What is the most appropriate diagnostic test for a patient found to have a painless abdominal mass during examination?

CT Abdomen and Pelvis with IV Contrast is the Most Appropriate Initial Test

For a patient with a painless abdominal mass, CT abdomen and pelvis with IV contrast is the definitive first-line diagnostic test. 1

Why CT with IV Contrast is the Optimal Choice

The American College of Radiology explicitly recommends CT abdomen and pelvis with IV contrast as the most appropriate initial investigation to characterize a painless abdominal mass, determine its organ of origin, assess for malignancy, and guide definitive management. 1 This recommendation is based on CT's ability to:

• Alter diagnosis in 49-54% of patients with abdominal pathology and change management plans in 42% of cases 1
• Characterize tissue enhancement patterns that distinguish benign from malignant lesions and evaluate vascular involvement 1
• Detect the mass origin, size, and relationship to surrounding structures with high accuracy 1

CT Protocol Specifications

• Single-phase examination with IV contrast is typically sufficient for diagnosis without requiring pre-contrast or delayed phases 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
• IV contrast is essential for characterizing nodular wall thickening, soft tissue attenuation, and enhancement patterns that differentiate malignant from benign processes 2

Why Other Options Are Inappropriate

Plain Radiography (X-ray)

• Severely limited diagnostic value with sensitivity of only 49% even for bowel obstruction 1
• Provides no tissue characterization and cannot determine organ of origin or assess for malignancy 2
• Should not be obtained first as it will not change management and only delays definitive diagnosis 1

MRI

• Not first-line due to longer acquisition times, limited availability, higher cost, and inability to adequately assess calcifications that may be diagnostically important 1
• While MRI can characterize masses, CT is preferred for initial evaluation due to faster acquisition and broader availability 2

Biopsy

• Should not be performed without cross-sectional imaging first as this risks complications and may be unnecessary if imaging reveals a clearly resectable lesion 1
• Biopsy is typically guided by CT findings after initial characterization, not performed blindly 3

Critical Clinical Pearls

• If the mass is pulsatile, urgent CT angiography (CTA) is required to evaluate for aneurysm, with measurements using outer-to-outer wall diameter perpendicular to the aortic long axis 2, 1
• Any concern for contained rupture requires immediate CT without and with contrast 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

Common Pitfalls to Avoid

• Do not start with plain films thinking they provide useful screening information—they have poor sensitivity and will delay definitive diagnosis 2, 1
• Do not proceed to biopsy before obtaining cross-sectional imaging, as the mass location, vascularity, and resectability must be determined first 1
• Do not order CT without IV contrast unless there is a contraindication, as contrast is essential for characterizing the mass and detecting malignancy 2, 1