Atypical Lipoma : MRI

Case Report: 55 yr old male patient  with hx of swelling buttock shows  a large fat signal intensity SOL displacing glutei/ involving sciatic foramen with compression of the nerve with a pelvic component with some nodules and septa suggesting well differentiated lipo sarcoma or atypical lipoma.

Teaching points by Dr MGK Murthy , Mr Harinath 

Lipoma is very common clinical and radiological finding usually in all locations 

Liposarcoma is per say is the commonest soft tissue neoplasm of retroperitoneum

4 varieties of liposarcoma exist 

(a) Well differentiated variety shows >75% fat  tissue (lipocytes)  and  broadly resembles Lipoma in Imaging. However can be  differentiated  by subtle differences  like larger size/ broader septa and more nodules .Both show mass effect  & do not show enhancement making contrast study redundant .

(b) Myxoid variety  ,  belongs to intermediate grade malignancies  ,is the commonest  liposarcoma  ,shows <10% fatty tissue on histology ,  on Imaging displays predominantly   water signals (T1 and T2 relaxations times similar)  with intense and marked enhancement on contrast 

(c) Pleomorphic and  (d) Round cell varieties  contain small amount or NO fat and show heterogenous and less intense enhancement on contrast  and  belong to high grade malignancies