Benign bone tumors

Classification and origin

According to the World Health Organization (WHO) nomenclature, musculoskeletal neoplasms are divided into groups based on their tissue of origin. Tumors may originate from bone, cartilage, muscle, or connective tissue.

The following main categories are distinguished:

• Osteogenic — bone-forming tumors.
• Chondrogenic — cartilage-forming neoplasms.
• Fibrogenic — originating from fibrous tissue.
• Vascular lesions.
• Tumors developing from the embryonic notochord (spinal structures).
• Lesions with a high number of osteoclastic cells.
• Hematopoietic (blood-forming) bone neoplasms.
• "Other mesenchymal tumors" — a broad group including frequently encountered benign pathologies: simple bone cysts (simple bone cysts), lipomas (lipomas), and fibrous dysplasia (fibrous dysplasia). The WHO also classifies metastatic disease in this category.

Neoplasms occur in patients of all ages. Important exceptions to the age rules are secondary malignancies (can develop at any age after radiation or chemotherapy) and osteosarcoma (osteosarcoma), which has a second peak in incidence in patients over 50 years of age against the background of Paget's disease (Paget's disease).

Aggressiveness assessment (Grade) and staging (Stage)

To plan patient management, it is necessary to determine the degree of cellular malignancy and the stage of the process. These parameters apply to both benign and malignant processes.

Degree of malignancy (grade) predicts the biological behavior of the neoplasm. It is established primarily based on the histological picture, but also takes into account imaging signs of growth pattern and destruction. The rating scale includes 4 levels:

1. 0 — benign tumor (benign);
2. Low grade (low grade);
3. Intermediate grade (intermediate grade);
4. 3 — high grade (high grade).

Stage (stage) describes the anatomical extent of the tumor (localized, with regional or distant metastases). Two systems are used for staging:

• TNM system by AJCC: evaluates the size of the primary lesion (T — Tumor), lymph node involvement (N — Node), and the presence of metastases (M — Metastasis).
• Enneking system (Enneking Staging System): developed specifically for orthopaedic oncology and comprehensively evaluates grade, anatomical location of the lesion, and metastatic status.

Clinical presentation

Symptoms directly depend on the location and specific type of neoplasm. Benign tumors often have a prolonged asymptomatic course.

Main clinical presentation variants:

• Incidental finding (incidentaloma): asymptomatic non-aggressive lesions discovered on imaging performed for another reason.
• Local symptoms: localized pain, tissue swelling, and a palpable mass resulting from node growth.
• Compression syndrome: a growing tumor can compress adjacent structures (especially nerve trunks), causing neurological symptoms locally or distally to the lesion site.
• Pathological fracture (pathological fracture): a bone fracture occurs with minimal trauma (or none at all). A growing mass weakens healthy bone tissue, and such a fracture often becomes the very first sign of an occult disease.
• General symptoms: fever, night sweats, unexplained weight loss, and fatigue are not characteristic of benign processes. Their appearance indicates the malignant nature of the lesion.

Diagnostic imaging and radiographic criteria

Radiography (X-ray) is the first-line diagnostic method, which, combined with clinical presentation, often allows for a diagnosis. Advanced methods (MRI, CT, PET) are used to assess the soft tissue component and detail the extent.

There are 4 key radiographic criteria for evaluating bone lesions:

1. Number of lesions. Multiple lesions may indicate fibrous dysplasia, bone islands (enostoses), enchondromatosis (multiple enchondromas), or a non-oncological process (e.g., osteomyelitis).
2. Lesion size. Helps in differential diagnosis. For example, a lesion with features of osteoid osteoma measuring more than 1.5 cm is classified as an osteoblastoma. Size also indicates biological behavior: thickening of the cartilaginous cap in osteochondroma greater than 1.5–2.0 cm indicates malignant transformation.
3. Localization. The affected bone is assessed (adamantinoma is typical for the tibia, and osteoblastoma for the posterior elements of the vertebrae) along with the intraosseous location: longitudinal (diaphysis, metaphysis, epiphysis) or transverse (medullary, endosteal, cortical, periosteal).
4. Signs of aggressiveness. Periosteal reaction, mineralization pattern, soft tissue component, and zone of transition (zone of transition) are evaluated. Benign tumors have a "geographic" pattern: clear margins, a narrow zone of transition, and a sharp sclerotic rim. Malignant ones are distinguished by a non-geographic pattern, infiltrative growth, and a wide zone of transition (an important exception is osteomyelitis, which can also have a wide zone of transition due to high inflammatory aggressiveness).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Osteogenic tumors: differences between osteoid osteoma and osteoblastoma
• Benign cartilage-forming tumors and enchondromatosis
• Enneking Staging System
• Fibrous dysplasia and simple bone cysts
• Radiological patterns: geographic and infiltrative growth

Other Topics in "Orthopedics"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.