# Abdominal and Pelvic Trauma

## Epidemiology and Mechanisms

### Overview

Abdominal trauma is a leading cause of preventable death in trauma patients. Blunt abdominal trauma results most commonly from motor vehicle collisions, followed by falls, assaults, and sports injuries. Penetrating abdominal trauma is caused by gunshot wounds and stab wounds. The fundamental challenge is that the physical examination is unreliable in 20 to 40 percent of cases due to intoxication, distracting injuries, altered mental status, and spinal cord injury.

### Anatomic Considerations

Intraperitoneal organs include the spleen (the most commonly injured organ in blunt trauma), the liver (the second most common in blunt and the most common in penetrating trauma), the small bowel, and the stomach. Retroperitoneal organs — the kidneys, pancreas, aorta, IVC, and the second through fourth portions of the duodenum — are easily missed on initial evaluation. Pelvic organs include the bladder, uterus, rectum, and iliac vessels. An important anatomic consideration is that the diaphragm extends to the fourth intercostal space at full expiration, meaning that "thoracoabdominal" wounds can injure abdominal contents.

## FAST Examination

### Technique

The Focused Assessment with Sonography for Trauma (FAST) examines four views: the right upper quadrant (Morrison's pouch, which is the most sensitive location for detecting free fluid), the left upper quadrant (splenorenal recess), the suprapubic view (pouch of Douglas or rectovesical space), and the subxiphoid view (for pericardial effusion). The examiner looks for anechoic free fluid representing blood. The exam takes 2 to 3 minutes when performed by an experienced operator.

### Performance Characteristics

The FAST exam has a sensitivity of 73 to 88 percent for significant hemoperitoneum (operator and body habitus dependent) and a specificity of 95 to 100 percent. However, a negative FAST does not exclude intra-abdominal injury — sensitivity for solid organ injury without significant free fluid is poor, and hollow viscus injury is frequently missed. The minimum detectable volume of free fluid is approximately 200 to 500 mL, varying by location and operator. False negatives occur with obesity, subcutaneous emphysema, early presentations before significant bleeding, retroperitoneal hemorrhage, and isolated hollow viscus injury.

### Clinical Application

The clinical application follows a simple framework. An unstable patient with a positive FAST should go to operative intervention. An unstable patient with a negative FAST should prompt consideration of other hemorrhage sources (chest, pelvis, retroperitoneum, or external bleeding), with repeat FAST or diagnostic peritoneal lavage performed. A stable patient with a positive FAST should undergo CT of the abdomen and pelvis with IV contrast to characterize the injury. A stable patient with a negative FAST should receive serial examinations, with CT obtained if clinical concern persists.

### Extended FAST (eFAST)

The extended FAST adds bilateral thoracic views for pneumothorax and hemothorax detection. Lung sliding is assessed, and absent sliding suggests pneumothorax. The eFAST is more sensitive than supine chest X-ray for pneumothorax.

## CT in Abdominal Trauma

### Indications

CT of the abdomen and pelvis with IV contrast is indicated for hemodynamically stable patients with a concerning mechanism or exam findings, significant mechanisms with an unreliable exam (intoxication, GCS below 15, or distracting injuries), seat-belt sign or steering wheel injury, hematuria, pelvic fracture, and a positive FAST in a stable patient (to characterize and grade the injury).

### Key Findings

Free fluid without solid organ injury should raise suspicion for hollow viscus injury (mesenteric or bowel injury). Active contrast extravasation indicates ongoing hemorrhage that may require angioembolization or operative intervention. Pneumoperitoneum indicates hollow viscus perforation and is an operative finding. Solid organ injury grading using the AAST scale guides subsequent management decisions.

### Limitations

The patient must be hemodynamically stable for transport to the scanner. Oral contrast delays evaluation and is generally not recommended for trauma CT. Hollow viscus injuries may have subtle findings, requiring a high index of suspicion. CT with IV contrast is the standard trauma protocol.

## Solid Organ Injury Management

### Splenic Injury

The spleen is the most commonly injured organ in blunt abdominal trauma. The AAST grading system ranges from grade I (subcapsular hematoma less than 10 percent or laceration less than 1 cm deep) to grade V (shattered spleen or hilar vascular injury). Non-operative management (NOM) is successful in 60 to 90 percent of blunt splenic injuries in hemodynamically stable patients. Requirements for NOM include hemodynamic stability, absence of peritonitis, a reliable serial examination, and an available operating room. Angioembolization is used for grades III through V with a contrast blush or moderate hemoperitoneum. Post-splenectomy vaccinations — pneumococcal, meningococcal, and Haemophilus influenzae type b — should ideally be given 14 days postoperatively but may be administered at discharge if adherence is a concern.

