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10.3 Pathology of the Kidney
a
337
b
c
de
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Fig. 10.14 US in UPJO (including CDS). ( a ) Typical appearance of high-grade “hydronephro-
sis” (grade IV°) with signifi cantly dilated collecting system, thinned parenchyma and renal
enlargement (+….+) in UPJO. ( b ) Cyst-like appearance of grossly enlarged collecting system
(HN V) in UPJO; peripheral rim-like parenchyma hardly visible but enables differentiation
against MCDK (i.e. central parenchyma, no connections between cystic structures). ( c ) Axial sec-
tion of mild UPJO with only little distension of calices and caliceal neck (
parenchyma (
2
+….+) with persisting cortico-medullary differentiation (HN grade III°). ( d ) Axial
section: dilatation of extrarenal pelvis (+ +) but practically no dilatation of intrarenal system. ( e )
Same patient as in ( d ) CDS reveals an additional renal artery crossing the pelvi-ureteric junction,
possibly causing (intermittent) partial obstruction with dilatation of renal pelvis. ( f ) Gross dilata-
tion of collecting system and pelvis in severe, fetally decompensated UPJO. Echogenic, unstructured and narrow parenchyma full with multiple cysts of different sizes (“obstructive dysplasia”).
( g , h ) Importance of hydration: kidney scanned in non-hydrated ( g ) and well-hydrated ( h ) state,
the latter after furosemide- induced diuretic stress. Note signifi cant change in dilatation of renal
1
+ +) and collecting system impressively demonstrating importance of proper patient prep-
pelvis (
aration for US studies
1
+…+) and preserved
338
abc
10 Ultrasound of the Urogenital Tract
fed
Fig. 10.15 POM/MU – M-mode. ( a ) Two cystiform structures depicted behind well-fi lled bladder
lateral to uterus (proper TGC adaptation essential – automatic image optimisation programmes
will not always work for this): to differentiate ovarian cysts from (bilateral) megaureter, longitudinal paramedian section is necessary. ( b , c ) Dilated ureter (+ +) behind well-fi lled urinary bladder
in axial ( b ) and longitudinal ( c ) section; the latter nicely exhibiting short narrow distal/transmural
section (obstructive megaureter). ( d ) M-mode documents lack of peristalsis in dysplastic widened
ureteral segment (neonate with primary megaureter). ( d ) Signifi cantly dilated renal collecting sys-
tem in child with megaureter. Note cystiform fl uid-fi lled structure below lower pole of kidney (+
+) representing loop of tortuous megaureter. ( e ) Pelvi-ureteric junction has kink-like anatomy
explaining intermittent secondary upper obstruction in addition to megaureter
Uretero-Vesical Junction Obstruction (UVJO)/Obstructive Megaureter (POM/MU)
Defi nition
Aetiology: stenosis at UVJ or regional dysplasia of ureter with lack of peristalsis,
causing impaired urinary drainage. Potentially associated with anatomic changes at
ostium (low insertion, ureterocele, ectopic ureteric insertion, duplex systems, etc.).
US Findings
Dilatation of ureter, more or less thickening of wall and varying impairment of peristalsis (can be documented by video clips/M-mode) (Fig. 10.15 ):
• Hyperperistalsis indicates stenosis.
• Lack of peristalsis hints at decompensation or dysplastic-atonic segment.
• In complications (e.g. infection): echoes in ureter.
NOTE : Dilatation of ureter does not necessarily correlate with dilatation of renal
collecting system – associated kink/relative UPJO will increase intrarenal distension (HN II°–V°).
CDS
No specifi c fi ndings. Assessment of ureteric infl ow jet may be helpful but potentially
misleading. Improves depiction of ostium – thus identifi cation of atypical insertion.
10.3 Pathology of the Kidney
339
Additional Investigations
IVU replaced by (diuretic contrast-enhanced) MRU; for anatomic display
T2-MRU.
VCUG/ce-VUS for differentiation of dilating VUR.
MAG3 scintigraphy – used for drainage assessment, split renal size and function
and assessment of ureteral peristalsis (or dynamic MRU).
Posterior Urethral Valve (PUV)
Defi nition
Most common in baby boys. Has a number of forms. Severe distal obstruction often
associated with upper tract pathology – high probability of congenital renal dysplasia and chronic renal failure.
