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Lipoma

Definition

  • Abnormal mass or masses composed of mature adipocytes. Other elements may also be present

Diagnostic Criteria

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

Original posting : July 29, 2007
Last update: May 8, 2011

Variant: Adenolipoma of Skin

Diagnostic Criteria

  • Superficially located
  • May not be well encapsulated
  • Contains entrapped eccrine glands
  • The term adenolipoma is also used for a variety of lesions containing fat that occur in a number of organs
    • We do not consider these to be related to lipomas

Clinical

  • No clinical significance to this pattern

Bibliography

  • Del Agua C, Felipo F. Adenolipoma of the skin. Dermatol Online J. 2004 Oct 15;10(2):9.
  • Hitchcock MG, Hurt MA, Santa Cruz DJ. Adenolipoma of the skin: a report of nine cases. J Am Acad Dermatol. 1993 Jul;29(1):82-5.

Variant: Angiolipoma

Diagnostic Criteria

  • Circumscribed subcutaneous mass
    • Frequently multiple
    • Rarely >2 cm
    • We consider infiltrating intramuscular tumors to be intramuscular hemangiomas
    • We consider spinal angiolipoma to be a distinct entity
  • Composed of mature fat with numerous small blood vessels
    • Vascular component may be patchy
      • Frequently accentuated in subcapsular area
    • Vessels are predominantly capillaries
    • Fibrin thrombi are almost always present
    • Fibrosis may be associated with vascular component
    • Cellular variant
      • Defined as 95% cellular, angiomatous tissue
      • Spindle cells abundant in cellular areas
      • Only mild pleomorphism
      • Mitotic figures inconspicuous
      • Have been associated with usual angiolipomas in the same patient
      • No clinical significance

Supplemental Studies

  • CD34 and CD31 stain endothelium of vessels
  • Genetic studies have generally shown no abnormalities
    • Contrasts with ordinary lipomas

Differential Diagnosis

  • The typical angiolipoma can be confused only with an ordinary lipoma

Kaposi Sarcoma Cellular Angiolipoma
Patches, plaques or nodules Subcutaneous nodules
Associated with HIV Associated with typical angiolipomas
Poorly localized Circumscribed
Cytologic atypia No atypia
Slits with red cell extravasation Small vessels with fibrin thrombi

Spindle Cell Hemangioendothelioma Cellular Angiolipoma
Poorly localized Circumscribed
Frequent cavernous vessels Small vessels with fibrin thrombi
Biphasic spindle and epithelioid cells Small vessels and spindle cells
Not associated with typical angiolipomas Frequently associated with typical angiolipomas

Angioleiomyoma Cellular Angiolipoma
Infrequent fat component (but may be seen) Fat component focal but present
Large thick walled vessels Vascular component is predominantly capillaries
No fibrin thrombi Fibrin thrombi

Angiomyolipoma Angiolipoma
Myoid component No myoid component
Large thick walled vessels Vascular component is predominantly capillaries
HMB45 positive HMB45 negative

Clinical

  • Common lesion
  • Age range 16-84 years, median 24 years
    • Usually adult onset
  • Most common on arms and trunk
    • Uncommon on legs, hands, head, face and neck
  • Frequently multiple
    • Commonly 2-4 nodules
    • Occasionally innumerable nodules
      • Multiple cases may be familial
  • May be painful
    • One of the five painful tumors of the skin (see Lists at left)
    • Very difficult to treat if too many nodules to resect
  • Recurrences very rare

Bibliography

  • Hunt SJ, Santa Cruz DJ, Barr RJ. Cellular angiolipoma. Am J Surg Pathol. 1990 Jan;14(1):75-81.
  • Sciot R, Akerman M, Dal Cin P, De Wever I, Fletcher CD, Mandahl N, Mertens F, Mitelman F, Rosai J, Rydholm A, Tallini G, Van den Berghe H, Vanni R, Willen H. Cytogenetic analysis of subcutaneous angiolipoma: further evidence supporting its difference from ordinary pure lipomas: a report of the CHAMP Study Group. Am J Surg Pathol. 1997 Apr;21(4):441-4.
  • Lin JJ, Lin F. Two entities in angiolipoma. A study of 459 cases of lipoma with review of literature on infiltrating angiolipoma. Cancer. 1974 Sep;34(3):720-7.
  • Howard WR, Helwig EB. Angiolipoma. Arch Dermatol. 1960 Dec;82:924-31.
  • Hattori H. Epidural angiolipoma is histologically distinct from its cutaneous counterpart in the calibre and density of its vascular component; a case report with review of the literature. J Clin Pathol. 2005 Aug;58(8):882-3.
  • Cina SJ, Radentz SS, Smialek JE. A case of familial angiolipomatosis with Lisch nodules. Arch Pathol Lab Med. 1999 Oct;123(10):946-8.

