What is a lipoma? A human lipoma is a benign tumor that occurs in adipose tissue. It is surrounded by a thin connective tissue capsule that forms an envelope, and within the tumor there are bundles of connective tissue that are divided into fat lobes, which are then transformed into micro lobes, which are then divided into clusters of normal fat cells. Some lipomas contain a large amount of connective tissue or blood vessels in addition to a large amount of fatty tissue, forming a complex lipoma, such as angiomyolipoma, fibrolipoma, and muscle lipoma. They can occur in any part of the body, most often in the subcutaneous fat layer, and in very few cases they can become malignant. They commonly occur clinically under the skin of the shoulder, back and buttocks and require surgery when they are large. It is a particularly common benign tumor, mostly seen in middle-aged people (40 to 60 years old). Lipomas that are widespread throughout the body are called pleomorphic lipomas, also called painful lipomas (Dercum’s disease) and painful obesity disease, and are most often seen in women, often accompanied by generalized obesity, with clinical manifestations of fatty deposits of plaques with spontaneous pain or tenderness. Polymorphic lipomas are rare and occur in men over middle age. They are mostly found in the shoulder and neck, with a diameter of 1-13 cm, growing slowly, but a few of them have accelerated recently. Pathological manifestations: The tumor tissue is well-defined and the tumor cells are highly pleomorphic. Although areas of mature adipocytes are seen, most of the adipocytes are of different sizes and about half of the tumors contain adipocytes or vacuolated cells, which exist in a small amount of mucinous interstitium with a large number of dense, interlaced collagen bundles. Multiple overlapping nuclei may be present within the tumor cells, or they may be arranged as petal-shaped giant cells. Intranuclear chromosomal splitting signs are rare, and there is no necrotic tissue. Treatment: The primary treatment for any lipoma is surgery, with complete excision being the mainstay. Lipomatosis is a diffuse, multi-layered growth of a lipoma in multiple locations and is called lipomatosis. In patients with various forms of lipomatosis, fat is deposited in a large amount at a particular site, and the various forms of lipomatosis are generally similar in presentation. The lesions are yellow and have the same appearance as normal fat, except for the site of involvement and the degree of diffuse fatty infiltration. The histomorphologic features of all the different types of lipomatosis are the same, containing mature adipocytes in lobular or lamellar distribution, sometimes in diffuse growth, and in some cases infiltrating other tissues such as skeletal muscle. Diffuse overgrowth of adipose tissue around the bladder and rectum is seen in pelvic lipomatosis. The massive proliferation of lipomatous tissue in the abdominal cavity may cause displacement of organs. Patients with pelvic lipomatosis may have urinary frequency, perineal pain, constipation and abdominal back pain, which may eventually lead to intestinal obstruction and hydronephrosis. II. Pathogenesis The pathogenesis of lipomatosis is not well understood. Mutations in mitochondrial genes may be associated with symmetrical lipomatosis, and the similarity between HIV lipid metabolism disorder and symmetrical lipomatosis suggests that the pathogenesis may also be due to mitochondrial DNA damage caused by HIV treatment drugs. 1. Congenital diffuse lipomatosis: Lipomas are found after birth, are frequent and diffuse, and are commonly found in one limb or part of the finger or toe joint. The tumor grows with age, with unclear border and soft texture. Congenital diffuse lipomatosis may involve the trunk, most of one limb, head and neck, abdomen, pelvis, and intestines, and may be combined with giant limbs and giant fingers/toes. It may be complicated by diffuse venous hemangioma or myxomatosis and bone hypertrophy, which together with extensive hemangioma or neurofibroma constitute a giant limb deformity, sometimes requiring amputation due to discomfort or excess weight of the limb itself. 2, benign symmetric lipomatosis (BSL): also known as Madelung,’s disease, Launois-Bensaude disease, multiple symmetric lipomatosis, hypertrophic neck syndrome, acquired diffuse lipomatosis, etc., first reported by Brodie in 1846, Madelung made a detailed description in 1888, The disease was further described by Launo and Bensaude in 1898 and defined as multiple symmetrical lipomatosis, a clinically rare benign disease. In symmetric lipomatosis, there is a restrictive or diffuse hyperplasia of adipose tissue in the neck, axilla, groin, femur, or other areas, forming plaques with a symmetrical distribution. In symmetric lipomatosis, fat is deposited diffusely in the upper part of the body, especially in the neck. Peripheral and central nervous system lesions may be present in patients with symmetric lipomatosis. Patients with diffuse fat deposition in the neck may present with laryngeal obstruction and vena cava compression or may have difficulty with neck movements due to diffuse lipomatous fat accumulation in the neck, which may even affect whistling. Important pathological changes in benign symmetric lipomatosis: adipocytes are smaller than normal adipocytes and relatively uniform in size. General pathological changes: no envelope, adipocytes smaller than normal adipocytes, relatively uniform in size. Clinical features: symmetrical distribution in the subcutaneous tissues of the neck, shoulders, chest, abdomen, groin or buttocks, and the location can be deep. There are usually no conscious symptoms. It can compress the airway and vital organs. This condition is common in adult males (20 to 52 years old) and can be familial. 3. Familial lipomatosis: Multiple lipomas on the body surface have a family tendency, also known as familial lipomatosis. It is genetically related, and the tumors are multiple and can be hundreds, usually small and often subcutaneous, and can also be associated with central nervous system diseases. 4. Steroidal lipomatosis: Fat is deposited heavily in the face, sternal region and shoulder (buffalo shoulder). Among the disorders of fat metabolism in HIV lipomatosis are visceral fat deposition, breast hypertrophy, cervical fat pad formation, hyperlipidemia and insulin resistance, but also fat consumption in the face and extremities. 5, painful lipomatosis: also known as Dercum’s disease, mostly seen in women, often accompanied by general obesity, clinical manifestations of fatty deposits plaques, with spontaneous pain or tenderness. IV. Epidemiological features of lipomatosis Diffuse lipomatosis is usually seen in individuals under 2 years of age, but it can also occur in adults. Pelvic lipomatosis is most commonly seen in black males, with an age of onset between 9 and 80 years. Symmetrical lipomatosis is common in middle-aged men of Mediterranean ancestry. Many patients have a history of liver disease and excessive alcohol intake. Steroidal lipomatosis can occur in patients treated with hormonal therapy or excessive production of endogenous adrenocorticotropic hormones. HIV-associated lipodystrophy is common in AIDS patients treated with protease inhibitors and can be seen in other forms of antiviral therapy. In acquired diffuse lipomatosis, fat is deposited diffusely in the upper part of the body, especially in the neck, in symmetric lipomatosis. In pelvic lipomatosis there is a diffuse overgrowth of adipose tissue around the bladder and rectum. In steroidal lipomatosis, fat is deposited heavily in the face, sternal region and shoulders (buffalo shoulders). in HIV lipodystrophy, there is visceral fat deposition, breast hypertrophy, cervical fat pad formation, hyperlipidemia and insulin resistance, and also fat depletion in the face and extremities. V. Immunophenotype Like normal adiposity, adipose tissue is positive for Vimentin and S-100. VI. Treatment Treatment is mainly surgical resection. There are conventional surgical excision and minimally invasive liposuction excision. VII. Prognostic factors All idiopathic lipomatosis has a tendency of local recurrence after surgery. The treatment is surgical removal of excess fat. Large fat deposits in the neck have the potential to cause laryngeal obstruction leading to death. Fat in steroidal lipomatosis can recover when hormone levels decline. Experimental drugs (such as recombinant growth hormone) have been used in the treatment of HIV-associated lipodystrophy.