Ultrasound examination (ultrasound)
Ultrasonography is the most informative and safest imaging modality for evaluating structures of the retroperitoneal space and lesser pelvis. High-frequency transducers are used for quality scanning, and the examination is initiated with a full urinary bladder. A filled bladder serves as an acoustic window for assessing the lower urinary tract, ureteral orifices, and internal genitalia.
Features of infant kidneys (under 6 months of age):
- Absence of fat in the renal sinus.
- The medullary substance (pyramids) is large and hypoechoic — it is important not to mistake this normal variant for cysts or pelvicalyceal system dilation.
- The renal cortex is hyper- or isoechoic relative to the liver (unlike in adults).
- The average length of a newborn kidney is about 4.5 cm, with a more spherical shape. For accurate size assessment, it is preferable to calculate the volume using the formula: `0.523 × length × width × depth`.
Additional techniques include color Doppler flow imaging (CDFI) to assess blood flow in trauma, infections, and tumors, as well as diuretic ultrasonography with furosemide to differentiate obstruction from simple dilation.
Micturitional cystourethrography (MCUG)
MCUG is the only generally accepted method that details urethral anatomy. The method involves radiation exposure and requires catheterization.
Indications:
- Assessment of vesicoureteral reflux (VUR) following recurrent infections.
- Suspected posterior urethral valves in boys.
- Complex malformations of the urinary tract.
Procedure protocol:
- A sterile feeding tube or suprapubic puncture is used. In neural tube defects, latex precautions must be strictly observed.
- A water-soluble iodinated contrast agent is administered dropwise (by gravity) from a height of no more than 60 cm (physiological pressure of 30–40 cm H₂O). Rapid injection with a syringe is unacceptable — it causes artificial reflux and distorts capacity.
- Images are acquired during the filling phase and during micturition (after catheter removal in cooperative children). In the first year of life, cyclic filling (up to 3 times) is often used to increase the likelihood of detecting reflux.
- A baseline scout radiograph without contrast is not performed prior to the procedure.
Radionuclide methods and cross-sectional imaging
If functional assessment or tumor staging is required, the algorithm is supplemented with other modalities:
- Contrast-enhanced urosonography (ce-VUS): utilizes microbubble contrast. It is a non-ionizing alternative for reflux evaluation.
- Radioisotope cystography (direct and indirect): delivers significantly lower radiation exposure than MCUG. Direct radionuclide cystography with 99mTc-pertechnetate is used to evaluate reflux in infant girls, as their urethral anatomy is typically normal.
- Computed tomography (CT): due to high radiation exposure (up to 10 mSv), it is used much less frequently in pediatric urolithiasis than in adults. It is indicated only for stones confirmed on ultrasound and accompanied by pain, as well as in complex trauma.
- Magnetic resonance imaging (MRI): provides excellent anatomical and functional information without radiation, and is particularly useful in evaluating tumors and in older children who are able to lie still.
Briefly: answers to topical questions
What are the grades of vesicoureteral reflux (VUR) according to the international classification based on cystography?
There are 5 grades of severity of vesicoureteral reflux depending on the height of urine ascent and the degree of upper urinary tract dilation.
- Grade I — reflux is confined to the ureter, the ascent does not reach the renal pelvis, no dilation is present.
- Grade II — total reflux to the renal pelvis and calyces without dilation, calyceal fornices retain their sharp angles.
- Grade III — mild or moderate dilation of the ureter and pelvicalyceal system, blunting of the calyceal fornices.
- Grade IV — marked dilation and tortuosity of the ureter, significant expansion of the renal pelvis and calyces with rounding of the fornices.
- Grade V — end-stage with severe dilation and tortuosity of the ureter (megaureter), gross expansion of the pelvicalyceal system, and clubbing of the calyces.
What radiographic signs are characteristic of posterior urethral valves in boys during micturitional cystourethrography?
During micturitional cystourethrography in boys with posterior urethral valves, a number of characteristic radiographic signs are revealed.
- Trabeculation of the wall — alteration of the urinary bladder contour.
- Volume changes — a very large or small urinary bladder with diverticula.
- Vesicoureteral reflux (VUR) — unilateral or bilateral urine ascent with decreased renal function on the affected side.
- Visualization of the valve — an acute-calibre transition is identified.
Cases without reflux may also occur, accompanied by ureterovesical junction obstruction and secondary pelviureteric junction obstruction.
What are the absolute and relative contraindications to micturitional cystourethrography?
The provided materials indicate that acute sepsis is a contraindication to micturitional cystourethrography (MCUG). A detailed classification of absolute and relative contraindications is not presented. MCUG is used to rule out bladder outlet obstruction and evaluate vesicoureteral reflux. In a number of European countries, contrast-enhanced voiding urosonography (ce-VUS) is used instead of MCUG to assess reflux in order to avoid radiation exposure.
Which specific contrast agents are used for contrast-enhanced urosonography (ce-VUS) in children?
The sources indicate that microbubble contrast is used for contrast-enhanced voiding urosonography (ce-VUS). Microbubbles are described as an inert gas within a stabilizing shell. Specific trade names or chemical designations of the drugs are not specified in the provided materials.
To calculate normal bladder capacity in a child under 8 years of age, add 1 to the age and multiply by 30. Example for 4 years: (4 + 1) × 30 = 150 mL.
Class and exam questions
Why do renal pyramids in newborns look different on ultrasound?
Unlike in adults, in infants under 6 months of age, the medullary substance is large and hypoechoic. An inexperienced physician might mistakenly mistake this physiological norm for cysts or pelvicalyceal system dilation.
Can contrast media be administered with a syringe during voiding cystourethrography?
No, the contrast must be administered dropwise by gravity from a height of 30–40 cm above the table (maximum 60 cm). Injection with a syringe creates excessive pressure, leading to false vesicoureteral reflux or barotrauma.
What is the role of CT in diagnosing kidney stones in children?
Due to high radiation exposure (dozens of times greater than radiography), CT in urolithiasis is rarely used. The method is indicated if calculi are detected on ultrasound and accompanied by severe pain syndrome, or when planning complex surgery.
What else to study on this topic
- Normal ultrasound anatomy of the gonads in girls across different age periods
- Imaging features of the testes in newborns and adolescents (blood flow Doppler sonography)
- Comparative radiation exposure in radionuclide studies (DMSA, MAG3, DTPA)
- Distal loopogram: indications and procedure technique in colostomies
- ESPR algorithm for standardized evaluation of urinary tract dilation
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