Diagnostic Approach to Painless Abdominal Mass
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 provides comprehensive characterization of the mass, determines its organ of origin, assesses for malignancy, and guides definitive management with superior diagnostic accuracy. 1 The American College of Radiology specifically recommends this as the most appropriate initial investigation for abdominal masses. 1
Key Diagnostic Advantages of CT
CT alters the diagnosis in 49-54% of patients with abdominal pathology and changes management plans in 42% of cases, demonstrating its critical impact on clinical decision-making. 2, 1
IV contrast is essential because it characterizes tissue enhancement patterns that distinguish benign from malignant lesions and evaluates vascular involvement. 1
Including the pelvis in the scan is critical because masses may extend into the pelvis or arise from pelvic organs, which was essential in 75.5% of surgical cases. 1, 3
CT detects nodular or irregular wall thickening, soft tissue attenuation, lymphadenopathy, and distant metastases that are crucial for diagnosis and staging. 2
Why Other Options Are Inappropriate
Plain Radiography (X-ray)
- Abdominal X-ray has severely limited diagnostic value, with sensitivity of only 49% even for bowel obstruction and provides no tissue characterization. 1, 4
- Plain films should not be obtained first as they will not change management and only delay definitive diagnosis. 1, 5
- Radiography has low overall sensitivity for detecting abdominal masses and cannot determine their nature or origin. 2
MRI
- 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
- MRI is typically chosen over CT only when specific indications exist, not for initial evaluation of an undifferentiated mass. 2
Biopsy
- 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
- Proceeding directly to biopsy without imaging fails to assess the mass's extent, relationship to surrounding structures, resectability, and presence of metastases—all critical for treatment planning. 1
Specific CT Protocol
A single-phase CT abdomen and pelvis with IV contrast is typically sufficient for diagnosis without requiring pre-contrast or delayed phases. 1 This protocol:
- Provides adequate tissue characterization through enhancement patterns 1
- Evaluates vascular anatomy and resectability 1
- Assesses for lymphadenopathy and distant metastases 2
Critical Clinical Pearls
- If the mass is pulsatile, urgent CT angiography (CTA) is mandatory to evaluate for aneurysm. 1
- Any concern for contained rupture requires immediate CT without and with contrast to detect signs of imminent rupture. 1
- Ultrasound may have been performed first in resource-limited settings and can specify the origin in 75.5% of cases, but CT provides superior diagnostic accuracy when available. 3