Variant: Cartilaginous Metaplasia in Lipoma (Chondrolipoma)

Diagnostic Criteria

  • Lipoma containing areas with true cartilage formation
  • May coexist with osseous metaplasia (ossifying lipoma)

Differential Diagnosis

Cartilaginous Metaplasia in a Lipoma (Chondrolipoma) Chondroid Lipoma
Contains true hyaline cartilage No true cartilage

Clinical

  • No clinical significance to this pattern
  • Several cases reported in breast and pharynx

Bibliography

  • Ohtsuka H. Chondrolipoma of the popliteal fossa and Japanese reports. J Dermatol. 2006 Mar;33(3):202-6.
  • Banev SG, Filipovski VA. Chondrolipoma of the breast--case report and a review of literature. Breast. 2006 Jun;15(3):425-6.
  • Halaas YP, Mra Z, Edelman M. Chondrolipoma of the oropharynx. Ear Nose Throat J. 2001 Mar;80(3):146-7.
  • Katzer B. Histopathology of rare chondroosteoblastic metaplasia in benign lipomas. Pathol Res Pract. 1989 Apr;184(4):437-45.

Variant: Chondroid Lipoma

Diagnostic Criteria

  • Well circumscribed, may be encapsulated
  • Three components seen in all cases
    • Mature adipose tissue may be interspersed or compartmentalized
    • Myxoid or hyaline chondroid matrix prominent
      • Alcian blue and colloidal iron positive
        • Vaiable sensitivity to hyaluronidase
      • Hemorrhage, sclerosis and calcification may be seen
    • Vacuolated cells
      • Usually in nests or cords
      • May be in lacunae
      • Vacuoles of variable size
        • Cells with fine droplets resemble hibernoma cells
        • Cells with large droplets resemble lipoblasts
      • Cytoplasm may also be granular or fibrillar
      • May be glycogen positive
      • Nuclei usually oval and regular
        • May be central or peripheral
        • Nucleoli inconspicuous or small
        • Pleomorphic nuclei reported in only 1/20 cases
        • Mitotic figures reported in only 1/20 cases

Supplemental Studies

  • Immunohistology
S100 positive
CD68 90%
Keratin 30%
EMA negative
HMB45 negative
Actin negative
  • Balanced translocation t(11;16)(q13;p12-13)

Differential Diagnosis

Cartilaginous Metaplasia in a Lipoma (Chondrolipoma) Chondroid Lipoma
Contains true hyaline cartilage No true cartilage

Extraskeletal Myxoid Chondrosarcoma Chondroid Lipoma
Fibrous septa create lobules No fibrous septa
No mature fat Mature fat part of lesion
Cells more uniform Frequent variation in cell size
t(9;22) or t(9;17) t(11;16)

Chondroma of Soft Tissue Chondroid Lipoma
Contains true hyaline cartilage No true cartilage
No fat component Mature fat part of lesion
May contain multinucleated giant cells No multinucleated cells

Myxoid Liposarcoma Chondroid Lipoma
Plexiform vasculature No prominent plexiform vasculature
No chondroid matrix Chondroid matrix
Cells more uniform Frequent variation in cell size
t(12;16) t(11;16)

Lipoblastoma Chondroid Lipoma
Uniform population of lipoblasts Variable size of vacuolated cells
No chondroid matrix Chondroid matrix
Restricted to children Age range 14-75
Deletions of 8q(11-13) t(11;16)

Parachordoma Chondroid Lipoma
No mature fat Mature fat part of lesion
EMA positive EMA negative
Keratin positive Keratin variable
Trisomy 15, monosomy 1, 16, 17 t(11;16)

Clinical

  • Age 14-75 years, median 36
  • May be subcutaneous or in deep soft tissue
  • Most on extremities or trunk
    • None reported in retroperitoneum
  • Benign, no recurrences

Bibliography

  • Ballaux F, Debiec-Rychter M, De Wever I, Sciot R. Chondroid lipoma is characterized by t(11;16)(q13;p12-13). Virchows Arch. 2004 Feb;444(2):208-10.
  • Gisselsson D, Domanski HA, Hoglund M, Carlen B, Mertens F, Willen H, Mandahl N. Unique cytological features and chromosome aberrations in chondroid lipoma: a case report based on fine-needle aspiration cytology, histopathology, electron microscopy, chromosome banding, and molecular cytogenetics. Am J Surg Pathol. 1999 Oct;23(10):1300-4. Erratum in: Am J Surg Pathol 2000 Jan;24(1):165.
  • Thomson TA, Horsman D, Bainbridge TC. Cytogenetic and cytologic features of chondroid lipoma of soft tissue. Mod Pathol. 1999 Jan;12(1):88-91.
  • Kindblom LG, Meis-Kindblom JM. Chondroid lipoma: an ultrastructural and immunohistochemical analysis with further observations regarding its differentiation. Hum Pathol. 1995 Jul;26(7):706-15.
  • Meis JM, Enzinger FM. Chondroid lipoma. A unique tumor simulating liposarcoma and myxoid chondrosarcoma. Am J Surg Pathol. 1993 Nov;17(11):1103-12.

