Adipocytic tumors





Benign tumors and reactive conditions


Lipoma


Definition





  • A benign dermal or subcutaneous mesenchymal tumor composed of mature adult-type adipose tissue



Clinical features


Epidemiology





  • The most commonly encountered mesenchymal tumor



  • Majority of patients are adults



  • No sex predilection



Presentation





  • Most cases are asymptomatic



  • Occasionally painful when compressing nerves



  • Slowly growing, but size is variable



  • Usually solitary



  • Multiple lipomas may be associated with neurofibromatosis, multiple endocrine neoplasia syndromes, or Bannayan syndrome (hemangiomas and multiple lipomas)



Prognosis and treatment





  • Treated mostly for aesthetic reasons



  • Cured by conservative surgical excision



  • Recur only if incompletely excised and then only rarely



  • Not associated with progression to liposarcoma



Pathology


Histology





  • Resemble normal adult-type adipose tissue



  • Lobules of adipocytes bounded by thin fibrous septa



  • Adipocytes have large single lipid vacuole in their cytoplasm and eccentrically located small nuclei



  • May show areas of fat necrosis and increased fibrosis after trauma



  • No atypia, pleomorphism, mitoses, or hyperchromasia



Immunohistochemistry/special stains





  • Adipocytes express S100 protein



Genetic profile





  • True neoplasms



  • Translocation at 12q14 involving HMGA2 gene is the most common aberration, often with LPP (3q27)



  • 6p21-23 rearrangements involving HMG1B gene are also seen



Main differential diagnoses





  • Normal adipose tissue



  • Pseudolipomatosis cutis



  • Atypical lipomatous tumor


Fig. 1


Lipoma.

Deeper lipomas are well-circumscribed neoplasms composed of mature adipose tissue essentially indistinguishable from normal fat.



Fig. 2


Lipoma.

High-power view of mature adipocytes exhibiting minimal size variation and small, eccentric nuclei.



Fig. 3


Lipoma.

Intradermal lipoma is a well-demarcated dermal neoplasm. It is composed of lobules of mature adipose tissue bounded by fibrous septa.



Fig. 4


Lipoma.

High-power view of intradermal lipoma. Note the mature adipocytes.




Lipomatosis


Definition





  • Diffuse overgrowth of mature adipose tissue



  • The disease presents in two forms: multiple symmetric lipomatosis (Launois-Bensaude syndrome) and asymmetric lipomatosis



Clinical features


Epidemiology





  • Rare disorder, commonly associated with obesity



  • Some familial cases show evidence of autosomal-dominant mode of inheritance



  • Common in children less than 2 years of age



  • Adults can occasionally be affected



  • Can present in trunk, head and neck, and extremities



Presentation





  • Painless, diffuse enlargement of affected area due to fat accumulation



  • Rapid growth is characteristic



Prognosis and treatment





  • Recurrence after palliative surgical removal is common



  • Usually cured by radical surgical excision



  • Although benign, can be fatal due to laryngeal obstruction



Pathology


Histology





  • Sheets and lobules of mature adipocytes



  • No encapsulation



Immunohistochemistry/special stains





  • The mature adipocytes strongly express S100 protein



Main differential diagnoses





  • Intramuscular lipoma



  • Atypical lipomatous tumor



Multiple symmetric lipomatosis (Launois-Bensaude syndrome)





  • The most common form of lipomatosis characterized by symmetrical deposition of adipose tissue in the trunk and head and neck area



  • Two variants exist: diffuse and localized



  • The diffuse variant usually affects the trunk of male children



  • The localized variant characteristically affects the cervical area of adult males and can present with laryngeal obstruction



  • Patients can present with neuropathy



Asymmetric lipomatosis





  • Asymmetric deposition of adipose tissue affecting any part of the body



  • Less common than the symmetric form of lipomatosis



  • Can present with macrodactyly or gigantism of affected body area



Lipomatosis of Nerve


Definition





  • A rare hamartomatous condition characterized by fatty infiltration of epineurium of a major nerve



  • Also known as fibrolipoma of nerve, fibrolipomatous hamartoma of nerve, macrodystrophia lipomatosa, perineural lipoma, and intraneural lipoma



