Abdominal CT: bladder injuries

Severe blunt force injuries to the pelvis not only cause fractures but can also injure the urinary bladder. This can happen due to the projection of bone fragments into the bladder wall or due to sudden increases in pelvic pressure causing the bladder wall to tear and rupture.

CT cystogram

Delayed phase images might reveal the injury, but in many cases, these images are not enough to exclude subtle bladder injuries as the bladder is not sufficiently filled.

Therefore, if there is concern of a bladder injury based on the mechanism of trauma and the presence of pelvic fractures, a dedicated CT cystogram is needed. A CT cystogram involves filling the bladder with contrast and performing a CT of the pelvis to see if any contrast leaks out.

Bladder distension with contrast and contraction of the musculature that occurs with filling will reveal more subtle injuries.

Below is a sagittal CT cystogram image, which involves filling the bladder with bright contrast material so that it is fully distended and any leaks become evident.

Bladder injuries can be categorized as one of two types:

• Intraperitoneal rupture. This involves the dome and causes urine to spill into the peritoneal cavity and surround the bowel loops.
• Extraperitoneal rupture. This is usually anterior and the leaking urine is confined to the space surrounding the bladder.

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Intraperitoneal bladder rupture

Intraperitoneal ruptures are more often associated with sudden increases in pelvic pressure. This can cause the dome of the bladder to rupture and urine will leak into the peritoneal cavity.

Intraperitoneal bladder rupture can be surprisingly difficult to diagnose because sometimes the only indication of bladder injury on the initial trauma scan may be unexplained simple fluid in the pelvis.

With intraperitoneal rupture, the bladder often becomes decompressed after rupture. Since the injury is at the bladder dome, it can be difficult to see on imaging. In this case, there is unexplained free, water-density fluid of 15 HU in the pelvis, raising suspicion of a bladder injury.

The trauma CT sagittal image shows us there is some thickening of the bladder dome, which increases our suspicion of an injury.

A CT cystogram was then performed. Filling the bladder with contrast allows us to see the characteristic location of the injury—the bladder dome—where contrast will leak into the peritoneal cavity.

The appearance of bright contrast surrounding small bowel loops is diagnostic of an intraperitoneal rupture. On the coronal image, we can also appreciate the defect where contrast is leaking out and surrounding the bowel loops.

Treatment

Surgical repair is used to treat intraperitoneal bladder ruptures.

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Extraperitoneal bladder rupture

Extraperitoneal bladder rupture is often associated with pelvic fractures. The bladder usually ruptures anteriorly into the extraperitoneal space in front of the bladder, also known as the prevesical space or the space of Retzius, and urine does not spill freely into the abdominal cavity.

Extraperitoneal bladder rupture can range from very subtle to a large defect.

The patient’s trauma scan below has quite a lot of fluid accumulating outside the front of the bladder in the prevesical space (space of Retzius). The fluid has a simple fluid density of 15 HU. There is a visible defect in the anterior bladder wall, indicating injury.

A follow-up cystogram was performed and showed a gaping hole in the bladder, confirming injury. When contrast was inserted into the bladder, it leaked into the prevesical space but not into the peritoneal cavity or surrounding bowel loops.

Treatment

Even if there is a large injury, extraperitoneal bladder rupture can usually be managed nonoperatively with catheter placement, which will facilitate healing of the bladder wall.

In trauma cases, be sure to verify whether you are dealing with an intraperitoneal or extraperitoneal bladder rupture.

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References

• Top 100 CT scan quiz. LITFL

Radiology Library: Abdominal Trauma. Musculoskeletal injuries

• Hartung MP. Abdominal Trauma: rib fractures
• Hartung MP. Abdominal CT: spinal fractures
• Hartung MP. Abdominal CT: body wall injuries
• Hartung MP. Abdominal CT: pelvic fractures
• Hartung MP. Abdominal CT: bladder injuries

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