Case bb -  Extraperitoneal bladder rupture

Contrast is seen anterior, superior, and to the left of the bladder (1, 2).  This indicates a bladder rupture.  Unlike in the previous case, the extravasated contrast remains in the retroperitoneum.  It does not outline bowel.  It is not seen surrounding the intra-abdominal organs.  This is an extraperitoneal bladder rupture.  There is also bladder wall thickening and adjacent free air.

Extraperitoneal bladder ruptures are complications of abdominal trauma, pelvic fractures, and urologic procedures.  Most extraperitoneal ruptures are associated with distracted pelvic fractures.  It was originally thought that bone fragments from the pelvis poked a hole in the bladder wall. However, it is now thought that there is shear injury to the bladder wall.  The base of the bladder is held firmly in place.  If there is rapid deacceleration, the wall can rip at these points of attachment. 

Contrast anterior and superior to the bladder is located in the space of Retzius.  This is a peritoneal reflection between the peritoneal cavity, the bladder, and the anterior abdominal wall. The anatomy is nicely outlined on sagittal reformats (1, 2).  The reformats were created on images obtained after the bladder was drained.   Do not mistake contrast in this area as intraperitoneal.  Also, this space allows for communication between the left and right pelvic sidewalls.  For example, if a patient undergoes right sided femoral artery catheterization and subsequently has a hematoma, blood can track into the left groin by crossing through the space of Retzius.    Unless there is contrast or hemorrhage in this space, this area is usually a collapsed "virtual space."

Extraperitoneal bladder ruptures are usually treated conservatively.

Take home points:

• A CT cystogram should be performed whenever there is suspicion of a bladder injury.  Signs of bladder injury include bladder wall thickening, pelvic hematoma, intraluminal clot, and frank hematuria.  Always include precontrast, post contrast, and post-drainage images. 
• Extraperitoneal bladder ruptures are often associated with pelvic fractures or urological procedures.  They are treated conservatively.
• Extravasated urine that interdigitates between loops of bowel means there is an intraperitoneal bladder rupture.