Imaging in Paediatric Urology

Pediatric Imaging

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Although secondary reflux can be described, it is not necessarily graded, since the prognosis for spontaneous resolution by grade is different from that for primary reflux. By this time, the glomerular filtration rate GFR will have increased sufficiently for the renal scan to be more accurate. However, patients with a solitary kidney or bilateral hydronephrosis have no normal kidney to compare with the dilated kidney. In these patients, radionuclide renal scanning before the first month of life may be necessary to assess whether relief of an obstructive process is indicated.

Diuretic furosemide renal scanning with MAG-3 is used to measure relative renal function and to assess the degree of obstruction by measuring the length of time the radionuclide takes to wash out of the renal pelvis. A greater emphasis is placed on the relative function of the hydronephrotic kidney than on the washout time. The obstructive washout time, typically defined as longer than 20 minutes, may be an indication for intervention. In this case, the timing of the next renal scan depends on the severity of the hydronephrosis. A patient with unilateral severe hydronephrosis and near-symmetric function on renal scanning should undergo repeat renal scanning within 3 months of the initial evaluation.

If follow-up renal scanning continues to reveal symmetric function between the normal kidney and the hydronephrotic one, the interval between follow-up studies may be increased to 6 months. Alternating between RBUS and renal scanning during follow-up can also be useful.

Three normal anatomic variants extrarenal pelvis, wide infundibula, compound calyces appear as a dilated renal collecting system on ultrasonography and thus mimic obstructive uropathy. If symmetrical function is observed and the renal pelvis is full with a rapid washout, these variants should be suspected. Monitoring with ultrasonography may be sufficient. Magnetic resonance urography MRU is becoming more widely used for the evaluation of UPJ obstruction because it provides both anatomic and functional information with a single examination.

The need for general anesthesia in young children and the cost of MRU have limited its use to date. In UPJ obstruction, MRU can accurately define the site of ureteral narrowing and assess for a possible crossing vessel. Congenital megaureter is another antenatally detected abnormality. Hydroureteronephrosis is observed to the level of the bladder on initial US. If the megaureter is associated with a kidney whose function is nearly equal to that of the contralateral kidney and if the diameter of the dilated ureter is 1 cm or less, the process is likely to be benign and rarely necessitates surgery.

As with the UPJ, relative renal function should be weighed more than an obstructive drainage curve or washout time. With careful observation, the dilatation slowly resolves, and the renal function is usually preserved.

The indications for radiographic evaluation of UTIs are rapidly changing. These recommendations were based on the Birmingham Reflux Trial, which showed that renal scarring in children older than 5 years is unusual. The RIVUR trial assessed daily antibiotic prophylaxis against placebo in patients with VUR to determine the efficacy of the current standard of care ie, daily prophylaxis.

These changes were reflected in subsequent guidelines for the management of UTI. Significant controversy surrounded this recommendation, and many pediatric urologists disagreed with the AAP guidelines. Because RBUS is noninvasive, it is a useful initial test. US reveals any upper-tract abnormalities hydronephrosis, dilated ureter, ureterocele that would predispose to bacterial colonization.

In most cases, it does not affect management of the acute infection. Repeat imaging with RBUS is necessary in patients with known obstructive urologic abnormalities who develop a febrile UTI to ensure that no new process eg, an obstructing stone has developed. Knowing when to discontinue antibiotic therapy is sometimes useful in patients who have required long-term treatment for pyelonephritis. In such cases, gallium scanning reveals when inflammation has resolved. For patients who have a single UTI in the neonatal period, normal findings on RBUS, and no evidence of reflux on VCUG, some clinicians have recommended prophylaxis for 6 months while the immune system gains competence and the kidneys grow.

If the decision is made to proceed with VCUG, it can be safely performed in patients with acute pyelonephritis when they are afebrile and clinically improved, near the end of their hospital stay. One practical consideration that decreases the utilization of DMSA scanning is the need for significant sedation or general anesthesia in young children in order to obtain adequate images; another is the radiation exposure involved. Areas of diminished perfusion on a DMSA scan during an acute infection do not necessarily correspond to areas that will develop a pyelonephritic scar later.

DMSA scanning can be very useful in patients with a possible infection above the bladder level who have chronic bacteriuria eg, a patient with continent reconstruction who relies on clean intermittent catheterization for reservoir emptying. MRU can demonstrate pyelonephritis and may be more successful than DMSA in distinguishing acute pyelonephritis from scarring. These patients may have abnormal renal development or renal dysplasia, which should not be confused with postpyelonephritic renal scarring. Reflux in patients with high-grade reflux and associated renal abnormalities is unlikely to resolve by age 16 months.

For primary nocturnal enuresis without a history of infection, imaging is not required.

