Diagnostic ultrasound ( PDFDrive )

1358 PART IV Obstetric and Fetal Sonography
repeating antenatal ultrasound, postnatal ultrasound, and
antibiotic prophylaxis ater delivery based on the recently
published consensus guidelines 133 :
1. Low-risk group: If isolated mild UT dilation is detected at
16 to 27 weeks’ gestational age, a repeat ultrasound is recommended
at 32 weeks or later to reassess the RPD, kidneys,
bladder, and AFV. Parents are counseled that it is a common
inding and may be physiologic or transient, and that the risk
of postnatal uropathy is small. If the ultrasound at 32 weeks’
gestational age or later shows resolution (RPD < 7 mm) and
no other indings, no further prenatal or postnatal follow-up
is necessary. If UT dilation persists (RPD 7 to <10 mm), two
postnatal renal ultrasound scans should be performed: the
irst at more than 48 hours but less than 1 month ater birth,
and the second exam 1 to 6 months later.
2. Increased-risk group: For fetuses in this category, a repeat
ultrasound in 4 to 6 weeks is recommended, but the frequency
of sonographic monitoring is at the discretion of the health
care provider, depending on the indings. Prenatal consultation
with pediatric specialists (nephrology, urology) is also recommended,
especially in situations that may result in marked
renal dysfunction or possible surgical intervention. For fetuses
with RPD of 10 mm or greater at the third-trimester ultrasound,
our approach is to initiate antibiotic prophylaxis ater
delivery, pending the results of the postnatal renal
ultrasound.
Ureteropelvic Junction Obstruction
Obstruction at the UPJ is the most common cause of nonphysiologic
neonatal hydronephrosis, 164-166 with an incidence of 1 in
2000 live births. 167 It is also one of the most common reasons
for postnatal surgery of the UT. 128,164 Most cases of UPJ obstruction
are functional (caused by a muscular abnormality) rather than
the result of ixed anatomic lesions such as ibrous adhesions,
kinks, valves, or aberrant vessels. 168 However, the etiology of
functional obstruction is multifactorial and likely polygenic, with
no known cause in most cases. 165 UPJ obstruction is more common
in males, more frequently unilateral, and more oten on the let
side. 169
On sonography, a dilated renal pelvis with or without caliectasis
is identiied. he ureter and the bladder are not dilated. Severe
chronic obstruction leads to efacement of the calyces and thinning
of the renal cortex (SFU grade 4) (Fig. 39.29). Rarely, the renal
pelvis may be extremely dilated, appearing as a large, unilocular
cystic mass. Rupture of the collecting system results in the
development of a perirenal urinoma (Fig. 39.30, Video 39.7).
his “pop-of ” mechanism may protect the obstructed kidney
from further prenatal damage and may diminish the degree of
hydronephrosis. he afected kidney should be carefully assessed
for renal dysplasia, however, because the probability of a nonfunctional
dysplastic ipsilateral kidney is about 80%. 170
he AFV is usually normal. When unilateral hydronephrosis
is accompanied by oligohydramnios, a search for contralateral
renal pathology is warranted (e.g., renal agenesis, multicystic
renal dysplasia). UPJ obstruction may be associated with VUR
and extrarenal abnormalities. When the contralateral kidney is
normal, the prenatal detection of unilateral UPJ obstruction
FIG. 39.29 Ureteropelvic Junction Obstruction. Longitudinal scan
shows moderate caliectasis and extremely dilated renal pelvis (P), with
thinning of the cortex (arrows).
FIG. 39.30 Perirenal Urinoma. Transverse scan of fetal abdomen
at 22 weeks’ gestation shows a large perirenal urinoma (*) displacing
and compressing the kidney, which demonstrates dilated calyces and
pelvis (P) caused by ureteropelvic junction obstruction. See also Video
39.7.
should not alter obstetric management. In cases of unilateral
UPJ obstruction diagnosed before 24 weeks, severe dilation (RPD
> 15 mm) is predictive of impaired postnatal renal function in
the afected kidney. 171 When there is bilateral UPJ obstruction,
the prognosis depends on the severity and duration of obstruction
and on the AFV. Serial ultrasound evaluations are necessary to
assess the AFV, progression of hydronephrosis, and development
of renal dysplasia. Early delivery is rarely indicated, except when
there is progressive bilateral obstruction with severe oligohydramnios.
Treatment algorithms for hydronephrosis due to UPJ
obstruction include both conservative and surgical approaches
depending on the severity of the hydronephrosis.
Vesicoureteral Junction Obstruction and
Primary Megaureter
Vesicoureteral junction obstruction is more common in males
and is bilateral in up to 25% of cases. 172 Coexisting anomalies