral valves[12], while in our study it was the case in 11 out of 17 patients, six with unilateral VUR, all on the left side, and five with bilateral VUR.

Unlike our findings other investigators found that unilateral reflux was present in about 11% to 23.9% [13, 14] of patients with left ureter affected twice as often as the right..

Reflux in association with PUV indicates a worse prognosis of the involved kidney, however the non-refluxing renal unit is protected from the increased hydrostatic pressure in the collecting system by the “pop-off” effect of the refluxing renal unit[13]. Low grade, VUR the consequences of high intra-vesical pressures will usually resolve following valve ablation[12]. In our study none of the unilateral refluxing units were resolved. However the high grades of reflux which our patients had tend to be associated with non-functioning, dysplastic kidneys, this association of unilateral reflux, renal dysplasia and PUV is known as VURD syndrome[12, 13].

In our study, four patients with left VUR, had poor function on Isotope renal scan and two had nephro-ureterectomy with histological changes of renal dysplasia.The exact cause of VURD syndrome is unknown. However Macki and Stephens [15, 16] have advanced a “bud theory” relating renal dysplasia to abnormal location of the unilateral bud arising form the wolffian duct.They suggest that renal dysplasia is not necessarily the result of reflux but is often associated with abnormal orifice morphology and VUR in that each may result from an abnormal ureteral bud.

In conclusion the renal function is apparently protected by co-existent “pop-off’ mechanism and the prognosis is usually excellent due to preservation of the contralateral kidney.

 

References 

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