Mesenchymal Tumours: Benign and Malignant Types

Mesenchymal Tumors

• Mesenchymal tumors originate from mesenchymal tissues (connective tissue, fat, bone, cartilage, smooth muscle, striated muscle, blood vessels, and peripheral nerves)

Benign Mesenchymal Tumors

Connective Tissue Tumors

• Lipoma: benign tumor of fatty tissue, rare malignant transformation
  • Sites of origin: subcutaneous fatty tissue of the back, shoulder region, and buttocks
  • Gross picture: capsulated, well-circumscribed, yellowish, and soft
  • Microscopic picture: lobules of mature adult fat cells separated by delicate fibrovascular tissue septa within a capsule
• Fibroma: benign tumor arising from fibrous connective tissue
  • Sites of origin: skin, subcutaneous tissue, fascia, and tendons
  • Gross picture: capsulated, soft or hard
  • Microscopic picture: interlacing bundles of fibroblasts having spindle-shaped nucleus with tapering ends
• Desmoid tumor: recurring fibroma arising from the muscular aponeurosis of the abdominal wall
  • May be due to trauma and repeated pregnancy
  • Locally infiltrative and recurs after surgical removal, but does not show evidence of malignancy

Cartilaginous Tumors

• Chondroma: benign tumor of hyaline cartilage
  • Sites of origin: ends of long bones, short bones (enchondroma), flat bones (sternum, pelvis, and scapula), and extraskletal soft tissue chondroma and bronchial chondroma
  • Gross picture: well-circumscribed, hard tumor mass, may be lobulated or rounded
  • Microscopic picture: islets of cartilage separated by fibrous tissue septa, rare malignant transformation

Bony Tumors

• Osteoma: benign tumor of bone
  • Types:
    • Compact or ivory osteoma: affects the membranous bone as the skull
      • Gross picture: smooth surface, hard mass
      • Microscopic picture: concentrically compact bone lamellae
    • Osteoid osteoma: very painful, affects adults, more common in males
      • Sites of origin: the tumor arises in any bone, commonly in the cortex
      • Gross picture: solitary, less than 1 cm, radiolucent small lesion (nidus) surrounded by dense sclerosing margins
      • Microscopic picture: center of osteoid and poorly mineralized woven bone surrounded by dense calcified bone
    • Cancellous osteoma (osteochondroma)
      • Sites of origin: from the epiphyseal cartilage of a growing long bone
      • Gross picture: uncapsulated mass projecting from bone and covered by epiphyseal cartilage
      • Microscopic picture: formed of irregular bone trabeculae covered by cartilaginous cap

Muscular Tumors

• Rhabdomyoma: very rare benign tumor of striated skeletal muscles and heart muscle
• Leiomyoma: common benign tumor of smooth muscle
  • Sites of origin: uterus, GIT (stomach, esophagus, and intestine), and other areas where smooth muscles are present
  • Microscopic picture: interlacing bundles of smooth muscle with fibrous stroma, the muscle fibers are running in various directions

Vascular Tumors

• Hemangioma: benign tumor of vascular endothelium
  • Types:
    • Capillary hemangioma
    • Cavernous hemangioma
• Lymphangioma: benign tumor or hamartoma composed of lymphatic vessels

Nervous Tumors

• Schwannoma: benign tumor of Schwann cells
• Neurofibroma: benign tumor of peripheral nerves

Malignant Mesenchymal Tumors (Sarcoma)

• Sarcoma: malignant tumor of connective (mesenchymal) tissues
• Characters of sarcoma:
  • Less common than carcinoma
  • Affects younger age group than carcinoma
  • Size: bulky masses with areas of hemorrhage and necrosis
  • Microscopic picture: very cellular, individual cells are arranged singly and separated by intercellular stroma
  • Metastasis: occurs early by blood due to high vascularity, spreads commonly to the lung
• Classification of sarcoma: according to the tissue of origin
  • Types of differentiated sarcoma:
    • Fibrous tissue: fibrosarcoma
    • Fatty tissue: liposarcoma
    • Bone tissue: osteosarcoma
    • Cartilage tissue: chondrosarcoma
    • Smooth muscle: leiomyosarcoma
    • Striated muscle: rhabdomyosarcoma
    • Nerves: neurofibrosarcoma
    • Blood vessels: angiosarcoma

Locally Malignant Tumors

• Characteristics:
  • Slow rate of growth than frank malignant tumors
  • Local invasion and destruction by infiltration only without distant metastasis
  • Microscopic features of malignancy
  • Prognosis: may recur, especially after incomplete removal
• Examples:
  • Basal cell carcinoma
  • Giant cell tumor of bone (osteoclastoma)
  • Adamantinoma of the mandible
  • Some intracranial tumors (craniopharyngioma)
  • Carcinoid tumor of the intestine
  • Bronchial adenoma (carcinoid)
  • Desmoid tumor or fibromatosis