Diagnostic Approach to Abdominal Masses

Initial Evaluation

The American College of Radiology 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, 2
CT detects the mass origin, size, and relationship to surrounding structures with high accuracy, altering diagnosis in 49-54% of patients with abdominal pathology and changing management plans in 42% of cases 1, 2

CT with IV contrast is essential for characterizing tissue enhancement patterns that distinguish benign from malignant lesions and for evaluating vascular involvement 3, 4
Abdominal X-ray has severely limited diagnostic value for abdominal masses, with sensitivity of only 49% even for bowel obstruction, and provides no tissue characterization 1, 5
MRI abdomen is not first-line because it has longer acquisition times, limited availability, higher cost, and cannot adequately assess calcifications that may be diagnostically important 6, 2

The American College of Radiology recommends using CT abdomen and pelvis with IV contrast as the single-phase examination, which 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, and this was critical in 75.5% of cases in one surgical series 3

Any concern for contained rupture requires immediate CT without and with contrast to detect the "crescent sign" and other signs of imminent rupture 7
Pulsatile masses mandate urgent CT angiography (CTA) to evaluate for aneurysm, with measurements using outer-to-outer wall diameter perpendicular to the aortic long axis 7, 6
Surgical planning details, including vascular anatomy, resectability, and optimal surgical approach, can be determined by CT 7

Plain radiographs should not be obtained first as they will not change management and only delay definitive diagnosis 1, 8, 2
Biopsy should not be performed without cross-sectional imaging as this risks complications and may be unnecessary if imaging reveals a clearly resectable lesion 7, 6

The European Society for Medical Oncology recommends imaging assessment followed by biopsy/excision for suspected gastrointestinal stromal tumors (GIST) presenting as abdominal masses >2 cm 9, 10
The American College of Radiology suggests that biopsy without imaging guidance has lower success rates and higher complication risks, emphasizing the importance of imaging before biopsy 11

The National Comprehensive Cancer Network advises against blind biopsy for abdominal masses, instead recommending image-guided biopsy for tissue diagnosis before definitive treatment 9