Diagnostic ultrasound ( PDFDrive )

1348 PART IV Obstetric and Fetal Sonography
A
B
FIG. 39.15 Obstructive Cystic Dysplasia. (A) Coronal image of fetus at 23 weeks with ureteropelvic junction obstruction shows increased
echogenicity of the kidney (calipers) with small cortical cysts (arrows), indicative of irreversible renal damage. (B) Sagittal image at 34 weeks shows
the cysts have increased in size and the kidney is large. There is some functioning renal tissue, as luid is seen in the slightly dilated renal
pelvis (P).
urine low. 83 he size of the kidneys varies from small to normal
to markedly enlarged. In some cases the enlargement is caused
partly by the presence of cysts and partly by hydronephrosis.
Cysts are usually present in the subcapsular area of the cortex.
In a fetus with obstructive uropathy, the sonographic identiication
of cortical cysts is indicative of renal dysplasia (i.e., irreversible
renal damage) 84 (Fig. 39.15). Dysplastic kidneys may also demonstrate
cortical thinning and increased echogenicity relative to
the surrounding fetal structures, with loss of corticomedullary
diferentiation. However, increased cortical echogenicity is not
a speciic inding, 85 and a diagnosis of renal dysplasia cannot
be made on the basis of increased parenchymal echogenicity
alone. Furthermore, it is important to recognize that not all
dysplastic kidneys have sonographically visible cysts or increased
cortical echogenicity, so one cannot accurately predict the absence
of renal dysplasia. Renal function relates directly to the degree
of dysplasia, which determines the prognosis of patients surviving
the perinatal period.
In general, if the obstruction is early and complete, the renal
parenchymal indings will be predominantly macroscopic cysts
and will simulate multicystic renal dysplasia. Sonographic distinction
between MCDK and obstructive cystic renal dysplasia may
be diicult, especially in the absence of hydronephrosis. In
obstructive cystic renal dysplasia, recognizable parenchyma
surrounds the relatively small cysts, whereas in MCDK, no normal
renal parenchyma can be identiied between cysts, and the cysts
can be of varying size and can be quite large. Obstructive cystic
renal dysplasia most oten occurs with urethral obstruction.
herefore sonographic evidence of urethral obstruction is helpful
in suggesting the diagnosis. In addition, renal dysplasia from
lower UT obstruction frequently involves both kidneys, whereas
bilateral MCDK occurs in only 19% to 24% of cases. 71,72
Autosomal Recessive Polycystic Kidney Disease
he incidence of autosomal recessive polycystic kidney disease
(ARPKD) is 1 in 20,000 live births. In the past this was termed
“infantile polycystic kidney disease,” but the presentation can
be ater the neonatal period; thus the preferred term is “autosomal
recessive polycystic kidney disease.” It primarily involves the
kidneys and biliary tract. he clinical spectrum is wide and varies
from the perinatal form, with severe renal disease, minimal
hepatic ibrosis, and early death from pulmonary hypoplasia, to
the juvenile form, with minimal renal disease, marked hepatic
ibrosis, and longer survival. Difuse dilation of the renal collecting
tubules produces numerous cysts smaller than 2 mm, predominantly
in the medulla. Both kidneys are enlarged, but a smooth
contour is maintained. he cut surface has a spongelike appearance,
with small cysts that tend to be arranged perpendicular
to the renal capsule (Fig. 39.16).
Sonography reveals bilateral reniform enlargement of the
kidneys (see Fig. 39.16). here is poor delineation of the intrarenal
structures. he numerous tiny cysts are usually smaller than the
limit of sonographic resolution, but they create multiple acoustic
interfaces, accounting for the characteristic increased renal
echogenicity. 86 In a fetus, the inding of bilateral, very large (>4
standard deviations), difusely hyperechoic kidneys with poor
corticomedullary diferentiation, with or without visible cysts,
is most likely due to ARPKD. 67,87 Another typical pattern is very
large kidneys with a peripheral hypoechoic rim surrounding the
centrally increased echogenicity or hyperechoic pyramids
(reversed corticomedullary diferentiation) (Fig. 39.17, Video
39.6). 67 When renal function is abnormal, there is oligohydramnios,
and the bladder is small or absent.
Usually, but not always, ultrasound shows evidence of ARPKD
by 24 to 26 weeks’ gestation. 88,89 Autosomal recessive PKD may
be diagnosed by ultrasound in the second trimester based on
the characteristic renal abnormalities, especially if the fetus is
at risk. 88 However, because of the variability in phenotypic
expression and gestational age at onset, the kidneys may appear
normal initially, only becoming abnormal later. 88 hus a normal
sonogram in a fetus at risk for ARPKD does not exclude this
disease, and prenatal diagnosis using sonography can be unreliable,
especially in early pregnancy. ARPKD is inherited in an
autosomal recessive manner, and thus the recurrence risk is 25%.