### Hepatic Injury

The liver is the most commonly injured organ in penetrating abdominal trauma. AAST grading ranges from I to VI. Non-operative management is successful in up to 80 percent of blunt hepatic injuries. Angioembolization is indicated for active extravasation. Complications include delayed hemorrhage, biloma, bile leak, and hepatic abscess. Grade V and VI injuries with hemodynamic instability require damage control surgery with perihepatic packing.

### Renal Injury

Hematuria is the most common finding in renal injury, but the degree of hematuria does not correlate with injury severity. AAST grading ranges from I to V. Non-operative management is standard for grades I through IV in stable patients. Grade V injuries (shattered kidney or renal pedicle avulsion) usually require operative management. Angioembolization is used for contained vascular injuries.

## Hollow Viscus Injury

### Small Bowel Injury

The small bowel is the most commonly injured hollow organ in penetrating trauma. Blunt mechanisms include deceleration (causing mesenteric tears), seat-belt compression, and direct blows. CT findings include free fluid without solid organ injury, bowel wall thickening, mesenteric stranding, and pneumoperitoneum. Diagnosis is often delayed, making serial abdominal exams critical. All small bowel injuries require operative repair.

### Colon and Rectal Injury

Colon and rectal injuries result primarily from penetrating mechanisms. Primary repair is now standard for most colon injuries, with diversion or colostomy reserved for destructive injuries, significant contamination, or hemodynamic instability. Extraperitoneal rectal injuries may be managed with proximal diversion.

### Gastric and Diaphragm Injury

Gastric injury is usually caused by penetrating mechanisms, and blood in the nasogastric aspirate is suggestive. All diaphragmatic injuries require repair because they do not heal spontaneously.

## Pelvic Trauma

### Pelvic Fracture Classification

Pelvic fractures are classified by mechanism. Lateral compression (LC) fractures are the most common, producing internal rotation of the hemipelvis with lower hemorrhage risk. Anteroposterior compression (APC) fractures produce an "open book" injury with external rotation, higher hemorrhage risk, and disruption of the pelvic venous plexus. Vertical shear (VS) fractures carry the highest mortality with complete hemipelvic instability. Combined mechanism fractures display mixed patterns.

| Type | Mechanism | Pelvic Deformity | Hemorrhage Risk | Stability |
|------|-----------|-----------------|-----------------|-----------|
| Lateral Compression (LC) | Side impact | Internal rotation | Lower | Variable |
| Anteroposterior Compression (APC) | Front-to-back force | "Open book" (external rotation) | Higher | Unstable |
| Vertical Shear (VS) | Axial load (fall from height) | Cephalad displacement | Highest | Grossly unstable |

### Hemorrhage in Pelvic Fractures

Pelvic fractures can cause life-threatening hemorrhage, with venous sources accounting for 80 to 90 percent of bleeding. Estimated blood loss can exceed 3 to 4 liters. Sources include the presacral venous plexus (the most common source), internal iliac branches, bone surfaces, and soft tissue.

### Pelvic Binder

The pelvic binder is applied at the level of the greater trochanters (not the iliac crests). It circumferentially compresses the pelvis to reduce volume, tamponade venous bleeding, and approximate fracture fragments. Either commercial binders or improvised options (a sheet wrapped and clamped) can be used. The binder should not be removed until hemodynamic stability is achieved and definitive management is planned. Pelvic binders are rarely contraindicated in lateral compression fractures with overriding fragments.

### Management Algorithm for Unstable Pelvic Fractures

The management algorithm begins with pelvic binder application and massive transfusion protocol activation. If the patient remains unstable after binder placement and resuscitation, options include angioembolization (for arterial sources), preperitoneal pelvic packing (for venous sources, which is gaining favor as a bridge or alternative), and REBOA (an emerging option with zone III placement). External fixation is considered for persistent mechanical instability.

### Associated Injuries

Bladder injury should be suspected with gross hematuria and a pelvic fracture. A CT cystogram (which must be a retrograde fill study, not simply delayed images) distinguishes extraperitoneal bladder injury (managed with Foley catheter drainage) from intraperitoneal bladder injury (which requires operative repair). Urethral injury is suggested by blood at the meatus, a high-riding prostate, or perineal ecchymosis, and a retrograde urethrogram must be performed before attempting Foley catheterization. Open pelvic fractures carry mortality rates up to 50 percent and require operative management.

