Etiology and Diagnosis of Leg Masses

Epidemiological Evidence

The most common cause of a leg mass is a benign lipoma, as stated in the 2025 UK guidelines for soft tissue sarcomas, which represents the highest quality and most recent evidence available, with lipomas vastly outnumbering malignant lesions 1
By far the most common soft tissue mass of the limbs and torso seen in primary care is benign lipoma, with the guidelines emphasizing that despite large increases in referrals for suspected sarcomas, the percentage of patients who actually have sarcoma after direct referral from primary care remains low 1

Superficial masses are overwhelmingly most commonly lipomas, with ultrasound demonstrating 94.1% sensitivity and 99.7% specificity for identifying them, according to the American College of Radiology 2
Deep-seated masses are manyfold less common than benign lipomas but tend to be larger, deep-seated, and preferentially located in the lower limb, as noted by the British Journal of Cancer guidelines 1
Malignant masses, such as soft tissue sarcomas, present most commonly as a painless enlarging mass, but they remain rare compared to benign abnormalities like lipomas and cysts, as stated by the British Journal of Cancer 3, 1

Ultrasound is the most effective initial triage tool for evaluating leg masses, particularly for superficial lesions, with the majority of soft-tissue lumps being diagnosed as benign lipomas, and patients can be safely reassured when ultrasound features are typical, according to the British Journal of Cancer and the American College of Radiology 1, 2
When ultrasound is uncertain or clinical concern persists, MRI provides the most accurate information for extremity masses and helps distinguish benign from malignant lesions, as recommended by the British Journal of Cancer 1