Makindo Medical Notes

Osteochondroma is the most common benign bone tumour, characterized by a cartilage-capped bony projection arising from the external surface of a bone. It typically occurs near the growth plates of long bones, particularly around the knee and proximal humerus. While often asymptomatic and discovered incidentally, osteochondromas can sometimes cause pain, mechanical disturbances, or, rarely, malignant transformation.

About

• Definition: Osteochondroma is a benign bone tumour consisting of both bone and cartilage, protruding from the metaphysis of long bones.
• Types:
  • Solitary Osteochondroma: A single lesion, usually asymptomatic and found incidentally.
  • Multiple Osteochondromas (Hereditary Multiple Exostoses, HME): An inherited condition characterized by multiple osteochondromas, often leading to skeletal deformities.

Classification

Type	Description
Solitary Osteochondroma	A single benign bone growth, typically asymptomatic and discovered incidentally on imaging studies.
Multiple Osteochondromas (HME)	An autosomal dominant inherited condition featuring multiple osteochondromas, often associated with limb deformities and a higher risk of malignant transformation.

Epidemiology

• Most common benign bone tumour, accounting for approximately 20-50% of all benign bone tumours.
• Typically diagnosed during the first two decades of life, correlating with bone growth periods.
• More prevalent in males than females.
• Hereditary Multiple Exostoses (HME) affects about 1 in 50,000 individuals.

Pathophysiology

• Osteochondromas arise from the growth plate (physis) of long bones, extending outward.
• Comprised of a bony stalk covered by a cartilaginous cap, reflecting the growth plate's characteristics.
• In HME, multiple osteochondromas result from mutations in the EXT1 or EXT2 genes, which are involved in heparan sulfate synthesis.
• Rarely, osteochondromas can undergo malignant transformation into chondrosarcoma, particularly in HME.

Clinical Features

• Asymptomatic Cases: Often discovered incidentally on X-rays taken for other reasons.
• Symptomatic Cases:
  • Localized pain or discomfort at the site of the osteochondroma.
  • Mechanical symptoms such as limited joint movement, especially if the growth impinges on nearby structures.
  • Neurovascular compression leading to numbness, tingling, or weakness if nerves or blood vessels are entrapped.
  • Visible or palpable bony mass protruding from the bone.

Diagnosis

• Clinical Examination: Palpation of a painless, hard bony mass protruding from the bone near a joint.
• Imaging Studies:
  • X-Ray: Shows a bony protrusion with a continuous cortex and medullary cavity extending from the parent bone.
  • Computed Tomography (CT) Scan: Provides detailed images of the bone structure and helps assess the extent of the lesion.
  • Magnetic Resonance Imaging (MRI): Evaluates the cartilage cap thickness; a cap thicker than 1.5-2 cm in adults may suggest malignant transformation.
• Biopsy: Rarely needed unless there is suspicion of malignancy based on imaging findings.
• Genetic Testing: Considered in cases of Multiple Osteochondromas to identify mutations in EXT1 or EXT2 genes.

Management

• Observation: Asymptomatic osteochondromas typically require no treatment. Regular follow-up may be necessary to monitor for changes.
• Surgical Excision:
  • Indicated for symptomatic osteochondromas causing pain, mechanical interference, or neurovascular compression.
  • Performed by orthopedic surgeons, involving the removal of the bony stalk and cartilaginous cap.
  • Recurrence is rare if the entire cartilaginous cap is excised.
• Management of Malignant Transformation:
  • Suspicion arises if there is rapid growth, increased pain, or changes in imaging characteristics (e.g., thickening of the cartilage cap).
  • Requires prompt surgical intervention with possible oncological evaluation.
  • Treatment may involve wide resection and, in some cases, chemotherapy or radiotherapy depending on the extent of malignancy.
• Genetic Counseling: Recommended for individuals with Multiple Osteochondromas due to its hereditary nature.

Prognosis

• Excellent for solitary osteochondromas with appropriate management.
• Multiple Osteochondromas may lead to skeletal deformities and have a higher risk of malignant transformation (~1-5%).
• Early detection and surgical intervention of symptomatic lesions improve outcomes and prevent complications.

Complications

• Malignant Transformation: Development of chondrosarcoma in the osteochondroma, particularly in hereditary cases.
• Mechanical Issues: Limb length discrepancies, angular deformities, or joint dysfunction.
• Neurovascular Compression: Entrapment of nerves or blood vessels leading to neurological deficits or vascular insufficiency.

References

• