Renal & Urinary Tract Imaging in Obstructive Uropathy Dr Omolola Mojisola Atalabi FWACS,FMCR, MBA (Ib) Senior Lecturer Consultant Radiologist College of Medicine/ University College Hospital Ibadan, Nigeria

Declaration No conflict of interest Nothing to declare

Objective To refresh the common causes of renal obstructive uropathy in children To know the common imaging modalities including modalities like MAG-3, DMSA & DTPA scan Indications for each modality Advantages and disadvantages of each modality To understand the rationale behind the usage of the different imaging modalities

Introduction Obstructive uropathy (OU) is a structural or functional hindrance of normal urine flow. It can cause renal impairment in all age groups. urinary tract obstruction can lead to permanent damage to the urinary tract. Infravesical obstruction can lead to changes in the bladder, such as trabeculation, cellule formation, diverticula, bladder wall thickening, and, ultimately, detrusor muscle decompensation. Progressive back pressure on the ureters and kidneys can occur and can cause hydroureter and hydronephrosis. The ureter can then become dilated and tortuous, with the inability to adequately propel urine forward.

Introduction II Hydronephrosis can cause permanent nephron damage and renal failure. Urinary stasis along any portion of the urinary tract increases the risk of stone formation and infection, and, ultimately, upper urinary tract injury. Urinary tract obstruction can cause long-lasting effects to the physiology of the kidney, including its ability to concentrate urine. The causes in children may be congenital or acquired.

Congenital Causes Pelvi-ureteric junction obstructions (PUJ) Posterior urethral valves (PUV), Urethral atresia, Phimosis Meatal stenosis. Associated anomalies include imperforate anus vertebral malformations. N Eke, SN Elenwo. Obstructive uropathy in children: A review Port Harcourt Medical Journal Vol. 1 (3) 2007: pp. 137-144

Acquired causes Calculi, Post-traumatic and Post-inflammatory strictures and Meatal stenosis.

Causes of urinary tract obstruction Site of obstruction /Possible causes Within the lumen Blood clot. Calculi. Sloughed papillae. Tumour of renal pelvis or ureter.

Causes of urinary tract obstruction cont... Within the wall Ureteric, urethral or ureterovesical stricture. Congenital megaureter. Bladder neck obstruction Congenital urethral valves. Pinhole meatus. Neurogenic bladder Functional failure due to denervation (e.g. following spinal trauma, multiple sclerosis.

Consideration Imaging should be tailored to confirm clinical impressions and should either guide in the initial management of urologic conditions or help to modify the therapeutic plan. Use imaging modalities that are devoid of ionising radiation where possible. When the use of ionising radiation is unavoidable, the ‘ALARA’ principle must be obeyed

Imaging Modalities Plain X ray Ultrasonography ( Prenatal and postnatal) Intravenous pyelography or urography Retrograde urethrography Micturating cysto urethrography (MCU) Computerized tomography scan Radionucleotide studies Retrograde pyelography Nephrostography Magnetic resonance imaging

USS Attributes USS of the kidneys and bladder is a useful imaging modality as an initial study. It is a noninvasive, inexpensive study that does not involve radiation exposure or depend on renal function. It is the initial study of choice in pregnant women. USS is a very useful source of imaging in patients with intravenous pyelography (IVP) dye allergies or elevated creatinine levels, In children, this is often part of the initial workup for obstructive processes. It is sensitive in revealing renal parenchymal masses, hydronephrosis, a distended bladder, and renal calculi. The accuracy of this imaging modality depends heavily on the experience of the sonologist / sonographer.

USS Dilatation of the upper urinary tract is often detected using prenatal ultrasonography performed at or after 20 weeks' gestation (approximately 1% of pregnancies). Such findings may require sequential ultrasonography of the fetus. Depending on the degree of dilation, bilaterality, and presence of other anomalies, prenatal consultation by a pediatric urologist may be indicated. Follow-up renal and bladder ultrasonography should be performed after the first day of life if anomalies are detected prenatally. Newborns have a physiologic oliguria on the first day of life that can lead to false-negative ultrasonography findings. If the findings are normal at this point, ultrasonography should be repeated 4-6 weeks later.

