A 34-year-old male presents to the emergency department after a high-speed motor vehicle collision. He is hemodynamically unstable with a blood pressure of 85/50 mmHg and a heart rate of 130 bpm. The patient has abdominal pain but no external signs of trauma. After a FAST (Focused Assessment with Sonography for Trauma) exam showing free fluid in the abdomen, which of the following should raise suspicion for a retroperitoneal injury?
Isolated rib fracture
Abdominal bruising and Cullen's sign
Pelvic fracture and lumbar spine fracture