Lipomas

Abstract

Definition: A benign tumor constituted by well-differentiated adipocytes.

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Definition: A benign tumor constituted by well-differentiated adipocytes.

Epidemiology: The most common among soft tissue tumors. It is more frequently observed between 40 and 60 years of age and prevails in females when it is superficial, whereas in males when it is deep and multiple.

Localization: (a) Superficial (frequent): in the subcutaneous tissue of the back, shoulder, neck, and proximal extremities. (b) Deep (rare): within or between muscles or adherent to bone, tendons, joints or nerves. In 5 % of cases lipomas are multiple with symmetrical distribution in the dorsum and proximal upper limb.

Clinical: Solitary lump, slow growing, and painless unless there is nerve compression. Superficial lipoma never grows large size (average 4 cm.) and it is movable. Deep lipoma tends to be larger (average 10 cm) and with a spherical, fixed, and firm mass.

Imaging: On X-ray, a radiolucent mass with or without calcification or ossification; mild cortical thickening when parosteal. On CT scan, a lobulated, sharply marginated radiolucency with homogeneous density. On MRI, an encapsulated, bright mass without enhancement after contrast administration; signal intensity equal to that of fat; regular thin septation. On angiography, avascular. On bone scan, there is no uptake.

Histopathology: It is often lobulated with a very thin true capsule and pseudocapsule fibrous, thick, and adherent to the surrounding tissues. Soft on palpation, pale yellow in color, lipoma is constituted by lipocytes, mature “signet ring” cells. Vessels are not very apparent, because they are thin and compressed by lipocytes. On immunohistochemistry, all lipomas are diffusely positive for S-100 and vimentin. Spindle cell and pleomorphic lipoma are also positive for CD34.

Course and Staging: a) Superficial lipoma: easily diagnosed, asymptomatic, generally stage 1, but it may behave as active stage 2 lesion. According to AJC classification, lipoma is more frequently stage Ia. b) Deep lipoma: an extensive anatomo-pathological study with multiple specimens is necessary to exclude liposarcoma lipoma-like. Usually, stage 2 or stage Ib according to AJC classification. Malignant changes are exceptional.

Treatment: Marginal excision is curative. Recurrence is rare (<5 %).

Variants	Age	Sex	Clinical	Gross	Histology
Angiolipoma	20	Male	<2 cm/forearm	Firm	Lipocytes +
			Subcutaneous	Yellow/reddish	Network of capillaries with fibrin thrombi
			Pain
Spindle cell lipoma	Adult	Male	4 cm/back	Soft	Lipocytes +
			Subcutaneous	Yellow/whitish	Vessels + spindle cells +
			Painless		Myxoid matrix +
					Collagenous bands
Pleomorphic lipoma	Adult	Male	4 cm/back	Firm	Lipocytes +
			Subcutaneous	Yellow/whitish	Bizarre floret-like multinucleated cells
			Painless
Lipoblastoma	<2	Male	3 cm/limbs	Lobulated translucid	Like myxoid liposarcoma
			Subcutaneous
			Painless
Lipomatosis	10	–	Large/diffused	Dense	Mature adipose
			Pain	Tissue infiltrating
Intranervous L	<30	Male	Hand/wrist	Hard	Surrounds and infiltrates the nerve
			Pain + neuropathy
Hibernoma	Adult	Male	4 cm/scapular	Firm	Central nucleus + Foam cytoplasm = Brown fat
			Subcutaneous
			Painless

FormalPara Immunohistochemical Panel

Usual Lipoma
VIM	+
S100	+

FormalPara Immunohistochemical Panel

Spindle Cell Lipoma
VIM	+
S100	+
CD34	+

Mature adipocytic cells organized in lobules with flat nuclei at the periphery and optically empty cytoplasms. No atypia of the cells