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15 Ultrasound oftheUrogenital Tract inNeonates, Infants, andChildren
381
• For assessing retrovesical structures (distal ureter, retrovesical space, internal
genitalia, etc.), adequate manipulation of TGC adaptation is necessary. Use ure-
teric jet for dening ostium position and assessing symmetry of urine inow.
Note Nodular wall component at bladder roof may be physiologic as remnant of
urachus. Furthermore in neonates the urachus may still be depicted for a couple of
weeks but without patent lumen. In neonates with still immature bladder function,
some residual urine does not indicate pathology.
15.2.2 Kidney
Parenchymal appearance changes with age:
• Neonatally—relatively thick parenchyma with accentuated cortico-medullary
differentiation and rather echogenic cortex (may be as echogenic than adjacent
liver tissue), with hypoechoic medullae. Distal medullae and papillae may exhibit
echogenicities (transient physiologic phenomenon that resolves spontaneously)
(Fig. 15.5). With age, cortico-medullary differentiation gets less pronounced;
echogenicity of cortex decreases. Echogenicity of distal medulla becomes homo-
geneously hypoechoic (Fig.15.6).
• Sometimes papilla and pelvic wall become more echogenic with some slight
echogenicity around central structures due to peripelvic fat and brosis.
• Calices and renal pelvis may be visible, particularly with modern high-resolution
transducers, without indicating urinary transport alteration (Fig.15.7).
• Assess fornices and papilla to demonstrate normal shape; assess renal pelvis wall
(should not be thickened). In the hilum, the renal vein and artery are to be recog-
nised and can be differentiated by following these structures to their vascular
origin, whereas the pelvis curses downwards towards ureteropelvic junction.
• Renal size: standardised measurements and volume calculation; compare with
age-/weight-adapted growth charts (Table15.1). Always compare to other side
Fig. 15.5 Normal neonatal kidney. (a) Longitudinal section of the right neonatal kidney with
length measurement (+…+). Note physiologically relatively high echogenicity of cortex (similar
to liver), pronounced cortico-medullary differentiation and some (transient) echogenicity in distal
medulla. (b) Axial section of the left kidney with measurements (callipers)—same appearance of
parenchyma as in (a). (c) Axial section, neonatal left kidney: same parenchymal appearance as in
(a, b) but some widening of renal pelvis (<5mm) with some slight prominence of the pelvic wall
(<1mm)—this may be normal, but may rectify a follow-up study
382
ab
M. Riccabona
Fig. 15.6 Normal kidney in childhood. (a) Longitudinal kidney scan (from dorsal) with length
measurement. (b) Axial scan of the right kidney through liver with measurement of diameter. (c)
Depictable extrarenal pelvis and proximal ureter (++) may be normal in a well-hydrated child
Fig. 15.7 (Normal) collecting
system in neonates and infants. (a,
b) Normal neonatal kidney, despite
(physiologically) prominent
cortico-medullary differentiation
and some dilatation of the collecting
system—but with normal
conguration of fornices and
papillae (PCD II)
Table 15.1 Renal size—normal values (according to Weitzel)
(a) Schematic drawing of longitudinal renal section and axes for renal size measurements, l length,
w width, d depth
(b) US image axial section from the left ank: cross section at hilus, orthogonal diameters for
volume calculation (+…+
tion: length measurement (callipers) for volume calculation
(c) Renal size (volume) in newborn (mL) versus body weight (kg)
), and US image of a newborn kidney (right ank); longitudinal sec-
1,2
(d) Normal renal volumes (mL) for the left kidney related to body weight (kg)
(e) Normal renal volumes (mL) for the right kidney related to body weight (kg)
15 Ultrasound oftheUrogenital Tract inNeonates, Infants, andChildren
383
(calculate relative renal volume: volume right+ left = 100%). If different/one
kidney enlarged or smaller (normal range= 40/45:55/60% relative renal vol-
ume), always meticulously try to assess potential reasons.
– Note that renal size increases with dilatation of collecting system—without
necessarily larger parenchymal volume.
CDS and PWD After nding vessels, identify them by ow direction; perform
spectral analysis from duplex trace. Slightly higher arterial RI (0.75–0.80) physiologic in neonates, then quickly maturing to normal adult values (RI~0.67±0.03)
(Fig.15.8). Also observe shape, particularly of systolic inow—attened and slow
acceleration of systolic upstroke typical for renal artery stenosis.