Clinical features


Epidemiology





  • Affected individuals are mostly newborns and young children



  • Female predilection



Presentation





  • The median nerve is the most common location, followed by the ulnar nerve



  • Slowly growing masses or macrodactyly



  • Can be asymptomatic or associated with pain, paresthesia, or motor deficit



Prognosis and treatment





  • Benign condition, but management can be challenging



  • Surgical excision may result in permanent sensory and/or motor deficit



  • Incomplete removal is associated with high rate of recurrence



Pathology


Histology





  • Infiltration of epineurium and perineurium by mature adipose tissue admixed with fibrous tissue



  • Metaplastic bone formation is rarely seen



Main differential diagnoses





  • Intraneural lipoma



  • Diffuse lipomatosis



  • Traumatic neuroma


Fig. 1


Lipomatosis of nerve.

Mature adipose tissue surrounds individual nerve branches but is bounded by epineurium.



Fig. 2


Lipomatosis of nerve.

Fibrosis of the surrounding adipose tissue is often seen.



Fig. 3


Lipomatosis of nerve.

Extensive concentric fibrosis of the largest central nerve bundle.



Fig. 4


Lipomatosis of nerve.

A small nerve bundle with less surrounding fibrosis.




Adiposis Dolorosa


Definition





  • A rare condition characterized by multiple painful plaques of accumulated subcutaneous fat



  • Also known as Dercum disease



Clinical features


Epidemiology





  • Rare disorder, commonly associated with obesity



  • Affected individuals are mainly postmenopausal women



Presentation





  • Painful and tender plaques



  • Usually multiple



  • Most cases are located in the lower extremities and pelvic area



Prognosis and treatment





  • Benign condition cured by surgical excision



Pathology


Histology





  • Subcutaneous lobules of mature adipocytes



  • Fat necrosis can be seen



Immunohistochemistry/special stains





  • The mature adipocytes strongly express S100 protein



Main differential diagnoses





  • Lipoma



  • Other forms of lipomatosis



Piezogenic Pedal Papules


Definition





  • Multiple papules located at the internal aspects of the heels



Clinical features


Epidemiology





  • Commonly affects athletes, particularly marathon runners



  • Associated with Ehlers-Danlos and Prader-Willi syndromes as well as rheumatoid arthritis



  • Rarely familial



Presentation





  • Multiple asymptomatic skin-colored papules



  • Lesions become more pronounced after prolonged standing



  • Pressure may elicit pain



Prognosis and treatment





  • Conservative management includes intralesional steroid and anesthetic injection or compression treatment



  • Therapy outcome might not be satisfactory



  • Surgical intervention is usually more effective



Pathology


Histology





  • Mature adipose tissue herniating into the dermis



Immunohistochemistry/special stains





  • The mature adipocytes strongly express S100 protein



Main differential diagnoses





  • Intradermal lipoma



Fat Necrosis of the Morbidly Obese


Definition





  • Necrosis of subcutaneous adipose tissue as a result of obesity



  • It is thought to result from medial calcification of subcutaneous arterioles with subsequent ischemic necrosis of fat



Clinical features


Epidemiology





  • Usually affects distal extremities



  • Can affect thighs, abdomen, and other areas



  • Associated with chronic renal failure and hyperphosphatemia



Presentation





  • Painful induration and purplish discoloration of skin



  • Associated skin necrosis can lead to ulcer formation



  • Skin ulceration progresses rapidly as level of phosphate peaks



Prognosis and treatment





  • High mortality rate due to development of secondary infection



Pathology


Histology





  • Massive necrosis of subcutaneous adipose tissue with minimal inflammatory reaction



  • Calcification of subcutaneous arterioles with luminal narrowing


Fig. 1


Fat necrosis of the morbidly obese.

Low-power view showing extensive fat necrosis.



Fig. 2


Fat necrosis of the morbidly obese.

Necrosis involving the adipocytes as well as the vascularized fibrous septa.



Fig. 3


Fat necrosis of the morbidly obese.

Necrotic adipocytes and necrotic connective tissue septa are seen in this image.



Fig. 4


Fat necrosis of the morbidly obese.

Viable adipocytes can be seen in a patchy or geographical distribution.



Fig. 5


Fat necrosis of the morbidly obese.

