Magnetic Resonance and Computed Tomography in Pediatric Urology

2. Atoosa Adibi MD. Isfahan University Of Medical scienses Magnetic Resonance andComputed Tomography inPediatric Urology

3. 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

4. exception is: • following an US, additional diagnostic imaging for urolithiasisis needed • in the case of severe polytrauma,includingblunt abdominal trauma. • computed tomography (CT)

5. MR IMAGING OF THE URINARY TRACT

6. Indications: • congenital anomalies,mainlypelvicaliectasis and/or ureterectasis, • renal and bladder tumors. • Infections and vascular anomalies of the urinary tract

7. 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).

8. Precontrast MR urography demonstrating bilateral UVJO.

9. 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.

10. 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.

11. a sagittal T2 sequence • An axial T2 with fat saturation • A 3D T2 with fat saturation • The T1 fatsaturated +post contrast

12. axial plane in T2 with fat saturation The sagittalT1sequence with fat saturation

15. 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

16. 2. Cyst versus diverticulum: Calycealdiverticulumfills with contrast in a retrograde manner later than the calyces or renal pelvis. The delay(sometimes needs to be 1 hour or longer)

19. CT OF THE URINARY TRACT: URO-CT

20. 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.

21. try to find alternative modalities,completelyavoiding potential radiation exposure. • uro-CT needs to be considered as a secondary option if US and/or MR imaging are inadequate, unavailable,orcannot be performed and the clinical suspicion warrants further imaging clarification.

23. 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

24. Procedure • preceded at least by US • A multiphase study has rarely any place in pediatric uro-CT

25. 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.

26. splitting the contrast bolus and injecting at 2 different time points can produce both nephrographic and urographic phases simultaneously on one scan

27. 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

28. 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

29. 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

32. Assessment: …… • Diagnostic Utility: difference in usefulness between the 2 tests may not be clinically significant.

33. CT ANGIOGRAPHY • Indications: • Renovascularhypertension • traumatic renovascular injury • other less common renovascular disorders

34. 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.

35. The scan extends from the supraceliacaorta 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 two-thirds to one-half for an arterial phase scan. This allows a combination of an arterial and a urographic phase in one single acquisition.

36. 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)

37. a 3-year-old patient with hypertension and neurofibromatosis type I demonstrates a short-segment high-grade stenosis

38. 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.

40. Indications • Bladder trauma with or without known pelvic fracture and hematuria • workup for suspected delayed spontaneous rupture of augmented bladder

41. 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 ischialtuberosity. 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

42. 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.

44. 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 therenalarteries for suspected stenosis. Direct CT cystography may be necessary for evaluation of bladder rupture.

46. Diagnostic examination of the child with urolithiasis or nephrocalcinosis

47. 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.

48. 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 intra-observer variability and skills.

49. For the detecting and monitoring of nephrocalcinosis,high-resolution ultrasonography is the optimal imaging method .Nephrocalcinosis is classified according to the anatomic area involved.

50. 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.