What are the indications for a whole abdomen computed tomography (CT) scan in adult patients with a history of abdominal trauma, cancer, or symptoms suggestive of abdominal pathology, such as severe abdominal pain, vomiting, or changes in bowel habits?

Indications for Whole Abdomen CT Scan

Contrast-enhanced CT of the abdomen and pelvis is the primary diagnostic modality for evaluating suspected abdominal trauma, acute nonlocalized abdominal pain, and when clinical examination is unreliable due to altered mental status, intoxication, or distracting injuries. 1

Trauma Indications

Blunt Abdominal Trauma

• Perform contrast-enhanced thoraco-abdominal CT for all patients with suspected severe abdominal trauma to identify injuries and potentially reduce mortality. 1
• CT demonstrates excellent diagnostic performance for solid organ injuries (liver, spleen, kidney) with 98% sensitivity and 98% specificity. 1
• Performance is lower but still acceptable for hollow viscus injuries with 85% sensitivity and 96% specificity. 1
• For penetrating abdominal injuries, CT shows 81% sensitivity and 85% specificity, though performance is more limited than for blunt trauma. 1

Critical Caveat for Trauma

• Do not rely exclusively on CT for hollow organ injuries (bowel, mesentery) or penetrating trauma—maintain high clinical suspicion and consider serial examination or repeat imaging if initial CT is negative but clinical concern persists. 1
• CT signs like pneumoperitoneum or mesenteric infiltration have poor sensitivity (9%) for hollow viscus injury. 1
• Small bowel perforation can be missed on initial CT in up to 8-36% of cases depending on the study. 1

Non-Trauma Acute Abdominal Pain

Strong Indications for CT

• CT with IV contrast is the preferred initial imaging for nonlocalized abdominal pain with constipation, changing the leading diagnosis in 49% of patients and altering management in 42%. 2, 3
• CT identifies alternative diagnoses including diverticulitis, bowel obstruction, infectious enterocolitis, inflammatory bowel disease, and pelvic pathology. 2
• Particularly valuable when symptoms persist despite initial treatment or when alarm features are present (weight loss, blood in stool, family history of IBD or cancer). 2

When CT May Be Deferred

Patients with isolated blunt abdominal trauma are at low risk and may not require CT if ALL of the following are absent: 1

• Abdominal tenderness
• Hypotension
• Altered mental status (Glasgow Coma Scale <14)
• Costal margin tenderness
• Abnormal chest radiograph
• Hematocrit <30%
• Hematuria (≥25 RBCs/HPF)

This clinical decision rule allows selective imaging rather than routine scanning, as only 10-24% of patients scanned for blunt trauma have actual intra-abdominal injury. 1

Technical Considerations

Contrast Administration

• IV contrast is essential and should be used routinely for abdominal trauma CT. 1
• Oral contrast does NOT improve diagnostic accuracy for solid organ or most bowel injuries in trauma and delays scanning by 7-46 minutes. 1
• Oral contrast shows extravasation in only 2.9% of proven small bowel perforations. 1
• Skip oral contrast in trauma patients to expedite diagnosis without sacrificing accuracy. 1

Radiation Risk vs. Benefit

• The number needed to scan to save one life in severe trauma is 20-40 patients, while 322-1,250 scans are required to cause one lethal cancer. 1
• The mortality benefit substantially outweighs radiation risk in appropriate clinical scenarios. 1

Common Pitfalls to Avoid

• Never rely solely on plain radiography for acute abdominal evaluation—it has limited sensitivity and rarely changes management. 2
• Do not assume a negative CT rules out all pathology, especially for pancreatic, duodenal, and hollow viscus injuries—maintain clinical vigilance. 1, 4
• Avoid routine CT in low-risk trauma patients meeting all seven criteria above—this reduces unnecessary radiation exposure. 1
• In hemodynamically unstable patients, do not delay surgical intervention for CT—proceed directly to laparotomy. 1
• For persistent pain after negative CT, consider repeat CT at 12-24 hours with IV contrast or MRI rather than assuming no pathology exists. 4