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10.3 Pathology of the Kidney
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Fig. 10.30 Urinary tract trauma. ( a ) Blood sedimentation in urinary bladder after renal trauma.
( b ) Perirenal clear fl uid – consistent with posttraumatic urinoma. ( c , d ) Focal altered contour and
structure of kidney ( c ) after trauma – only aCDS ( d ) clearly demarks extent of renal injury. ( e )
Relatively normal appearance of kidney, but no perfusion on aCDS (colour box) – indicating
devascularisation due to hilar injury of the kidney
357
10.3.9 Renal Tumours
10.3.9.1 Benign Tumours
Mostly hamartoma, angioma, angiomyolipoma (tuberous sclerosis) and rarely
adenoma.
10.3.9.2 Pre- or Semimalignant Tumours
Nephroblastomatosis (remnants of metanephrogenic tissue, may develop into Wilms’
tumour), neonatal mesoblastic nephroma (mostly benign, rare malignant entities).
10.3.9.3 Malignant Tumours
Most commonly Wilms’ tumour (nephroblastoma), rhabdoid tumour, renal sarcoma, renal cell carcinoma – other entities rare.
US Findings (Fig.
10.31 ):
• Angiomyolipoma exhibits more or less typical echogenic tissue structure.
• Cystic nephroma appears as multicystic mass that may manifest segmentally
with tumourous enlargement, disruption of normal echogenicity, small septae,
usually with little perfusion. Larger solid areas, nodular wall structure, hyperaemia or large cystic components with haemorrhage may indicate another underlying entity (e.g. cystic Wilms’ tumour).
358
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10 Ultrasound of the Urogenital Tract
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Fig. 10.31 Renal tumours. ( a ) Focal echogenic renal tumour, typical for an angiomyolipoma. ( b , c )
Focal renal tumour of similar echogenicity as renal cortex on gray scale ( b ), better visible by its exophytic
behaviour and its (hyper)vascularity on CDS ( c ), in a patient with tuberous sclerosis – consistent with an
atypical angiomyolipoma – needs follow-up and sectional imaging. ( d ) Nephroblastomatosis: multiple
peripheral renal tumourous nodules, partially diffi cult to appreciate on gray scale, better outlined by aCDS.
( e ) Typical appearance of Wilms tumour: large mass with relatively homogenous tissue and cortex-like
echogenicity. ( f , g ) More and less cystic Wilms tumours. ( h ) 3DUS in an echogenic Wilms tumour, helpful
for more accurate tumour volume calculation; the right lower box shows a 2DUS image of same patient
with an additional exophytic nephroblastomatotic focus in upper pole (
system caused by impaired drainage due to compression of renal pelvis by the large tumour. ( i ) Focal renal
+…+) in a child with lymphatic leukaemia – consistent with renal involvement. ( j ) (Congenital)
lesion (
1
Renal tumour in a neonate with subtotal destruction of kidney, only leaving a subtle peripheral rim of original kidney parenchyma – consistent with a mesoblastic nephroma. ( k ) Atypical tumour (
girl. Most common DDx: rhabdoid Wilms tumour, renal sarcoma, renal cell carcinoma
+…+). Note dilatation of collecting
1
+…+) in an older
1
10.4 Renal Biopsy and Interventions
359
• Other tumours have nonspecifi c appearance of any mass lesion – may exhibit
pseudocapsule, growth from kidney, displacing surrounding structures, local
lymph node metastases and – particularly in Wilms’ tumour – relatively often
have vascular invasion with renal vein thrombosis reaching even into IVC and
up to right atrium (may also occur in renal cell carcinoma). Secondary necrotic,
cystic, haemorrhagic changes may be present.
• Assumption of entity depends more on age than on US/imaging fi ndings.
• Tumours usually large when diagnosed (different for angiomyolipoma/hamartoma).
DDx
Focal nephroma/infl ammatory pseudotumour, xanthogranulomatous pyelonephritis, infi ltration in systemic disease (lymphoma), hypertrophic column of Bertin,
other complex cysts.
Role of US
Initial diagnosis – fi nd/confi rm suspected lesion, defi ne size (volume calculation)/
relation to central renal structures, surrounding organs/tissue, assess patency of central structures (artery, vein, pelvis), give fi rst information on stage (infi ltrating/local/
liver metastases?).
