Surgical Pathology Criteria–

Spindle Cell Lipoma

Differential Diagnosis

Spindle Cell Lipoma vs. Pleomorphic Lipoma

Spindle Cell Lipoma Angiolipoma
Predominantly back of neck, upper back, shoulders Very rare on neck, upper back
Usually solitary Frequently multiple
CD34 positive CD34 stains only endothelium and scattered cells
Prominent spindle cell component Prominent vascularity
No fibrin thrombi Frequent fibrin thrombi
May contain pleomorphic cells (admixed pleomorphic lipoma) No pleomorphic cells

Spindle Cell Lipoma Ectopic Hamartomatous Thymoma
Lacks epitihelioid nests Has epithelioid nests
Has ropy collagen Lacks ropy collagen
Keratin, p63 and smooth muscle actin negative Keratin, p63 and smooth muscle actin positive
Both contain spindle cell and adipose components and both are CD34 positive in the spindled component

Spindle Cell Lipoma Fibrolipoma
Predominantly back of neck, upper back, shoulders Various locations
Prominent spindle cell component Lacks prominent spindle cells
CD34 positive CD34 negative
Ropy bundles of collagen Lacks ropy collagen

Spindle Cell Lipoma Fibrolipomatous Hamartoma of Nerve
Predominantly back of neck, upper back, shoulders Usually involves median nerve
Does not involve nerves Infiltrates and surrounds large nerve
Usually age 40-70 Presents under age 30
No neural symptoms Neural symptoms

Spindle Cell Lipoma Myolipoma
Restricted to back of neck, upper back, shoulders Predominantly pelvic
Scant cytoplasm Tapered cytoplasm in spindle cells
Ropey collagen frequent No ropey collagen
CD34 positive CD34 negative
Actin negative Actin positive

Spindle Cell Lipoma Sclerotic Lipoma
Ropy bundles of collagen Diffuse collagen
Usually has cellular areas Hypocellular
CD34 extensive positivity CD34 negative to rare

Spindle Cell Lipoma Atypical Spindle Cell Lipomatous Tumor
Restricted to back of neck, upper back, shoulders Various locations
Bland spindle cells Mild to moderate atypia of spindle cells
Ropy collagen bundles No ropy collagen
Circumscribed May be infiltrative
Uniformly strong CD34 CD34 only 5% reactive
Rb loss in all cases Rb normally expresed in 40$
MDM2 and CDK4 negative to weak focal in 5% (FISH negative)

Spindle Cell Lipoma Schwannoma or Neurofibroma
S100 negative except for mature fat S100 positive
Uniformly strong CD34 CD34 only scattered small spindle cells

Spindle Cell Lipoma Solitary Fibrous Tumor
Fat is integral part of lesion Fat only at infiltrative border
May contain pleomorphic cells if admixed with pleomorphic lipoma No large pleomorphic cells
Ropey collagen bundles Finely dispersed collagen
Lacks staghorn vessels Frequent staghorn vessels

Myxoid Liposarcoma Spindle Cell Lipoma with Myxoid Stroma
Infrequent prominent spindle cell component Prominent spindle cell component
Prominent "chicken wire" vascular pattern Lacks "chicken wire" vascular pattern
No dense collagen bundles Dense collagen bundles
Very rare in subcutis or dermis Usually in subcutis or dermis
CD34 negative or scattered small cells CD34 widely positive
t(12;16) or t(12;22) Frequent abnormalities of chromosomes 13 or 16

Myxolipoma Spindle Cell Lipoma with Myxoid Stroma
Lacks prominent spindle cell component Prominent spindle cell component
May have prominent vascularity Vascularity rarely prominent
No dense collagen bundles Dense ropy collagen bundles
Location variable Largely restricted to back, shoulders, posterior neck

Spindle Cell Lipoma Intramuscular or Juxta-articular Myxoma
Cellular areas Uniformly paucicellular
Superficial Deep
May contain pleomorphic cells (admixed pleomorphic lipoma) Lacks large pleomorphic cells

Spindle Cell Lipoma, Myxoid Predominant Superficial Angiomyxoma
Usually has areas of typical spindle cell lipoma Lacks areas of typical spindle cell lipoma
Parallel arrays of spindle cells in areas Randomly arranged cells
Ropey collagen bundles Lacks ropey collagen
Lacks neutrophils or entrapped adnexae Frequent neutrophils and entrapped adnexae

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