Myogenic, Lipogenic, and Neural Tumors

By admin On Oct 13, 2024

Ovid: Oncology and Basic Science

Editors: Tornetta, Paul; Einhorn, Thomas A.; Damron, Timothy A.

Title: Oncology and Basic Science, 7th Edition

> Table of Contents > Section
II – Specific Bone Neoplasms and Simulators > 5 – Benign Bone Tumors
> 5.4 – Myogenic, Lipogenic, and Neural Tumors

5.4

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

Pathophysiology

Same as for soft tissue counterparts (see Chapter 11)
Histopathology
- Leiomyoma of bone (see Fig. 11-30 in Chapter 11)
  - Interlacing bundles with uniform spindle cells
  - Immunohistochemistry: positive for smooth muscle actin, desmin
- Lipoma of bone (see Fig. 11-3)
  - Fatty tissue surrounds normal trabeculae.
  - Some tumors have necrosis, foamy histiocytes, and fibrous tissue.
- Schwannoma (see Fig. 11-26)
  - Spindle cells with wavy nuclei, often palisading within more hypercellular areas intermixed with hypocellular areas
  - Immunohistochemistry: positive for S100 diffusely

Classification

All of these lesions are classified by Enneking’s classification of benign tumors.
- Latent (most) or active (few); generally none of these lesions are aggressive
Lipoma of bone (intraosseous lipoma)
- Intramedullary lipoma: central
- Parosteal lipoma: surface lesion

Diagnosis

Physical Examination and History

Leiomyoma of bone
- Pain
Lipoma of bone
- Intramedullary lipoma
  - Typically presents as a painless bone lesion discovered incidentally or during evaluation of pain from another cause
  - Occasionally may produce achy mild pain or, rarely, pathologic fracture
- Parosteal lipoma
  - Asymptomatic bump
Schwannoma
- Usually asymptomatic incidental finding
- Occasionally mildly to moderately painful bone lesion with slow growth

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Radiologic Features

Radiography

Leiomyoma of bone
- Lucent, often multilocular, surrounded by sclerotic geographic rim
Lipoma of bone
- Geographic central radiolucency surrounded by thin sclerotic geographic rim
- Cockade sign: central mineralized radiodensity with badge appearance (nearly diagnostic when present but not universal)
Schwannoma
- Nonspecific geographic radiolucency

Magnetic Resonance Imaging

Leiomyoma of bone: nonspecific
Lipoma of bone
- Peripheral homogenous signal intensity
  that is the same as subcutaneous fat in all sequences often surrounding
  central mineralized region with characteristics of cortical bone (not
  universally present)
Schwannoma: nonspecific

Treatment

Surgical Indications/Contraindications (also see Chapter 4.2, Treatment Principles)

Nonoperative Management

Most of these lesions—leiomyoma of bone,
lipoma of bone, and intraosseous schwannoma—should be treated with
observation, particularly if they are incidental, asymptomatic findings.
Lipoma of bone should usually be diagnosed by radiographic studies and does not require biopsy.

Surgical Management

Biopsy may be necessary to establish the diagnosis, especially for leiomyoma of bone and intraosseous schwannoma.
For symptomatic lesions, intralesional excision (curettage) suffices.

Results and Outcome

Observation

There is essentially no risk of malignant degeneration of these lesions.
Observation is an acceptable alternative to surgery, and many patients remain asymptomatic and never require surgery.

Surgery

For each of these lesions, a simple curettage results in a negligible recurrence rate.