Variant: Fibrolipoma

Diagnostic Criteria

Differential Diagnosis

  • Atypical lipomatous tumor is frequently composed of mature adipose tissue with fibrous areas
    • Atypical cells should be visible at low power

Fibrolipoma Sclerotic Lipoma
Focal fibrous tissue in a lipoma Focal fat in a predominantly fibrous lesion
Various locations Predominantly located on fingers

Clinical

  • No clinical significance to this pattern

Bibliography

  • Tayyeb MT, Neff JR, Bridge JA. A case report of fibrolipoma with t(12;16)(q13;q24). Cancer Genet Cytogenet. 1993 Jun;67(2):145-6.

Variant: Myelolipoma

Diagnostic Criteria

  • Circumscribed mass composed of mature fat and bone marrow elements
    • Fat component usually predominates
    • May have prominent lymphoid component
  • Most often occurs in adrenal
    • Most common extra-adrenal site is pelvis

Differential Diagnosis

Extramedullary Hematopoeisis Myelolipoma
Poorly circumscribed Circumscribed
Overrun fat Fat integral to tumor
No prominent lymphoid component Lymphocytes may be prominent
Hematologic abnormalities associated No hematologic abnormalities

Lipoblastoma with Extramedullary Hematopoiesis Myelolipoma
Immature fat cells present No immature fat cells
Areas with vascular myxoid stroma Lacks vascular myxoid stroma
Usually under age 10, virtually always under 20 Usually over age 40

Clinical

  • Usually over age 40
  • May be quite large (25 cm) and multiple
  • Not associated with hematologic abnormalities
  • May cause symptomatic hemorrhage
  • Benign

Bibliography

  • Bishop E, Eble JN, Cheng L, Wang M, Chase DR, Orazi A, O'Malley DP. Adrenal myelolipomas show nonrandom X-chromosome inactivation in hematopoietic elements and fat: support for a clonal origin of myelolipomas. Am J Surg Pathol. 2006 Jul;30(7):838-43.
  • Lam KY, Lo CY. Adrenal lipomatous tumours: a 30 year clinicopathological experience at a single institution. J Clin Pathol. 2001 Sep;54(9):707-12.

Variant: Myolipoma (Lipoleiomyoma)

Diagnostic Criteria

  • Composed of mature fat and bland smooth muscle
    • Muscle predominates in most cases
      • Usually evenly interspersed
      • Focal smooth muscle overgrowth in one reported case
      • Muscle in short fascicles
    • Both components lack any atypical features
      • No cytologic atypia or lipoblasts
      • No floret cells
      • No mitotic figures
      • No necrosis
  • Stroma may be sclerotic or hyalinized
    • Occasionally myxoid
    • No prominent vascular component

Supplemental Studies

  • Spindle cells positive for actin, desmin
    • CD34 negative
  • HMB45 has not been tested to our knowledge

Differential Diagnosis

Angiomyolipoma Myolipoma
Abnormal large vessels No abnormal vascular component
Epithelioid perivascular cells No epithelioid component
HMB45, MelanA positive HMB45, MelanA not reported

Atypical Lipomatous Tumor with Smooth Muscle Metaplasia Myolipoma
Atypical cells present No atypical cells
Fibrous septa frequent Fibrous septa absent
Floret cells or lipoblasts frequent No floret cells or lipoblasts

Spindle Cell Lipoma Myolipoma
Restricted to back of neck, upper back, shoulders Predominantly pelvic
Scant cytoplasm Tapered cytoplasm in spindle cells
CD34 positive CD34 negative
Actin negative Actin positive

Low Grade Leiomyosarcoma Infiltrating Fat Myolipoma
Fat is overrun (asymmetrically involved) Fat is integral to lesion (throughout)
May have atypia, mitotic figures No atypia or mitotic figures

