and urinary tract
kidneys and adrenals, located below the level of the stomach, on either
side and anterior to the spine, are visible by ultrasonography from as
early as 9 weeks of gestation and in all cases from 12 weeks. The renal
echogenicity is high at 9 weeks but decreases with gestation; the adrenals
appear as translucent structures with an echodense cortex.
and transverse sections of the abdomen can be used to study the kidneys.
In a longitudinal scan, kidneys appear as elliptical areas, while on transverse
scan they appear as roundish structures at both sides of the spine. The
kidneys appear slightly hypoechoic, compared to the liver and bowel loops.
At 20 weeks, the kidneys show a hyperechoic capsule and the cortical area
is slightly more echogenic than the medulla. With progressing gestation,
fat tissue accumulates around the kidneys, enhancing the borders of the
kidneys in contrast with the other splanchnic organs. At 26–28 weeks,
renal pyramids can be detected, and the arcuate arteries can be seen pulsating
in their proximity. Both the renal length and circumference increase with
gestation, but the ratio of renal to abdominal circumference remains approximately
30% throughout pregnancy. The anteroposterior diameter of the renal pelvis
should be < 5 mm at 15–19 weeks, < 6 mm at 20–29 weeks and
< 8 mm at 30–40 weeks. The normal ureters
are rarely seen in the absence of distal obstruction or reflux. The fetal
bladder can be visualized from the first trimester (in about 80% of fetuses
at 11 weeks and more than 90% by 13 weeks); changes in volume over time
help to differentiate it from other cystic pelvic structures.
agenesis is the consequence of failure of differentiation of the metanephric
blastema during the 25–28th day of development and both ureters and kidneys
and renal arteries are absent.
renal agenesis is found in 1 per 5000 births, while unilateral disease
is found in 1 per 2000 births.
agenesis is usually an isolated sporadic abnormality but, in a few cases,
it may be secondary to a chromosomal abnormality or part of a genetic
syndrome (such as Fraser syndrome), or a developmental defect (such as
VACTERL association). In non-syndromic cases, the risk of recurrence is
approximately 3%. However, in about 15% of cases, one of the parents has
unilateral renal agenesis and in these families the risk of recurrence
the condition is suspected by the combination of anhydramnios (from 17
weeks) and empty fetal bladder (from as early as 14 weeks). Examination
of the renal areas is often hampered by the oligohydramnios and the ‘crumpled’
position adopted by these fetuses, and care should be taken to avoid the
mistaken diagnosis of perirenal fat and large fetal adrenals for the absent
kidneys. The differential diagnosis is from preterm rupture of membranes,
severe uteroplacental insufficiency and obstructive uropathy or bilateral
multicystic or polycystic kidneys. Vaginal sonography with high-frequency,
high-resolution probes is useful in these cases.
to visualize the renal arteries with color Doppler is another important
clue to the diagnosis in dubious cases, both with bilateral and unilateral
agenesis. Prenatal diagnosis of unilateral renal agenesis is difficult
because there are no major features, such as anhydramnios and empty bladder,
to alert the ultrasonographer to the fact that one of the kidneys is absent.
renal agenesis is a lethal condition, usually in the neonatal period due
to pulmonary hypoplasia. The prognosis with unilateral agenesis is normal.
POLYCYSTIC KIDNEY DISEASE (POTTER TYPE I)
this condition, the markedly enlarged kidneys are filled with numerous
cortical cysts and dilated collecting ducts. The disease has a wide spectrum
of renal and hepatic involvement and it is subdivided into perinatal (this
is the most common), neonatal, infantile and juvenile types on the basis
of the age of onset of the clinical presentation and the degree of renal
tubular involvement. Although recurrences tend to be group-specific, we
have seen one family in which the four subdivisions were each represented
in the four affected infants.
polycystic kidney disease is found in about 1 per 30 000 births.
is an autosomal recessive condition. The responsible gene is in the short
arm of chromosome 6 and prenatal diagnosis in families at risk can be
carried out by first-trimester chorion villous sampling.
diagnosis is confined to the types with earlier onset (perinatal and probably
the neonatal types) and is based on the demonstration of bilaterally enlarged
and homogeneously hyperechogenic kidneys. There is often associated oligohydramnios,
but this is not invariably so. These sonographic appearances, however,
may not become apparent before 24 weeks of gestation and, therefore, serial
scans should be performed for exclusion of the diagnosis.
perinatal type is lethal either in utero or in the neonatal period
due to pulmonary hypoplasia. The neonatal type results in death due to
renal failure within the 1st year of life. The infantile and juvenile
types result in chronic renal failure, hepatic fibrosis and portal hypertension;
many cases survive into their teens and require renal transplantation.