Later-follow-up, assessment of complications.
Additional Investigation
• Sectional imaging by MR (or CT, if MR unavailable) mandatory, particularly in
suspected malignancy – adhere to local tumour imaging protocols.
• Sometimes US-guided biopsy (varies with country/continent).
10.4 Renal Biopsy and Interventions
Also see Chap. 2 for general recommendations/guidelines.
10.4.1 Renal Biopsy
Biopsy often necessary for histologic assessment of renal parenchymal disease –
biopsy of focal renal lesions far less common than in adults, particularly in Europe.
Renal biopsy should always be performed under US guidance for reducing risks:
• Standardised procedure with pre-interventional assessment, time out, periinterventional guidance, postinterventional follow-up.
• Standardised protocols should be used.
• Pre-interventional US performed to assess kidney for potential dilatation, thickness of renal parenchyma, potential biopsy risks (e.g. abnormal vessels or preexisting arteriovenous malformations/fi stula) and impaired access. At that time
needle length/size defi ned – depending on depth of kidney, size of sample
required, thickness of parenchyma.
• Most commonly 20–18(−16) Gauge needles with 1.2(−2) cm core length advisable, potentially using coaxial technique.
• Use of steering device (biopsy guide) and (semi-)automated biopsy guns helpful.
• Thereafter validation of indication and coagulation check, informed consent,
time out.
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10 Ultrasound of the Urogenital Tract
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Fig. 10.32 Renal biopsy. ( a ) Renal biopsy, dorsal approach to lower pole of left kidney: needle path
outlined by dotted lines , needle (echogenic line) already advanced to renal capsule. ( b ) Needle now
fi red, position and depth of needle nicely visualised by image from cine-loop documentation. ( c )
aCDS superiorly helps to depict postinterventional subcapsular haematoma which in early stages is
of similar echogenicity as renal cortex; also observe triangular perfusion defect in lower pole, indicating regional perfusion defect due to injury of respective vessel causing a small infarction. ( d , e )
Postinterventional follow-up (3 h after procedure) depicts focal aliasing on CDS, consistent with an
arteriovenous fi stula; respective fl ow alterations of feeding artery and draining vein assessed by
spectral analysis (e) confi rming shunt fl ow by demonstrating arterialised fl ow pattern in draining vein
• US - guided biopsy (see also Chap. 2, and Figs. 2.12 and 2.13 ): performed in
prone position (for native kidneys) – with support under belly to avoid displacement of lower pole of left kidney (usually targeted to avoid injury of adjacent
liver on right side).
– Local and systemic analgesia/sedation may be necessary with adequate
monitoring.
– Biopsy direction – parallel to major segmental vessels branching into periph-
ery; CDS helpful to avoid large vessels.
– Real-time monitoring of needle positioning and biopsy using cine loop
advisable.
• Post-biopsy US: check for potential post-biopsy complications (e.g. bleeding,
haematoma, haematuria, infarction and AV fi stula), recommended immediately
afterwards, 3–6 h and 24 h after intervention. Standardised post-biopsy management helpful (Fig.
10.32 ).
• See also ESPR/ESUR recommendations in Pediatr Radiol (2014 -in press).
10.4.2 Drainage/Nephrostomy
US enables safe access to dilated system or abscess. Steering devices attached to
transducer sometimes helpful; alternatively freehand technique used. Always defi ne
10.4 Renal Biopsy and Interventions
361
adequate access that allows for suffi cient parenchymal coverage of targeted area to
avoid leakage/urinoma formation.
Access achieved commonly using trocar or Seldinger technique; additional sup-
plementing fl uoroscopy may be helpful to assess leakage, positioning and anatomy
after contrast instillation once successful access is gained under US guidance or for
Seldinger technique using guide wires and dilatation of parenchymal tract (see
Chap. 2 , and Figs. 2.14 and 1.13 ).
10.4.3 Postoperative Imaging
To assess postoperative anatomy, to detect complications and to evaluate success.
For assessment of VUR recurrence or insuffi cient success of cystoscopic tech-
niques, ce-VUS can be performed as alternative to VCUG even intraoperatively.