Necrotic adipocytes often retain their shape but lose nuclear staining.



Fig. 6


Fat necrosis of the morbidly obese.

Histiocytes infiltrate the adipose tissue. Note the arteriolosclerosis.




Nevus Lipomatosus Superficialis


Definition





  • A rare cutaneous hamartomatous lesion characterized by multiple small collections of adipocytes within the dermis



Clinical features


Epidemiology





  • Affected individuals are children or adolescents



  • Adults present with solitary variant



  • No sex predilection



Presentation





  • Multiple painless papules



  • Size ranges from few millimeters up to 2 cm



  • Most commonly affect the gluteal area, upper thighs, and lower back



Prognosis and treatment





  • Cured by simple excision



Pathology


Histology





  • Nonencapsulated lesion composed of variable number of fatty lobules deposited in the upper portion of the dermis



  • The lobules condense around blood vessels and are interspersed by loose fibrous tissue



  • Secondary changes include perifollicular fibrosis, follicular hyperkeratosis, and epidermal atrophy



Immunohistochemistry/special stains





  • The mature adipocytes strongly express S100 protein



Main differential diagnoses





  • Lipofibroma



  • Fibroepithelial polyp


Fig. 1


Nevus lipomatosus superficialis.

A lesion in the upper dermis composed of variably sized lobules of mature adipocytes.



Fig. 2


Nevus lipomatosus superficialis.

The overlying epidermis is slightly atrophic.



Fig. 3


Nevus lipomatosus superficialis.

The adipocytic lobules are separated by fibrous septa.



Fig. 4


Nevus lipomatosus superficialis.

High-power view demonstrates mature adipocytes with small, eccentric nuclei. Note the interspersed collagen fibers.




Fibrohistiocytic Lipoma


Definition





  • A rare variant of lipoma characterized by the presence of fibrohistiocytic proliferation in addition to the conventional lipomatous component



Clinical features


Epidemiology





  • Strong predilection for young adult males



  • Anterior aspect of trunk is most commonly affected



Presentation





  • Small, painless, subcutaneous lesions



  • Usually solitary



Prognosis and treatment





  • Cured by local excision



  • No reports of recurrence or metastasis



Pathology


Histology





  • Well-circumscribed subcutaneous lipomas with fibrohistiocytic foci



  • Fibrohistiocytic foci depict slightly plump, bland-looking spindle cells arranged in fascicles in a collagenous stroma



  • May exhibit minimal inflammation and/or hemosiderin deposition



Immunohistochemistry/special stains





  • Tumor cells express CD34 and calponin



  • Fibrohistiocytic component lacks S100 protein expression



Main differential diagnoses





  • Benign fibrous histiocytoma



  • Spindle cell lipoma



  • Atypical lipomatous tumor



  • Dermatofibrosarcoma protuberans


Fig. 1


Fibrohistiocytic lipoma.

A circumscribed neoplasm admixing mature lipomatous cells and a spindle cell component.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)



Fig. 2


Fibrohistiocytic lipoma.

The spindle cells have a fibrohistiocytic pattern.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)



Fig. 3


Fibrohistiocytic lipoma.

The adipose tissue and spindle cells can be admixed.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)



Fig. 4


Fibrohistiocytic lipoma.

The non-adipocytic component can be predominant in areas.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)



Fig. 5


Fibrohistiocytic lipoma.

Intimate juxtaposition of mature adipocytic cells and fibrohistiocytic cells.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)



Fig. 6


Fibrohistiocytic lipoma.

The nuclei are banal, and the cytoplasm is somewhat amphophilic.

(Courtesy of Julie Fanburg-Smith, Washington, DC, USA.)