Note Flow velocities also vary with age (and are inuenced by many different also
systemic factors—see Chap. 3); good Doppler angle (<60°) potentially with respective angle correction (angle >20°) mandatory for ow velocity measurements.
Fig. 15.8 Normal aCDS of kidney. (a) CDS of main renal vessels—median ventral access:
left renal vein (red) running in front of renal artery (encoded in blue) and passing anteriorly
to abdominal aorta. (b) Further normal course of left renal vein (arrow) between abdominal
aorta and superior mesenteric artery till entering inferior vena cava (IVC); due to some narrowing increased flow velocity and some flow turbulence causing aliasing on CDS. (c)
Accessory renal arteries, which can be a normal variant, but may also be associated with
urinary obstruction due to vascular impairment of proximal ureter/pelvi-ureteric junction.
(d) Normal aCDS of a healthy kidney—axial section. (e) Normal duplex trace of main/segmental renal artery
384
Fig. 15.9 Retro-aortal left renal vein. (a) Abnormal course of left renal vein accessed
through kidney from a longitudinal (coronal) flank view: blue-coded vein courses distally
instead of running cranially parallel to renal artery. Note some aliasing at the area the vein
reaches abdominal aorta. (b) Ventral median axial view: left renal vein (encoded red ) passes
behind abdominal aorta with tapering due to some compression between aorta and vertebral body
M. Riccabona
15.2.2.1 Normal Variants
Number of variations that do not necessarily indicate pathology: parenchymal
bridge/hypertrophic column of Bertin in (incomplete) duplex kidney, rotation/position anomalies, caliectasis, extrarenal pelvis, persisting renunculae, other contour
alterations (e.g. “splenic bump”), variations in vessels such as accessory renal arteries/veins and retroaortic left renal vein (Fig.15.9).
Duplex Kidney
US Findings
Central parenchymal bridge, sometimes disproportionate upper and lower collecting systems, potentially associated dysplasia with lack of cortico-medullary differentiation and increased echogenicity commonly of the upper pole moiety
parenchyma (Fig.15.10):
• Obstruction most commonly in the upper system, rarely involves the lower
pole system.
• Meyer–Weigert rule—ureter of the lower system drains latero-cranially into
bladder with risk of VUR, whereas ureter of the upper pole system usually drains
distal-medially, may even insert ectopically, may be associated with ureterocele
and often is obstructive.
• Lower system commonly reuxing (reux nephropathy? secondary obstruction/
kinking?).
15 Ultrasound oftheUrogenital Tract inNeonates, Infants, andChildren
Fig. 15.10 Duplex kidney. (a) Duplex kidney (+…+2), longitudinal ank view: no distension of
renal collecting system, only parenchymal bridge in the middle of kidney (
central pelvis echoes indicates duplication. (b) Duplex kidney, longitudinal ank view: disproportional dilatation of the lower collecting system. (c) Duplex kidney, longitudinal ank view tilted
medially: two separate ureters of the upper and the lower moiety seen, with different grade of
distension of respective collecting system. (d) Duplex kidney, longitudinal ank view: signicant
dilatation of the upper moiety with unstructured, narrow, echogenic parenchyma; the lower moiety
exhibits normal parenchymal structure: NOTE: signicantly reduced vascularity on aCDS in dysplastic upper moiety. (e) Huge, cystiform dilatation of the upper moiety of duplex kidney with
rim-like residual dysplastic parenchyma, only slight dilatation of the lower system—not to be
mistaken for a renal cyst
+…+) interrupting
1
385
Tip Always try to assess whether there is one common extrarenal pelvis or two
ureters leaving kidney; also try to visualise precise ostial anatomy (1 or 2 ostia? 2
jets from one side? etc.). Particularly for this (sometimes challenging) task good
hydrating is essential.
Ectopic Kidneys
US Findings
May be anywhere in the retroperitoneum, may be small and dysplastic, sometimes
only cystic remnants are seen. Even intrathoracic position possible—then close to
diaphragm and paramedian dorsally (Fig.15.11).
Note Small ectopic kidneys may drain ectopically and can still have function—this
may cause symptoms such as urinary dribbling (when inserting into vagina or distal
to sphincter). If both kidneys not seen in normal position; meticulous search of
entire abdomen mandatory.
