Lipoma (tumor)

LIPOMA, tumor (from Greek lipos-fat), synonym fatty tumor, lipoblastoma, a frequently occurring benign tumor from fatty tissue. Lipomas are sharply limited at the periphery from surrounding tissues. Their size varies: from a forest nut to the head of an adult person and larger. The color is yellow, more or less saturated, from pale yellow to ochre yellow. The surface of the tumor is covered with a dense capsule. The lobular structure of it is often determined already upon external palpation. The lobes and the lobules included in them consist of fatty syncytium, which constitutes the parenchyma, and connective tissue septa of the stroma, carrying vessels within them. From normal adipose tissue, lipomas differ in larger size and unevenness of the parenchyma cells and the fat droplets contained in them, as well as less regularity in the distribution of connective tissue septa. Into each lobule enters one vessel, the capillaries of which do not anastomose with the capillaries of neighboring lobules and collect into one draining vessel. Depending on the size of the lobules and the greater or lesser development of connective tissue, hard (L. durum, L. fibrosum, or lipofibroma) and soft lipomas (L. molle) are distinguished. In some lipomas, expansion of blood and lymphatic vessels is observed, which is defined as L. teleangiectaticum and lymphangiectaticum. Sometimes the fatty parenchyma of lipomas transforms into mucous tissue (L. myxomatodes). The splitting of neutral fat of cells with formation of fatty acids is the reason for lime deposition (L. petrificans). In rare cases, perhaps due to trauma, foci of softening appear: the structure of fatty tissue disappears, and individual fat droplets merge into large accumulations (fat cysts). In areas that have undergone mucous transformation, accumulations of mucus may be observed. Occasionally lipomas contain bone tissue (lipoma ossificans). Virchow distinguished two types of lipomas: hyperplastic and heteroplastic. True lipomas are heteroplastic, i.e., they are formed not by simple increase of pre-existing fatty syncytium, but by neoplasm from other primordia, just as normal fatty syncytium (according to Toldt) is formed from a special primordium. The histogenesis of lipomas has not yet been studied more precisely. - Localization is diverse. Lipomas most often develop where adipose tissue is normally located: in the skin and subcutaneous tissue on the back, shoulders, buttocks, on the neck, limbs, anterior abdominal wall, retroperitoneal tissue, etc. Subcutaneous lipomas sometimes hang on a stalk (L. pendulum). Sometimes in such pendulous lipomas, sharp edema and development of fat cysts occur (dermatolipomatosa). Deep subfascial lipomas are found on the neck, between the trachea and esophagus (Hirschel), rarely on the feet, on fingers; also rare in the kidneys, uterus, broad ligaments, spermatic cord, adrenal glands, intracranial, in the heart, parotid gland, intrapleural, in the liver. Lipomas are more often single; but multiple lipomas are also observed; cases of symmetric development of lipomas are known. Sometimes such lipomas are associated with nerves (neurolipoma). - Lipomas are benign tumors both anatomically and clinically; but with certain localization they can lead to severe symptoms. Thus, intraperitoneal lipomas can be the cause of intestinal intussusception. It is interesting that with the general disappearance of fat depending on general exhaustion, lipomas not only remain unchanged, but even continue to grow. - In the etiology of lipomas, heredity has a certain significance. Many authors attribute the cause of some lipomas, e.g., kidney lipomas, intracranial lipomas, to wandering embryonic primordia. However, there is no doubt that lipomas can develop from mature elements, normal for a given organism. From true lipomas, tumor-like hyperplasias on the basis of various conditions should be distinguished. Such are retrorectal accumulations of fat (lipoma retrorectale), development of fat on the back and lateral surfaces of the neck-"Madelung's fatty neck" (L. annulare colli), occurring in obesity; then tree-like growths of fat in joints and tendons (L. arborescens), observed in chronic inflammations; so-called "vacant" fat growths in atrophy of other organs: muscles, kidneys (pseudohypertrophia lipomatosa) also do not belong to tumors. All the listed phenomena refer to pseudolipomatoses. - Treatment of lipomas is exclusively surgical-excision; difficulties occur only with very large lipomas (e.g., retroperitoneal).