Micturating Cystourethrography (VCUG)
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Direct answer
Voiding films make this study: a catheter placed aseptically fills the bladder with iodinated contrast under fluoroscopy, but the diagnosis lives in the voiding phase, when vesicoureteric reflux and urethral pathology reveal themselves under pressure. Reflux is graded I through V — I ureter only, II adding the pelvicalyceal system without dilatation, III with mild dilatation and slight blunting, IV with progressive dilatation and loss of fornices, V with gross dilatation and tortuous ureters. In a boy with a poor stream, the voiding study shows a dilated posterior urethra with an abrupt calibre change at the membrane — posterior urethral valves, the diagnosis that must not leave the department unnamed. Radiation is the technique's burden, and contrast-enhanced voiding ultrasonography now offers a radiation-free alternative in centres that can perform it.
What you must remember
- Protocol: catheterisation, retrograde bladder filling with dilute iodinated contrast, filling-phase spot images, then voiding-phase imaging including an oblique of the male urethra; a post-void film completes the study.
- Reflux grading ladder: I ureter; II ureter, pelvis and calyces without dilatation; III mild-to-moderate dilatation with slight calyceal blunting; IV moderate dilatation with loss of fornical sharpness; V gross dilatation, tortuous ureter, clubbed calyces.
- Posterior urethral valves: dilated posterior urethra ending abruptly at the valve, with a visible valve ledge, bladder wall trabeculation and diverticula, and often unilateral reflux or a "valve bladder"; the male-infant poor-stream study.
- Indications in current practice: recurrent or febrile urinary infection with abnormal ultrasound or after agreed infection counts, follow-up of known reflux, and suspected urethral obstruction — the first-infection reflex VCUG of older teaching has been pared back.
- Associations to state: reflux nephropathy scars on DMSA, duplex systems with reflux into the lower moiety ureter, ureterocele, bladder exstrophy follow-up and neurogenic bladder assessment.
- Voiding matters diagnostically: reflux and valves appear or worsen during micturition; a study terminated before voiding is an incomplete study, and stating this is examinable.
- Female urethra: a short, mildly distensible normal channel; urethral obstruction in girls is rare, so a stricture-like picture demands re-thinking.
- Alternatives: radionuclide cystography for reflux follow-up (lower dose, less anatomic detail) and contrast-enhanced voiding ultrasonography where available.
A boy who cannot aim his stream
A nine-month-old boy, two febrile urinary infections, an ultrasound showing bilateral hydronephrosis with a thick-walled bladder and a left duplex collecting system. MCUG is performed: the bladder fills with a trabeculated, irregular outline; during voiding the posterior urethra balloons to several times the calibre of the anterior urethra, stopping abruptly at a translucent ledge — posterior urethral valves. Simultaneously, contrast refluxes up the left duplex system's lower-moiety ureter, hydronephrotic and tortuous — grade IV-V reflux. The post-void film retains contrast in the dilated left ureter. The report names both: valves for cystoscopic ablation, and high-grade reflux into the lower moiety that will need prophylaxis and DMSA scarring assessment. Every teaching point of the chapter is in one study — filling films for the bladder, voiding films for the urethra and reflux, and the post-void film for residual — and the sequencing explains why an incomplete, catheter-cut-short study misses precisely the findings that changed this child's management.
Grading-boundary errors
Grade III and IV confusion tops the list: the dividing line is fornical blunting (III) versus loss of the fornices with progressive dilatation (IV), while ureteric tortuosity is the signature of V — exam stems are built around exactly these boundaries. Second, mistaking a full but unvoided study for normal: reflux is dynamic and pressure-dependent, so the voiding phase is not an optional extra; a "normal" MCUG without documented voiding is uninterpretable. Third, overcalling the catheter: the catheter itself can induce reflux or mimic residual, and cyclic filling in infants improves detection precisely because the first void relaxes the detrusor. A final practical note: MCUG should follow, not precede, treatment of active urinary infection — filling an infected bladder under pressure invites urosepsis, a contraindication the exam expects you to state unprompted.
Frequently asked questions
How is vesicoureteric reflux graded on MCUG?
Grade I into the ureter only, II into non-dilated pelvicalyceal systems, III with mild dilatation and blunting, IV with moderate dilatation and loss of fornices, and V with gross dilatation and a tortuous ureter.
What does MCUG show in posterior urethral valves?
A dilated posterior urethra with an abrupt calibre change at the valve, often with a visible ledge, trabeculated thick-walled bladder and secondary reflux — in a boy with a poor stream.
Why must the voiding phase be included in VCUG?
Reflux and urethral obstruction are pressure phenomena that appear or worsen during micturition, so a study terminated before voiding cannot exclude either diagnosis.
When is MCUG indicated after urinary tract infection in a child?
Not reflexively after a first infection: after recurrent or atypical, febrile infection, when ultrasound is abnormal, or per current guideline thresholds agreed with paediatric nephrology.
What radiation-free alternatives exist for reflux assessment?
Contrast-enhanced voiding ultrasonography detecting intraluminal echogenic contrast in the ureters, and radionuclide cystography for follow-up studies, both trading anatomic detail for a lower dose.