Benign Mesenchymal Tumors: Lipoma

Study Notes

A benign tumor of adipose tissue
Can occur almost anywhere, but commonly found in subcutaneous tissue, especially in shoulders, neck, back, and buttocks
Gross picture: Capsulated, globular or ovoid, yellowish, soft, and greasy
Microscopic picture: Lobules composed of mature fat cells (adipocytes) separated by fibrovascular septa

A rare, benign tumor of fibrous tissue
Found in dermis and subcutaneous tissue, as well as in organs such as the ovary, wall of the gastrointestinal tract, and bone
Gross picture: Capsulated, grayish, firm, globular or ovoid mass
Microscopic picture: Variable proportions of fibroblasts, collagen, and blood vessels; fibroblasts appear as spindle-shaped cells with elongated nuclei

A benign tumor of cartilage
Can occur within the interior of a bone (enchondroma), on the surface of a bone (subperiosteal or juxtacortical chondroma), or in extraskeletal soft tissue
Gross picture: Globular, well-demarcated mass, often nodular or lobulated
Microscopic picture: Nodules of cartilage composed of hyaline matrix and cartilage cells (chondrocytes) residing in lacunae

A developmental tumor-like abnormality (hamartoma) rather than a true neoplasm
Arises from aberrant lateral growth of the epiphyseal cartilage
Occurs in long bones and stops growing after puberty
Gross picture: Single or multiple (multiple exostosis, osteochondromatosis), with a mushroom-shaped lateral projection composed of a bony stalk and head covered by a cartilaginous cap
Microscopic picture: Cancellous bone covered by cartilage

A benign bone tumor, commonly found in the cortex and less commonly in the medullary cavity
Sites: Any bone, with the femur and tibia being the most common
Gross picture: Solitary, less than 2 cm in diameter, pink, gritty, and friable
Microscopic picture: Trabeculae of osteoid and poorly mineralized woven bone prominently rimmed by osteoblasts
Complications: Causes characteristic nocturnal pain that is dramatically improved by aspirin (prostaglandin E2)