Clinical

  • Rarely reported
  • Age 28-73
  • Sites of involvement
    • Females: pelvic, retroperitoneal, suprapubic,inguinal
    • Males: inguinal, abdominal wall, back
    • Other sites include eyelid, spinal cord and pericardium
  • No known association with tuberous sclerosis
  • No recurrences reported (limited followup)

Bibliography

  • Takahashi Y, Imamura T, Irie H, Tanaka F, Fukushima J, Fukusato T, Harasawa A, Shiga J. Myolipoma of the retroperitoneum. Pathol Int. 2004 Jun;54(6):460-3.
  • Guillou L, Coindre JM. Newly described adipocytic lesions. Semin Diagn Pathol. 2001 Nov;18(4):238-49.
  • Michal M. Retroperitoneal myolipoma. A tumour mimicking retroperitoneal angiomyolipoma and liposarcoma with myosarcomatous differentiation. Histopathology. 1994 Jul;25(1):86-8.
  • Meis JM, Enzinger FM. Myolipoma of soft tissue. Am J Surg Pathol. 1991 Feb;15(2):121-5.

Variant: Myxolipoma / Angiomyxolipoma

Diagnostic Criteria

  • Lipoma with prominent myxoid areas
  • Must not contain lipoblasts
  • If richly vascular, termed angiomyxolipoma
    • Thin and thick walled vessels
    • May be dilated

Supplemental Studies

  • Spindle cells in myxoid areas
    • Positive for CD34
    • Negative for S100, smooth muscle actin, desmin
  • Genetic studies have shown t(7;13) and t(8;12)

Differential Diagnosis

Myxoid Liposarcoma Myxolipoma / Angiomyxolipoma
Prominent "chicken wire" vascular pattern Lacks "chicken wire" vascular pattern
May have lipoblasts Lacks lipoblasts
Very rare in subcutis or dermis Usually in subcutis or dermis
CD34 negative or scattered small cells CD34 widely positive in myxoid areas
t(12;16) or t(12;22) t(7;13) or t(8;12) reported

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

Clinical

  • No clinical significance to this pattern

Bibliography

  • Lee HW, Lee DK, Lee MW, Choi JH, Moon KC, Koh JK. Two cases of angiomyxolipoma (vascular myxolipoma) of subcutaneous tissue. J Cutan Pathol. 2005 May;32(5):379-82.
  • Tardio JC, Martin-Fragueiro LM. Angiomyxolipoma (vascular myxolipoma) of subcutaneous tissue. Am J Dermatopathol. 2004 Jun;26(3):222-4.

 

Variant: Ossifying Lipoma

Diagnostic Criteria

Clinical

  • No clinical significance to this pattern
  • Several cases reported with parosteal location

Bibliography

  • Obermann EC, Bele S, Brawanski A, Knuechel R, Hofstaedter F. Ossifying lipoma.Virchows Arch. 1999 Feb;434(2):181-3.
  • Katzer B. Histopathology of rare chondroosteoblastic metaplasia in benign lipomas. Pathol Res Pract. 1989 Apr;184(4):437-45.

     

     

Variant: Sclerotic Lipoma / Fibroma-like Lipoma

Diagnostic Criteria

  • Circumscribed subcutaneous nodule
    • Occasional cases with entrapped nerve, eccrine glands or arrector pili muscle
  • Extensive sclerotic collagen bundles
    • Ranges from highly sclerotic to myxo-collagenous
      • Generally haphazard but may be whorled or concentric
    • Vessels range from inconspicuous to prominent
  • Spindled or stellate cells in sclerotic areas
    • Hypocellular
    • At most focal mild atypia
    • Mitotic figures rare
    • Bi- or multinucleated cells may be present
      • Rare cases with floret cells
  • Admixed mature fat cells
    • Usually less than 10% of lesion
      • Range 5-50%
    • May be more prominent at periphery

Supplemental Studies

 

  • Immunohistology of spindled cells
CD99 rare to many
CD34 neg to rare
Smooth muscle actin neg to rare
S100 neg to rare
Factor XIIIa neg
CD31 neg
CD68 neg
  • Mature fat cells are S100+

 

Differential Diagnosis

Sclerotic Fibroma / Storiform Fibroma Sclerotic Lipoma
Prominently concentric lamellar collagen Collagen infrequently lamellar
Factor XIIIa and CD34 positive Factor XIIIa and CD34 negative to rare
May be associated with Cowden disease Not associated with Cowden disease

Fibrolipoma Sclerotic Lipoma
Focal fibrous tissue in a lipoma Focal fat in a predominantly fibrous lesion
Various locations Predominantly located on fingers

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

Desmoplastic Fibroblastoma Sclerotic Lipoma
Fat is not intrinsic to tumor Fat is intrinsic to lesion

