Background: To describe the sonographic appearance of soft tissue lipomas with pathological correlation.
Material and Method: Patients presenting with clinically palpable soft tissue masses who underwent ultrasound examination and excision with documentary pathological diagnosis of lipomas were collected for this retrospective study. Institutional review board approval was obtained and informed consent was waived. All sonographic images were reviewed by musculoskeletal radiologist and resident in consensus. The sonographic findings were recorded and analyzed. The available pathologic slices were reviewed by pathologist.
Results: Fifty-two pathologically documented lipomas were available. Four patterns of sonographic appearance of the softtissue lipomas were categorized. The most common pattern was well-organized, heterogeneous echogenicity with multiple clearly defined long smooth continuous internal echogenic lines parallel to the long axis of the lesions. The second pattern was disorganized heterogeneous mixed hypo- and hyper-echogenicity with some irregular, interrupted, internal echogenic lines. The third pattern showed disorganized heterogeneous hyper-echoic mass with some irregular, interrupted internal echogenic lines. The last pattern was rather homogeneous echogenic mass with short interrupted, irregular internal echogenic lines. There were available pathological slices for review in 29 lesions, which were distributed among all four sonographic categories. These lipomas showed variable fibrous and vascular components without atypical cell or myxoid component.
There are no distinct histological features in any of the four groups.
Conclusion: The soft tissue lipomas contain some internal echogenic lines parallel to the long axis of the masses. The
sonographic appearances of the lipomas are variable and no distinct histological correlation is identified.

Keyword: Soft tissue lipoma, ultrasound