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Daytime wetting may necessitate US to look for upper-tract and bladder changes due to dysfunctional voiding. In older boys who present with new daytime wetting and who do not improve with the usual behavioral modifications for dysfunctional voiding, VCUG should be considered to look for a late presentation of PUV. Constant dribbling in a female who appears to void normally suggests ureteral ectopy, with an opening below the urinary sphincter to the urethra, perineum, or vagina.

All can facilitate the planning of surgery by delineating the anatomy of the ectopic ureter, but MRU is especially helpful in defining the pelvic course of the ectopic ureter, and it does not expose the child to radiation. Doppler US of the kidney is performed to determine whether the mass is solid or cystic and reveals whether the tumor has invaded the inferior vena cava IVC.

Although the differential diagnoses of urologic causes of an abdominal mass are beyond the scope of this article, all lesions can be approached by determining whether they are solid or cystic and by determining the organ from which they arose. Cystic lesions may be due to hydronephrosis, multicystic dysplastic kidney, or cystic renal disease. Simple renal cysts that are detected incidentally on US can be monitored for 1 year to ensure that the cysts are not enlarging and that no new cysts are appearing, suggestive of autosomal dominant polycystic kidney disease.

If US reveals no changes, it need not be repeated unless the patient has pain or infection. Cysts are classified according to the Bosniak criteria, which take into account enhancement of cyst walls, septations, calcifications within cysts, solid components, and thickness of the cyst wall. Renal tumors that can be cystic include necrotic Wilms tumor, multilocular cystic nephroma, and renal cell carcinoma RCC. Solid masses are more ominous and may represent Wilms tumor , neuroblastoma , RCC, congenital mesoblastic nephroma, or other less common tumors eg, malignant rhabdoid tumors.

Wilms tumor arises from the kidney and is most often detected as a large asymptomatic abdominal mass. Neuroblastoma, which commonly arises from the adrenal gland, often manifests as a mass and constitutional symptoms eg, fever or weight loss. Wilms tumor commonly displaces and compresses vessels. Neuroblastoma also displaces and compresses vessels but is more often infiltrative and encapsulating. Unilateral Wilms tumors are managed with surgery followed by chemotherapy, whereas bilateral tumors are managed with chemotherapy followed by nephron-sparing surgery to each kidney.

Congenital mesoblastic nephroma, a rare nonencapsulated benign tumor, is the most common solid renal lesion in neonates. RCC is unusual in young children and is more common in adolescents. It can occur in young patients with tuberous sclerosis and von Hippel-Lindau syndromes.

Angiomyolipomas are common in patients with tuberous sclerosis and should be embolized when they approach 4 cm in size because spontaneous bleeding and pain are likely. Other conditions that predispose children to the development of renal tumors nephroblastomatosis, Wilms include Beckwith-Wiedemann syndrome, hemihypertrophy, sporadic aniridia, Denys-Drash syndrome, and trisomy In these children, US is performed at regular intervals approximately every 4 months until age 7 years.

A thorough history and physical examination are necessary to differentiate renal or ureteral pain from musculoskeletal pain. Pain that is altered by positional change is likely to originate in the muscles of the torso or the flank.

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In patients with flank pain, fever, and pyuria, pyelonephritis can be diagnosed and treated without immediate imaging. Failure to respond to therapy within the usual 48 hours should prompt renal US to look for infection associated with significant obstructive uropathy, which may necessitate placement of a percutaneous nephrostomy. Renal and ureteral calculi are best imaged with noncontrast spiral CT.

If intermittent UPJ obstruction is considered but imaging findings do not support the diagnosis, the patients should be sent home with instructions to return immediately for imaging US or IVU when they are symptomatic. Once symptomatic UPJ obstruction is diagnosed, surgery is indicated. Postoperative renal scanning or IVU should reveal good drainage from the repaired kidney.

The pattern of hematuria can suggest its source. Initial hematuria or terminal hematuria is usually associated with urethral pathology. Total hematuria is usually due to renal or bladder pathology. Hematuria associated with blunt injury is best evaluated with CT of the abdomen and pelvis. If blood at the meatus is observed in a male with a history of pelvic trauma, perform retrograde urethrography RUG before placement of a urethral catheter.

Hematuria, gross or microscopic, and colicky pain suggestive of obstructive ureteral calculi can be initially evaluated with RBUS and an abdominal plain film. If the symptoms are severe or progressive and the imaging is inconclusive, noncontrast spiral CT of the abdomen and pelvis is the definitive test for renal or ureteral calculi.

In children, initially evaluate painless gross hematuria with US to exclude a renal anomaly or mass, as well as the possibility of bladder tumor eg, rhabdomyosarcoma or, more rarely, transitional cell carcinoma. Transitional cell carcinoma is rare in children and is almost always low-grade. Cystitis may produce bullous lesions and may mimic a bladder tumor, as is the case with nephrogenic adenoma, a benign inflammatory lesion. In an adolescent male with painless terminal hematuria, normal RBUS findings favor the diagnosis of urethrorrhagia or benign urethritis, a benign condition due to self-limited nonbacterial urethral inflammation.

