MCU (micturating cystourethrogram), also called VCUG, is an X-ray/fluoroscopy test performed while the bladder fills and during urination. A thin catheter is used to fill the bladder with contrast. The study can show vesicoureteric reflux (urine going back toward the kidneys), the shape of the bladder neck and posterior urethra, urethral narrowing and conditions such as posterior urethral valves in children. The test provides information that a standard ultrasound cannot, but it uses a small amount of radiation and requires catheterisation.

Why is MCU ordered?

• Suspected vesicoureteric reflux, especially in selected children with urinary infections or abnormal urinary tracts.
• Posterior urethral valve assessment in boys.
• Evaluation of the bladder neck and posterior urethra.
• Complex urethral stricture or pelvic fracture urethral injury, often combined with RGU.
• Assessment of leakage or fistula in selected postoperative situations.

What happens during the test?

After cleaning the urethral opening, a small catheter is passed into the bladder. Contrast is instilled until the bladder is adequately full. Images are taken during filling and while the patient passes urine. The catheter may be removed for voiding depending on protocol. Children often need calm explanation and parental support rather than routine sedation because voiding is an essential part of the test.

Common report findings

Vesicoureteric reflux (VUR)

VUR means contrast travels from the bladder back into one or both ureters and kidneys. It is traditionally graded from I to V based on how far contrast travels and the degree of dilatation. The grade is one factor among age, infections, kidney scars and bladder function.

Posterior urethral valves

In boys, a dilated posterior urethra with a narrow downstream segment and abnormal bladder may suggest posterior urethral valves. The diagnosis and treatment pathway is clinical and often involves cystoscopy.

Bladder trabeculation or diverticula

An irregular thick-walled bladder can indicate long-standing high-pressure voiding or bladder dysfunction. Imaging does not by itself identify whether the cause is obstruction or abnormal bladder muscle/nerve function.

Urethral narrowing

A narrowing seen during voiding may complement RGU, especially for posterior urethral or bladder-neck problems.

Is radiation a concern?

Fluoroscopy uses ionising radiation, so paediatric protocols aim to use the lowest dose that still answers the clinical question. The expected diagnostic benefit should justify the exposure. Ultrasound can answer many structural questions, but it cannot replace MCU when reflux or dynamic urethral anatomy must be demonstrated.

After the test

Mild burning or frequent urination for several hours can occur after catheterisation. Drinking fluids is often advised unless another medical condition requires restriction. Fever, persistent pain, inability to urinate or worsening urinary symptoms should be reported.

When the result needs specialist review

• High-grade or bilateral reflux.
• Abnormal posterior urethra or suspected posterior urethral valves.
• Significant bladder trabeculation with high residual urine.
• Complex stricture, fistula or postoperative leak.
• Recurrent febrile UTI with urinary tract abnormalities.

Urine infection around MCU

Because the test requires catheterisation, active symptomatic UTI is usually treated before an elective MCU unless the study is being performed for a specific urgent reason. If fever, new significant burning or foul urine develops after the study, contact the treating team. In children with recurrent febrile UTI, the MCU result should be interpreted alongside renal ultrasound and, when indicated, cortical imaging rather than viewed as an isolated reflux grade.

How MCU findings are interpreted in context

In children, reflux grade is only part of risk assessment. Recurrent febrile UTI, renal cortical defects/scarring, bladder-bowel dysfunction and age influence follow-up. In adults with urethral disease, the study is often used less for reflux and more for the bladder neck/posterior urethra during voiding.

A “spinning-top” urethra, incomplete bladder emptying or reflux seen only at high filling pressure may raise questions about voiding dysfunction. These findings should be matched with symptoms, ultrasound and, in selected cases, urodynamics rather than treated from the X-ray label alone.

How the result changes management

In children, reflux grade is only one part of the decision. Age, febrile UTI history, kidney scars, bladder-bowel dysfunction, renal growth and whether reflux improves over time are also important. A high grade does not automatically mean surgery, and a low grade is not irrelevant if infections or renal injury continue.

When MCU is performed for suspected posterior urethral valves or urethral obstruction, the voiding images are particularly important. Bladder changes alone are indirect; the urethral appearance during voiding is what helps localise the problem.

What to bring for consultation

• MCU/VCUG images and report.
• Ultrasound KUB findings.
• Urine culture history.
• Creatinine and renal scan if already performed.
• For urethral disease: RGU, uroflowmetry and previous surgical records.

FAQs

Related reading

• RGU Test Explained
• Ultrasound KUB Report Explained
• DTPA / Renal Scan Explained
• Trabeculated Bladder on Ultrasound
• Urologist in Latur

References

• European Association of Urology. EAU Guidelines on Urological Infections. 2026 https://uroweb.org/guidelines/urological-infections
• RadiologyInfo.org (ACR/RSNA). Renal (Kidney) Scintigraphy. Last reviewed June 15, 2026 https://www.radiologyinfo.org/en/info/renal