Myogenic, Lipogenic, and Neural Tumors

Sean V. McGarry

C. Parker Gibbs

Myogenic, lipogenic, and neural tumors affecting bone are much less common than they are in soft tissues. The three most common benign bone lesions that fall into these categories are leiomyoma of bone, lipoma of bone, and schwannoma. Lipoma of bone, also commonly referred to as intraosseous lipoma, has both intramedullary and parosteal subtypes. Only the bone lesions will be discussed here; their soft tissue counterparts are discussed in Chapter 11, Benign Soft Tissue Tumors.

Pathogenesis

Etiology

The etiology for this group of rare tumors is unknown. Chromosomal abnormalities well described in soft tissue lipomas have been reported in some parosteal lipomas.

Epidemiology

Leiomyoma of bone
- Very rare
- Age: Adults >30 (only exceptionally in children)
- Gender: male = female
- Common locations: facial bones (#1 = mandible) outweigh extragnathic bones (#1 tibia)
Lipoma of bone (intrausseous lipoma)
- Rare (<0.1% primary bone tumors)
- Majority intramedullary; few parosteal
- Intramedullary lipoma
  - Age: second to eighth decade, with median age in 40s
  - Male:female 1.6:1
  - Common locations
    - Metaphyseal in long bones: proximal femur > tibia > fibula
    - Calcaneus
Parosteal lipoma
- Age: peaks in fifth and sixth decades
- Male > female (small difference)
- Common locations
  - Diaphyseal in long bones: femur > humerus > tibia
Schwannoma
- Very uncommon (<1% primary bone tumors)
  - Only benign osseous neurogenic tumor
  - Neurofibromas do NOT arise within bone.
  - Bone lesions in patients with neurofibromatosis-1 are NOT usually neurogenic tumors.
- Common locations
  - Mandible and sacrum or spine