Intramuscular and intermuscular lipoma: neglected diagnoses.

Fifty-four cases of lipoma arising either within or between skeletal muscles are presented. Of these, 52 were identified in a systematic review of 2478 tumours of adipose tissue diagnosed and treated in one hospital over a 25 year period. Intramuscular lipomas account for 1.8% of fatty tumours, arise predominantly in middle to late adult life and, in our series, are commonest on the trunk. They may be divided into infiltrative and well-circumscribed types, respective local recurrence rates being 19 and 0%. Intermuscular lipomas are comparatively rare, 0.3% of fatty tumours, have a similar age distribution and arise most often in the anterior abdominal wall; none of the seven cases recurred. It is important that both pathologists and surgeons appreciate the significant tendency of infiltrative intramuscular lipomas to recur. Hence, preventative surgical measures may be undertaken and worries that the lesion may be sarcomatous can be avoided. Differential diagnosis, most importantly from well-differentiated liposarcoma, is discussed.