Transcript Magnetic Resonance and Computed Tomography in Pediatric Urology

MAGNETIC RESONANCE AND
COMPUTED TOMOGRAPHY IN
PEDIATRIC UROLOGY
Atoosa Adibi MD.
Isfahan University Of Medical scienses
 Ultrasound (US) is the most widely used and
primary imaging modality for the urinary tract in
children.
 magnetic resonance (MR) imaging as second step,
particularly in pediatric patients.
an advanced pediatric radiology unit :
most routine uroradiologic examinations can be
performed with US and MR imaging
exception is:
 following an US, additional diagnostic
imaging for urolithiasis is needed
 in the case of severe polytrauma,including
blunt abdominal trauma.

computed tomography (CT)
MR IMAGING OF THE URINARY
TRACT
Indications:
 congenital anomalies,mainly pelvicaliectasis
and/or ureterectasis,
 renal and bladder tumors.
 Infections and vascular anomalies of the
urinary tract
 precontrast, postcontrast, and dynamic
postcontrast studies.
 The precontrast sequences are optimal for depicting
the urine-filled pelvicalyceal system and ureter and
provide exquisite morphologic detail.
 After administering intravenous (IV) contrast,
performing dynamic sequences is a better choice for
the kidneys, as it provides the information of a non
dynamic contrast study in addition to functional
information with depiction of the arterial, venous,
nephrographic, and urographic phases.
The postcontrast dynamic study can be conducted
as MR angiography (MRA).
Precontrast MR urography demonstrating bilateral UVJO.
Procedure
 Preparation:Hydration with IV fluid administration
starting a half hour before the scan
 A bladder catheter is placed.( A distended bladder
may have a negative effect on the excretion of
urine)
 The urine bag is placed below the level of the
scanner table
 Furosemide (Lasix) is administered IV at a dose of 1
mg/kg (maximum 20 mg), 10 minutes before the
procedure.
 It is best to place the patient in the prone
position if we are evaluating the contrast
excretion into the pelvicaliceal system.
 Gadolinium-DTPA (Magnevist), has higher
(1.208) specific gravity than urine (1.002–
1.030) and settles in the dependent position.
 a sagittal T2 sequence
 An axial T2 with fat saturation
 A 3D T2 with fat saturation
 The T1 fa tsaturated +post contrast
axial plane in T2 with fat saturation
The sagittal T1sequence with fat saturation
Procedural and scan
modifications
1. Ectopic ureter: the precontrast series may
suffice to depict the morphologic findings
and the postcontrast part needs to be
added only if functional evaluations of the
kidneys are requested
2. Cyst versus diverticulum: Calyceal
diverticulum fills with contrast in a retrograde
manner later than the calyces or renal pelvis.
The delay(sometimes needs to be 1 hour or
longer)
CT OF THE URINARY TRACT: URO-CT
 the main attractions for using uro-CT in
pediatrics are availability, fast speed, less
frequent/no need for sedation, and lesser
cost.
 CT may be used as a confirmatory secondary
modality, as in the case of CT for urolithiasis.
 try to find alternative modalities,completely
avoiding potential radiation exposure.
 uro-CT needs to be considered as a secondary
option if US and/or MR imaging are
inadequate, unavailable,or cannot be
performed and the clinical suspicion
warrants further imaging clarification.
 It is important to note that in blunt abdominal
trauma in children, renal lesions are more frequent.
than in adults because of a nonossified thoracic
cage, thin abdominal wall, and paucity of perirenal
fat.
 try not to overdo CT, even in the setting of
