Lipomas

Abstract

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

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, 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, 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. Possible association with hereditary familial multiple lipomatosis (FML).

Imaging: On X-ray, a radiolucent mass rarely with 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. Soft on palpation, pale yellow in color, lipoma is constituted by mature adipocytes with no atypia. Vessels are not very apparent, because they are thin and compressed by lipocytes.

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 subcutaneous pain	Firm yellow/reddish	Lipocytes + network of capillaries with fibrin thrombi
Spindle cell Lipoma	Adult	Male	4 cm/back subcutaneous painless	Soft yellow/whitish	Lipocytes + vessels + spindle cells + myxoid matrix + collagenous bands
Pleomorphic Lipoma	Adult	Male	4 cm/back subcutaneous painless	Firm yellow/whitish	Lipocytes + bizarre floret-like multinucleated cells
Lipoblastoma	<2	Male	3 cm/limbs subcutaneous painless	Lobulated translucid	Like myxoid liposarcoma
Lipomatosis	10	–	Large/diffused pain	Dense tissue infiltrating	Mature adipose tissue
Intranervous L	<30	Male	Hand/wrist pain + neuropathy	Hard	Surrounds and infiltrates the nerve
Hybernoma	Adult	Male	4 cm/scapular subcutaneous painless	Firm	Central nucleus + foam cytoplasm = brown fat

Spindle Cell/Pleomorphic Lipoma

Immunohistochemical panel
• CD34	+
• Rb	+/−

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