Tumors

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TUMOURS OF ADIPOSE TISSUE Gul Shaikh Friday 30 th Sep, 2011.

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LIPOMA Benign tumor of fat. M ost common soft tissue tumor of adulthood. They are sub classified according to particular morphologic features as conventional lipoma , fibrolipoma , angiolipoma , spindle cell lipoma , myelolipoma , and pleomorphic lipoma . Some of the variants have characteristic chromosomal abnormalities.

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Lipoma : Low-power view of a tumor of the tongue demonstrating a mass of mature adipose tissue,

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Lipomas are: Soft mobile painless (except angiolipoma ) usually cured by simple excision.

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• Lipoma . High-power view of the same lesion. Note the similarity of the tumor cells to normal fat.

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The most common mesenchymal neoplasm. M ost examples occur on the trunk and proximal portions of the extremities. Lipomas of the oral and maxillofacial region are much less frequent. The pathogenes of lipomas is uncertain, but they appear to be more common in obese people. However. the metabolism of lipomas is completely independent of the normal body fat. If the caloric intake is reduced, lipomas do not decrease in size, although normal body fat may be lost.

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Clinical Features Oral lipomas are usually soft, smooth s urfaced nodular masses that can be sessile or pedunculated . Typically, the tumor is asymptomatic and often has been noted for many months or years before diagnosis. Most are less than 3 cm in size, but occasional lesions can become much larger. Although a subtle or more obvious yellow hue often is detected clinically, deeper examples may appear pink. The buccal mucosa and buccal vestibule are the most common intraoral sites and account for 50% of all cases. Some buccal cases may not represent true tumors, but rather herniation of the buccal fat pad, which may occur subsequent to surgical removal of third molars. Less common sites include the tongue, floor of the mouth, and lips. Most patients are 40 years of age or older; lipomas are uncommon in children. Although lipomas elsewhere in the body are reported to be twice as common in females as in males, oral lipomas are characterized by a more balanced sex distribution,

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Lipoma : Nodular mass of the posterior buccal mucosa.

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Histopathologic Features Most oral lipomas are composed of mature fat cells that differ little in microscopic appearance from the surrounding normal fat. The tumour is usually well circumscribed and may demonstrate a thin fibrous capsule. A distinct lobular arrangement of the cells often is seen. On rare occasions, central cartilaginous or osseous metaplasia may occur within an otherwise typical lipoma .

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A number of microscopic variants have been described. The most common of these is the fibrolipoma , characterized by a significant fibrous component intermixed with the lobules of fat cells. The remaining variants are rare. A ngio lipoma consists of an admixture of mature fat and numerous small blood vessels. Myxoid lipomas exhibit a mucoid background and may be confused with myxoid liposarcomas .

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Morphology The conventional lipoma , the most common subtype, is a well-encapsulated mass of mature adipocytes that varies considerably in size. It arises in the subcutis of the proximal extremities and trunk, most frequently during mid-adulthood. Infrequently, lipomas are large, intramuscular, and poorly circumscribed. Histologically, they consist of mature white fat cells with no pleomorphism .

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The spindle cell lipoma demonstrates variable amounts of uniform appearing spindle cells in conjunction with a more typical lipomatous component. Pleomorphic lipomas are characterized by the presence of spindle cells plus bizarre, hyperchromatic giant cells; they can be difficult to distinguish from a pleomorphic liposarcoma , Intramuscular (infiltrating) lipomas often are more deeply situated and have an infiltrative growth pattern that extends between skeletal muscle bundles.

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Treatment and Prognosis Lipomas are treated by conservative local excision, and recurrence is rare. Most microscopic variants do not affect the prognosis. Intramuscular lipomas have a higher recurrence rate because of their infiltrative growth pattern , but this variant is rare in the oral and maxillofacial region.

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LIPOBLASTOMA / LIPOBLASTOMASIS

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HIBERNOMA

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LIPOSARCOMA

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LIPOSARCOMA Liposarcomas are one of the most common sarcomas of adulthood and appear in those in their forties to sixties. They are uncommon in children. They usually arise in the deep soft tissues of the proximal extremities and retroperitoneum . N otorious for developing into large tumors.

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Morphology: Histologically, liposarcomas can be divided into: well-differentiated, myxoid , round cell, and pleomorphic variants.

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The myxoid and round cell variant of liposarcoma has a chromosomal abnormality in most cases. The cells in well-differentiated liposarcomas are readily recognized as lipocytes . In the other variants, most of the tumor cells are not obviously adipogenic , but some cells indicative of fatty differentiation are almost always present. These cells are known as lipoblasts ; they mimic fetal fat cells and contain round clear cytoplasmic vacuoles of lipid that scallop the nucleus. The myxoid and round cell variant of liposarcoma has a chromosomal abnormality in most cases.

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Myxoid liposarcoma with abundant ground substance in which are scattered adult-appearing fat cells and more primitive cells, some containing small lipid vacuoles ( lipoblasts ).

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The well-differentiated variant is relatively indolent,. T he myxoid type is intermediate in its malignant behavior Round cell and pleomorphic variants usually are aggressive and frequently metastasize. All types of liposarcoma recur locally and often repeatedly unless adequately excised.

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