386
Fig. 15.11 Ectopic kidney. (a) Pelvic ectopic kidney (++) visualised behind and above well-lled
urinary bladder, sitting in front of spine. (b) Cystic dysplastic ectopic kidney (++) sitting in front
of psoas muscle distally to its normal position, only seen by meticulous search using graded compression; some residual parenchyma seen—ureter was draining ectopically into vagina causing
constant dribbling
Fig. 15.12 Horseshoe kidney. Parenchymal bridge
(callipers) of a horseshoe kidney depicted in front of
aorta, IVC, and vertebral body connecting the right and
the left moiety; mesenteric vessels seen in front of renal
parenchyma in this axial abdominal midline section
M. Riccabona
Renal Agenesis
Only compatible with extrauterine life only if unilateral—single (hypertrophic) kidney on other side. Often constitutes end point of disturbed foetal development, e.g.
dysplastic or cystic kidney regressed and cannot be seen any longer. In these children high probability of ipsilateral genital malformation should be explicitly
searched for.
Note Bilateral renal agenesis fatal, usually diagnosed prenatally, leads to severe
hypoplasia of lung.
Fusion Anomalies andOther Rare Findings
Horseshoe kidney—most common anomaly: lower poles attached at midline, form
parenchymal bridge in front of aorta (Fig.15.12); associated with impairment of
urinary drainage, higher risk for being injured in abdominal trauma.
Cross-fused dystopia, triple kidney, and other rare variations—not addressed
in detail.
Bladder anomalies—such as duplex bladder rare; bladder exstrophy not target of
US investigations (only for assessing kidneys).
15 Ultrasound oftheUrogenital Tract inNeonates, Infants, andChildren
387
15.3 Pathology oftheKidney
15.3.1 Congenital Conditions
15.3.1.1 Dysplasia/Hypoplasia
Definition
Structural alteration of renal tissue with more or less impaired function; may be
focal or diffuse, unilateral or bilateral; often associated with severe obstructive
uropathy and/or VUR; congenital/inherited or syndromic.
US Findings
Commonly increased parenchymal echogenicity with reduced cortico-medullary
differentiation, potentially with cysts (Fig.15.13)—see also cystic kidney disease
(below). May be smaller.
CDS Potential cortical vascular rarefaction on Power Doppler, with increased
resistance (RI↑), depending on/associated with functional impairment; also pseudonormal ow patterns with reduced systolic velocity.
15.3.1.2 Cystic Renal Disease
Definition
Often inherited, genetic, congenital condition—even if cysts only manifest later
in life.
However, secondary and acquired cystic disease exists, as well as cystic
tumours.
New insight into pathogenesis of genetic conditions—new term “Ciliopathies”
(also explains the involvement of other organs such as liver) and/or uromodelin
Fig. 15.13 Hypodysplastic and cystic kidney disease. (a) Small, relatively normal looking kidney
(+ +) in a child with end-stage renal failure due to bilateral renal hypodysplasia. (b) Dysplastic
kidney with completely disrupted parenchymal structure (similar as in ARPKD (“pepper and salt”
appearance)). (c) Echogenic widened cortical parenchyma with cortical cyst in another cystic dysplastic malfunctioning neonatal kidney in systemic-syndromatous disease
388
M. Riccabona
disturbances. Based on these new insights and genetic as well as pathophysiologic considerations with respect to therapeutic implications a recent recommendation was outlined to help with deciding on imaging and follow-up in those
conditions (Schaefer etal. Imaging of kidney cysts and cystic kidney diseases in
children. Consensus paper by an ad hoc committee. Radiology 2019)
(Table15.2b).