Lipofibromatosis


Definition





  • A benign fibrofatty neoplasm presenting in childhood



Clinical features


Epidemiology





  • More common in males



  • Develops in infancy and childhood (mean age 1 year)



  • Already present at birth in a substantial number of cases (about 15%)



Presentation





  • Slowly growing and ill-defined painless mass



  • Size of the lesion usually between 2 and 5 cm



  • Wide anatomical distribution with predilection for hands and feet



Prognosis and treatment





  • Benign proliferation, associated with high rate of nondestructive recurrence(s) (about 70%)



  • Diffuse involvement of the limbs can result in deformities of the underlying bone



  • Risk factors for local recurrence(s) include congenital onset, male gender, incomplete excision, and increased mitotic rate



  • Complete surgical excision generally curative, but may be difficult to achieve



Pathology


Histology





  • Poorly delineated proliferation in the subcutis and/or deep soft tissues



  • Two main components are mature fat and fibroblastic spindle-shaped cells



  • Adipose tissue component




    • Integral part of the tumor



    • Usually the predominant component



    • Composed of mature adipocytes



    • Variably sized and poorly demarcated lobules




  • Fibroblastic spindle cell component




    • Formation of fascicles, typically growing along the fat septa



    • Mild cytological atypia



    • Mitoses absent or rare in the majority of cases



    • Increased mitotic rate associated with increased likelihood of local recurrence



    • Small to moderate amounts of collagen



    • Focal myxoid change occasionally present




  • Univacuolated cells




    • Usually encountered at the interface between the fibroblastic and adipocytic component



    • Characterized by a single vacuole in the cytoplasm



    • Likely represent degenerating adipocytes, lipid-rich fibroblasts, or transitional cells between fibroblast and adipocyte



    • Seen in the majority of lesions




  • Entrapment of normal structures, including vessels, nerves, skin adnexa, and skeletal muscle within the tumor



  • Pigmented melanocytic spindled or dendritic cells (similar to the ones found in Bednar tumor) exceptionally seen among the lesional cells



Immunohistochemistry/special stains





  • Not contributory



  • Focal S100 protein positivity in the spindle cell component occasionally detected



  • β-catenin negative



Main differential diagnoses





  • Juvenile hyaline fibromatosis



  • Fibrous hamartoma of infancy



  • Calcifying aponeurotic fibroma



  • Lipoblastoma


Fig. 1


Lipofibromatosis.

An ill-defined neoplasm composed of proliferative fibrous tissue with islands of adipose tissue.



Fig. 2


Lipofibromatosis.

Adipocytic and fibroblastic components are intimately admixed.



Fig. 3


Lipofibromatosis.

Area with marked spindle cell fibroblastic proliferation with interspersed adipose tissue, somewhat resembling desmoid fibromatosis.



Fig. 4


Lipofibromatosis.

The process infiltrates the underlying skeletal muscle.



Fig. 5


Lipofibromatosis.

The spindle cell fibroblasts reveal bland nuclear features.



Fig. 6


Lipofibromatosis.

The adipocytic component also demonstrates benign cytology.




Lipoblastoma/Lipoblastomatosis


Definition





  • Lipoblastoma and lipoblastomatosis are lesions characterized by the presence of lobules of fetal-type adipose tissue



  • Lipoblastoma is localized while lipoblastomatosis is the diffuse form of the disease



Clinical features


Epidemiology





  • Lipoblastoma/lipoblastomatosis are considered the fetal counterpart of the adult lipoma and lipomatosis, respectively



  • Most patients are infants or young children less than 3 years of age



  • Boys are much more commonly affected than girls



  • The extremities are the most common location followed by the mediastinum, the trunk, the retroperitoneum, and the head and neck



Presentation





  • Discrete or diffuse superficial, painless masses of fatty tissue



  • Small lesions, usually measure 2 to 5 cm



Prognosis and treatment





  • Benign condition



  • Localized form of disease is readily cured by total resection



  • Lipoblastomatosis may recur on some occasions mainly due to inability to completely excise the lesion



  • Untreated cases may undergo maturation into an adult-type lipoma/lipomatosis



Pathology


Histology





  • Lobules of mature adipocytes admixed with lipoblasts in varying stages of development



  • Number of lipoblasts present in the tumor tends to decrease as the patient age increases



  • Lipoblastomatosis is less lobulated and may infiltrate skeletal muscle tissue



  • May have prominent fibrous septa and myxoid matrix



Genetic profile





  • 8q11~13 rearrangements resulting in HAS2 PLAG1 or COL1A2 PLAG1 fusion genes is common



  • Gain of chromosome 8 seen in some cases



Main differential diagnoses





  • Atypical lipomatous tumor



  • Myxoid liposarcoma



  • Lipofibromatosis


Fig. 1


Lipoblastoma.

