High‐Resolution Ultrasonography in an Aggressive Thenar Intramuscular Lipoma

Lipomas are seen mainly during mid adulthood and represent the most cornmon benign soft tissue tumors of this age group. Subcutaneous, most often asymptomatic, soft mobile masses are by far the most frequent manifestationand are known to arise typically from superficial areas of the trunk and proximal extremities. Conversely, deep-seated lipomas, such as the intramuscular lipoma, are relatively rare but may pose a diagnostic challenge, especially regarding their differentiation from liposarcomas. Certain morphologic features described in magnetic resonance imaging (MRI), such as irregular margins and interdigitations with skeletal muscle, isointensity with subcutaneous fat, and absence of solid nonadipose tissue, seem to favor the diagnosis of an intramuscular lipoma. Although ultrasonography has played a major role in the study of subcutaneous fatty tumors, at times the appearance can be variable. We believe that the combination of high-frequency transducers and Doppler flow studies, together with appropriate training, can be of considerable value in the assessment of these lesions. Here we describe ultrasonographic details of this neoplasm, obtained with the use of high-resolution transducers.