Abdominal gunshots and CT scanning are usually thought to be mutually exclusive. The usual algorithm generally means a prompt trip to the operating room. But as with many things in the management of trauma, there are always exceptions. The key is to understand when exactly one of those exceptions is warranted.
Exception 1: Did it really enter the abdomen? Gunshots have enough energy that they usually do get inside. However, freaky combinations of trajectory and body habitus do occur. There are three tests that must be passed in order to entertain the possibility that the bullet may not have made it inside your patient: physiology, anatomy, and physical exam. For physiology, the patient must be completely hemodynamically stable. Anatomically, the trajectory must make sense. If the known wounds and angles allow a tangential course make sense, then fine. But if there is a hole in the epigastrium and another next to the spine, you have to assume the bullet went straight through. Finally, the physical exam must be normal. No peritonitis. No generalized guarding. Focal tenderness only in the immediate area of any wounds. If all three of these criteria are passed, then a CT can be obtained to demonstrate the trajectory.
Exception 2: Did it enter an unimportant area of the abdomen? Well, there’s really only one of these, and that’s the area involving the right lobe of the liver and extending posteriorly and lateral to it. If the bullet hole(s) involve only this area, and the three tests above are passed, CT may confirm an injury that can be observed. However, there should only be a minimal amount of free fluid, and no soft tissue changes of any kind adjacent to bowel.
Exception 3: A prompt trauma lap was performed, but you think you need more information afterwards. This is rare. The usual belief is that the eyes of the surgeon provide the gold standard evaluation during a trauma lap. For most low velocity injuries with an easily understood trajectory, this is probably true. However, high velocity injuries, those involving multiple projectiles, or complicated trajectories (side to side) can be challenging for even the most experienced surgeon. Some areas (think retroperitoneum or deep in the pelvis) are tough to visualize completely, especially when there’s blood everywhere. These are also the cases most likely to require damage control surgery, so once the patient has been temporarily closed, warmed and resuscitated, a quick trip to CT may be helful in revealing unexpected shrapnel, unsuspected injuries, or other issues that may change your management. Even a completely unsurprising scan can provide a higher sense of security.
Bottom line: CT of the abdomen and gunshots to that area may actually coexist in some special cases. Make sure the physiology, anatomy and physical exam criteria are passed first. I also make a point of announcing to all trainees that taking these patients to CT is not the norm, and carefully explain the rationale. Finally, apply the concept of the null hypothesis to this situation. Your null hypothesis should state that your patient does not need a CT after gunshot to the abdomen, and you have to work to prove otherwise!