pediatric trauma
Procedure
 preceded at least by US
 A multiphase study has rarely any place in
pediatric uro-CT
 arterial phase: a bolus triggering , or a delay of 8
to 20 seconds
 Nephrographic phase: delay of 70 to 100 seconds
 the excretory phase: delay can be 5 to 15
minutes.
 Additional CT angiography and/or urography are
not routinely performed.
 For renal trauma, mostly a nephrographic phase
acquisition will suffice.
splitting the contrast bolus and injecting at 2
different time points can produce both
nephrographic and urographic phases
simultaneously on one scan
Diagnostic Utility
 In trauma cases, a meticulously conducted
abdominal US and Doppler study is adequate
to exclude major renal injury in children.
 In the follow-up of traumatic renal findings,
US is also the imaging modality of choice
uroCT and urolithiasis
Suspected stone of the urinary tract when an
US
with color Doppler does not depict a stone, but
secondary signs are present, or an US is
inconclusive/ negative, and high clinical
suspicion remains
 a well-hydrated patient is optimal.
 The patient is placed in prone position to be
able to differentiate an impacted stone at
the ureterovesical junction from that of a
mobile bladder calculus
 Assessment: ……
 Diagnostic Utility: difference in usefulness
between the 2 tests may not be clinically
significant.
CT ANGIOGRAPHY
Indications:
 Renovascular hypertension
 traumatic renovascular injury
 other less common renovascular disorders
 For optimal power injection of the contrast, a
suitable size of peripheral IV catheter is
necessary
(neonate, 24 G; infant, 22/24 G;
>1 year, 20/22 G).
The IV access is first tested with saline at
the same flow rate planned for contrast
injection.
 The scan extends from the supraceliac aorta to
the upper external iliac arteries
 Alternatively, a split-bolus technique may be
used, injecting one third to one-half of the
contrast volume beforehand and the other twothirds to one-half for an arterial phase scan. This
allows a combination of an arterial and a
urographic phase in one single acquisition.
Assessment
In renovascular hypertension, the focus is on
morphologic changes of the renal arteries
(stenoses,aneurysms, beadings) and
secondary signs
(poststenotic dilatation, collateral formation,
focal parenchymal perfusion defects,
asymmetric nephrogram, parenchymal
scarring)
a 3-year-old patient with hypertension and neurofibromatosis type I demonstrates a
short-segment high-grade stenosis
CT CYSTOGRAPHY
Active contrast filling of the urinary bladder, to
detect extraluminal contrast, which is an
indicator of rupture.
Direct CT cystography entails retrograde
filling of the bladder and indirect CT
cystography
passive antegrade filling of the bladder after
IV contrast administration.
Indications
 Bladder trauma with or without known pelvic
fracture and hematuria
 workup for suspected delayed spontaneous
rupture of augmented bladder
Procedure
For direct CT cystography before bladder catheterization:
 exclude urethral injury
An age appropriate Foley catheter is placed; the balloon is
not inflated. A precontrast scan is performed from
the diaphragm to the ischial tuberosity. A drip infusion
is prepared with diluted (10%) water-soluble
contrast (eg, 50 mL in 450 mL 0.9% NaCl solution).
The bladder is filled until the patient starts
to void or the maximal bladder capacity ([age 1, 2]
30, mL) is reached.
Wait for about 5 minutes and rescan the abdomen and
pelvis. If no contrast extravasation is visualized, it
may be necessary to perform further delayed
scan of just the pelvis

