Why Did Lipoma Grow Back After Removal?

The most common reason for a re-growth of a Lipoma is a possible incomplete removal of the original Lipoma leaving elements behind. A second and much more rare reason is that it was NOT a Lipoma after all but a low grade cancer masquerading as a Lipoma. The re-growth needs to be removed with wider margins this time and the pathology slides need to be compared by a good pathologist to make sure to get to the bottom of why this happened.

I agree with Dr. Aldea.  Either the lipoma was incompletely removed, or it was not a lipoma and something more serious.

Are you sure it was a lipoma?  A lipoma grossly looks like a lipoma and your surgeon would have suspected otherwise.  However, if it was sent to pathology, review the report and make sure the final diagnosis was a lipoma.