Ultrasound of lipomatous tumors

Musculoskeletal lipomatous lesions constitute a significant proportion of lesions encountered in routine clinical practice. These lesions may arise from a broad range of tissues, including soft tissues, bone, neurovascular structures, and synovium. Although most are benign, accurate differentiation from malignant counterparts, such as liposarcoma, is essential to avoid delays in diagnosis and ensure appropriate management. Certain lipomatous lesions demonstrate characteristic imaging features that allow confident diagnosis based on imaging alone, whereas others may present with atypical appearances requiring further evaluation. Ultrasound serves as the first-line imaging modality for assessment of most lipomatous tumors, offering high-resolution evaluation and effective initial characterization of lesion morphology, internal architecture, vascularity, and relationship to fascial planes. Assessment of lesion depth relative to the superficial and deep fascia is a key discriminator, as superficial lesions are more commonly benign, whereas deep-seated lesions carry a higher risk of malignancy. Ultrasound also enables dynamic assessment and direct correlation with the site of clinical concern. In selected cases, further evaluation with magnetic resonance imaging (MRI) and/or histological confirmation is required. MRI is particularly indicated for indeterminate lesions, large or deep-seated masses, rapidly enlarging lesions, atypical morphology, suspicious or disorganized vascularity, and when there is concern for involvement of bone, joints, or adjacent neurovascular structures. This review provides a practical summary of the sonographic evaluation of lipomatous tumors, encompassing both non-neoplastic and neoplastic entities, with emphasis on key ultrasound features, risk stratification, follow-up strategies, and appropriate use of adjunctive imaging in complex or diagnostically challenging cases.