10.4.3.1 After VUR Treatment
Cystoscopic Treatment
Injection of material at ostium under cystoscopic guidance
US can assure patency of ostium by proving ureteric infl ow jet, may depict
impaired drainage (too large deposits), causing ureteral/pelvi-caliceal distension,
potentially associated with stenotic peristalsis of ureter.
Deposits usually seen as echogenic focus in vicinity to transmural distal ureter
– may cause twinkling (Fig. 10.32 ).
NOTE : Some transient dilatation of ureter normal, may disappear
spontaneously; only if additional new dilatation of pelvi-caliceal system noted,
obstruction needs to be considered – then may need further functional
assessment/potentially guided drainage/stenting.
Antireflux Surgery
Different surgical techniques used, ostium appearance varies depending on performed surgery:
• Commonly altered course/potentially altered insertion of ureter visualised.
• Ureter infl ow jet more diffi cult to depict.
• Initially ureteric wall thickened/swollen, some ureteral dilatation.
• Only in signifi cant obstruction higher degree of dilatation of collecting system
observed – some transient mild dilatation often seen in early postoperative phase, particularly if drains acting as foreign body placed causing reduced ureteral peristalsis.
NOTE : With full bladder there may be kinking of ureter at insertion causing (tran-
sient? intermittent?) obstruction.
Other complications:
• Rarely perivesical haematoma/urinoma – will usually resolve spontaneously
provided suffi cient bladder drainage.
• Rarely intervesical clots, commonly catheters (often placed for fi rst days).
NOTE : Search for bladder wall injury with urinoma formation, try to localise
potential drains.
Findings in reimplantation for megaureter similar as with antirefl ux surgery
– preexisting dilatation of ureter and wall thickening persist, even in good result
with good function.
362
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10 Ultrasound of the Urogenital Tract
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Fig. 10.33 Postoperative US. ( a ) Swollen ostium after reimplantation of a megaureter; patency docu-
mented by CDS exhibiting ureteric infl ow jet. ( b ) Echogenic deposit at ostium after cystoscopic treat-
ment of VUR (defl ux instillation). ( c ) JJ catheter in physiologically stilldilated renal pelvis after
pyeloplasty. ( d ) Dilated renal collecting system after surgery, with sedimented echoes in calyx, consis-
tent with postoperative intraluminal blood. ( e ) Perivesical fl uid accumulation after accidental injury to
bladder wall in cystoscopic unroofi ng of a huge ureterocele, consistent with a perivesical urinoma
10.4.3.2 Findings After Pyeloplasty
Early assessment should focus on depiction of perfusion defi cits – persisting dilatation normal, does not indicate persisting obstruction:
• Assess position of drain/tip of JJ stent, potentially urinoma/haematoma and postoperative infarctions. Furthermore haematoma/echoes in collecting system (Fig. 10.33 ).
• Asymmetrically elevated RI/slightly impaired renal perfusion physiologic in
early postoperative setting. Sometimes sectional infarction (vascular damage).
• Perfusion should normalise unless persisting obstruction/chronic damage/scarring is present.
• In early state dilatation often less due to stents or drains – when withdrawn,
some (particularly intrarenal) dilatation persists, degree of extrarenal dilatation
depends on amount of resected pelvis, does not correlate with potentially
persisting obstruction. Only gradually dilated system will eventually become
narrower over time, renal pelvis usually is immediately smaller due to partial
resection perioperatively – does not indicate absence of obstruction.
• Physiologically some transient increased echogenicity with reduced corticomedullary differentiation (reactive swelling).
• Eventually renal parenchyma normalises – except for those with scarring/persistent damage.
• Renal (parenchymal) growth best monitored using volume calculations – also try
to assess pelvi-ureteric junction, ureteric infl ow jet into bladder, potentially additional vessels and scarring.
• Additional imaging: MAG3 scintigraphy and/or MR urography, rarely focused IVU.
10.5 Re na l Transplant
NOTE : US poor in assessing/grading drainage – achieved by scintigraphy/MR
urography; some centres perform pressure tests before withdrawal of postoperative
catheter from collecting system under fl uoroscopic surveillance (pressure point for
contrast drainage into ureter should be <10 cm H 2 O).
363
10.4.3.3 After Various Interventions
A variety of interventional procedures exist – balloon dilatation, percutaneous
drainage/stenting, endoscopic unroofi ng of ureteroceles, etc.
