The lucky penny: an illustration of the bullet rule.

tory of penetrating trauma sustained multiple gunshot wounds to his torso and left leg. The patient was hemodynamically stable and received a score of 15 on the Glasgow Coma Scale. His clothing was removed, and he was noted to have six bullet wounds: one in the left upper quadrant, one in the left flank, one suprapubic, one in the midline of the lower back, one in the left lateral thigh and one in the left buttock (Figure 1). All of the wounds were small (< 1 cm diameter), semicircular skin defects with no substantial associated loss of soft tissue. Further examination showed that the patient had diffuse peritonitis and gross hematuria. His lower limbs were neurovascularly intact, but severe abdominal pain caused him to move them with difficulty. Sonography showed intraperitoneal fluid. Radiographs of his torso and left leg showed two bullets in his left thigh (Figure 2A) and none in his torso. Based on these findings and the patient’s recollection of being shot from behind, we believed wound 2 represented the entrance wound of one bullet, wound 1 was the corresponding exit wound, wound 5 was the entrance wound of a second bullet and wound 3 its corresponding exit wound. Because two bullets ap peared to be visible on a radiographic image of the patient’s left thigh, we surmised that wounds 4 and 6 represented the entrance wounds of two separate bullets. During a laparotomy, injuries to the patient’s bowel and bladder were identified and repaired. The wound to the patient’s left thigh was also explored during surgery, as what was thought to be a bullet was palpable superficially. However, this “bullet” was in fact a Canadian penny that had apparently been struck by a bullet and driven into the subcutaneous tissues of the thigh (Figure 2B). The bullet itself was deeper in the thigh and was left in situ. The “bullet rule” has been previously de scribed and is used to avoid missing important injuries by better understanding the potential trajectory and location of bullets. The rule states that the sum of the number of bullet wounds and actual bullets seen on diagnostic imaging should always be an even number. Bullets can either traverse the body and leave both entrance and exit wounds, or they can enter and remain in the body. In the latter case, the patient would have one bullet wound and one bullet visible on imaging. For our patient, finding a penny instead of a bullet led us to look for another in situ bullet, as he now had six bullet wounds and only one bullet evident on imaging (i.e., a sum of 7). Postoperative radiographs located the missing bullet in the soft tissues of the patient’s right thigh (Figure 3). Presumably, one bullet entered the patient’s left buttock, struck his pelvis and deflected through the soft tissues of his right thigh. Fortunately, there was no associated vascular or bony injury to the patient’s right leg.