Intravenous Urography IVP involves the injection of contrast into the venous system and a series of KUB radiographs over time. It can be performed in patients with a normal creatinine value (< 1.5 mg/dL) for visualization of the urinary tract. It provides both anatomical and functional information. Delayed calyceal filling, delayed contrast excretion, prolonged nephrography results, and dilatation of the urinary tract proximal to the point of obstruction characterize obstruction. IVU is superior to CT scan in revealing small urothelial upper tract lesions. If IVU is inadequate, retrograde pyelography can be performed to completely visualize the renal pelvis or ureter. Contraindication: Known contrast allergy

Micystourethrogram (MCUG)/ Voiding cystourethrogram (VCUG) A MCUG or VCUG, is a fluoroscopic technique for watching a person's urethra and urinary bladder while the person voids. The technique consists of catheterizing the person in order to fill the bladder with a radiocontrast agent, Under fluoroscopy the radiologist watches the contrast enter the bladder and looks at the anatomy of the patient If the contrast moves into the ureters and back into the kidneys, the radiologist makes the diagnosis of vesicoureteral reflux, and gives the degree of severity a score.

Retrograde Urethrography/ Cystography : Radiographic contrast is injected into the urethral meatus via Foley catheter at the distal urethra. Ideally Fluoroscopy is used to visualize the entire urethra for stricture or any abnormalities.

Cystoscopy with retrograde pyelography Retrograde pyelography is performed in the operating room with a cystoscope in the bladder. Radiographic dye is injected into each ureteral orifice. Then, with the use of fluoroscopy, any ureteral or renal pelvis filling defects or abnormalities can be visualized. The contrast load does not interfere with renal function and can be used in patients with elevated creatinine levels. It can also be used in patients with an IVP dye allergy because the contrast remains extravascular.

Nuclear Renogram Radioisotope renography is a form of kidney imaging involving radioisotopes that allows a nuclear medicine physician or radiologist to visualize the kidneys and learn more about how they are functioning. After injection into the venous system, the compound is excreted by the kidneys and its progress through the renal system can be tracked with a gamma camera. If the kidney is getting blood, but there is an obstruction lower down, the contrast will not pass beyond the level of the obstruction, whereas if there is a partial obstruction then there is a delayed transit time for the radioisotope to pass. If the kidney is not getting blood for example, it will not be viewed at all, even if it looks structurally normal on medical ultrasonography or magnetic resonance imaging.

Nuclear Renogram A renal scan can be performed to determine the differential function of the kidneys, as well as to demonstrate the concentrating ability, excretion, and drainage of the urinary tract. Lasix can be administered with the renal scan to verify delayed excretion and the presence of obstruction. More information can be gathered by calculating time activity curves; with normal kidney perfusion, peak activity should be observed after 3–5 minutes. The relative quantitative information gives the differential function between each kidney's filtration activity.

Nuclear Renogram NR is the best imaging study to differentiate a multi-cystic kidney from hydronephrotic kidney. A CAT scan would require sedation, it exposes the child to more radiation and it is more expensive. Notice that, unlike x-rays, nuclear renogram images show the right kidney on the viewer's right. Multi-cystic kidneys do not function.

CT A CT scan is very useful in providing anatomic details It provides information regarding the urinary tract, as well as any possible retroperitoneal or pelvic pathologic condition that can affect the urinary tract via direct extension or external compression. A noncontrast CT scan should be obtained to assess for calculi. If calculi are found, flat-plate radiography of the abdomen (KUB) should be obtained to help determine calcium content and stone shape and to assist in monitoring the progress of the stone. Its progress can be observed with periodic simple radiography. A contrasted CT scan is needed to provide information on renal pathology. If delayed contrast images are obtained, CT urography with 3-dimensional reconstruction can provide excellent visualization of the entire upper urinary tracts.

Magnetic resonance imaging MRI is not a first-line test used to evaluate the urinary tract. In patients who cannot tolerate a CT scan with contrast, an MRI with gadolinium can be performed to reveal any enhancing renal lesions. MRI is useful in delineating specific tissue planes for surgical planning, as well as in evaluating the presence or extent of a renal vein or inferior vena cava thrombus in cases of renal tumors. MRI does not reveal urinary stones well so is not often used.

Cystoscopy Cystoscopy is the placement of a small camera called a cystoscope through the urethral meatus and passing through the urethra into the bladder. Any abnormalities in the urethra, prostatic urethra, bladder neck, and bladder can be visualized. This can be performed in the office or in the operating room.

