Path Quiz Case-64

           Case 64: Case history and images

Chondroid lipoma is one of the most recently described (Abstract) rare, benign variant of lipomatous tumour .
[ If the pathologist is unaware of the entity he may consider a sarcoma either of adipose tissue - a round cell liposarcoma - or of cartilage- an extraskeletal myxoid chondrosarcoma.]

Age and sex: Chondroid lipoma occurs predominantly in the third decade of life , mostly in females (female-male ratio, 4:1).

Site: These are usually located in the subcutaneous tissue, superficial muscular fascia, or skeletal muscles, especially in proximal limbs and limb girdles.

Gross: Encapsulated and lobulated mass usually about 4cm in maximal dimension.

Microscopic features: The tumour is composed of a varying admixture of eosinophilic multivacuolated cells arranged in strands, nests and sheets together with mature adipocytes.These are present in a myxoid and chondroid-like stroma. Multivacuolated cells contain contain fat and glycogen (demonstrated by periodic acid–Schiff and Oil-red-O stains) and may resemble chondroblasts or hibernoma cells. There may be areas of fibrosis and hemosiderin deposition. There is little pleomorphism and mitotic activity is low.

Immunohistochemistry:  Usually Vimentin and S 100 protein positive (strongly in adipocytes, weakly in lipoblasts.) CD68 and cytokeratins may be positive  in some cases.  EMA is negative. MIB1 proliferation index less than 1%.

Cytogenetics: Revealed a balanced translocation t (11,16) (q13; p12–13).

Differential Diagnosis: Image Link1 ; Image Link2 ; Image Link3 ; Image Link4 ; Image Link5

 1. Myxoid liposarcoma - Characterized by a plexiform vascular network and higher cellularity with true lipoblasts.

2.Extraskeletal myxoid chondrosarcoma - Tumour is more lobulated with fibrous septa and presence of a thin peripheral capsule. There is absence of adipocytes and lipoblasts. Tumoral chondroblasts are more round and have few or no intracytoplasmic vacuoles.

3. Extraskeletal chondroma - Located in the distal extremities,  multinucleated giant cells and true cartilaginous areas are present. There are no intracytoplasmic fat vacuoles.

4. Mixed tumor -There are foci of epithelial differentiation, lipoblasts are absent.