US Findings
• Thickened bladder wall, trabeculation, (pseudo-)diverticula, enlarged capacity,
typical valve-like confi guration of bladder neck (particularly well seen by perineal US during voiding attempts) (Fig.
10.16 ).
• Secondary high-grade VUR or obstruction by thickened bladder wall, associated
with more or less renal dysplasia, dilation of collecting system, potentially popoff urinoma (Fig.
10.17 ) – the latter will prevent kidney from further damage.
CDS
Demonstrates renal perfusion; helps assessment of severely dysfunctional kidneys.
ce-VUS may show valve (perineal approach during voiding); VUR may show pop-
off urinoma.
DDx
• Prune belly syndrome (hypoplastic abdominal wall, cryptorchidism, hypoplastic
prostate, hypoplasia of posterior urethra, commonly associated with complex
urinary tract anomalies/dilated ureters with less-dilated intrarenal collecting system and dysplastic parenchyma).
• Neurogenic bladder.
• High-grade VUR.
Additional Investigations
• Initial confi rmation by VCUG recommended.
• Early urinary drainage either by bladder relief or nephrostomy.
• Renal function assessed by DMSA scintigraphy (best results after approx. third
month of life – as it only works with suffi cient renal function after renal immaturity has ceased).
• Rarely MRU (in additional complex pathology).
• No indication for IVU.
Vesico-Ureteric Reflux (VUR)
Defi nition
Insuffi cient urinary ostia (primary/secondary); refl ux of urine from bladder to ureter/renal collecting system – with more or less dilatation of ureter and/or caliceal
system. Grading I°–V° according to international classifi cation.
340
a
10 Ultrasound of the Urogenital Tract
b
cd
e
f
g
Fig. 10.16 US in posterior urethral valve (PUV). ( a ) Longitudinal section of large bladder with
impressive wall thickening and obstruction of ureteral ostium ( arrow ) in baby with PUV. ( b ) Cross
section through wall-thickened urinary bladder (after drainage via catheter) shows dilated ureter
behind bladder and trabeculation. ( c ) Normal perineal US in baby boy (no voiding). ( d ) Perineal
US, neonate: open bladder neck and proximal urethra to pelvic fl oor when trying to void – not to
be confused with PUV (as on VCUG). ( e ) Normal male urethra during voiding on ce-US.
( f ) Typical valve confi guration of PUV on perineal US during voiding. ( g ) ce-VUS: valve-like
urethra confi guration nicely demonstrated during voiding; catheter only seen in basic image,
contrast agent better visualised in left, dedicated contrast-specifi c image
10.3 Pathology of the Kidney
a
bc
d
Fig. 10.17 Pop-off urinoma in PUV with renal dysplasia. ( a ) Dysplastic kidney in neonate with
PUV, dilated pelvis and dysplastic cysts. ( b ) Complex fl uid formation adjacent to relatively normal
looking kidney in PUV, consistent with caliceal rupture and pop-off urinoma which seems to have
a protective effect reducing renal damage. ( c ) Same neonate as in ( b ): good vascularisation of renal
parenchyma, large urinoma in front of kidney. ( d ) Dual/split image technique, dorsal axial scan
through both kidneys including aCDS: obviously signifi cant difference in renal size and perfusion,
left kidney severely damaged (same can also be seen in other patients with high-grade VUR without PUV)
341
US Findings
Indirect signs in bladder: bladder wall thickening, trabeculation, lateralisation of
ostium and gaping ostium. Varying dilatation of ureter that may exhibit wall thickening. Post-void increase of dilatation of collecting system and pelvic urothelial
thickening (Fig. 10.18 ).
CDS
Ureteric infl ow jet may be atypical, asymmetric and originate from lateralised
ostium.
Sometimes, particularly with particles in urine, VUR can be directly visualised
by reversed colour fl ow signals in ureter.
NOTE : These have to originate from within bladder through ostium – as otherwise
refl ected retrograde fl ow from closed ostium may mimic VUR.
ce-VUS (see also Chap. 2 ): refl ux of US contrast agent into ureter/pelvi-caliceal
system – with more or less distension, depending on VUR grade. Grading of VUR
achievable by ce-VUS (correlates with standard VUR grading on VCUG – see
Table 1.3 , Figs. 1.24 , 2.7 , 2.8 , and 10.18 ).
