Evaluation of Soft-Tissue Masses

Initial Imaging Approach

The American College of Radiology recommends beginning with plain radiographs of the affected area as the first imaging study, followed by ultrasound for further characterization, with radiographs serving as the fundamental first step in evaluating any suspected soft-tissue mass, though they may be unrewarding for small, deep-seated, or non-mineralized lesions 1, 2
Radiographs can identify intrinsic fat in approximately 11% of soft-tissue masses, detect calcification in 27% of cases, and reveal bone involvement in 22% of cases, and may be diagnostic for specific entities such as phleboliths within hemangiomas, osteocartilaginous masses, or peripherally mature ossification of myositis ossificans 1, 2

Ultrasound is the most useful initial imaging modality for characterizing the mass, with diagnostic accuracy of 94.1% sensitivity and 99.7% specificity for superficial soft-tissue masses, and should assess for characteristic features such as hyperechoic or isoechoic appearance compared to surrounding fat, well-circumscribed margins, and minimal to no internal vascularity on Doppler examination 1, 2, 3
Red flags requiring advanced imaging include heterogeneous echotexture, increased vascularity, irregular margins, size >5 cm, deep location, or rapid growth 2, 4

MRI without and with contrast is indicated if the mass demonstrates any concerning features on ultrasound or clinical examination, and provides superior spatial orientation and can differentiate benign lipomas from atypical lipomatous tumors in up to 69% of cases 2, 4
Specific indications for MRI include mass size >5 cm in diameter, deep-seated location, rapid growth, pain or tenderness, and atypical ultrasound features 2, 4

Core needle biopsy (preferably ultrasound-guided) is indicated for any mass with suspicious features on imaging or clinical examination, and is superior to fine-needle aspiration in terms of sensitivity, specificity, and correct histological grading 1, 4, 5, 6
Image-guided biopsy is preferred over palpation-guided biopsy, allowing confirmation of biopsy accuracy and placement of a marker clip 7

Small, superficial, asymptomatic masses with typical imaging features can be observed with clinical follow-up at 6-12 months to assess for growth, while surgical excision is indicated if the mass is symptomatic, rapidly growing, or if there is patient anxiety 4
Expedite referral to orthopedic oncology or a specialist sarcoma multidisciplinary team before performing biopsy if the institution is not equipped for definitive treatment, and complete surgical excision is the standard treatment for symptomatic, rapidly growing, large (>5 cm), or atypical masses 1, 4

Do not rely on physical examination alone, as it correctly identifies only 85% of lipomas, highlighting the necessity of diagnostic imaging, and all deep-seated masses or those in the lower limb should raise concern for atypical lipomatous tumors, even if they appear benign on superficial assessment 1, 2, 3
Ultrasound is considerably less accurate for deep masses compared to superficial ones, and soft-tissue sarcomas, though rare (<1% of malignancies), have high mortality rates, requiring urgent evaluation with MRI and potential referral to orthopedic oncology 1, 2