What is the role of ultrasound in evaluating acute abdominal pain?

Ultrasound for Acute Abdominal Pain

Ultrasound is the initial imaging test of choice specifically for right upper quadrant pain to evaluate for gallbladder disease, but CT with contrast is preferred for most other locations of acute abdominal pain. 1, 2

Imaging Selection Based on Pain Location

Right Upper Quadrant Pain

• Ultrasonography is the definitive first-line imaging modality for patients presenting with right upper quadrant pain, primarily to evaluate for acute cholecystitis and biliary pathology 1, 2, 3
• This recommendation is based on ultrasound's high sensitivity and specificity for detecting gallstones, gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy's sign 1

Right Lower Quadrant Pain

• CT of the abdomen and pelvis with IV contrast is the initial imaging test of choice for evaluating right lower quadrant pain, with 95% sensitivity and 94% specificity for appendicitis 1, 2, 3
• Ultrasound may be considered as an alternative initial study in specific populations where radiation exposure is a concern (pregnant women, women of reproductive age, children) before proceeding to CT if results are inconclusive 2, 3

Left Lower Quadrant Pain

• CT with contrast is recommended as the initial imaging test, with sensitivity >95% for detecting diverticulitis and its complications (abscess, perforation, fistula) 2, 3

Nonspecific or Diffuse Abdominal Pain

• CT of the abdomen and pelvis with IV contrast is the optimal initial choice, especially when fever or serious illness is suspected 2, 3
• CT alters the leading diagnosis in 49% of patients and changes management plans in 42% of cases with nonlocalized abdominal pain 3

Specific Clinical Scenarios Where Ultrasound Excels

Ultrasound provides particular diagnostic value in several acute conditions beyond right upper quadrant pain:

• Abdominal aortic aneurysm and its complications: Critical for rapid bedside assessment in unstable patients 4, 5
• Hemoperitoneum in trauma patients: Rapid detection of free fluid using focused assessment 4, 5
• Ectopic pregnancy: Essential first-line imaging in women of childbearing age with positive β-hCG 2, 5
• Renal/ureteral colic: Can identify hydronephrosis and stones, though non-contrast CT remains more sensitive 4
• Bowel obstruction: Can detect dilated bowel loops and absent peristalsis 5

Critical Limitations of Ultrasound

When Ultrasound is Inadequate

• Conventional radiography has limited diagnostic value for most causes of acute abdominal pain and should not be routinely ordered 1, 6, 3
• Ultrasound is operator-dependent with variable sensitivity compared to CT for conditions like appendicitis and diverticulitis 3
• After a non-diagnostic or negative ultrasound, CT with IV contrast is the definitive next step rather than repeating ultrasound or obtaining plain films 3

Specific Pitfalls to Avoid

• Do not assume a negative ultrasound rules out serious pathology, as ultrasound has high specificity but lower sensitivity for many intra-abdominal conditions compared to CT 3
• Do not delay CT imaging in clinically deteriorating patients while pursuing additional non-diagnostic ultrasound views 3
• Always obtain β-hCG testing before imaging in all women of childbearing age to avoid missing ectopic pregnancy and to guide imaging choices 2, 6, 3

Radiation Considerations

• Ultrasound and MRI avoid ionizing radiation exposure, making them preferred in pregnant patients, children, and young adults when clinically appropriate 1, 3
• Consider using ultrasound as the initial imaging method for suspected appendicitis before proceeding to CT, particularly in radiation-sensitive populations 1, 2
• Abdominal CT exposes patients to approximately 10 mSv of radiation compared to annual background radiation of 3 mSv 3

Special Population Considerations

Pregnant Patients

• Ultrasound is the first-line imaging modality, with MRI without contrast as the preferred next step if ultrasound is non-diagnostic 3
• MRI has 97% sensitivity and 95% specificity for diagnosing appendicitis in pregnancy 3

Women of Reproductive Age

• Always consider gynecologic causes (ectopic pregnancy, ovarian torsion, pelvic inflammatory disease) 2
• Transvaginal or transabdominal pelvic ultrasound is the initial imaging study when gynecologic etiology is suspected 3

Elderly Patients

• Have higher likelihood of malignancy, diverticulitis, and vascular causes requiring CT evaluation 2
• May present with atypical symptoms requiring more thorough evaluation even with normal laboratory tests 2

Systematic Ultrasound Approach

Point-of-care ultrasound using systematic protocols (such as the ACUTE-ABDOMEN mnemonic) can expedite diagnosis and management in emergency settings by integrating evaluation of: aortic aneurysm, IVC collapse, perforated viscus, trauma/free fluid, ectopic pregnancy, appendicitis, biliary tract, distended bowel, obstructive uropathy, and gonadal torsion 5