How is acute abdomen diagnosed?

Diagnostic Imaging for Acute Abdomen Conditions

For diagnosing acute abdomen conditions, the imaging modality should be selected based on the suspected diagnosis, patient characteristics, and location of pain, with CT being the preferred initial imaging for non-pregnant adults with non-localized abdominal pain. 1

General Approach to Acute Abdomen Imaging

Non-pregnant Adults

• Non-localized abdominal pain: CT abdomen and pelvis with IV contrast is the preferred initial imaging modality 1
• Right upper quadrant pain: Ultrasound is the recommended first-line imaging 1
• Right lower quadrant pain (suspected appendicitis): CT abdomen and pelvis with IV contrast 1
• Left lower quadrant pain (suspected diverticulitis): CT abdomen and pelvis with IV contrast 1
• Suspected intra-abdominal abscess: CT abdomen and pelvis with IV contrast 1
• Suspected cholecystitis/cholangitis: Ultrasound as initial imaging; HIDA scan, MRI/MRCP, or CT for inconclusive cases 1

Pregnant Patients

• Suspected appendicitis: Ultrasound as initial imaging; MRI for inconclusive results 1
• Suspected cholecystitis/cholangitis: Either ultrasound or MRI can be used as initial imaging 1
• Suspected intra-abdominal abscess: Either ultrasound or MRI can be used 1
• Suspected diverticulitis: Either ultrasound or MRI can be considered 1

Pediatric Patients

• Suspected appendicitis: Ultrasound as initial imaging; MRI or CT with IV contrast for inconclusive results 1
• Suspected intra-abdominal abscess: Ultrasound as initial imaging; MRI or CT for inconclusive results 1

Specific Acute Abdomen Conditions and Their Imaging

Appendicitis

• Adults: CT abdomen/pelvis with IV contrast
• Children: Ultrasound first, followed by MRI or CT if inconclusive
• Pregnant patients: Ultrasound first, followed by MRI if inconclusive
• Key imaging findings: Appendiceal diameter >6mm, wall thickening, periappendiceal fat stranding

Cholecystitis

• All patients: Ultrasound as first-line imaging
• Key findings: Gallstones, gallbladder wall thickening, pericholecystic fluid, sonographic Murphy's sign
• Inconclusive cases: HIDA scan, MRI/MRCP, or CT with IV contrast

Diverticulitis

• Adults: CT abdomen/pelvis with IV contrast
• Pregnant patients: Ultrasound or MRI
• Key findings: Colonic wall thickening, pericolonic fat stranding, diverticula

Small Bowel Obstruction

• All non-pregnant patients: CT abdomen/pelvis with IV contrast
• Key findings: Dilated small bowel loops, transition point, decompressed distal bowel

Intra-abdominal Abscess

• Adults: CT abdomen/pelvis with IV contrast
• Children: Ultrasound first, followed by CT or MRI if inconclusive
• Pregnant patients: Ultrasound or MRI
• Key findings: Fluid collection with enhancing rim, air bubbles, surrounding inflammation

Important Considerations and Pitfalls

• IV contrast use: Generally recommended for CT in acute abdomen to improve diagnostic accuracy, but non-contrast CT may be appropriate in certain situations like renal insufficiency 1
• Radiation concerns: Consider ultrasound or MRI for pregnant patients and children to minimize radiation exposure 1
• Operator dependency: Ultrasound quality is highly dependent on the operator's skill and patient factors (obesity, bowel gas) 1, 2
• Clinical correlation: Imaging findings should always be interpreted in the context of clinical presentation and laboratory findings 3
• Timing considerations: Delays in appropriate imaging can increase morbidity and mortality, especially in conditions like mesenteric ischemia or perforated viscus 4
• Post-bariatric surgery patients: Require special attention as anatomical alterations can make imaging interpretation challenging; CT with oral and IV contrast is preferred 1

Special Populations

Elderly Patients

• Lower threshold for advanced imaging as they may present with atypical symptoms and have higher risk of serious pathology 3
• CT is often preferred due to the higher prevalence of multiple comorbidities

Immunocompromised Patients

• Lower threshold for CT imaging as infections may present with minimal findings 1
• Consider broader differential diagnoses including opportunistic infections

Post-surgical Patients

• CT with oral and IV contrast is generally preferred to evaluate for complications like anastomotic leak, abscess, or obstruction 1

By following these imaging recommendations based on patient characteristics and suspected diagnosis, clinicians can optimize the diagnostic approach to acute abdomen conditions while minimizing unnecessary radiation exposure and improving patient outcomes.