What is the most appropriate diagnostic test to evaluate a painless abdominal mass?

CT Abdomen and Pelvis with IV Contrast

CT abdomen and pelvis with IV contrast is the most appropriate initial diagnostic test for evaluating a painless abdominal mass. 1

Why CT is the Preferred Initial Test

CT with IV contrast is essential because it characterizes the mass origin, determines tissue enhancement patterns to distinguish benign from malignant lesions, assesses size and relationship to surrounding structures, evaluates vascular involvement, and guides definitive management. 1 The American College of Radiology specifically recommends this as the most appropriate initial investigation for painless abdominal masses. 1

Diagnostic Impact

• CT alters the leading diagnosis in 49-54% of patients with abdominal pathology and changes management plans in 24-42% of cases. 2, 1
• CT correctly identifies the organ of origin and assesses for malignancy with high accuracy. 1
• Including the pelvis in the scan range is critical because masses may extend into the pelvis or arise from pelvic organs, which was essential in 75.5% of cases in surgical series. 1

Technical Protocol

• A single-phase examination with IV contrast is typically sufficient for diagnosis without requiring pre-contrast or delayed phases. 1
• IV contrast is essential for assessing nodular wall thickening, soft tissue attenuation patterns, and enhancement characteristics that distinguish malignant from benign lesions. 2
• Neutral oral contrast (water or dilute barium) may be added when gastric or bowel pathology is specifically suspected. 2

Why NOT the Other Options

Plain Radiography (Not Listed but Worth Mentioning)

• Abdominal X-rays have severely limited diagnostic value with only 49% sensitivity even for bowel obstruction and provide no tissue characterization. 1
• Plain films should not be obtained first as they will not change management and only delay definitive diagnosis. 1

MRI Abdomen (Option B)

• MRI is not first-line because it has longer acquisition times, limited availability, higher cost, and cannot adequately assess calcifications that may be diagnostically important. 1
• While MRI showed 88% accuracy for all final diagnoses in one comparative study versus 38% for CT, this study involved only 26 highly selected patients who underwent all three modalities, making it not generalizable to initial evaluation. 3
• MRI is typically reserved for specific indications after initial CT evaluation, not as the primary diagnostic test. 2

Biopsy (Option C)

• Biopsy should not be performed without cross-sectional imaging as this risks complications and may be unnecessary if imaging reveals a clearly resectable lesion. 1
• CT must be obtained first to characterize the mass, determine if it is amenable to percutaneous biopsy, and guide the biopsy approach if tissue diagnosis is needed. 2
• Many masses can be definitively diagnosed and managed based on CT characteristics alone without requiring biopsy. 1

Critical Clinical Pearls

• Any pulsatile mass mandates urgent CT angiography (CTA) to evaluate for aneurysm, with measurements using outer-to-outer wall diameter perpendicular to the aortic long axis. 1
• If there is concern for contained rupture, immediate CT without and with contrast is required to detect the "crescent sign" and other signs of imminent rupture. 1
• Surgical planning details, including vascular anatomy, resectability, and optimal surgical approach, can be determined by the initial CT. 1