A 20-year-old man is brought to the emergency department after a motor vehicle collision. Blood pressure is 130/84 mm Hg, pulse is 108/min, and respirations are 18/min. The airway is intact, and breath and heart sounds are normal. There is bruising across the central lower abdomen and the suprapubic area is tender to palpation. Chest x-ray and pelvic x-ray reveal no fractures. Bedside ultrasound shows intraperitoneal free fluid. Urine dipstick test is positive for blood. CT scan of the abdomen and pelvis is most likely to reveal which of the following injuries in this patient?
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This patient's suprapubic tenderness and hematuria (ie, urine dipstick test positive for blood) in the setting of blunt trauma are concerning for a bladder injury. The additional presence of intraperitoneal free fluid (possibly urine) is further suggestive of injury to the bladder dome.
The bladder is a hollow pelvic organ located just posterior to the pubic symphysis. Although the bladder is extraperitoneal, the bladder dome is covered by peritoneal lining and extends into the peritoneal cavity when distended with urine. Blunt lower abdominal trauma can abruptly increase intravesical pressure (especially when the bladder is full) and cause the bladder to rupture at the dome, where it is most distended and least supported by surrounding structures. As a result, urine is diverted from the urinary tract into the peritoneal cavity and can be seen on imaging as intraperitoneal free fluid. Peritonitis often does not develop acutely in these patients because urine typically does not contain pathogenic bacteria.
(Choices A and C) The anterior bladder wall and the bladder neck are extraperitoneal structures. Therefore, a rupture in these locations would lead to extraperitoneal extravasation of urine rather than intraperitoneal leakage of urine. In addition, such ruptures are almost always accompanied by pelvic fracture.
(Choice D) The kidney is a retroperitoneal structure. Therefore, renal laceration typically causes retroperitoneal bleeding and flank pain rather than intraperitoneal free fluid and suprapubic tenderness.
(Choice E) Urethral injuries can be categorized into anterior and posterior injuries. Anterior urethral injuries are commonly caused by direct penile trauma (eg, straddle injuries, penile fracture). Posterior urethral injuries are frequently associated with pelvic fracture and may (in cases of membranous transection) cause a high-riding prostate. Although urethral injury may cause blood at the urethral meatus and/or hematuria, it does not lead to intraperitoneal free fluid because the urethra is an extraperitoneal structure.
Educational objective:
The dome of the bladder rises into the peritoneal cavity when distended with urine. Blunt lower abdominal trauma can abruptly increase intravesical pressure and rupture the bladder dome, spilling urine into the intraperitoneal cavity.