V. RENAL FUNCTION (Tables 6 and 17)
Of the 12 patients we had in the prospective phase, renal
function tests (BUN and creatinine) were done only by 9 (3 did not do because
of financial constraints). BUN is not a good predictor of renal function
because of its variability with factors as dietary proteins, fever, hydration
and liver damage. GFR as calculated from timed urine collection and serum
creatinine is often inaccurate in infants because of problems in collection of
the urine (45). A nadir creatinine valve less than or equal to 0.8 mg /dl by 12
months of age has been described a good predictor of good renal function at the
time of final evaluation (38). Serum creatinine is valid only as it relates to
muscle mass, therefore a blanket endorsement of 0.8 mg/dl at 1 year of age
doesn't take into account the variability in body size (45). So we calculated
the GFR from COCKCROFT's FORMULA considering the weight, age and serum
creatinine. No patient had GFR above 100 ml/min/1.73m2 at diagnosis
and only 2 had GFR above 50 ml/min/1.73m2 at diagnosis. At the end
of the follow-up 6 patients had improved GFR (one above 100 ml/min/1.73
m2, two between 50 and 100 ml/min/1.73 m2 and three below
50 ml/min/1.73m2. Contrarily in 2 patients it dropped, from 46 to 30
in one, and from 61 to 36 ml/min/l.73m2 in the other. In one patient
it remained stable at 15 ml/min/1 .73m2. An important observation is
that despite these low GFR, these children manifested no signs of renal
failure.
In man, the relationship between the duration of obstruction
and the degree of recovery of renal function after release is not known (48).
Return of function depends upon many factors other than the length of
obstruction, such as absence of infection,
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presence of an intrarenal or extrarenal pelvis in the
obstructed kidney, and the degree of pyelolymphatic and pyelovenous blood flow
(48). However the ultimate objective in the management of infants and children
with obstructive uropathies is long-term preservation of renal function
(36).
Chronic renal failure occurs in a significant number of
children with a history of posterior urethral valves (32, 49). Causes include
intrauterine renal dysplasia and hydronephrotic damage, vesico-ureteral reflux,
continued bladder outlet obstruction and vesical dysfunction, (23, 49),
postnatal UTI, hyperfiltration and glomeoulosclerosis. Abnormal bladder
compared to these other factors for causing end-stage renal disease remains
unknown (49). The valve bladder syndrome, involves a poorly compliant,
small capacity bladder leading to upper tract dilatation and renal compromise
that is amendable to improvement via bladder augmentation with intestine
(32).
Although the choice of surgical treatment for patients with
PUV often involves an attempt to stop the course of progressive renal failure,
many are born with severe renal dysplasia that leads to inevitable progressive
renal failure regardless of the primary method of treatment (32). HENNEBERRY
and STEPHENS proposed that renal dysplasia associated with posterior urethral
valves is not secondary to reflux or transmitted high pressures, but rather
results from aberrant caudal budding of the ureter from the mesonephric duct
with subsequent abnormal induction of mesenchyma (37). Renal dysplasia occurs
before the 10th week of gestation before ultrasound can diagnose
(3). The experience of CLOSE C.E. et al (32) suggest that there is a window for
healing in neonates that is limited to the first few months of life with
primary valve ablation.
Ultrasonographic demonstration of corticomedullary junctions
in infancy appears to be a useful, favourable prognostic index in boys with
posterior urethral valves and possibly other obstructive uropathies (50). The
single ultrasonographic parameter showing significant correlation with eventual
renal function was the appearance of the corticomedullary junctions. Additional
ultrasonographic findings, including hydroureteronephrosis, cortical
echogenicity, cortical thickness, bladder wall thickness
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and the degree of posterior urethral dilation, had poor
predictive valve.
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