Indirect CT
cystography is performed after IV contrast administration
and antegrade filling, particularly in the
setting of polytrauma. This includes occlusion of
the Foley catheter, if present, when the patient arrives
in the CT suite and a delay of 5 to 10 minutes
after the IV contrast administration before rescanning
the abdomen and pelvis.
However,the indirect cystography is much less reliable
in the diagnosis of bladder rupture.
KEY POINTS:
 Ultrasound is the primary imaging modality for the pediatric urinary tract.

Magnetic resonance (MR) imaging needs to be the second imaging option
after ultrasound in children.

Functional MR urography (fMRU) provides comprehensive morphologic
and functional information.

Computed tomography (CT) is the imaging choice in children only in the
following circumstances:
 (1) inadequate ultrasound for urolithiasis, and (2) blunt abdominal trauma in
the setting of polytrauma.

The choice of CT over MR for uroradiologic imaging is mainly for ancillary
reasons: availability, fast speed, no sedation, and low cost.

In children, CT angiography (CTA) of the urinary tract is primarily performed
for evaluation of therenal arteries for suspected stenosis. Direct CT
cystography may be necessary for evaluation of bladder rupture.
Diagnostic examination of the child
with urolithiasis or nephrocalcinosis
Stones of all composition, with the exception of
drugs (e.g. indinavir) and matrix (protein),
have distinguishing characteristics of
echogenicity and shadowing on
ultrasonography.
Ultrasonography has the additional advantages
of wide availability, avoidance of ionizing
radiation, ready detection of hydronephrosis,
and ability to define some aspects of the
anatomy of the urinary tract.
stones as small as only 1.5–2 mm in diameter
can be visualized on ultrasonography (US),
the success of this imaging method
clearly depends on inter-observer and intraobserver variability and skills.
For the detecting and monitoring of
nephrocalcinosis,high-resolution
ultrasonography is the optimal imaging
method .Nephrocalcinosis is classified
according to the anatomic area involved.
Some pitfalls in the renal ultrasonography of
neonates, and especially preterm infants,
have to be noted:
 Tamm–Horsfall protein (THP) deposits within
the renal calyces may look like
nephrocalcinosis .
 THP deposition,however, disappears within
1–2 weeks, and follow-up will show
completely normal kidneys.
the echogenicity of the renal cortex in
neonates is physiologically increased,
hence detection of cortical
nephrocalcinosis can be difficult and may
become evident only some weeks later
when a rim of cortical calcification
becomes visible.
Normal, still hyperechoic kidney of a preterm infant
Tamm–Horsfall kidney
medullary nephrocalcinosis (NC) grade 1
medullary NC grade II
(mild increase of echogenicity at whole pyramid)
medullary NC grade III
(more severe hyperechogenicity of entire pyramid);
Diffuse corticomedullary NC
vesicoureteral reflux in
children
 Imaging studies are the basis of diagnosis and
management of VUR. The standard imaging
tests include renal and bladder
ultrasonography and voiding
cystourethrography (VCUG).
Indications for imaging studies
are as follows:
 Imaging after the first UTI is indicated in all
children younger than 5 years, children of any
age with febrile UTI, and boys of any age with
UTI
 Children with prenatally identified
hydronephrosis should be evaluated postnatally;
however, ultrasonography performed during the
first 3 days of life may have a high rate of falsenegative results because of relative dehydration
during the neonatal period
 Although the traditional approach in children
with UTI has been evaluation for VUR with
VCUG or radionuclide cystography (RNC),
some authorities now advocate that children
with a history of febrile UTI undergo a
dimercaptosuccinic acid (DMSA) renal scan,
to assess for evidence of kidney involvement,
kidney scarring, or both; if DMSA scan
findings are positive, VCUG is recommended.
 One approach is to perform RNC as the initial
screening test in girls and then to perform
standard VCUG when VUR is observed. Other
clinicians use VCUG for the initial diagnosis
and use RNC for follow-up studies.
VCUG is the criterion standard in diagnosis of VUR, providing
precise anatomic detail and allows grading of the reflux. The
International Classification System for VUR is as follows[3] :
 Grade I - Reflux into nondilated ureter
 Grade II - Reflux into renal pelvis and calyces without dilation
 Grade III - Reflux with mild to moderate dilation and minimal
blunting of fornices