Obstructive Uropathy In children, obstruction may be more commonly due to UPJ or UVJ obstruction, ectopic ureter, ureterocele, megaureter, or posterior urethral valves. Prenatal screening with ultrasonography is important in early identification of obstruction. In addition, children with incontinence or urinary tract infection need a workup because they may also have some type of urinary tract obstruction.

Share History with the managing team The clinical presentation of urinary tract obstruction varies with the location, duration, and degree of obstruction. Thus, a thorough history and physical examination are key in the patient evaluation. Share the clinical findings!!!!

Prenatal diagnosis

Prenatal diagnosis

Prenatal diagnosis

Distended urinary bladder prenatal USS

Prenatal diagnosis

Ureteropelvic junction (UPJ) obstruction Ureteropelvic junction (UPJ) obstruction is defined as an obstruction of the flow of urine from the renal pelvis to the proximal ureter UPJO is one of the most common birth defects of the ureteroccurring in 1 per 1000-2000 newborn and far the most common cause of pediatric hydronephrosiss.  It is more common in males and affects the left kidney more than the right.  A blockage in both kidneys occurs in about 10-15% of the cases. Widespread use of antenatal ultrasonography and the advent of modern imaging techniques have resulted in earlier and more common diagnosis of hydronephrosis

UPJO

Normal

USS UPJO

Grade 4 hydronephrosis

Grade 3 Hydronephrosis

Grade 4 hydronephrosis

USS Renal calculus

Urolithiasis & Ureteric calculus Note echogenic area with shadowing

IVU

IVU

Digital Subtraction IVU

Medullary Calcification

IVU. Bladder view

KUB renal stone

Plain Xray staghorn calculi

Renal Calculus

CT can detect evolving calculus

Complication

None Functioning Kidney

VUR Urinary tract infections in children are sometimes associated with vesicoureteral reflux, which can lead to renal scarring if it remains unrecognized. Since the risk of renal scarring is greatest in infants, any child who presents with a urinary tract infection prior to toilet training should be evaluated for the presence of reflux

Primary VUR Insufficient submucosal length of the ureter relative to its diameter causes inadequacy of the valvular mechanism. This is precipitated by a congenital defect/lack of longitudinal muscle of the intravesical ureter resulting in an ureterovesicular junction (UVJ) anomaly

Secondary VUR In this category the valvular mechanism is intact and healthy to start with but becomes overwhelmed by raised vesicular pressures associated with obstruction, which distorts the ureterovesical junction. The obstructions may be anatomical or functional. Secondary VUR can be further divided into anatomical and functional groups as follows: Anatomical: Posterior urethral valves; urethral or meatal stenosis. Functional: Bladder instability, neurogenic bladder and non-neurogenic neurogenic bladder Urinary tract infections may cause reflux due to the elevated pressures associated with inflammation.

Grading of reflux Grade I – reflux into non-dilated ureter Grade II – reflux into the renal pelvis and calyces without dilatation Grade III – mild/moderate dilatation of the ureter, renal pelvis and calyces with minimal blunting of the fornices Grade IV – dilation of the renal pelvis and calyces with moderate ureteral tortuosity Grade V – gross dilatation of the ureter, pelvis and calyces; ureteral tortuosity; loss of papillary impressions

VUR The younger the age of the patient and the lower the grade at presentation the higher the chance of spontaneous resolution. Most (approx. 85%) of grade I & II cases of VUR will resolve spontaneously. Approximately 50% of grade III cases and a lower percentage of higher grades will also resolve spontaneously

Vescico ureteric reflux

Urinary Bladder & Ureters

VUJ Calculus

VUR

Grade 2 VUR

Cystourethrography showing normal bladder and ureter

PUV

PUV: Bladder Diverticula

PUV

Oblique voiding cystourethrogram  Urachal remnant, posterior urethral valves, and reflux. A large urachal remnant extending from the superior aspect of the small-capacity bladder. Reflux, which is reported in about one-third of children with posterior urethral valves, is also present in this case. Although the valve is clearly seen (arrow), the secondary changes are not well developed due to aberrant micturition into the urachal remnant and ureter.