US Findings
Usually anechoic structures with dorsal amplication (Fig.15.14). Depending on
size, content, and border, classied into various degrees of complexity (adapted
from the Bosniak CT Classication, though without having enhancement pattern
Table 15.2 DDx and imaging of renal cystic conditions
a
(a) Schematic drawing illustrating typical appearance of different renal cystic diseases and conditions (Adapted from Riccabona et al. 2012, Pediatr Radiol:42; and Riccabona (ed) Pediatric
Urogenital Radiology, 3rd edition, Springer 2019, p.560)
b
15 Ultrasound oftheUrogenital Tract inNeonates, Infants, andChildren
Table. 15.2 (continued)
389
Prenatal suspicion of CDKmultidisciplinary care in pregnancy &
(Single) simple cyst Detailed medical & family history,
Cystic dysplasia or MCDK
Bilateral or unilateral cystic
dysplasia / MCDK without
contralateralcompensatory
hypertrophy
Unilateral cystic dysplasia or
MCDK with contralateral
hypertrophy
(Classical & CGS) TSCFollow-up, (unenhanced) MRI after
Acquiredcystickidneydisease follow-up_of native kidneys in patients
Nephronophthisis Regular kidney imaging not required
ADTCKD - former “medullary
cystic kidney disease” or
“medullary sponge kidney”
BBS, HNF1B disease - also
includesformer “glomerulocystic kidney disease”
Complicated cyst Work-up for DDx and characterization
Cystic tumorDiagnostic work-up and follow-up;
post-natally
thorough clinical examination
At risk of progressive kidney disease –
nephrological / clinical follow up, only
little contribution of imaging
Ensure continued appropriate
compensatory hypertrophy
puberty
on renal replacement therapy & after
renal transplantation
Not defined
Depends on type of renal & urinary
tract involvement
at least initially mandatory
follow applicable oncology protocols
Regular US monitoring,
at least 1 follow-up US –
no CEUS, MRI or CT
Imaging follow-up not
necessary (unless for
other reasons)
Serial US of contralateral
kidney, less focus on
MCDK if uncomplicated
Annual US until puberty,
initial MRI for atypical
AML invisible for US
Annual US in selected
population. No need in
other acquired cysts once
stable &/or known cause
(post-traumatic …)
Liver US in children with
respective genetic risks,
no regular kidney US
Maybe annual US (only if
symptomatic?);
Plain film or CT?
regular US if significant
structural kidney/urinary
tract abnormalities
US (including CEUS),
If indecisive: ce-MRI
(CE)US + sectional ceimaging
, preferably MRI Table
(b) Some recommendations on how to image cystic kidney disease (CDK) based on an European
consensus statement (adapted from Gimpel et al. Imaging of Kidney Cysts and Cystic Kidney
Diseases in Children: An International Working Group Consensus Statement. Radiology 2019)
available on US: from grade I=uncomplicated simple cyst to grade IV=severely
complicated, highly suspicious cyst).
• Better characterisation of complex cyst can be achieved by CEUS using contrast
dynamics similarly to CT/MRI (but note that UCA are purely intravascular and
NOT excreted into urine—thus differentiation cyst versus urinoma/calyceal
diverticula/tertiary calyx not reliable).
390
Fig. 15.14 Cystic kidneys: dysplastic cyst, multicystic dysplastic kidney (MCDK). (a) Typical
MCDK with large, not connected, peripheral cysts; some central echogenic dysplastic residual
parenchyma. (b) Severe foetal obstructive uropathy with multiple cortical cysts and dysplastic
parenchyma in a neonate
M. Riccabona
Classication of cysts with recommendations on imaging work-up and follow up imaging needs—see Table15.2:
• Simple cyst: (isolated/single) uncomplicated cyst (no content/completely
anechoic, smooth margin, thin wall, no solid component, etc.), localised, with or
without growth. Rarely seen in neonates and infants.
• Multiple cysts: often associated with parenchymal dysplasia or genetic/inherited
cystic kidney disease.
• Complicated cyst(s): as anywhere else—internal echoes and sedimentation, sep-
tae, thick wall, irregular border, solid/nodular components, conglomerates of
cysts, large, irregular shape; vascularised compartments best seen by aCDS.These
need follow-up/diagnostic work-up, sometimes additional imaging.
Inherited/Congenital Cystic Disease
Often part of ciliopathy complex (autosomal dominant and recessive cystic kidney
disease—ARPKD and ADPKD; glomerulocystic and medullary cystic kidney disease—GCKD and MCKD; and nephronophthisis/tuberous sclerosis complex)
(Table15.2):
• ARPKD: enlarged hyperechoic kidneys bilaterally, with disrupted echotexture
and potential regional echogenicities (“salt and pepper appearance”) due to
microcysts (too small to be resolved by US), with or without some dilatation of
collecting system. Often associated with liver brosis (maybe initial manifesta-
tion of disease) (Fig.15.15).
• ADPKD: larger parenchymal cysts, can be conglomerated or isolated, single or
multiple (associated with cysts in other parenchymal organs, vascular problems
such as aneurysms); need comprehensive follow-up including all respective
changes (Fig.15.15).
• Syndromic cystic kidney disease: many syndromes exhibit renal cysts. Some also
carry increased risk for nephroblastomatosis/malignant degeneration.