Spindle Cell Lipoma

Definition

• Predominantly subcutaneous lesion composed of mature fat and bland spindle cells

Diagnostic Criteria

• If subcutaneous, must be located in posterior neck, upper back and shoulders
  • Well circumscribed in these locations
  • If located in other sites, must be restricted to dermis or submucosa
    • Most reported in thigh, groin, buttock, face, hands, oral
    • Less frequently encapsulated
• Variable amount of adult fat
  • 10-90% of lesion
    • Rare lesions lacking fat have been reported (see below)
  • No lipoblasts
• Small bland spindle cells with scant cytoplasm
  • Elongate nuclei
  • Mitotic figures absent
• Spindle cells arranged in short parallel arrays
  • "School of fish"
  • Nuclei may palisade
• Bundles of dense ropey collagen
• Stroma may be myxoid
  • Vessels may be prominent, arborizing, thick walled
  • Cartilaginous and osseous metaplasia reported in one case
• CD34 positive, usually extensive
• Mast cells may be numerous
• Variants may have distinctive patterns
  • Vascular spindle cell lipoma
    • Branching dilated or cleft like-spaces
      • Papillary projections of tumor cells into the spaces
      • Spaces usually cell free
    • Spaces lined by endothelial cells with lymphatic phenotype
      • D2-40 positive, CD31 focal or negative
    • Previously termed pseudovascular spindle cell lipoma
      • Based on studies without D2-40
    • Recognized based on location, areas of typical spindle cell lipoma patterns and CD34 positvity
  • Fibrous spindle cell lipoma
    • Abundant fibrous stroma
    • Bundles of collagen
    • EVG negative
    • Recognized based on location, areas of typical spindle cell lipoma patterns and CD34 positvity
  • Fat free (or almost free)
    • May include above variant patterns
    • May be predominantly myxoid
    • Plexiform or curvilinear vasculature and vascular hyalinization may be prominent
    • Recognized by location, CD34 reactivity and presence of areas with typical features of spindle cell lipoma
  • Rare tumors combined with hibernoma have been reported
    • No distinct clinical features
• Frequent histologic overlap with pleomorphic lipoma
  • Occasional to frequent cells with large atypical nuclei
  • If pleomorphic features present, diagnosis is restricted to posterior neck, upper back and shoulders
• May form a spectrum with Mammary Type Myofibroblastoma and Ccellular Angiofibroma
• All have deletion or rearrangement of 13q14 with loss of nuclear Rb
• All are benign

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting : July 29, 2007
Last update: 3/14/16

Supplemental studies

Immunohistology

Genetic analysis

• Spindle cell lipopma and pleomorphic lipoma demonstrate the same genetic findings
  • Abnormalities of chromosome 16 resulting in deletions of 16q13-qter
  • Frequent deletions within 13q

Differential Diagnosis

• Pleomorphic lipoma
• Mature fat with admixed other components
  • Angiolipoma
  • Ectopic hamartomatous thymoma
  • Fibrolipoma
  • Fibrolipomatous hamartoma of nerve
  • Myolipoma
  • Sclerotic lipoma
  • Spindle cell variant atypical lipomatous tumor
• Predominantly spindled
  • Nerve sheath tumor
  • Solitary fibrous tumor
• Predominantly myxoid
  • Myxoid liposarcoma
  • Myxolipoma
  • Myxoma, intramuscular or juxta-articular
  • Superficial angiomyxoma

Spindle Cell Lipoma vs. Pleomorphic Lipoma

• We consider these to be part of a spectrum
• Mixtures are common
• If atypical cells are present, location becomes definitional
  • Restricted to posterior neck, upper back, shoulders

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

Clinical

• Approximately 1.4% of fatty neoplasms
• Age range 20-74, most between 40-70
• 90% male
• Nearly all in subcutis of posterior neck, upper back or shoulders
  • Infrequent histologically identical tumors found in other sites
    • Must be pure spindle cell lipoma (no pleomorphism)
    • Must be located in dermis or submucosa
  • Histologically identical tumors in deep soft tissue are best considered atypical lipomatous tumors
    • Very little experience to permit prediction of behavior
• Rarely familial or multiple

Grading / Staging / Report

• Grading and staging are not applicable
• Mangerial category
  • Ia (Local excision is almost always curative; metastasis never occurs)

Lists

Lipogenic tumors

• Angiomyolipoma
• Hemosiderotic Fibrohistiocytic Lipomatous Lesion
• Hibernoma
• Lipofibromatosis
• Lipoma
• Lipomatosis
• Lipoblastoma / lipoblastomatosis
• Pleomorphic lipoma
• Spindle cell lipoma
• Atypical lipomatous tumor
• Liposarcoma
  • Dedifferentiated
  • Myxoid
  • Pleomorphic
  • Unclassified
• Atypical Spindle Cell Lipomatous Tumor

CD34 positive neoplasms (frequent and strong)

• Angiosarcoma
• Cellular angiofibroma
• Dermatofibrosarcoma protuberans
• Epithelioid sarcoma
• Glomus tumor
• Gastrointestinal stroma tumor
• Giant cell angiofibroma
• Hemangioendothelioma
• Hemangiopericytoma
• Inflammatory fibroid polyp
• Ischemic fasciitis
• Juxtagomerular cell tumor
• Kaposi sarcoma
• Leukemia, myeloid
• Leukemia, acute lymphoblastic
• Liposarcoma, dedifferentiated
• Lymphangioendothelioma
• Meningioma
• Neurofibroma
• Pleomorphic hyalinizing angiectatic tumor
• Pleomorphic lipoma
• Proximal type epithelioid sarcoma
• Solitary fibrous tumor
• Spindle cell lipoma
• Superficial acral fibromyxoma
• Superficial angiomyxoma
• Superficial myofibroblastoma
• Carcinoma and melanoma are essentially never CD34 positive

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