What is the indication for a CT (Computed Tomography) angiogram of the abdomen and pelvis in an adult patient presenting with abdominal or pelvic pain?

CT Angiography of the Abdomen and Pelvis: Clinical Indications

CT angiography (CTA) of the abdomen and pelvis is primarily indicated for detecting active arterial hemorrhage, vascular injuries, mesenteric ischemia, and vascular complications in trauma or acute abdominal conditions where arterial phase imaging is critical for diagnosis and treatment planning.

Primary Indications for CTA Abdomen/Pelvis

Trauma and Active Hemorrhage

• CTA is the preferred imaging modality for detecting active arterial bleeding in blunt abdominal trauma, particularly when assessing abdominopelvic viscera and soft tissues 1
• CTA demonstrates superior sensitivity for detecting splenic vascular injuries compared to standard portal venous phase CT alone 1
• Unstable pelvic fractures (vertical shear and anterior-posterior compression injuries) are associated with higher rates of active hemorrhage that can be accurately diagnosed by CTA and may require surgical or vascular interventional treatment 1
• CTA allows for assessment of pseudoaneurysm formation and other arterial injuries requiring 3D reconstructions for detailed evaluation 1

Acute Gastrointestinal Bleeding

• When a patient presents with overt large-volume upper GI bleeding and is clinically unstable or when the bleeding source location is unclear, visceral angiography (which can follow CTA) detects bleeding rates as low as 0.5 mL/min 1
• CTA serves as a critical bridge to interventional angiography, allowing simultaneous treatment by embolization 1
• Early performance of angiography (within first 5 hours of presentation) is associated with significantly higher visualization of extravasation, making timely CTA essential 1

Mesenteric Ischemia

• CTA of the abdomen and pelvis provides the best accuracy and inter-reader agreement for grading mesenteric vessel stenosis compared to MRA and ultrasound, with sensitivity and specificity of 95-100% 1
• CTA is the first-line imaging technique for both acute and chronic mesenteric ischemia, having replaced conventional angiography as the primary diagnostic modality 1
• CTA accurately diagnoses median arcuate ligament syndrome as a potential cause of chronic ischemia 1
• CTA can exclude other causes of chronic abdominal pain while evaluating vascular pathology 1

Severe Pelvic Inflammatory Disease Complications

• The American College of Radiology recommends contrast-enhanced CT abdomen and pelvis for detecting complications in severe PID, particularly when clinical presentation is unclear or ultrasound is nondiagnostic 2
• CT with IV contrast demonstrates 89% sensitivity for urgent diagnoses compared to 70% for ultrasound 2
• CT accurately identifies tubo-ovarian abscess appearing as complex cystic masses with thick enhancing walls 2

Right Lower Quadrant Pain in Young Women

• When ultrasound is nondiagnostic or equivocal in young women with right lower quadrant pain, CT with IV contrast should be obtained to achieve 94% sensitivity for appendicitis and 89% sensitivity for urgent diagnoses 3
• CT can identify ovarian torsion findings including enlarged, hypoenhancing ovary, swirling appearance of vascular pedicle, and abnormal ovarian orientation 3

Critical Technical Considerations

Contrast Administration

• IV contrast is essential for CTA—noncontrast CT has significantly lower sensitivity for detecting both visceral organ and vascular injuries and should be avoided when possible 1
• Arterial phase imaging is required for optimal detection of active bleeding and vascular injuries 1
• Portal venous phase imaging may be obtained in conjunction with arterial phase as well as delayed imaging for comprehensive evaluation 1

Oral Contrast

• Oral contrast is NOT recommended in trauma settings as it does not alter sensitivity or specificity for blunt abdominal injuries and delays definitive diagnosis 1

Common Pitfalls to Avoid

• Failing to use IV contrast is a critical diagnostic error, as the bulk of evidence supporting CT in acute abdominal/pelvic conditions refers specifically to contrast-enhanced imaging 2
• Ordering standard "CT abdomen/pelvis with contrast" instead of specifically requesting CTA when arterial phase imaging is needed—these are distinct procedures 1
• Relying on noncontrast CT when vascular pathology is suspected, which has inadequate sensitivity for vascular injuries 1

When Alternative Imaging May Be Preferred

• MRI may be considered when CT findings are inconclusive or for detailed surgical planning, demonstrating 95% sensitivity and 89% specificity for certain pelvic pathology 2
• Ultrasound with Doppler serves as an appropriate initial screening tool for chronic mesenteric ischemia in fasting patients, though CTA remains superior for definitive diagnosis 1
• In pregnant trauma patients, ultrasound (FAST) should be prioritized when possible to avoid radiation, though CT remains necessary when ultrasound is inadequate 1