Surgical Pathology Criteria

Atypical Lipomatous Tumor

Differential Diagnosis

 

Lipoma vs Atypical Lipomatous Tumor (Well Differentiated Liposarcoma)

Pleomorphic Lipoma vs Atypical Lipomatous Tumor

Hibernoma with predominant mature fat Atypical Lipomatous Tumor
Small, central bland nuclei in vacuolated cells Lipoblasts, if present, have atypical nuclei
Lacks atypical nuclei Contains atypical nuclei
Frequently superifcial Rarely superficial
MDM2, CDK4, p16 negative MDM2, CDK4, p16 most positive

Myxoid Liposarcoma Atypical Lipomatous Tumor
No large atypical nuclei Large atypical nuclei present
Prominent "chicken wire" vascular pattern Lacks "chicken wire" vascular pattern
Rare as a primary lesion in retroperitoneum Frequently occurs in retroperitoneum
MDM2 and CDK4 4% by immunohistology but 1/5 MDM2 by FISH MDM2 and CDK4 most positive

Pleomorphic Liposarcoma Atypical Lipomatous Tumor
Lacks mature fat Prominent mature fat
Highly cellular Low cellularity
Mitotic figures frequent Mitotic figures rare
MDM2 and CDK4 negative MDM2 and CDK4 most positive

Fat Necrosis Atypical Lipomatous Tumor
Small central nuclei Large eccentric nuclei
Nuclei not indented by vacuoles Vacuoles indent nuclei in lipoblasts
Foamy cells frequently fill spaces of dead lipocytes Lipoblasts scattered

Angiomyolipoma Atypical Lipomatous Tumor
Large atypical blood vessels No large vascular component
Large epithelioid cells No large epithelioid cells
HMB45 positive HMB4 negative
MDM2 and CDK4 negative MDM2 and CDK4 most positive

Subconjunctival herniated fat and fat adjacent to renal cell carcinomas have been reported to simulate atypical lipomatous tumor

Low Grade Myxofibrosarcoma Atypical Lipomatous Tumor
No lipoblasts Lipoblasts frequently present
Hypocellular Moderate cellularity
Perivascular grouping of cells No perivascular pattern
May have atypical mitotic figures No atypical mitotic figures
May have marked pleomorphism Mild to moderate atypia

MFH and other pleomorphic sarcomas vs Atypical Lipomatous Tumor

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