## Penetrating Abdominal Trauma

### Gunshot Wounds

All gunshot wounds violating the peritoneal cavity generally require exploratory laparotomy because of the high energy transfer and unpredictable trajectory. CT can help determine trajectory and identify injuries in select stable patients.

### Stab Wounds

Stab wounds are more amenable to selective non-operative management. Anterior abdominal stab wounds in stable, non-peritoneal patients may be managed with serial abdominal examinations every 2 hours for 12 to 24 hours. Local wound exploration is performed first — if the fascia is not violated, discharge is safe. If the fascia is violated in a stable patient, CT or serial exams are appropriate. Flank and back stab wounds traditionally warranted triple-contrast CT (IV, oral, and rectal), though IV-only CT is increasingly accepted.

### Diagnostic Peritoneal Lavage/Aspiration (DPL)

DPL has been largely replaced by FAST and CT but retains a role in specific scenarios. A positive DPL is defined as more than 10 mL of gross blood on aspiration, or lavage fluid with more than 100,000 red blood cells per cubic millimeter, more than 500 white blood cells per cubic millimeter, bile, food particles, or bacteria. DPL is highly sensitive but non-specific, leading to non-therapeutic laparotomies. It remains useful in unstable patients when FAST is indeterminate and CT is not feasible.

<image>A four-panel ultrasound image set demonstrating the FAST examination. Panel 1: RUQ view showing Morrison's pouch (hepatorenal recess) with an anechoic stripe of free fluid between the liver and right kidney. Panel 2: LUQ view showing the splenorenal recess with free fluid. Panel 3: Suprapubic transverse view showing free fluid surrounding the bladder in the pelvis. Panel 4: Subxiphoid view showing the heart with no pericardial effusion (normal). Each panel is labeled with anatomical landmarks and arrows pointing to free fluid where present.</image>

<image>A pelvic fracture classification diagram showing three major types. Panel 1: Lateral compression (LC) — anterior view of pelvis with arrows showing inward force on one hemipelvis, resulting in internal rotation, sacral compression fracture, and ipsilateral pubic rami fractures. Panel 2: Anteroposterior compression (APC) — anterior view showing outward "open book" force with widening of the pubic symphysis and sacroiliac joints, with disruption of the anterior and posterior sacroiliac ligaments. Panel 3: Vertical shear (VS) — anterior view showing cephalad displacement of one hemipelvis with complete disruption of all ligamentous attachments. Hemorrhage risk increases from LC to APC to VS.</image>

<image>A flowchart for the management of blunt abdominal trauma. Starting with "Hemodynamically stable?" If no, proceed to FAST. If FAST positive, go to OR for exploratory laparotomy. If FAST negative, consider other hemorrhage sources (chest, pelvis, retroperitoneum), repeat FAST, or DPL. If hemodynamically stable, proceed to CT abdomen/pelvis with IV contrast. CT results branch into: solid organ injury (grade and consider NOM vs. angioembolization vs. OR), hollow viscus injury (operative management), or negative CT with persistent concern (serial abdominal exams, repeat imaging).</image>

## Clinical Pearls

A negative FAST does not exclude intra-abdominal injury — it rules in hemoperitoneum but has limited sensitivity for solid organ injuries without significant free fluid and misses hollow viscus injury entirely. Free fluid on CT without solid organ injury should be considered hollow viscus injury until proven otherwise. Non-operative management is now standard for most solid organ injuries in hemodynamically stable patients, and the ED physician's role is to ensure stability, grade the injury, and coordinate with surgery. Pelvic binders must be placed at the greater trochanters, not the iliac crests. Blood at the urethral meatus in the setting of a pelvic fracture mandates a retrograde urethrogram before attempting Foley catheterization. Serial abdominal exams remain the cornerstone of evaluating anterior stab wounds managed non-operatively. Post-splenectomy vaccinations are easily forgotten in the trauma setting, so the need should be documented and follow-up ensured.

## References

- Stengel D, et al. Systematic review and meta-analysis of emergency ultrasonography for blunt abdominal trauma. *Br J Surg*. 2001;88:901-912.
- Coccolini F, et al. WSES classification and guidelines for liver trauma. *World J Emerg Surg*. 2016;11:50.
- Coccolini F, et al. WSES guidelines for splenic trauma. *World J Emerg Surg*. 2017;12:40.
- Cullinane DC, et al. EAST practice management guideline for the nonoperative management of blunt hepatic injury. *J Trauma*. 2012;73:S288-S293.
- Costantini TW, et al. AAST/WTA prospective study on non-operative management of penetrating abdominal trauma. *J Trauma Acute Care Surg*. 2018;84:886-893.