342
a
bc
10 Ultrasound of the Urogenital Tract
d
e
f
Fig. 10.18 Vesico-ureteric refl ux. ( a ) Left kidney, axial view before voiding: no distension of
collecting system/renal pelvis. ( b ) Same girl, same section after voiding: signifi cant widening of
the renal pelvis indicating dilating VUR. ( c ) Urothelial sign: thickened wall of non-distended renal
pelvis – a nonspecifi c sign for VUR, involvement in UTI, obstruction, congestions, etc. ( d ) Duplex
ureter – the upper and more lateralised ostium (draining lower moiety of respective kidney) is gapping, indicative of VUR. ( e ) ce-VUS shows contrast refl ux into proximal ureter and renal collect-
ing system. ( f ) Comparison of two kidneys in same patient showing different size and pelvic wall
thickening associated with different degree of VUR
NOTE : Always assess renal parenchyma for signs of dysplasia/scars after
infections.
Connatal dysplasia in severe VUR (common in baby boys, PUV) called
“congenital refl ux nephropathy”.
Postnatally VUR itself does not cause renal damage, only in conjunction with
recurrent upper UTI.
Additional Investigations
VCUG – particularly in boys, preoperatively, for detailed analysis not only of
urethra (also ureter, potential diverticula ...). Rarely bladder function studies are
performed.
10.3 Pathology of the Kidney
343
Fig. 10.19 Twinkling sign/ureteric stone. ( a ) Distal ureteric stone ( 1 + …+) with some dilatation
of ureter and only little shadowing, only depictable with suffi ciently fi lled urinary bladder.
( b ) Urethral stone (
(same patient as b ). ( d ) Pelvic fl oor rhabdomyosarcoma, visualised through bladder (
presses + displaces urethra (U,
a
c
1
+.... +) depicted by perineal US. ( c ) Twinkling sign caused by urethral stone
1
+…+), causing urethral obstruction
b
d
2
+…+) com-
DMSA scintigraphy for assessing renal parenchyma damage (might be replaced
by MR in future).
IVU outdated.
Secondary Obstruction
Defi nition
Number of causes such as urolithiasis or compression (by tumours, retroperitoneal
fi brosis, etc.).
US Findings
Acute obstruction usually does usually not exhibit signifi cant dilatation – unless
there is preexisting chronic drainage impairment/other forms of dilatation.
Increased echogenicity of parenchyma and swollen and enlarged kidney.
Potentially perirenal oedema/stranding.
Concretions/stones (urolithiasis): usually echogenic structure with dorsal shadowing, distended collecting system or ureter narrows after level of obstruction.
CDS
In acute severe obstruction, there is diminished peripheral vasculature (a)CDS.
Asymmetrically elevated RI in acutely obstructed kidney.
In total obstruction, lack of ureteric infl ow jet from affected ureter – otherwise
asymmetric (even ipsilateral dominant) ureteric jet (e.g., from haematuria).
Twinkling sign from stone (Fig.
10.19 , see Fig. 1.18 ).
344
10 Ultrasound of the Urogenital Tract
Role of US
Perfect initial diagnostic tool:
• In children, stones can be visualised in nearly all parts of urinary tract, particu-
larly in kidney, at pelvi-ureteric junction, in distal ureter – provided suffi ciently
fi lled bladder allows access. Even urethra (by perineal US) (Fig. 10.19d ).
NOTE : Following dilated ureter downwards from renal pelvis will often allow depic-
tion of obstructing stone even in mid/lower ureter, e.g. at pelvic vessel crossing.
Furthermore initial US allows tailoring of further examinations. Adjacent compressing structures can usually be visualised, too; potential for US-guided intervention.
Additional Investigations
• Kidney-ureter-bladder fi lm (KUB).
• Focused IVU or stone CT (particularly in complex and equivocal situation where
it is increasingly preferred):
– Not indicated with same frequency as in adults – due to radiation burden.
• Role of MR is yet undefi ned.
• See also ESPR/ESUR recommendations – Pediatr Radiol (2010) 40:1315.