DYSPLASTIC KIDNEY DISEASE (POTTER TYPE II)
dysplastic kidney disease is thought to be a consequence of either developmental
failure of the mesonephric blastema to form nephrons or early obstruction
due to urethral or ureteric atresia. The collecting tubules become cystic
and the diameter of the cysts determines the size of the kidneys, which
may be enlarged or small. Exploration of the renal fossa in some cases
reveals no renal artery, renal vein, ureter or cysts, suggesting that
renal agenesis and dysplastic kidneys may be at different ends of a spectrum
of renal malformation. This is further supported by the finding that,
in about 15% of cases with multicystic kidneys, there is contralateral
dysplastic kidney disease is found in about 1 per 1000 births.
the majority of cases, this is a sporadic abnormality but chromosomal
abnormalities (mainly trisomy 18), genetic syndromes and other defects
(mainly cardiac) are present in about 50% of the cases.
the kidneys are replaced by multiple irregular cysts of variable size
with intervening hyperechogenic stroma. The disorder can be bilateral,
unilateral or segmental; if bilateral, there is associated anhydramnios
and the bladder is ‘absent’.
multicystic dysplastic kidney disease is fatal before or soon after birth,
due to pulmonary hypoplasia. Unilateral disease is associated with a normal
prognosis. There is still controversy in the postnatal management of patients
with a multicystic kidney; some urologists advocate prophylactic nephrectomy,
but the majority adopt an expectant approach because the kidney gradually
shrinks and may disappear. The parents and family should also be scanned
to exclude autosomal dominant branchio-to-renal syndrome.
TYPE III RENAL DYSPLASIA
type III renal dysplasia is characterized by markedly enlarged irregular
kidneys with innumerable cysts of variable sizes interspersed among normal
or compressed renal parenchyma. It is the common morphological expression
of autosomal dominant adult polycystic kidney disease (APKD) and of other
Mendelian disorders such as tuberous sclerosis, Jeune syndrome, Sturge–Weber
syndrome, Zellweger syndrome, Lawrence Moon Biedl syndrome and Meckel–Gruber
syndrome. Both kidneys are generally equally enlarged and only rarely
is one involved so slightly that it remains of normal size. One-third
of the cases have cysts in the liver, pancreas, spleen or lungs and one-fifth
are found to have cerebral aneurysms.
polycystic kidney disease (APKD)
in 1000 people carry the APKD mutant gene. Adult polycystic kidney disease
is usually asymptomatic until the third or fourth decade of life, and,
although histological evidence of the disease is likely to be present
from intrauterine life, the age of onset of gross morphological changes
that are potentially detectable by ultrasonography is uncertain. Rarely,
however, kidneys that are anatomically similar may cause death in infancy
or early childhood and the condition has been designated as ‘adult variety
occurring in infancy’.
diagnosis by ultrasonography is confined to a few case reports and the
kidneys have been described as enlarged and hyperechogenic with or without
multiple cysts. Unlike infantile polycystic kidneys, where there is a
loss of the corticomedullary junction, in APKD there is accentuation of
this junction. The amniotic fluid volume is either normal or reduced.
kidney size is usually smaller than that of the infant polycystic kidneys.
In counseling affected parents with APKD, it should be emphasized that
the prenatal demonstration of sonographically normal kidneys does not
necessarily exclude the possibility of developing polycystic kidneys in
adult life. Nevertheless, prenatal diagnosis can now be made from chorion
villous sampling and DNA analysis.
term ‘obstructive uropathy’ encompasses a wide variety of different pathological
conditions characterized by dilatation of part or all of the urinary tract.
When the obstruction is complete and occurs early in fetal life, renal
hypoplasia (deficiency in total nephron population) and dysplasia (Potter
type II; formation of abnormal nephrons and mesenchymal stroma) ensue.
On the other hand, where intermittent obstruction allows for normal renal
development, or when it occurs in the second half of pregnancy, hydronephrosis
will result and the severity of the renal damage will depend on the degree
and duration of the obstruction. Dilatation of the fetal urinary tract
frequently, but not absolutely, signifies obstruction. Conversely, a fetus
with obstruction may not have any urinary tract dilatation.
degrees of pelvicalyceal dilatation are found in about 1% of fetuses.
Mild hydronephrosis or pyelectasia is defined by the presence of an anteroposterior
diameter of the pelvis of >
4 mm at 15–19 weeks, >
5 mm at 20–29 weeks and >
7 mm at 30–40 weeks. Transient hydronephrosis may be due to relaxation
of smooth muscle of the urinary tract by the high levels of circulating
maternal hormones, or maternal–fetal overhydration. In the majority of
cases, the condition remains stable or resolves in the neonatal period.