After Biopsy , Drainage , etc. – See above.
US Findings after other interventions :
Depend on performed procedure. Used to evaluate/document dilatation of collecting system, potential echoes/structures within system, position of drainages and
stents, assessment of haemorrhage or urinoma and renal perfusion.
After Extracorporeal Lithotripsy ( ESWL )
• Assess residual concretions, amount of disintegration and potential persisting
obstruction (particularly at site of ureteropelvic/uretero-vesical junction) by
residual deposits.
• Tissue damage by shock wave (oedema, haematoma/diffuse swelling/rupture –
either of surrounding tissue and/or kidney).
• Some transient perfusion impairment (reduced peripheral vasculature on aCDS,
elevated RI due to low diastolic fl ow) – commonly resolves spontaneously.
10.5 Renal Transplant
US used for pre-, peri-, post-transplant assessment (see also ESPR/ESUR recommendations in Pediatr Radiol 2014, in press):
• Pre-transplant assessment of donor: assess potential preexisting conditions;
insure that living donor left with suffi ciently functional kidney.
• Recipient evaluation: preexisting renal disease, bladder (capacity/function), major
vessels for planning anastomosis (diameter, patency, course of arteries and veins).
• During transplantation: CDS to assess perfusion of freshly implanted kidney
(to depict early potential compromise of vascular anastomosis allowing for
immediate repair).
• After transplantation: repeated follow-up to assess for proper function/potential
complications.
10.5.1 Normal US Findings in Renal Transplant
Commonly large, in right/left iliac fossa, size/shape depend on donor organ. Corticomedullary differentiation often pronounced. CDS exhibits normal vascular architecture
– some transient aliasing at anastomosis during early postoperative period; use aCDS to
demonstrate peripheral normal (perfused) vasculature. Segmental perfusion defects may
correspond to site of biopsy/infarctions (e.g. sacrifi ced accessory/polar arteries). Spectral
trace of arterial and venous fl ow profi les as in normal healthy kidneys (Fig. 10.34 ).
364
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10 Ultrasound of the Urogenital Tract
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Fig. 10.34 Renal transplant/PTLD. ( a ) Typical appearance of the parenchyma of a renal trans-
plant, with prominent cortico-medullary differentiation; pelvis visible, also some fl uid at upper
pole. ( b ) aCDS demonstrates normal peripheral vascularity; reduced colour coding of medullae is
physiological. ( c ) CDS with spectral trace shows altered and reduced arterial peripheral fl ow and
markedly turbulent and accelerated venous fl ow due to severe renal swelling– a sensitive, but nonspecifi c sign (in this case rejection). ( d ) Perirenal fl uid collection – DDx: postoperative urinoma,
liquefi ed haematoma, lymphatic fl uid collection. ( e ) Focal complex hypoechoic liquid lesion adja-
cent to vascular anastomosis with preserved fl ow in vessels – seromatous transformation of a
perivascular postoperative haematoma (DDx: thrombosed aneurysm). ( e ) Focal hypoechoic nodule
in transplanted kidney; the child also had similar nodules in original kidney as well as a group of
enlarged mesenteric nodes, consistent with PTLD
NOTE : RI changes nonspecifi c – depend on number of partially systemic/extrare-
nal factors. Persisting singularly renal fi ndings such as elevated RI (> 80), increased/
fast venous fl ow, pathologic fl ow pattern (e.g. delayed systolic upstroke, aliasing/
turbulence), etc. Indicate transplant problems, as well as signifi cantly decreased
(peripheral) perfusion, particularly on aCDS (e.g. peripheral halo/rim sign).
10.5.2 Pathologic US Findings
Early Post - transplant Findings (Fig. 10.34 ):
• Perirenal haematoma, cyst formation – may represent lymphocele, urinoma.
• More or less dilatation of collecting system with potentially swelling/thickening of
urothelium.
• Peripheral zones of contusion or infarction (e.g. site of initial biopsy).
• Malposition of drain/catheter – fi ndings comparable to respective US appearance
in native kidney.
• aCDS: assess focal turbulent fl ow, peripheral minor perfusion, segmental perfusion defects – guide spectral analysis.
• Spectral analysis: impaired diastolic fl ow, impaired systolic infl ow, missing/
turbulent venous fl ow – signs for vascular complications.
