During the secondary survey of a 28-year-old woman with blunt abdominal trauma, the trauma surgeon must differentiate between a solid organ injury (liver laceration) and a hollow viscus injury (small bowel perforation). Which finding is the most reliable discriminator between these two injury patterns?

## Discriminating Solid Organ from Hollow Viscus Injury ### Pathophysiologic Distinction **Key Point:** Solid organ injuries (liver, spleen, kidney) typically present with **hemorrhage and free fluid** on imaging, whereas hollow viscus injuries (bowel perforation) present with **pneumoperitoneum** (free air) and **peritoneal contamination** with minimal initial free fluid. ### Clinical Comparison Table | Feature | Solid Organ Injury (Liver) | Hollow Viscus Injury (Bowel) | |---------|---------------------------|------------------------------| | **FAST finding** | **Free fluid (blood)** | Minimal/no free fluid initially | | **Pneumoperitoneum** | Absent | **Present (pathognomonic)** | | **Peritoneal signs** | Develop later (if bleeding) | **Immediate/early** | | **Mechanism** | Bleeding into peritoneum | Bacterial contamination | | **Onset of peritonitis** | Gradual (hours) | **Rapid (minutes–hours)** | | **CT/imaging** | Laceration with blood | Free air under diaphragm | | **Immediate management** | Observation ± transfusion | **Urgent surgical exploration** | ### The Discriminating Feature **High-Yield:** The combination of **free fluid on FAST + peritoneal signs + pneumoperitoneum on CT/X-ray** is pathognomonic for hollow viscus injury. Pneumoperitoneum is the single most specific finding—it indicates perforation of a gas-containing viscus (stomach, small bowel, colon). **Clinical Pearl:** In contrast, a liver laceration may show free fluid on FAST (blood), but **pneumoperitoneum is absent** unless there is concurrent hollow viscus injury. The presence of free air is the key discriminator. **Mnemonic:** **SOAP** — **S**olid organ = **O**nly blood; **H**ollow = **A**ir + **P**eritonitis ### Secondary Survey Context During the secondary survey: 1. **FAST examination** identifies free fluid (nonspecific—could be blood or bowel contents) 2. **Peritoneal examination** (guarding, rebound, rigidity) suggests peritoneal irritation 3. **Imaging (CT or upright CXR)** reveals **pneumoperitoneum** → **hollow viscus injury** → urgent surgery 4. **Absence of air** → likely solid organ injury → consider conservative management if hemodynamically stable **Warning:** Early in hollow viscus injury, free fluid may be minimal or absent on FAST; do NOT rely on FAST alone. Always obtain imaging (CT or upright CXR) to look for free air. [cite:ATLS 10th Edition Ch 5; Sabiston Textbook of Surgery 21e Ch 19]