10.3.2 Inflammatory Renal Parenchymal Conditions
Role of US
Perfect initial diagnostic imaging method and for follow-up (and US-guided biopsy
for DDx).
Additional Imaging
DMSA scintigraphy in acute or chronic setting (for scars, wait 4–6 months after
infection):
• Complicated infections or DDx of pseudotumours may require MR (or CT, if
MR is not available).
• IVU usually not indicated in children (rare exceptions, e.g. unless there is a suspected
obstructing stone).
• Additional nephro-urologic work-up of potentially underlying/associated condi-
tion recommended.
• Imaging algorithm for paediatric UTI: see ESPR/ESUR recommendation Pediatr
Radiol (2008) 38:138.
10.3.2.1 Pyelitis
Defi nition
In children isolated pyelitis is rare – potentially associated with VUR. Commonly
associated with interstitial bacterial nephritis.
US Findings
Thickened echogenic renal pelvic wall and echoes within collecting system, which
tends to be enlarged, hypotonic and wide (Fig. 10.20 ).
Secondary stone formation or fungus may be present; fungus usually similar to a
stone, often larger and somewhat polygonal shaped; dorsal shadowing less than
with a typical concretion, may cause secondary obstruction.
10.3 Pathology of the Kidney
ab c
de
Fig. 10.20 US in urinary tract infection (UTI). ( a ) Echogenic content fl oating throughout bladder
in UTI. ( b ) Echogenic debris (clot and fi brin) sitting at bladder base in haemorrhagic cystitis.
( c ) Enlarged kidney, with swollen urothelium of lax and slightly distended renal pelvis in an infant
with upper UTI (acute pyelonephritis). ( d ) Enlarged kidney with disrupted cortico-medullary dif-
ferentiation and increased echogenicity in upper UTI with diffuse renal involvement. ( e ) aCDS
depicts multi-segmental perfusion defects in same child as ( d ); these local manifestations were less
depictable on gray scale US
345
10.3.2.2 Acute Pyelonephritis (aPN)/Interstitial Nephritis
Defi nition
Haematogenous or ascending infection, bacterial or viral, sometimes atypical
(tuberculosis).
US / CDS Findings
Focal/diffusely altered parenchymal echogenicity – commonly increased, swollen
kidney, in focal infection even pseudotumours, regional swelling (“lobar nephronia”), peripelvic increased/broadened echogenicity and perirenal oedema, often
associated with fi ndings as in pyelitis.
Regionally/segmentally decreased vascularity – particularly well seen on aCDS,
diffuse asymmetrically reduced vascularity on power Doppler in diffuse infection
(Fig. 10.20 ).
10.3.2.3 Necrosis and Abscess Formation
US / CDS Findings
Increasingly inhomogeneous defect, hypoechoic structural alteration with eventually
complex cystic confi guration and rim-like margin; may resemble complicated cyst.
Focal perfusion defect, potentially capsular hyperaemia (Fig. 10.21 ); CEUS may
enhance depiction and aid DDx.
346
a
bc
10 Ultrasound of the Urogenital Tract
d
Fig. 10.21 Complications in UTI, DDx, scarring. ( a ) Focal necrotic cortical area (+....+) seen as
hypoechoic sphaeric lesion in severely prolonged upper UTI; note also broadened peripyelonal
echogenicity and hazy cortico-medullary differentiation of swollen kidney. ( b ) Multiple necrotic
( dark ) segmental defects throughout kidney in severe diffuse/multifocal necrotising pyelonephritis.
( c ) Same patient as in ( b ): aCDS demonstrates only minimal residual central perfusion – eventually
entire kidney had to be removed. ( d ) Sphaeric focal complex liquid lesion in a child after UTI, with
sparing of vessels on aCDS – consistent with early apperaence in formation of an renal abscess
a
Fig. 10.22 Scarring. ( a ) Focal scar with clubbed calix and destroyed cortex after upper pole aPN. ( b )
Small peripheral scar (+ +) seen as perfusion defect on aCDS, not easily depictable by gray scale US
b
10.3.2.4 Scarring
US / aCDS Findings
• Regional narrowing of parenchyma with contour alteration, disrupted/abnormal
cortico-medullary differentiation and clubbing of affected calix.
• Regional small strip-like defect, particularly well seen on aCDS (Fig. 10.22 ).