Fibroma of Tendon Sheath Sclerotic Lipoma
Lacks intrinsic fat Fat intrinsic to lesion
Smooth muscle actin positive Smooth muscle actin negative to rare
Both are common on the fingers

Superficial Acral Fibromyxoma Sclerotic Lipoma
Noncircumscribed Circumscribed
CD34 positive CD34 negative to rare
Lacks intrinsic fat component Fat is integral to lesion
Both are common on the fingers

Clinical

  • Rare, approximately 1/1000 fatty lesions
  • Age 7-72
  • Most reported on fingers or scalp
  • No relation found to Cowden disease
  • Benign, no documented recurrences

Bibliography

  • Laskin WB, Fetsch JF, Michal M, Miettinen M. Sclerotic (fibroma-like) lipoma: a distinctive lipoma variant with a predilection for the distal extremities. Am J Dermatopathol. 2006 Aug;28(4):308-16.
  • Zelger BG, Zelger B, Steiner H, Rutten A. Sclerotic lipoma: lipomas simulating sclerotic fibroma. Histopathology. 1997 Aug;31(2):174-81.

Variant: Intermuscular Lipoma

Diagnostic Criteria

  • Circumscribed lipoma between muscles in deep soft tissue
  • Composed of mature adipose tissue
    • No cytologic atypia

Differential Diagnosis

Intramuscular Lipoma Intermuscular Lipoma
Within skeletal muscle Between muscles
May be infiltrative or circumscribed Circumscribed
Recurrence rate 0-20% Virtually no recurrences

Lipoma vs Atypical Lipomatous Tumor (Well Differentiated Liposarcoma)

  • Diagnosis and behavior depends to a great extent on location
    • Dermis and subcutis of posterior neck, shoulders and upper back
    • Dermis and subcutis of all other sites
      • The vast majority are ordinary lipomas or angiolipomas
        • No cytologic atypia
      • Rare mature fatty neoplasms with cytologic atypia or lipoblasts are seen in these locations
        • Infrequent recurrences
        • Dedifferentiation is very rare
        • Natural (untreated) history is unknown
        • We designate such neoplasms as atypical lipomatous tumors but with a comment that aggressive behavior is rare in tumors arising in those sites
    • Deep soft tissues
      • Intramuscular, intermuscular and periosteal
        • Lipomas are well described in these locations
          • Must not have cytologic atypia or lipoblasts
          • Intramuscular lipoma may recur if incompletely excised
            • Rare large intramuscular lipomas have recurred with features of atypical lipomatous tumor
              • Genetic study for MDM2 amplification may be indicated in large or aggressively recurring intramuscular lipomas even in the absence of atypia
        • Atypical lipomatous tumor can occur in these locations
          • Infiltration is not relevant to the diagnosis
          • Requires cytologic atypia or lipoblasts
          • Frequent recurrences, rarely uncontrollable
          • Dedifferentiation rare
      • Retroperitoneum, spermatic cord, mediastinum
        • Vast majority of mature fatty neoplasms are atypical lipomatous tumors
          • (Most cord “lipomas” are merely pre-peritoneal fat squeezed through the inguinal ring, and not neoplasms)
          • Frequent recurrences, may be uncontrollable
          • May dedifferentiate and metastasize
        • Rare lipomas have been documented in the retroperitoneum (Macarenco)
          • Requires extensive sampling to exclude cytologic atypia and lipoblasts
          • Immunohistochemical and/or genetic studies are recommended before making this diagnosis
        • Myelolipoma frequently occurs in or around the adrenal
          • Megakaryocytes should not be confused with atypical cells of ALT
  • We consider atypical lipomatous tumor and well differentiated liposarcoma to be equivalent terms and primarily use the former, although both are acceptable (see discussion of these terms)
    • Some use WDL  for deep central tumors and ALT for those in other sites
  • Immunohistochemistry and/or in situ hybridization may be of use at any site
    • Lipomas are reported to be MDM2, CDK4, p16 negative
    • ALT are generally MDM2, CDK4, p16 positive
  • See subtypes of lipomas for specific differential diagnoses

Clinical

  • Virtually no recurrences

Bibliography

  • Fletcher CD, Martin-Bates E. Intramuscular and intermuscular lipoma: neglected diagnoses. Histopathology. 1988 Mar;12(3):275-87.

