Diagnostic ultrasound ( PDFDrive )

1364 PART IV Obstetric and Fetal Sonography
are favorable, placement of a permanent vesicoamniotic shunt
may be considered. Fetal urinary sodium (Na + ), calcium (Ca ++ ),
and β 2 -microglobulin (in combination) are the best predictors
of postnatal renal function. 215-220,222
Antenatal Predictors of Poor Postnatal
Renal Function
ULTRASOUND
Severe oligohydramnios, especially if early onset
Increased renal echogenicity
Renal cortical cysts
Slow bladder reilling after vesicocentesis
FETAL URINE
↑ Sodium level (Na + )
↑ Calcium level (Ca ++ )
↑ β 2 -Microglobulin level
FETAL BLOOD
↑ β 2 -Microglobulin level
FIG. 39.38 Vesicoamniotic Shunt. Arrows indicate catheter in the
decompressed bladder (B) and amniotic luid. Note normal amniotic luid
volume.
Initially, ixed cutof values were suggested for each variable
as prognostic predictors. 82 However, the normal levels of most
parameters vary with gestational age and must be interpreted
accordingly. Speciically, sodium and β 2 -microglobulin levels
decrease throughout gestation, whereas calcium and creatinine
values rise. 215,216,221 In general, more hypotonic fetal urine correlates
with a more favorable outcome. Some groups advocate that
sequential urine sampling over 48 to 72 hours is most relective
of true renal function because an initial bladder tap will obtain
urine that has been present for an extended period of time. 215,223,224
A systematic review of 23 papers and 572 pregnancies reported
that the two most accurate tests of fetal renal function were
calcium and sodium above the 95th percentile for gestation,
while β 2 -microglobulin was slightly less accurate. 225 A recent
retrospective study of fetal urine biochemistry in 72 cases of
megacystis diagnosed before 23 weeks gestation supported the
usefulness of β 2 -microglobulin, sodium, chloride, and calcium
in deining a poor renal prognosis. 226
It has been suggested that fetal blood levels of β 2 -microglobulin
may better assess glomerular iltration rate than urinary markers,
which generally relect tubular function. 227 Blood sampling for
electrolytes and β 2 -microglobulin may also be useful when no
urine can be collected by vesicocentesis. 224 Recently, advances
in proteomics have allowed the identiication of 26 fetal urinary
peptides that show promise in predicting renal function ater
birth, although they are not yet integrated into clinical practice. 228
To date, a urinary function proile, which combines a number
of biochemical and sonographic predictors, appears to be of
greatest clinical value. We use the reference values published by
Muller and colleagues for fetal urinary sodium, calcium, and
β 2 -microglobulin. 221 Only carefully selected fetuses with “favorable”
fetal urinary analysis, despite signiicant oligohydramnios,
are likely to beneit from in utero intervention; and in our center,
only a handful of the fetuses who are referred with LUTO go
on to such treatment.
Our approach is to counsel the parents extensively beforehand,
with input from a multidisciplinary team of fetal medicine,
pediatrics, urology, nephrology, and social work specialists.
Parents are also given the opportunity to speak to others who
have faced similar dilemmas. Before any decision is made, we
try to ensure that they have an unbiased and complete account
of the situation and are fully aware that, despite successful shunt
placement, renal failure or pulmonary hypoplasia may still
ensue. 227,229-231
Vesicoamniotic shunting is performed by the percutaneous
insertion of a small, plastic, double-coiled Silastic pigtail catheter
into the bladder under continuous ultrasound guidance. To
facilitate insertion, amnioinfusion is undertaken beforehand.
Antibiotic prophylaxis and tocolysis (rectal indomethacin and
oral calcium channel blockers) are used. We strive to place the
shunt anteriorly in the midline, ideally below the umbilical cord
insertion 224 (Fig. 39.38). Color Doppler is used to help avoid
maternal and fetal blood vessels. Early intervention is probably
necessary for this procedure to successfully prevent pulmonary
hypoplasia and preserve renal function. 195 Typically AFV is low
before intervention. Occasionally, intervention may be considered
in light of documented worsening of renal function on urinalysis
or progressively abnormal renal appearance on ultrasound, despite
a normal AFV. Rarely, it may be warranted to place the shunt
directly into a dilated renal pelvis rather than the bladder. Shunts
may become blocked or dislodged and will require replacement
in some cases.
Recently, fetal cystoscopy and laser ablation of the posterior
urethral valves have been introduced as an alternative diagnostic
and therapeutic approach to the management of obstructive
uropathy. 232,233 heoretical advantages include more physiologic
drainage by allowing “cyclic voiding,” determining the cause of
LUTO by diferentiating posterior urethral valves (PUV) from
urethral atresia, avoiding the need for amnioinfusion, and avoiding
shunt complications, such as migration and blockage.