Diagnostic ultrasound ( PDFDrive )

1814 PART V Pediatric Sonography
A
B
C
FIG. 52.54 Autosomal Recessive Polycystic Kidney Disease
(ARPKD). (A) Transverse image of neonate shows symmetrically enlarged
kidneys illing the abdomen. LK, Left kidney; RK, right kidney; S, spine.
A macrocyst is present in the right kidney (arrow). (B) Longitudinal
image of right kidney demonstrates loss of normal corticomedullary
differentiation, hypoechoic subcapsular cortex, and multiple cysts of
varying size within the medullary region. (C) High-resolution transverse
image of left kidney reveals multiple dilated subcapsular cortical collecting
ducts (between arrows).
Autosomal Dominant Polycystic
Kidney Disease
Autosomal dominant polycystic kidney disease (ADPKD) is the
most common inherited form of kidney failure that eventually
results in end-stage renal disease. It is characterized by bilateral,
progressive enlargement of focal cysts that occur in all portions
of the nephron, and variable extrarenal manifestations also occur.
Approximately 600,000 individuals in the United States are
afected, and 13 million people worldwide. 170
ADPKD is usually asymptomatic until middle age. However,
in about 2% to 5% of patients, ADPKD is seen in the neonatal
period, with substantial morbidity and mortality. hese early
manifestations of ADPKD may be indistinguishable from ARPKD
and can be diferentiated only on the basis of histologic or genetic
analysis. here is a familial incidence of childhood presentation,
with siblings of afected children demonstrating a greater risk
of early disease. 171
ADPKD is caused by dominant transmission of one of two
defective genes, PKD1 (mapped to chromosome 16p13.3 in 85%
of patients) or PKD2 (mapped to chromosome 4q13–23 in 15%
of patients). PKD1 encodes the protein polycystin-1 and PKD2
encodes polycystin-2. hese two proteins are localized to the
primary cilia in the epithelial cells that line the renal tubules
and interact to form a calcium channel receptor. Both are
important in the diferentiation, maintenance, and repair of renal
tubular cells and in determining the morphology of the renal
tubules. PKD1-associated disease is generally more severe than
PKD2-associated disease. However, there is signiicant phenotypic
heterogeneity. Unusually mild cases are believed to be due to
the transmission of so-called “hypomorphic” alleles (i.e., those
that have retained partial activity). 170,172
Most children with ADPKD are born with normal kidneys.
Normal ultrasound examination indings cannot exclude ADPKD
until ater the age of 35 years, particularly for PKD2 mutations. 173
he presence of at least two renal cysts (unilateral or bilateral)
in an individual younger than 30 years of age with a 1 in 2 risk
of PKD1 is suicient to establish the diagnosis. 174 Even a single
cyst in a genetically predisposed child is highly suspicious for
ADPKD because the prevalence of renal cysts in the general
pediatric population is low 175,176 (Fig. 52.55). he concomitant
presence of an extrarenal cyst in the liver or pancreas indicates
the diagnosis of ADPKD, although these are rare at initial
presentation in children. 176,177 Older children have larger and
more numerous renal cysts and develop progressive renal enlargement
(Fig. 52.56). Results from the Consortium of Renal Imaging
Studies in Polycystic Kidney Disease have shown that the larger
the cyst mass or renal volume, the worse the prognosis, regardless
of whether the cysts derive from an ADPKD1 or ADPKD2 gene
defect. 178
In third-trimester fetuses and infants with ADPKD in the
neonatal period, the kidneys are normal in size to mildly enlarged.
he cortex is hyperechoic compared with the liver or spleen with
hypoechoic medulla resulting in increased corticomedullary
diferentiation 179 (see Fig. 52.55). his appearance difers from
the usual appearance of ARPKD, in which the kidneys are markedly
rather than mildly enlarged and the medullae are hyperechoic.
A few small cysts may be seen in the cortex, medulla, or both
in ADPKD. Unlike the tubular cysts of ARPKD, the cysts in the
dominant form appear round. 167,180
Extrarenal manifestations include cysts of the liver, spleen,
pancreas, seminal vesicles, and arachnoid membrane. he liver
is the most common extrarenal site of involvement. Aneurysms