 

Variant: Intramuscular Lipoma

Diagnostic Criteria

  • Involves skeletal muscle
  • Composed of mature adipose tissue
    • No cytologic atypia
      • Rare large intramuscular lipomas have recurred with features of atypical lipomatous tumor
        • Genetic study for MDM2 amplification may be indicated in large or aggressively recurring intramuscular lipomas even in the absence of atypia
  • Most common in extremeties
  • May be circumscribed or infiltrative
  • If vascular component is prominent, should be classified as intramuscular hemangioma

Supplemental Studies

  • Cytogenetic studies show translocations, loss and other aberrations of
    • 12q14-15
    • 6p21-22
    • 13q12-14
    • 13q22

Differential Diagnosis

Intramuscular Lipoma Intermuscular Lipoma
Within skeletal muscle Between muscles
May be infiltrative or circumscribed Circumscribed
Recurrence rate 0-20% Virtually no recurrences

Lipoma vs Atypical Lipomatous Tumor (Well Differentiated Liposarcoma)

  • Diagnosis and behavior depends to a great extent on location
    • Dermis and subcutis of posterior neck, shoulders and upper back
    • Dermis and subcutis of all other sites
      • The vast majority are ordinary lipomas or angiolipomas
        • No cytologic atypia
      • Rare mature fatty neoplasms with cytologic atypia or lipoblasts are seen in these locations
        • Infrequent recurrences
        • Dedifferentiation is very rare
        • Natural (untreated) history is unknown
        • We designate such neoplasms as atypical lipomatous tumors but with a comment that aggressive behavior is rare in tumors arising in those sites
    • Deep soft tissues
      • Intramuscular, intermuscular and periosteal
        • Lipomas are well described in these locations
          • Must not have cytologic atypia or lipoblasts
          • Intramuscular lipoma may recur if incompletely excised
            • Rare large intramuscular lipomas have recurred with features of atypical lipomatous tumor
              • Genetic study for MDM2 amplification may be indicated in large or aggressively recurring intramuscular lipomas even in the absence of atypia
        • Atypical lipomatous tumor can occur in these locations
          • Infiltration is not relevant to the diagnosis
          • Requires cytologic atypia or lipoblasts
          • Frequent recurrences, rarely uncontrollable
          • Dedifferentiation rare
      • Retroperitoneum, spermatic cord, mediastinum
        • Vast majority of mature fatty neoplasms are atypical lipomatous tumors
          • (Most cord “lipomas” are merely pre-peritoneal fat squeezed through the inguinal ring, and not neoplasms)
          • Frequent recurrences, may be uncontrollable
          • May dedifferentiate and metastasize
        • Rare lipomas have been documented in the retroperitoneum (Macarenco)
          • Requires extensive sampling to exclude cytologic atypia and lipoblasts
          • Immunohistochemical and/or genetic studies are recommended before making this diagnosis
        • Myelolipoma frequently occurs in or around the adrenal
          • Megakaryocytes should not be confused with atypical cells of ALT
  • We consider atypical lipomatous tumor and well differentiated liposarcoma to be equivalent terms and primarily use the former, although both are acceptable (see discussion of these terms)
    • Some use WDL  for deep central tumors and ALT for those in other sites
  • Immunohistochemistry and/or in situ hybridization may be of use at any site
    • Lipomas are reported to be MDM2, CDK4, p16 negative
    • ALT are generally MDM2, CDK4, p16 positive
  • See subtypes of lipomas for specific differential diagnoses

Clinical

  • Recurrence rate 0-20%
    • Lower rate is well excised
    • Higher rate if infiltrative
  • Age 31-76

Bibliography

  • Bassett MD, Schuetze SM, Disteche C, Norwood TH, Swisshelm K, Chen X, Bruckner J, Conrad EU 3rd, Rubin BP. Deep-seated, well differentiated lipomatous tumors of the chest wall and extremities: the role of cytogenetics in classification and prognostication. Cancer. 2005 Jan 15;103(2):409-16.
  • Fletcher CD, Martin-Bates E. Intramuscular and intermuscular lipoma: neglected diagnoses. Histopathology. 1988 Mar;12(3):275-87.

 

Variant: Parosteal / Periosteal Lipoma

Diagnostic Criteria

  • Lipoma involving the periosteum
  • Mature fat with no cytologic atypia
  • Frequently exhibits metaplastic cartilage or bone

Supplemental Studies

  • One cytogenetic study has shown findings consistent with ordinary lipoma

Clinical

  • Benign

Bibliography

  • Rau T, Soeder S, Olk A, Aigner T. Parosteal lipoma of the thigh with cartilaginous and osseous differentiation: an osteochondrolipoma. Ann Diagn Pathol. 2006 Oct;10(5):279-82.
  • Petit MM, Swarts S, Bridge JA, Van de Ven WJ. Expression of reciprocal fusion transcripts of the HMGIC and LPP genes in parosteal lipoma. Cancer Genet Cytogenet. 1998 Oct 1;106(1):18-23.
  • Miller MD, Ragsdale BD, Sweet DE. Parosteal lipomas: a new perspective. Pathology. 1992 Jul;24(3):132-9.