A discrete dermal neoplasm composed of lobules of adipose tissue separated by fibrous septa.



Fig. 2


Lipoblastoma.

The neoplastic lobules are composed of adult- and fetal-type adipocytic components.



Fig. 3


Lipoblastoma.

Fetal-type adipocytes at various stages of development admixed with mature adipocytes.



Fig. 4


Lipoblastoma.

Numerous lipoblasts are seen with scattered mature adipocytes.



Fig. 5


Lipoblastomatosis.

A diffuse dermal neoplasm composed of lobules of adult- and fetal-type adipose tissue, identical to isolated lipoblastoma.



Fig. 6


Lipoblastomatosis.

High-power view demonstrating numerous lipoblasts with occasional mature adipocytes.




Lipoblastoma-Like Tumor of the Vulva


Definition





  • An extremely rare mesenchymal neoplasm characterized by adipocytic differentiation



Clinical features


Epidemiology





  • Adolescent and young adult females



Presentation





  • Superficial, painless vulvar masses



  • Can be cystic



  • Can have mucoid consistency



Prognosis and treatment





  • Cured with surgical resection



  • Recurrences and metastases have not been reported



Pathology


Histology





  • Well-circumscribed and lobulated



  • Lobules are composed of uniform spindle cells showing slightly eosinophilic cytoplasm and elongated nuclei and variable number of lipoblasts separated by thin fibrous septa



  • Lacks nuclear atypia and hyperchromasia



  • Plexiform, “chicken-wire” vascular networks are commonly seen



Immunohistochemistry/special stains





  • Fat cells express S100 protein



  • No CD34 expression



Main differential diagnoses





  • Lipoblastoma



  • Myxoid liposarcoma



  • Spindle cell lipoma



  • Aggressive angiomyxoma



  • Angiomyofibroblastoma


Fig. 1


Lipoblastoma-like tumor of the vulva.

Somewhat lobulated neoplasm with myxoid areas separated by fibrous stroma.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)



Fig. 2


Lipoblastoma-like tumor of the vulva.

Scattered univacuolar lipoblast-like cells are noted.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)



Fig. 3


Lipoblastoma-like tumor of the vulva.

Higher power view reveals bivacuolated lipoblast-like cells as well.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)



Fig. 4


Lipoblastoma-like tumor of the vulva.

Hypocellular myxoid areas can be seen.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)



Fig. 5


Lipoblastoma-like tumor of the vulva.

More cellular areas are highlighted in this picture.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)



Fig. 6


Lipoblastoma-like tumor of the vulva.

The spindle cells have bland nuclear features.

(Courtesy of Antonio Nascimento, São Paulo, Brazil.)




Angiolipoma


Definition





  • A benign dermal or subcutaneous encapsulated mesenchymal tumor composed of mature adult-type adipose tissue and thin-walled small blood vessels



Clinical features


Epidemiology





  • Mainly affects adolescents and young adults



  • Predilection for females



  • Familial in 5% of cases and shows autosomal-dominant mode of transmission



  • Most commonly encountered in the upper limbs, trunk, and distal extremities



Presentation





  • Many are painful



  • Commonly multiple



  • Size ranges from a few millimeters to 2 cm



Prognosis and treatment





  • Cured by conservative, complete surgical excision



  • No recurrence or metastasis reported



Pathology


Histology





  • Encapsulated tumors composed of adipocytes and variable number of thin-walled small blood vessels



  • Blood capillary vessels commonly show microthrombi



  • No atypia, pleomorphism, mitoses, or hyperchromasia



  • A rare cellular variant is recognized



  • Older lesions can show increased fibrosis



Immunohistochemistry/special stains





  • The adipocytes express S100 protein



  • The endothelial cells are highlighted by CD34, CD31, and ERG



Genetic profile





  • Low-level mutations of protein kinase D 2 have been demonstrated in 80% of cases



Main differential diagnoses





  • Lipoma



  • Hemangioma



  • Kaposiform hemangioendothelioma



  • Kaposi sarcoma



  • Angiosarcoma


Fig. 1


Angiolipoma.

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Oct 29, 2019 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Adipocytic tumors
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