After a motor vehicle collision, a patient with abdominal pain has a negative FAST exam. What organ injury is most likely if the patient subsequently develops rebound tenderness, fever, and elevated WBC?

The scenario presented describes a patient who initially has a negative FAST (Focused Assessment with Sonography for Trauma) exam but later develops rebound tenderness, fever, and elevated white blood cell count (WBC). These clinical signs suggest an inflammatory process, likely due to an injury that has led to peritoneal irritation or possibly an intra-abdominal infection.

The small bowel is particularly vulnerable to injuries from blunt abdominal trauma, which can occur in motor vehicle collisions. Even when a FAST exam is negative, it does not completely rule out small bowel injuries. Rebound tenderness indicates irritation in the abdominal cavity, which can result from a small bowel perforation or laceration, leading to peritonitis. Fever and elevated WBC count are also consistent with infection or inflammatory responses that could arise from such an injury.

While injuries to the large intestine, stomach, or kidney can also cause similar symptoms, they are less commonly associated with the acute presentation following a negative FAST, especially when rebound tenderness and signs of infection begin to emerge later on. Small bowel injuries often take time to manifest in this way, as opposed to other organs which might present with more immediate or different symptoms. Thus, a small bowel injury is the most likely culprit given these specific findings.