 

Variant: Lipoma Arborescens / Villous Lipomatous Proliferation of the Synovial Membrane / Synovial Lipomatosis

Diagnostic Criteria

  • Synovial lined villous proliferation
  • Villi are diffusely infiltrated by mature fat
  • Grossly appears as a yellow papillary process
  • Usually involves large joints

Clinical

  • May be associated with trauma and arthritis
  • Fully developed cases are infrequent but fatty infiltration of chronic papillary synovitis is common
    • May be a reactive process
  • May present as a chronically swollen joint

Bibliography

  • Hallel T, Lew S, Bansal M. Villous lipomatous proliferation of the synovial membrane (lipoma arborescens). J Bone Joint Surg Am. 1988 Feb;70(2):264-70.

Variant: Multiple Lipomas

Sporadic

  • May reach hundreds
  • Most appear during 40's and 50's

Familial Multiple Lipomatosis

  • About 1/3 of cases with large numbers of lipomas are familial
  • Usually involve forearms, thighs
  • Usually appear during adolescence
  • Autosomal dominant

Angiolipomas

  • Frequently are multiple, occasionally familial

Syndromes

  • Adiposis Dolorosa / Dercum Disease
    • Multiple painful subcutaneous lipomas or fatty accumulations
      • May not always be circumscribed
    • Usually lower extremities, pelvis or trunk
    • Frequently associated with obesity or alcoholism
  • Bannayan-Riley-Ruvalcaba / Bannayan-Zonana
    • Multiple congenital lipomas, macrocephaly, hemangiomas, mental retardation
  • Cowden syndrome
    • Multiple lipomas, GI hamartomatous polyps, trichilemmomas
    • Increased breast, endometrial and thyroid carcinoma
  • MERRF / Ekbom syndrome
    • MERRF = myoclonus, epilelpsy and ragged-red fibers
    • Lipomas, skeletal deformities, cerebellar ataxia, photomyoclonus
    • mtDNA tRNA mutation
  • Multiple endocrine neoplasia type 1
    • Lipomas and pancreatic, parathyroid, pitutitary tumors
  • Proteus syndrome
    • Lipomas, congenital pelvic lipomatosis, macrodactyly, exostoses, hemangiomas, linear sebaceous nevi

See also Lipomatosis

  • The distinction between multiple discrete lipomas and diffuse fatty overgrowth is not always clear

Bibliography

  • Campen RB, Sang CN, Duncan LM. Case records of the Massachusetts General Hospital. Case 25-2006. A 41-year-old woman with painful subcutaneous nodules. N Engl J Med. 2006 Aug 17;355(7):714-22.
  • Perriard J, Saurat JH, Harms M. An overlap of Cowden's disease and Bannayan-Riley-Ruvalcaba syndrome in the same family. J Am Acad Dermatol. 2000 Feb;42(2 Pt 2):348-50.
  • Zigman AF, Lavine JE, Jones MC, Boland CR, Carethers JM. Localization of the Bannayan-Riley-Ruvalcaba syndrome gene to chromosome 10q23. Gastroenterology. 1997 Nov;113(5):1433-7.
  • Fistarol SK, Anliker MD, Itin PH. Cowden disease or multiple hamartoma syndrome--cutaneous clue to internal malignancy. Eur J Dermatol. 2002 Sep-Oct;12(5):411-21.
  • Larsson NG, Tulinius MH, Holme E, Oldfors A. Pathogenetic aspects of the A8344G mutation of mitochondrial DNA associated with MERRF syndrome and multiple symmetric lipomas. Muscle Nerve. 1995;3:S102-6.
  • Traff J, Holme E, Ekbom K, Nilsson BY. Ekbom's syndrome of photomyoclonus, cerebellar ataxia and cervical lipoma is associated with the tRNA(Lys) A8344G mutation in mitochondrial DNA. Acta Neurol Scand. 1995 Nov;92(5):394-7.
  • Costa T, Fitch N, Azouz EM. Proteus syndrome: report of two cases with pelvic lipomatosis. Pediatrics. 1985 Dec;76(6):984-9.
  • Clark RD, Donnai D, Rogers J, Cooper J, Baraitser M. Proteus syndrome: an expanded phenotype. Am J Med Genet. 1987 May;27(1):99-117.