10.6 Adrenal Glands and Pararenal Space
NOTE : US poor in differentiating between various causes of acute transplant failure
(e.g. acute tubular necrosis, acute ischaemia, renal vein thrombosis, acute rejection).
• DDx narrowed by clinical signs with detailed history of surgery, US features –
eventually may need US-guided biopsy.
Late Post - transplant Findings
Entities : Lymphocele, infection, cyclosporine toxicity, vasculopathy/stenosis/aneurysm, rejection, urinary obstruction. Most fi ndings refl ect respective sonomorphologic features in native kidney.
Rejection :
Most sensitive sign – acute enlargement of transplant organ, RI not specifi c (tend to
be elevated). In suspected rejection only renal biopsy will eventually establish or
exclude the diagnosis:
• Some centres perform protocol driven biopsies; others only perform biopsy on
clinical indication.
NOTE : Helpful to have baseline US in stable uneventful post-transplant period to
allow for comparison during phases with transplant complications. Always include
assessment of potentially remaining native kidneys (e.g. cystic disease,
tumour) + major abdominal structures (e.g. post-transplant lymphoproliferative disease – PTLD, Fig. 10.34 ) on follow-up US.
Role of US
• Major imaging tool for assessment and follow-up, also at bedside.
• May help decisions on additional imaging.
Additional Investigations
• VCUG/ce-VUS, scintigraphy, MR urography/angiography.
• Rarely CT, interventional radiology for potential percutaneous treatment.
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10.6 Adrenal Glands and Pararenal Space
10.6.1 General Remarks
Prominent in fi rst months of life (length 10–12 mm), will then shrink to approximately 50 %.
Thereafter constant growth over years – eventually ends in puberty with normal
size (length ~ 2 cm). Medulla prominent in neonate; cortex later becomes prominent.
10.6.2 Typical Normal US Finding
V- or Y-shape structure situated on upper pole of kidney (Fig. 10.35 ):
• Shape variable, particularly in ectopic position of kidney.
• Centrally echoic, less echoic peripheral cortex, surrounded by more or less echogenic perirenal fat.
NOTE : In neonates adrenal gland easy to visualise; the older and more obese a
patient, the more diffi cult to assess by US.
Volume :
Various methods with partially complicated calculations reported. Rough estimate
of size achieved by maximal sagittal length.
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Fig. 10.35 Normal adrenal gland. ( a ) Normal shape and appearance of adrenal gland in neonate.
( b ) Enlarged view nicely showing typical neonatal differentiation of adrenal medulla and cortex.
( c ) Atypical shape of neonatal adrenal gland due to missing right kidney
10 Ultrasound of the Urogenital Tract
NOTE : Differentiation of prominent adrenal gland (e.g. reactive to stress/other
physiologic conditions) from hyperplasia/enlargement in other conditions may be
impossible.
Normal variations :
Hypoplasia/aplasia; associated with severe hormonal defi cits if bilateral.
Hypertrophy/hyperplasia diffi cult to defi ne sonographically, usually in combination
with clinical symptoms/syndrome and respective hormonal fi ndings.
10.6.3 Pathologic Findings
10.6.3.1 Adrenal Gland Haemorrhage
Typically in newborns, asphyxia, after trauma/stress – but also with sepsis, systemic
conditions.
• May occur fetally. Varies in size, uni- or bilateral.
• May cause displacement of surrounding structures (e.g. thus impairing renal
blood fl ow with consequent renal vein thrombosis).
• Rupture/retroperitoneal haematoma/haematoperitoneum extremely rare.
US Findings
• Initially inhomogeneously echogenic enlargement of adrenal gland with shape of
complex cyst (Fig. 10.36 ).
• Then increasingly hypoechoic with complex liquid aspect, septations,
sedimentations.
• Shrinkage/resolution, potentially with some remnant calcifi cation (echogenic,
with dorsal shadowing):
• Usually easy to differentiate from similar entities.
CDS : haemorrhagic cyst, complex dysplastic upper moiety of duplex kidney, para-
renal/subcapsular haematoma, psoas haematoma/abscess, urinoma, cystichaemorrhagic tumour.
Role of US :
In neonates US the ideal method; in older children sectional imaging may become
necessary, as well as in equivocal situations (provided a therapeutic consequence).