Diagnostic ultrasound ( PDFDrive )

1360 PART IV Obstetric and Fetal Sonography
Duplex Kidney Findings
Unilateral renal enlargement
Two separate noncommunicating renal pelves
Hydronephrosis of the upper and/or lower pole
Ipsilateral dilated ureter(s)
Ureterocele
Ureteroceles are cystic dilations of the intravesical submucosal
ureter. A careful evaluation of the urinary bladder is necessary to
detect the ureterocele, which is seen as a well-deined, thin-walled
cyst within the bladder (see Fig. 39.31B). he diagnosis is easy
when the bladder is partially full but can be overlooked if the
bladder is empty or only minimally distended. A full bladder
can compress the ureterocele, resulting in nonvisualization. A
small nonobstructive ureterocele may be an incidental inding.
However, most ureteroceles are detected prenatally during the
evaluation of hydronephrosis. 182 A large ureterocele may cross
the midline and obstruct the contralateral ureter or the bladder
outlet and cause bilateral hydronephrosis. Ureteroceles that are
large or prolapsed into the urethra may cause bladder outlet
obstruction. Fetal therapy, such as fetoscopic laser surgery to
decompress the distal urethral obstruction, can be helpful in cases
with progressive bladder outlet obstruction, oligohydramnios,
or concerns for permanent damage to the renal parenchyma. 183
Complicated duplex collecting systems are associated with
substantial morbidity. he prognosis depends on the degree of
renal damage from relux and obstruction. he outcome is
improved with prenatal diagnosis, because it allows planning of
postnatal care, including the administration of prophylactic
antibiotics from birth, reducing the incidence of UT infections
and renal function impairment. 181,184
Vesicoureteral Relux
VUR can be primary (incompetent valve mechanism at the UVJ)
or secondary (due to an obstruction in the UT and high detrusor
pressures). he main prenatal sonographic inding is hydronephrosis,
which may be unilateral or bilateral. he ureter may be
dilated. Intermittent dilation of the collecting system favors VUR.
Fluctuation or variation in the RPD (changing by more than
3 mm) during the course of an obstetric sonogram is strongly
associated with high-grade VUR (grade IV or V). 185 VUR may
be associated with other renal abnormalities, including UPJ
obstruction, duplex kidney, MCDK, and unilateral renal
agenesis. 177,186
he reported prevalence of VUR in children with prenatally
detected hydronephrosis varies widely because diferent RPD
cutof values are used for inclusion and diferent protocols for
postnatal investigations (voiding cystourethrography either in
all cases or only ater an abnormal postnatal renal ultrasound
examination). A systematic review of 18 studies showed a mean
prevalence of 15% for postnatal primary VUR ater prenatally
detected hydronephrosis. 187
A normal postnatal ultrasound study does not exclude VUR.
However, if two successive renal ultrasound examinations (at day
5 and at 1 month) were normal, voiding cystourethrography
showed abnormalities in only 6.7% of patients. 188 Neonatal relux
is more common in male infants. It is oten of low grade, with a
high rate of spontaneous resolution by 2 years of age. 189 However,
in those children with high-grade VUR, spontaneous resolution
is rare. here is a signiicant correlation between high-grade VUR
and indings of either renal dysplasia on ultrasound or renal damage
scars on DMSA renal scan. 189,190 Most neonates with VUR are
managed conservatively with antibiotic prophylaxis.
Lower Urinary Tract Obstruction
Fetal megacystis has been reported as early as 10 to 14 weeks’
gestation when the longitudinal bladder diameter is 7 mm or
more 191 (Fig. 39.32). In the second or third trimester, the deinition
of megacystis is more subjective but includes an enlarged bladder
that fails to empty over 45 minutes of observation. 192,193 At 10
to 14 weeks’ gestation, the incidence is 1 : 1600. 191 In a series of
145 fetuses with early megacystis, when the bladder diameter
measured 7 to 15 mm, chromosomal abnormalities were detected
in approximately 25% of cases. 194 In those with normal karyotype,
there was spontaneous resolution of the megacystis by 20 weeks’
gestation in 90% of cases. In contrast, with severe megacystis,
deined as bladder length greater than 15 mm, the risk of
chromosomal defects was 11%; and in the chromosomally normal
group, it was invariably associated with progressive, obstructive
uropathy. 194 herefore follow-up ultrasound and assessment of
karyotype in cases of identiied irst-trimester megacystis are
necessary to provide prognostic information and identify the
role, if any, of a diagnostic or therapeutic fetal procedure.
Causes of Fetal Megacystis
Posterior urethral valves
Urethral atresia or stricture
Ureterocele
Prune belly syndrome
Megalourethra
Cloacal malformation
Megacystis-microcolon–intestinal hypoperistalsis syndrome
FIG. 39.32 Megacystis in First Trimester. Transabdominal sagittal
image of a 12-week fetus shows a distended thick-walled bladder (arrow),
measuring 13 mm in length. There is no hydronephrosis.