I had an mri scan on lipoma on thigh. then needed contrast injection. why?

Enhancement : This is done to see if the tumor picks up any contrast. Benign lipoma should not enhance with contrast.

Speak to your doctor: You do not need MRI to diagnose lipoma , may be trying to rule out some thing , speak to your doctor will give you explanation.

Normal: When evaluating a soft tissue mass with MRI, contrast is used to help decide if the mass is benign or malignant. A simple lipoma is not malignant and does not enhance. A liposarcoma, or a malignancy which includes fatty tissues, will demonstrate some enhancement. If your mass enhances it may still be benign, but further evaluation with biopsy would be prudent to prove if it is benign or malignant.