What is the sonographic appearance of a lipoma?
Soft tissue lipomas may arise anywhere including within muscle, between tissue planes, or in subcutaneous fat. A lipoma residing in the subcutaneous tissue should be oval and homogeneously isoechoic or minimally hyperechoic. It is important to keep in mind that a simple lipoma does not have blood flow on Doppler imaging.
With gentle transducer pressure, the lipoma should be soft and compressible, a finding of diagnostic value which is uniquely interrogated with sonographic evaluation. Intramuscular lipomas are generally seated more deeply and therefore are more difficult to fully evaluate with Ultrasound.
Although somewhat nonspecific appearing, an intramuscular lipoma is relatively hyperechoic to background muscle. Given the difficulty in evaluating the margins of an intramuscular lipoma and because a deep lipomatous tumor is more likely to be malignant than a superficial one, contrast-enhanced MRI is often obtained to confirm the diagnosis of an intramuscular lipoma.