Soft tissue lesion on ultrasound: red flags of benign and malignant process (per ESSR/EFSUMB)
General approach to differentiation
According to the sources, the key principle is as follows: the absence of recognizable features of known benign superficial tumors should raise suspicion for malignancy (Diagnostic Ultrasound: Musculoskeletal, 2025). In other words, if a lesion does not fit the typical pattern of lipoma, ganglion cyst, fibromatosis, etc., it should be interpreted as potentially malignant until histological confirmation.
Ultrasound signs concerning for malignancy
According to the cited sources (Diagnostic Ultrasound: Musculoskeletal, 2025):
- Hypoechoic lesion with hyperemia and mineralization foci — a pattern characteristic of osteosarcoma recurrence.
- Moderate to marked internal disorganized vascularization on CDU — in myxoid sarcoma.
- Well-defined hypoechoic lesion with multiple small echogenic foci and mild acoustic enhancement — imaging suggestive of protruding dermatofibrosarcoma protuberans.
- Juxtacortical solid soft tissue thickening with hyperemia and echogenic "seams" (bone neoplasm) — findings favoring bone sarcoma or infection.
Features indicating specific tumor types
| Ultrasound finding | Probable nature (per source) |
|---|---|
| Hypoechoic, hyperemic, with mineralization | Primary/recurrent osteosarcoma |
| Hyperechoic, without hyperemia, without mineralization | Primary liposarcoma |
| Well-defined intratumoral anechoic/hypoechoic zones | Myxoid tissue |
Recurrence after treatment
The best diagnostic sign of recurrence is a discrete soft tissue lesion in the surgical area (Diagnostic Ultrasound: Musculoskeletal, 2025). Assessment is complicated by postoperative or post-radiation fibrosis and distortion of normal anatomical planes. The most common sites of recurrence are along the surgical scar and along the open biopsy tract. The echogenicity and vascularization of recurrence are variable but typically reflect the characteristics of the primary tumor.
Role of elastography
Elastography (strain, SWE) is applied as an adjunctive method for assessing stiffness of nodular lesions; strain elastography may yield false-positive results, whereas SWE in the given example correctly classified a soft nodule as benign (Diagnostic Ultrasound: Head and Neck, 2019). Specific threshold values for soft tissue lesions are not provided in the supplied excerpts [clarification needed].
Management
Upon detection of concerning features, ultrasound-guided biopsy for histology and MRI are indicated, which is superior to ultrasound in assessing disease extent (e.g., involvement of the growth plate/transphyseal spread) (Diagnostic Ultrasound: Musculoskeletal, 2025).
Frequently asked questions
What is the main criterion for suspicion of sarcoma on ultrasound?
The absence of recognizable features of known benign superficial tumors — this is sufficient to suspect malignancy (Diagnostic Ultrasound: Musculoskeletal, 2025).
How to differentiate tumor recurrence from postoperative fibrosis?
The best sign of recurrence is a discrete soft tissue lesion in the surgical area, most often along the scar and biopsy tract. Assessment is complicated by fibrosis and distortion of anatomical planes; the echogenicity and vascularization of recurrence typically reflect the primary tumor.
What CDU pattern is characteristic of malignant soft tissue lesions?
Moderate to marked internal disorganized vascularization; for juxtacortical processes — moderate to marked hyperemia, which is suggestive of bone sarcoma or infection.
What should be done when a suspicious lesion is detected?
Ultrasound-guided biopsy for histology and MRI, which better demonstrates disease extent including involvement of the growth plate.
Does elastography help in differentiation?
It is an adjunctive method for assessing stiffness; strain elastography may yield false-positive results, while SWE in the example correctly identified a soft benign nodule. Threshold values for soft tissues are not provided in the sources [clarification needed].