Not all patients with asymptomatic microhematuria require RBUS. First, confirm the diagnosis of microhematuria on the basis of the presence of red blood cells RBCs on microscopic examination of a freshly voided urine sample. If hypertension is present and if proteinuria and casts are found on microscopic examination of the urine, the patient has glomerulonephritis, and US may not be required; otherwise, US is usually necessary. If the mechanism of injury is significant, perform contrast CT of the abdomen and pelvis. Delayed CT images are useful to look for urinary extravasation.

Microhematuria is commonly associated with hypercalciuria in children. Some authors recommend a spot calcium-to-creatinine ratio to screen for hypercalciuria in children with microhematuria. The long-term significance of hypercalciuria and microhematuria in children is unclear, but patients with these conditions may be at increased risk for future nephrolithiasis.

Adrenal hemorrhage presents as a flank mass or appears as a complex cystic collection on US. Over time, the hemorrhage shrinks, but it may persist as a small speckled calcification.

Neuroblastoma can also have calcification and is occasionally cystic. Unlike an adrenal hemorrhage, however, neuroblastoma does not usually regress over 6 weeks. If neuroblastoma is suspected, perform the appropriate urine studies homovanillic acid [HVA] and vanillylmandelic acid [VMA]. Retrograde genitography and VCUG are helpful in outlining the level of confluence of the urethra, vagina, and colon when surgery is being planned. Baseline renal US is also necessary because renal agenesis, reflux, and megaureter are common associated findings.

MRI of the pelvis is an important ancillary study in complex cloacal cases. Multicystic dysplastic kidneys can be confused with dilated hydronephrotic kidneys. On US, multicystic kidneys generally tend not to have a reniform shape, show no connection between cysts, and do not show a dilated ureter. Renal scanning reveals that the multicystic kidney has no function.

Background

If renal US reveals classic findings of a multicystic dysplastic kidney and a contralateral hypertrophied kidney, a renal scan is not necessary for diagnosis. Simple renal cysts are rare in children. The differential diagnosis includes calyceal diverticulum, an early manifestation of autosomal dominant polycystic disease ADPKD. Autosomal recessive polycystic kidney disease ARPKD tends to present in children in a bimodal distribution, either a in infancy with enlarged kidneys, coexistent liver and biliary disease, and renal tubular ectasia or b during adolescence with enlarged kidneys, hepatic fibrosis, and portal hypertension.

Many syndromes are associated with cystic kidney disease, such as tuberous sclerosis, Meckel-Gruber, and von Hippel-Lindau. Autosomal-dominant polycystic kidneys are typically associated with multiple cysts of different sizes in older children and are rarely seen in infancy. It can also be asymmetric in its presentation. Differentiation is aided by careful US of the liver and a thorough family history. The overall renal length may be greater on US, and multiple abnormalities may be seen in the upper and lower poles. IVU reveals a drooping lily sign. VCUG may reveal lower-pole reflux, and the upper-pole system may be normal, dilated, cystic, or dysplastic.

If the upper pole is nonfunctional on IVU, too few calyces only those of the lower pole are observed, and the normally long upper-pole infundibulum is absent. The lower portion of a duplicated kidney usually accounts for two thirds of the function of a given kidney. Baseline renal US is usually performed, though upper urinary tract abnormalities are rare in patients with classic bladder exstrophy. Renal abnormalities are much more common in patients with cloacal exstrophy.

VUR is present in nearly all patients with exstrophic anomalies. After closure of the bladder, VCUG is useful to assess bladder capacity and to evaluate the competency of the bladder neck. Renal vein thrombosis, uric acid nephropathy, acute tubular necrosis , infection, and nephroblastomatosis are all causes of large kidneys. Diffuse enlargement may also suggest infiltrative processes, such as leukemia and lymphoma. If US findings are inconclusive, differential diagnoses can be evaluated by obtaining a complete blood count CBC and performing CT, urinalysis, and, in some cases, a percutaneous renal biopsy.

Baseline renal US is necessary to assess for hydronephrosis, stone disease, and bladder-wall thickening.

Uro-Radiology 2

It should be performed at birth, if possible. Upper-tract dilation due to high bladder storage pressure initially manifests as a dilated ureter behind the bladder.

The ability to classify patients into low-risk and high-risk groups depends on urodynamic findings. Some centers routinely perform baseline cystography. Urodynamic studies are performed in the newborn period and at age 1 year. If a child with a neurogenic bladder develops an infection or hydronephrosis, the storage function of the bladder may have changed. Cystography and urodynamic studies are then repeated to evaluate bladder storage function. Bilateral hydroureteronephrosis, a thick-walled bladder, and a dilated posterior urethra are observed on antenatal US in males with PUVs.

