Indications and Methodology of MDCT Cystography
In emergency surgery, computed tomography has virtually replaced standard radiography. The procedure is indicated for patients with gross hematuria (gross haematuria) associated with pelvic fractures (excluding isolated acetabular fractures), as well as in the presence of free fluid in the pelvic cavity or pelvic hematoma of unclear etiology.
Key Principles of Procedure:
- Prior to placing a urethral catheter, urethral injury must be reliably ruled out.
- Adequate visualization requires sufficient wall distension (bladder distension), which triggers detrusor contraction.
- Protocol: drip infusion of up to 400 mL of 4% contrast agent. The reservoir should be positioned no higher than 100 cm. The process is stopped once the required volume is reached or when detrusor contraction begins.
- Scanning is performed twice: with a fully distended bladder and after its evacuation.
Important: Standard pelvic CT with intravenous contrast and a clamped catheter (antegrade filling) cannot reliably rule out bladder rupture.
CT Findings in Bladder Ruptures
Tomography allows for precise determination of the rupture type, which is critical for choosing between conservative and surgical management.
- Extraperitoneal Bladder Rupture (Extraperitoneal bladder rupture, EBR). Most common. Contrast medium leaks into extraperitoneal tissues, forming a streaky pattern (streaky). The extravasate may take a "flame-shaped" (flame-shaped) or "molar-tooth" (molar-tooth) appearance. Fluid extends into the retropubic space, inguinal regions, thigh, or presacral fat. With a concomitant posterior urethral injury, contrast may extend into the perineum and scrotum.
- Intraperitoneal Bladder Rupture (Intraperitoneal bladder rupture, IBR). The defect is typically located at the dome (dome of the bladder). Contrast flows freely into the peritoneal cavity, outlining peritoneal recesses and bowel loops. Due to significant dilution by urine in a large space, the density of the extravasate on CT is lower than in extraperitoneal rupture.
- Combined Ruptures. Diagnosed in 5–10% of cases and combine the radiological signs of both types described above.
Micturitional cystourethrography (MCUG)
This procedure (micturating cystourethrography) is used primarily in pediatrics. It requires strict adherence to safety protocols. Active urinary tract infection is an absolute contraindication.
Execution Technique:
- In neonates, a small feeding tube is used; in older children, a Foley catheter. Critical point: the catheter balloon must be completely deflated to avoid masking bladder neck pathology and obstructing outflow.
- Warmed contrast is administered strictly via drip infusion from a maximum height of 60 cm (providing a pressure of 30–40 cm H₂O). Administration via syringe is strictly prohibited—this causes overdistension, artificial reflux, and distorts volume data.
- Imaging is performed with tight collimation (tight coning) to reduce radiation dose. In younger children, a cyclic filling technique is used: this increases the likelihood of detecting vesicoureteral reflux during successive micturition cycles.
Cystography in Transplantation
The method remains relevant following kidney transplantation. In the early postoperative period, cystography is necessary to reliably rule out injuries and bladder wall defects. In the long-term period, the procedure is indicated to diagnose transplant vesicoureteral reflux, especially if the patient reports recurrent pain or suffers from recurrent urological infections.
"Extraperitoneal Rupture: Flame or Tooth." Remember the visual extravasation patterns in EBR: flame-shaped or molar-tooth appearance.
Class and exam questions
Why is standard CT with intravenous contrast insufficient when trauma is suspected?
The antegrade approach (intravenous administration with a clamped catheter) fails to generate sufficient pressure to distend the bladder walls. The defect may remain apposed, and contrast extravasation will not occur.
What can lead to a false-negative result during MDCT cystography?
The diagnosis can be missed if less than 250 mL of contrast is administered, the rupture is small, the defect is obscured by an inflated Foley catheter balloon, intravesical blood clots are present, or detrusor muscle spasm occurs.
How to differentiate intraperitoneal from extraperitoneal rupture on CT based on contrast density?
In intraperitoneal rupture, the contrast agent enters the vast peritoneal cavity and is heavily diluted by urine. Therefore, on tomograms, such extravasation appears less dense (less radiopaque).
Does the management strategy differ for various types of bladder ruptures?
Yes, dramatically. Approximately 90% of extraperitoneal ruptures heal successfully within 10 days with indwelling catheter drainage. Intraperitoneal ruptures require emergency surgical closure to prevent peritonitis.
What else to study on this topic
- Radiological Anatomy and Urethral Injuries ("S-curve" sign)
- Goldman & Sandler Classification of Urethral Injuries
- Contrast-Enhanced Ultrasound of the Bladder (ce-VUS)
- Radioisotope Scintigraphy and Radiation Dose Comparison in Urology
- Evaluation of Renal Transplants Using Non-Contrast MR Angiography (SSFP)
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