Lipoma




CLINICAL SUMMARY


Lipoma is the most common soft tissue tumor and consists of benign adipose tissue. It is usually easy to identify on physical examination and on imaging studies. Subcutaneous lesions grow slowly and are typically asymptomatic, while intramuscular lipomas can cause mechanical pain and are more likely to require excision.




DIAGNOSTIC FEATURES


















History


  • Rare in children



  • Painless, slow growth when subcutaneous



  • Intramuscular lipomas can cause mild activity-related pain

Location


  • Superficial lipomas are more common in the shoulders, back, neck, and abdomen



  • Intramuscular lipomas are more common in the lower extremities

MRI


  • Uniform high signal on T1 and suppression on fat-suppressed images



  • MRI is diagnostic for lipoma when the lesion is identical to subcutaneous fat on all pulse sequences






IMAGING




































  • Lipomas are radiolucent relative to muscle on radiographs ( left ) and CT ( righ t). Note the small, thin single septum anteriorly on CT.



  • Intramuscular lipomas often attain large size before diagnosis.










  • The signal intensity of the lipoma should be the same as that of subcutaneous fat on all pulse sequences, as can be seen on these T1 ( left ) and fat-suppressed T2 ( right ) MRI images.










  • Subcutaneous lipomas can appear well encapsulated ( arrows ) and distinct from the surrounding subcutaneous tissue ( left ).



  • They can also appear to blend into the surrounding tissue ( arrow, right ). On physical examination, superficial lipomas have a soft, doughy consistency.










  • Lipomas can appear more complex in approximately 30% of cases, as observed in these periscapular ( left ) and thigh ( right ) lipomas.



  • While this may suggest a diagnosis of well-differentiated liposarcoma, as seen here, the septations in a lipoma should be less than 2 to 3 mm and not thicker than the nearby subcutaneous fat ( stars ).


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