Postnatal renal US is used to evaluate the renal parenchyma because recognition of corticomedullary differentiation correlates with better renal function. Varying degress of renal cystic dysplasia may be seen. VCUG is key in determining if valves are the cause of bilateral hydronephrosis in a newborn boy.

Postoperatively, the distention of the anterior urethra is improved, and the degree of distention of the posterior urethra should decrease. On antenatal US, the bladder should not be as thick-walled in patients with prune belly syndrome PBS as in patients with PUV; however, the bladder may be massively dilated. The kidneys have a variable appearance, from dysplasia to hydronephrosis. VCUG characteristically reveals a funneling, dilated prostatic urethra. The bladder is usually large and is sometimes associated with a patent urachus or urachal diverticulum.

The distal ureters are also dilated and tortuous. The anterior urethra varies and can be enlarged in the form of a scaphoid megalourethra or can be completely atretic.

Because most patients with PBS have VUR, the authors maintain indefinite antibiotic prophylaxis and try to avoid performing VCUG or other instrumentation of the lower urinary tract to avoid infecting the system. Patients should be monitored with renal US to assess hydronephrosis and renal scanning to assess function. Ureterocele is now often diagnosed with antenatal US.

If the patient presents with sepsis, urgent puncture of the ureterocele may be indicated to decompress and drain the infected system. If the patient is healthy, VCUG is helpful in determining whether the ureterocele is intravesical or ectopic and whether associated reflux is present. These are all prognostic factors that determine whether the patient requires surgery beyond an endoscopic puncture of the ureterocele. The authors have usually endoscopically punctured ureteroceles and maintained patients on prophylactic antibiotics.

VCUG is performed months post incision. If necessary, excision of the ureterocele and ureteral reimplantation are performed in the second year of life for associated reflux. A pseudoureterocele, due to a dilated ureter behind the bladder, mimics a ureterocele and is most commonly caused by an ectopic ureter inserting at or below the bladder neck. RUG reveals the location of the stricture but often does not outline the entire length of the stricture.

A thin catheter can sometimes be passed and VCUG performed to show the proximal extent of the stricture. If the stricture is too narrow, the patient may require a suprapubic tube to achieve bladder drainage, after which VCUG can be performed. The differential diagnoses include 1 weeping from an umbilical granuloma most common , 2 patent omphalomesenteric duct prolapse of bowel and very excoriated skin due to digestive enzymes , and 3 urachal pathology. US can often demonstrate urachal anomalies, such as a patent urachus, urachal cyst, or sinus. VCUG may determine if patency is present with the bladder dome.

RBUS is a useful tool in this setting. In neonates, the renal cortex is isoechoic or hyperechoic relative to the liver. In the immediate newborn period, the renal pyramids may be echogenic with transient stasis nephropathy due to Tamm-Horsfall protein. In children, the renal pyramids are hypoechoic, which allows for clear observation of the corticomedullary junction. Upper-tract hydronephrosis should always be reevaluated when the bladder is empty to determine the degree to which a full bladder affects the dilation. Doppler US provides additional information by showing renal perfusion and vascularity.

Areas of decreased blood flow with color-flow Doppler may indicate focal areas of acute pyelonephritis. The "twinkling artifact" improves the sensitivity of US for detecting small renal calculi. The average newborn kidney is approximately 4. Although antenatal compensatory hypertrophy was not previously thought to occur, it has been observed in patients with solitary or multicystic dysplastic kidney, in whom the newborn contralateral kidney is larger than normal. The presence of cortical cysts and increased echogenicity, indicators of dysplasia and poor function, are useful signs when a pyeloplasty in a minimally functioning kidney is being planned.

Nephrectomy should be considered in such patients. What abnormality is shown? This is a sagittal ultrasound scan of the pelvis of an elderly man. What structures are shown and what procedure has been performed? This IVU, performed in a child, shows several abnormalities. What unusual findings can be seen and what is the underlying cause of these findings? What abnormality is shown here in the plain abdominal X-ray of a lady who underwent hysterectomy and then developed recurrent bladder infections with left loin pain?

This is a bone scintigram in an elderly man with back pain and obstructive lower urinary tract symptoms. What does the scintigram show and what is the most likely cause of the abnormalities? This is the plain abdominal X-ray of a lady who had accidentally introduced a foreign body into her bladder. What is the foreign body and why had the patient inserted it into her bladder? This is an IVU in a child who presented with urinary infection and left loin pain.

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What does the X-ray show and how is this condition best managed? This 26 year old gentleman was involved in a road traffic accident which caused an open pelvic fracture. What abnormality is seen in this ultrasound scan of a testis?

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