In about 20% of cases, there may be an underlying ureteropelvic junction
obstruction or vesicoureteric reflux that requires postnatal follow-up
and possible surgery.
hydronephrosis, characterized by an anteroposterior pelvic diameter of
more than 10 mm and pelvicalyceal dilatation, is usually progressive and
in more than 50% of cases surgery is necessary during the first 2 years
a 150K clip of hydronephrosis
is usually sporadic and, although in some cases there is an anatomic cause,
such as ureteral valves, in most instances the underlying cause is thought
to be functional. In 80% of cases, the condition is unilateral. Prenatal
diagnosis is based on the demonstration of hydronephrosis in the absence
of dilated ureters and bladder. The degree of pelvicalyceal dilatation
is variable and, occasionally, perinephric urinomas and urinary ascites
may be present. Postnatally, renal function is assessed by serial isotope
imaging studies and, if there is deterioration, pyeloplasty is performed.
However, the majority of infants have moderate or good function and can
be managed expectantly.
is a sporadic abnormality characterized by hydronephrosis and hydroureter
in the presence of a normal bladder. The dilated ureter is tortuous, and
on ultrasound appears as a collection of cysts of variable size, localized
between the renal pelvis, which is variably dilated, and the bladder,
which is of normal morphology and dimensions. The etiology is diverse,
including ureteric stricture or atresia, retrocaval ureter, vascular obstruction,
valves, diverticulum, ureterocele, and vesicoureteral reflux. Ureteroceles
(visible as a thin-walled and fluid-filled small circular area inside
the bladder) are usually found in association with duplication of the
collecting system. In ureteral duplication, the upper pole moiety characteristically
obstructs and the lower one refluxes. The dilated upper pole may enlarge
to displace the non-dilated lower pole inferiorly and laterally.
sporadic abnormality is suspected when intermittent dilatation of the
upper urinary tract over a short period of time is seen on ultrasound
scanning. Occasionally, in massive vesicoureteric reflux without obstruction,
the bladder appears persistently dilated because it empties but rapidly
refills with refluxed urine. Primary megaureter can be distinguished from
ureterovesical junction obstruction by the absence of significant hydronephrosis.
hypoperistalsis syndrome (MMIHS)
is a sporadic abnormality characterized by a massively dilated bladder
and hydronephrosis in the presence of normal or increased amniotic fluid;
the fetuses are usually female. There is associated shortening and dilatation
of the proximal small bowel, and microcolon with absent or ineffective
peristalsis. The condition is usually lethal due to bowel and renal dysfunction.
obstruction can be caused by urethral agenesis, persistence of the cloaca,
urethral stricture or posterior urethral valves. Posterior urethral valves
occur only in males and are the commonest cause of bladder outlet obstruction.
The condition is sporadic and is found in about 1 in 3000 male fetuses.
With posterior urethral valves, there is usually incomplete or intermittent
obstruction of the urethra, resulting in an enlarged and hypertrophied
bladder with varying degrees of hydroureters, hydronephrosis, a spectrum
of renal hypoplasia and dysplasia, oligohydramnios and pulmonary hypoplasia.
In some cases, there is associated urinary ascites from rupture of the
bladder or transudation of urine into the peritoneal cavity.
therapy for obstructive uropathy
fetal lamb, ureteric ligation during the first half of gestation results
in dysplastic kidneys, whereas, in the second half of pregnancy, ureteric
ligation is associated with the development of hydronephrosis but preservation
of renal architecture. Ligation of the urethra and urachus in fetal lambs
at 100 days of gestation causes severe hydronephrosis and pulmonary hypoplasia;
decompression by suprapubic cystostomy at 120 days’ gestation reduces
the urinary tract dilatation and improves the survival rate. Similarly,
ureteric ligation at 65 days of gestation produces renal dysplasia, and
subsequent decompression prior to term prevents renal dysplasia and produces
reversible postobstructive changes; the degree of renal damage is proportional
to the length of time for which the obstruction existed.
by the results of these animal studies, and on the assumption that unrelieved
obstruction causes progressive renal and pulmonary damage, several investigators
in the 1980s performed in utero decompression of the urinary tract
in the human, either by open surgical diversion or by the ultrasound-guided
insertion of suprapubic vesico-amniotic catheters. Although these techniques
demonstrated the feasibility of intrauterine surgery, they did not provide
conclusive evidence that such intervention improves renal or pulmonary
function beyond what can be achieved by postnatal surgery. It is possible
that, in a few selected cases, intrauterine intervention may be beneficial.
of fetal renal function
evaluation of renal function relies on a combination of ultrasonographic
findings and analysis of fetal urine obtained by urodochocentesis or pyelocentesis.
Poor prognostic signs are:
The presence of bilateral multicystic or severely hydronephrotic kidneys
with echogenic kidneys, suggestive of renal dysplasia;
Anhydramnios implying complete urethral obstruction; and
High urinary sodium, calcium and b2
candidates for intrauterine surgery are fetuses with bilateral moderately
severe pelvicalyceal dilatation and normal cortical echogenicity, or severe
megacystis and oligohydramnios, or normal levels of urinary sodium, calcium
and b2 microglobulin.
2000, Pilu, Nicolaides, Ximenes & Jeanty