Benign Mesenchymal Tumors: Lipoma

Benign Mesenchymal Tumors

Lipoma

• 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

Fibroma

• 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

Chondroma

• 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

Osteochondroma (Exostosis, Cancellous Osteoma or Enchondroma)

• 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

Osteoma

Osteoid Osteoma

• 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)

Compact Osteoma (Ivory Osteoma)

• A benign tumor arising in membranous bones of the skull
• Gross picture: Hemispherical, noncapsulated, hard, ivory-like mass
• Microscopic picture: Concentrically arranged bone lamellae

Learn about lipoma, a type of benign tumor that arises from adipose tissue, its characteristics, and common sites of occurrence.