 

Supplemental studies

Immunohistology

  • Mature fat cells are S100 positive
  • See specific variant entries for other staining patterns
Immunohistochemistry of lipomatous tumors
  MDM2 CDK4 p16
Atypical lipomatous tumor 45-100% 84-92% 78-97%
Dedifferentiated liposarcoma 55-95 90-100 90
Myxoid / round cell liposarcoma 0-4 0-4 0
Pleomorphic liposarcoma 0 0 0
Lipoma 0-4 0-2 0
Spindle cell and pleomorphic lipoma 0-25 0-6 20
Angiomyolipoma 0 0  
Hibernoma 0 0 positive, variable
Lipoblastoma 0 (1 case) 0 (1 case) positive (1 case)

Genetic analysis

  • About half to 3/4 of ordinary lipomas have chromosomal abnormalities
    • Most involve 12q13-15
    • 6p21-23 and 13q12-14 may also be involved
  • See specific variants for other abnormalities
FISH/PCR of lipomatous tumors
  MDM2 FISH MDM2 QPCR CDK4 FISH CDK4 QPCR
Atypical lipomatous tumor 90-100% 72-100% 75-100% 69-100%
Dedifferentiated liposarcoma 100% 100% 100% 100%
Myxoid liposarcoma 20%      
Spindle cell / pleomorphic lipoma Negative Negative Negative Negative
Angiolipoma Negative      
Lipoma, NOS Negative Negative Negative Negative
Sarcomas 0-40% 0% 0% 0%
  • Spindle cell / pleomorphic lipoma showed 89% chromosome 12 polysomy
  • Differential Diagnosis

    Lipoma vs Atypical Lipomatous Tumor (Well Differentiated Liposarcoma)

    • Diagnosis and behavior depends to a great extent on location
      • Dermis and subcutis of posterior neck, shoulders and upper back
      • Dermis and subcutis of all other sites
        • The vast majority are ordinary lipomas or angiolipomas
          • No cytologic atypia
        • Rare mature fatty neoplasms with cytologic atypia or lipoblasts are seen in these locations
          • Infrequent recurrences
          • Dedifferentiation is very rare
          • Natural (untreated) history is unknown
          • We designate such neoplasms as atypical lipomatous tumors but with a comment that aggressive behavior is rare in tumors arising in those sites
      • Deep soft tissues
        • Intramuscular, intermuscular and periosteal
          • Lipomas are well described in these locations
            • Must not have cytologic atypia or lipoblasts
            • Intramuscular lipoma may recur if incompletely excised
              • Rare large intramuscular lipomas have recurred with features of atypical lipomatous tumor
                • Genetic study for MDM2 amplification may be indicated in large or aggressively recurring intramuscular lipomas even in the absence of atypia
          • Atypical lipomatous tumor can occur in these locations
            • Infiltration is not relevant to the diagnosis
            • Requires cytologic atypia or lipoblasts
            • Frequent recurrences, rarely uncontrollable
            • Dedifferentiation rare
        • Retroperitoneum, spermatic cord, mediastinum
          • Vast majority of mature fatty neoplasms are atypical lipomatous tumors
            • (Most cord “lipomas” are merely pre-peritoneal fat squeezed through the inguinal ring, and not neoplasms)
            • Frequent recurrences, may be uncontrollable
            • May dedifferentiate and metastasize
          • Rare lipomas have been documented in the retroperitoneum (Macarenco)
            • Requires extensive sampling to exclude cytologic atypia and lipoblasts
            • Immunohistochemical and/or genetic studies are recommended before making this diagnosis
          • Myelolipoma frequently occurs in or around the adrenal
            • Megakaryocytes should not be confused with atypical cells of ALT
    • We consider atypical lipomatous tumor and well differentiated liposarcoma to be equivalent terms and primarily use the former, although both are acceptable (see discussion of these terms)
      • Some use WDL  for deep central tumors and ALT for those in other sites
    • Immunohistochemistry and/or in situ hybridization may be of use at any site
      • Lipomas are reported to be MDM2, CDK4, p16 negative
      • ALT are generally MDM2, CDK4, p16 positive
    • See subtypes of lipomas for specific differential diagnoses

    Clinical

    • See variants for specific clinical features
    • Ordinary lipomas quite common
      • Some variants quite rare
    • Ordinary lipomas subcutaneous
      • Variants may occur in other sites
    • Benign
      • Recurrence rate depends on site

    Grading / Staging / Report

    • Mangerial category
      • Ia (Local excision is almost always curative; metastasis never occurs)

    Lists

    Lipogenic tumors

    Five painful tumors of skin

    Bibliography

    • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
    • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
    • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
    • See individual variants for additional literature
    Printed from Surgical Pathology Criteria: http://surgpathcriteria.stanford.edu/
    © 2005  Stanford University School of Medicine