Trabeculations

Urethrogram

Radio Isotope Tracers 99mTc-dimercaptosuccinicacid (99mTc-DMSA) amout of functioning cortical mass 99mTc-di-ethylene-tri-amine-pentacetate (99mTc-DTPA)- Cross kidney funtion 99mTc-mercaptoacetyltriglycine (99mTc-MAG3)( Tubular status) MAG3, 99mTc-DTPA and 99mTc-DMSA renal scintigraphy is currently considered as a robust, accurate and reproducible parameter, provided that it is calculated at a time when no escape of the tracer from the kidney has occurred (Piepsz et al., 1999; Bland and Altman, 1999)

99mTcdimercaptosuccinicacid (99mTc-DMSA) 99mTc-DMSA) is an agent that is actively taken up by the proximal and distal renal tubular cells, directly from the peritubular vessels It accumulates in the renal cortex (Miyazaki et al., 2010). This modality is primarily used for imaging functioning cortical mass and individual renal function (Ritchie et al.,2008). It is the most reliable method for assessing chronic cortical scarring.

99mTc-diethylenetriaminepentacetate (99mTc- DTPA) 99mTc-DTPA) is an agent that is freely filterable at the glomerulus, but it is neither secreted nor resorbed by the kidney tubules. This method is used to measure total and individual kidney functions. By using the gamma camera technique, glomerular filtration rate (GFR) is calculated for each kidney (Itoh, 2001)

99mTc-mercaptoacetyltriglycine (99mTc-MAG3) is a renal plasma flow agent almost exclusively excreted by secretion in the proximal tubules and not reabsorbed by the renal tubules It is good for evaluation of renal tubular function It simplifies and improves the quantification of renal clearance in children by virtue of its permanent availability, good imaging properties and low radiation exposure Tc-99m MAG3 dynamic scintigraphy is a rapid and practical method for imaging renal parenchyma in children with urinary system infections because it takes only five minutes hence does not require sedation in children.

MAG3 cont. detect and evaluate hyrdronephrosis determine relative (differential) renal function in the right and left kidneys detect and evaluate obstruction in the renal collecting system detect acute tubular necrosis evaluate renal function in children allergic to radiographic contrast evaluate renal perfusion and function in certain cases of renal immaturity evaluate renal trauma Confirm non functioning kidney

( MAG3） than with Tc-99m DMSA Yaylali OT et al Performance of technetium-99m mercaptoacetyltriglycine scintigraphy in evaluation of renal parenchymal lesions：A comparative study with technetium-99m dimercaptosuccinic acid Journal of Chinese Clinical Medicine;2009,9;Vol.4,No.9 The radiation exposure rate is significantly lower with Tc-99m Mercaptoacetyltriglycine ( MAG3） than with Tc-99m DMSA MAG3 in addition to its use in evaluating renal perfusion and function it is helpful in assessing cortical lesions.

BUT….. Its performance in determining renal parenchymal lesions is lower than that of Tc-99m DMSA. but its performance is poorer than Tc-99m DMSA i.e It is useful for the evaluation of split renal function -SRF and renal parenchymal lesions, but its performance is poorer than Tc-99m DMSA Therefore,Tc-99m MAG3 scintigraphy can be performed as a complementary method to Tc-99m DMSA scintigraphy , but it is not a preferable replacement for Tc-99m DMSA scintigraphy for the initial diagnosis and follow-up study of renal parenchymal lesions.

99mTc-MAG3 clearance values from the age of 1 year up to the age of 17 years (mean value <2 years: 98+/-57 ml/min; mean value >8 years: 208+/-66 ml/min). Normal clearance values for adults were achieved by the age of 8 years. Meyer G et al. Technetium-99m ercaptoacetyltriglycine clearance values in children with minimal renal disease: can a normal range be determined? Eur J Nucl Med. 1998 Jul;25(7):760-5

Examples of the renal scarring scoring system Examples of the renal scarring scoring system. (a) Normal left kidney, grade 1 scarring at the lower pole of the right kidney. (b) Grade 2 scarring in the right kidney, grade 3 in the left. (c) Grade 4 scarring in the left kidney.

Tumours

Complications of OU Recurrent infections Renal Damage Non Functioning kidney

Investigation USS Contrast studies Nuclide studies

Prenatal Hydronephrosis

Objective To refresh the common causes of obstructive uropathy in children To know the common imaging modalities including newer modalities like MAG-3, DMSA & DTPA scan Indications for each modality Advantages and disadvantages of each modality To understand the rationale behind the usage of the different imaging modalities

Attention!!!!! Atoto arere!!!!!! Important Notice!!!!! Always give good clinical information by filling the request card adequately. All the requested information on the card are very important and MUST be provided! Consult the Radiologist – Imaging is their specialty Go to www.imagegently.com and read about the image gently campaign and join us in our determination to reduce radiation dose to our children – our future.

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