The number of serious retroperitoneal, intraperitoneal, or vascular injuries that can occur, many of which require operative repair, complicates the evaluation of penetrating injuries to the flank or buttocks. Imaging assists in diagnosis and can direct selective conservative management. The choice of management, conservative or operative, is based on the emergency evaluation, making the emergency physician’s input essential to a correct decision and a clinically successful outcome.

PATHOPHYSIOLOGY

The flank is located between the anterior and posterior axillary lines, bordered superiorly by the sixth rib and inferiorly by the iliac crest. Although a penetrating wound to the flank can produce intraperitoneal injury with the associated findings of peritonitis or hemoperitoneum, it is possible that a penetrating flank injury could injure only the retroperitoneal organs. A solitary injury to the retroperitoneum from a penetrating flank injury may not induce peritoneal signs initially, and reliance on physical exam findings alone could lead to a delay in diagnosis, resulting in septic or hemorrhagic shock. Essentially any intra-abdominal organ is at risk for injury from a penetrating flank wound, and injuries to the kidney, ureter, bladder, liver, spleen, gallbladder, pancreas, colon, adrenal gland, diaphragm, stomach, duodenum, lung, esophagus, heart, and vascular structures have all been reported.^1,2,3,4

The path of a gunshot or stab wound to the flank could track in any direction. Once inside the abdominal cavity, bullets may ricochet off the bony structures of the spine and produce a unique bullet path and injury pattern. The extent of injury caused by a projectile depends on its velocity, with higher-velocity objects causing more injury than lower-velocity objects, as well as on the construction of the projectile, which affects the movement of the object once inside the abdominal cavity. The greater the surface area interface, the greater is the tissue damage. Stabbing injuries are low velocity and induce injury through direct contact with tissue.⁵

CLINICAL FEATURES

Obtain information about the mechanism of injury, how much time has passed since the event, and the nature of the weapon. In the case of a gunshot wound, determine the nature of the gun (e.g., shotgun, handgun, BB gun) and the distance between the gun and the patient at the time of the gun’s discharge. For gunshot wounds, attempt to identify an exit wound and reconstruct the bullet path. For stab wounds, determine the size of the weapon and, if possible, estimate a measure of the depth of penetration. Perform a rectal examination because the presence of red blood in the stool may indicate bowel injury. Note any blood around the urinary meatus or blood in a Foley catheter drainage that would suggest bladder or urethral injury.

DIAGNOSIS

Patients with penetrating flank trauma who are hemodynamically unstable or who have peritoneal signs require emergent laparotomy. Patients who are not taken emergently to the operating room require further evaluation to ascertain the extent of injury and to determine if the wound has penetrated the peritoneum and caused intraperitoneal organ injury. Evaluation of flank trauma represents challenges related to its unique anatomic position and potential for retroperitoneal injury with late manifestations. Few data exist on isolated penetrating flank trauma, and most of the recommendations for management come from studies of both flank and back trauma or flank and abdominal trauma.⁶ Several diagnostic modalities exist to further evaluate penetrating flank trauma, each with some degree of limitation in its ability to exclude injury. Table 264-1 lists the diagnostic modalities available (see also chapter 263, “Abdominal Trauma”). Triple-contrast CT scan can detect the trajectory of the penetrating object and evaluate the retroperitoneum and is highly accurate in detecting injuries requiring laparotomy, but is less sensitive for the detection of injuries to the diaphragm or colon.^2,3,7,8 US has limited ability to detect hollow viscous or retroperitoneal injury and cannot be used alone in penetrating flank trauma to exclude occult injury.^9,10,11 Diagnostic peritoneal lavage can detect intraperitoneal penetration, but cannot evaluate the retroperitoneum, and has a high false-positive rate leading to nontherapeutic laparotomy. Local wound exploration has a false-positive rate of 14% to 45%.⁷ Diagnostic laparoscopy is very sensitive for the detection of peritoneal violation and can help prevent the morbidity and mortality associated with unnecessary laparotomy.^11,12,13

LABORATORY TESTING

Table 264-2 lists the baseline laboratory and imaging studies that should be obtained.