Principles of Intravenous Urography
The examination traditionally begins with a plain abdominal radiograph of the kidneys, ureters, and bladder without contrast enhancement. Following contrast administration, bilateral symmetric nephrotomograms and delayed-phase images are acquired.
In clinical practice, IVU effectively demonstrates signs of pelviureteric junction obstruction. Mild hydronephrosis may be identified on the affected side: the calyces appear blunted, yet the fornices remain preserved. Meanwhile, contrast excretion is delayed—the renal pelvis shows prolonged and persistent contrast retention, while the distal ureter remains unfilled.
In modern diagnostics, the method is frequently combined with other modalities. For example, CT urography combined with retrograde contrast administration has significantly higher sensitivity and specificity for detecting urothelial tumors compared to conventional radiography.
Examination of the urethra and urinary bladder
Specialized fluoroscopic techniques with targeted views are used for detailed evaluation of the lower urinary tract:
- Retrograde urethrography (RUG): Used primarily for the anterior male urethra (navicular fossa, bulbar segment). Up to 50 mL of iodine-based contrast is gently injected into the urethra through a flushed catheter. The patient is positioned at a 45-degree angle with the lower thigh flexed. The method is indispensable following blunt perineal trauma to assess urethral ruptures, as well as to identify strictures (e.g., resulting from accidental balloon inflation of a catheter inside the urethra).
- Voiding cystourethrography (VCUG): Visualizes the posterior urethra and urinary bladder. Contrast is administered antegrade via a Foley catheter (14–18 F) or suprapubic needle. Images are acquired during the filling phase and directly during the act of micturition (micturition). The lateral projection is critically important for detecting subtle fistulous tracts. In children, this method serves as the gold standard for detecting and grading vesicoureteral reflux (VUR).
Role of ultrasound (US)
Ultrasound offers several advantages, such as safety and high resolution, which is particularly valuable in pediatrics. However, the method has strict limitations:
- Calculi: Ultrasound is significantly inferior to computed tomography in detecting stones.
- Renal tumors: Ultrasound sensitivity for masses less than 1 cm is only 26%.
- Bladder tumors: Despite high sensitivity (up to 95%) for transitional cell carcinoma, ultrasound must be supplemented by cystoscopy to rule out pathologies mimicking cancer (cystitis, hematoma, bladder outlet obstruction, endometriosis).
Ultrasound excels at detailing cystic renal lesions. The Bosniak classification allows categorizing them into benign (categories 1 and 2—simple septations) and suspicious (categories 3 and 4—presence of a solid component or focal thickening). However, one must keep a pitfall in mind: internal echoes can give a benign cyst a solid appearance, requiring CT verification.
Radionuclide diagnostics and functional assessment
Nuclear medicine methods provide invaluable data on renal function and urodynamics that cannot be obtained with standard IVU:
- 99mTc-DMSA scintigraphy: Highly sensitive for detecting cortical scars and parenchymal scarring (e.g., in the upper renal pole following recurrent infections). A disadvantage is the inability to distinguish acute pyelonephritis from an old scar.
- Diuretic renography: A key method in urinary tract dilation (e.g., to differentiate primary obstructive megaureter from non-obstructive). Tubular agents are used (99mTc-MAG3, 123I-hippuran).
For proper execution of the furosemide test, patient hydration (15 mL/kg 30 minutes prior to the test) and bladder emptying before imaging are critically important, as a full bladder distorts urodynamics. Normally, function is distributed evenly: 45% to 55% to each kidney.
Briefly: answers to topical questions
What criteria are used to categorize renal cysts according to the Bosniak classification?
The Bosniak classification criteria are based on contrast-enhanced computed tomography findings and include the assessment of attenuation, wall thickness, presence of septa, calcifications, solid components, and contrast enhancement.
- Category I (Type I) — simple cyst with water attenuation, thin wall, no septa, calcifications, solid components, or contrast enhancement.
- Category II (Type II) — cyst with thin septa, fine calcifications, or hyperdense cyst less than 3 cm without enhancement.
- Category IIF (Type IIF) — cyst with multiple thin septa, nodular calcification, or hyperdense cyst greater than 3 cm without visible enhancement.
- Category III (Type III) — thickened irregular or smooth walls and septa showing contrast enhancement.
- Category IV (Type IV) — features of Category III combined with independent soft-tissue solid components.
What complications and adverse reactions can occur following the intravenous administration of an iodinated contrast medium?
Intravenous administration of an iodinated contrast medium may lead to allergic, nephrotoxic, and local complications.
- Mild reactions — flushing, nausea, vomiting, headache, and mild urticaria.
- Severe anaphylactic reactions — shock, cardiac or respiratory arrest, seizures.
- Contrast-induced nephropathy (CIN) — an increase in serum creatinine by 0.5 mg/dL or 25% within 48–72 hours.
- Contrast extravasation — causes pain, blistering, as well as vascular or neurological impairment.
- Delayed thyrotoxicosis — may occur in patients with hyperthyroidism within 8 weeks post-administration.
What time intervals (in minutes) for radiographs are included in the standard intravenous urography protocol?
The standard intravenous urography protocol involves acquiring a series of radiographs at strictly defined time intervals following contrast administration.
- Plain radiograph — performed prior to contrast administration.
- 5-minute radiograph — intended to assess the nephrographic phase and visualize the renal parenchyma.
- 20- and 45-minute radiographs — required to assess excretory function and patency of the entire urinary tract.
- Post-micturition radiograph — allows evaluation of bladder emptying.
- Delayed radiograph — performed 6–12 hours later in cases of delayed excretion by one of the kidneys.
Class and exam questions
Can urography and CT be completely replaced by ultrasound?
No. Ultrasound has low sensitivity (26%) for detecting renal masses smaller than 1 cm and is significantly inferior to CT in visualizing calculi.
How does voiding cystourethrography (VCUG) differ from radioisotope cystography in reflux?
Radioisotope cystography delivers a lower radiation dose and is convenient for continuous monitoring, but lacks spatial resolution. VCUG provides an accurate anatomical picture of the urethra and bladder.
When is it appropriate to perform postnatal ultrasound for prenatally detected hydronephrosis?
Ultrasound should be performed during the first week of life, but strictly no earlier than 48 hours after birth. During the first two days, neonatal diuresis is physiologically reduced, which may yield false-negative results.
What else to study on this topic
- Bosniak classification of cystic renal lesions
- Protocol for diuretic renography with furosemide
- Differential diagnosis of megaureter in children
- Imaging algorithm for blunt perineal trauma (RUG)
- Ureteral ectopia: MRI visualization
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