The lucky penny: an illustration of the bullet rule

Discussion

Patients who sustain gunshot wounds are at risk for serious injuries and often require emergency surgery.3 All clothing should be removed and the patient’s entire body examined from head to toe to identify all gunshot wounds. Determining the trajectory of bullets is critical in evaluating these patients, as the trajectory can determine the need for surgery and prognosis. For example, selected tangential abdominal gunshot wounds may be managed nonoperatively.4^,5 Conversely, other trajectories may suggest unfavourable outcomes and the need for surgery to control damage.6

Determining the trajectory of a bullet can sometimes be straightforward. Entrance wounds often have typical signs such as muzzle marks, tattooing and soot. These signs may appear as dark, circular discolourations and punctate stippling on the skin surrounding the wound, created by the deposition of combusted and uncombusted gun powder exiting the barrel of the weapon. In addition, entrance wounds may have inverted, irregular edges with stellate lacerations caused by the injection of gases into the subcutaneous tissue.7 Exit wounds generally have everted, irregular edges, usually lack evidence of soot and tattooing and are often larger than entrance wounds.7 Furthermore, most bullets that enter the body travel in a straight line.2^,3 Thus, determining a bullet’s trajectory often only requires identifying the entrance and exit wounds and determining the straight line between the two points.

Substantial pitfalls exist, however, with applying this simple method. Although entrance and exit wounds can have typical appearances, this determination is not always clear in the acute setting, and misinterpretation may hinder criminal and legal investigations.8^–10 One such example is the forensic controversy that arose after the assassination of John F. Kennedy. The frontal wound in Kennedy’s neck was originally described by the attending emergency physician as being an entrance wound, thereby contributing to the confusion over the number of shots fired and the possibility of a second shooter. However, the trauma surgeons involved later testified that the wound in front of the throat could have been either an entrance or exit wound.11 As such, current forensic recommendations are that trauma clinicians not document the interpretation of wounds as “entrance” or “exit.” The wound should only be described in detail and, if possible, photographed.7^,9

Another pitfall in determining trajectory is the so-called “wandering bullet.” One reason for this phenomenon is deflection. Bullets that strike rigid changes in density, such as bone, will often be deflected from their initial course.12 Another explanation for a change in trajectory is bullet embolization, first reported by Schmidt in 1885 as described by Smalls and Siram.13 In that account, the bullet had penetrated the chest, entered the left pulmonary vein and embolized to the left femoral artery. Since that first description, numerous other authors have reported their experiences with bullet embolization.14^,15

The experience of our patient highlights the clinical importance of the bullet rule in helping to determine the trajectory of the wandering bullet and avoiding missed injuries. Accounting for all bullets and all bullet wounds allows for a basic reconstruction of each bullet’s trajectory, thus identifying organs and tissues at risk of damage. If the sum of bullet wounds and in situ bullets is not an even number, further diagnostic imaging is necessary to locate the missing bullet.