 Grade IV - Reflux with moderate ureteral tortuosity and dilation
of pelvis and calyces
 Grade V - Reflux with gross dilation of ureter, pelvis, and
calyces, loss of papillary impressions, and ureteral tortuosity
 In general, VCUG should be performed after
the child has fully recovered from the UTI.
However, some children demonstrate reflux
only during an episode of cystitis.
Radionuclide cystography
 Instillation of technetium-99m pertechnetate into the
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bladder and observation with a gamma camera is a highly
sensitive test for VUR
Advantages include substantially lower radiation doses
than with VCUG and the potential for increased sensitivity
because of the ability to conduct prolonged periods of
observation
Disadvantages primarily consist of the poor anatomic
detail, especially of the male urethra
Grade I reflux is poorly detected by this study, because the
distal ureters are commonly obscured by the bladder
Grading by nuclear cystography is limited to mild,
moderate, and severe grades.
 Pediatric Ureteropelvic Junction
Obstruction Workup
 Ultrasonography
 After the prenatal presumptive diagnosis UPJ obstruction
or other conditions causing hydronephrosis is made, the
neonate should undergo ultrasonographic evaluation, but
the timing is controversial. Transient neonatal dehydration
occurs 48-36 hours after birth, so follow-up
ultrasonography of mild-to-moderate cases of
hydronephrosis should be performed after this period. In
severe cases, such as very large renal pelvis, bilateral
hydronephrosis, solitary kidney, or oligohydramnios,
immediate evaluation within 48 hours must be performed;
severe hydronephrosis in spite of the oliguric status of the
child can suggest the need
 Postnatal evaluation consists of a urinary
tract study to determine whether the calyceal
pelvic dilation with or without renal cortical
thinning is present. The most widely used
grading system of the severity of
hydronephrosis on ultrasonography after
birth is SFU system, rather than the
anteroposterior diameter of the renal pelvis.
 The SFU grading system for hydronephrosis is as follows[19]
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:
Grade 0 - No hydronephrosis, intact central renal complex
seen on ultrasonography
Grade 1 - Only renal pelvis visualized, dilated pelvis on
ultrasonography, no caliectasis
Grade 2 - Moderately dilated renal pelvis and a few calyces
Grade 3 - Hydronephrosis with nearly all calyces seen, large
renal pelvis without parenchymal thinning
Grade 4 - Severe dilatation of renal pelvis and calyces with
accompanying parenchymal atrophy or thinning
Voiding cystourethrogram (VCUG)
 Vesicoureteral reflux (VUR) has been found in as
many as 40% of affected children. The degree of
reflux is often low grade, not contributing to
upper urinary tract obstruction, and it is likely to
spontaneously resolve. However, UPJ
obstruction may also be seen with severe VUR
when the tortuous dilated ureter develops a kink
in the UPJ area, which is relatively fixed to
surrounding structures, and may cause
secondary obstruction.
Diuretic renography
 Diuretic renography is the most widely used
noninvasive technique to determine the
severity and functional significance of UPJ
obstruction. Various protocols and techniques
have been developed, resulting in significant
variability in the interpretive criteria and
results.
Doppler ultrasonography
[
 The development of Doppler ultrasonography has
become another useful diagnostic modality in the
assessment of kidneys with ureteropelvic junction
(UPJ) obstructions. With duplex Doppler
ultrasonography, intrarenal vasculature can be
assessed to determine the resistive index. Normal
kidneys reliably demonstrate resistive indices less
than 0.7, and obstructed kidneys show higher values.
Administration of diuretics can aggravate the
preexisting obstruction, thereby aiding the diagnosis
by Doppler ultrasonography. It is especially reliable
in the preoperative diagnosis of aberrant-accessory
blood vessels associated with UPJ obstruction.
Intravenous pyelography (IVP)
 IVP has been used to evaluate UPJ obstruction,
but IVP may not provide adequate information
to determine the true obstruction, and it is
especially difficult to interpret in children. IVP
provides information about the obstruction and
contralateral side and especially facilitates
operative planning; however, infant urograms
are compromised by the immature renal
function, which impedes adequate visualization
of the collecting system. Bowel gas and
underlying bony structures also make
interpretation of the urogram difficult.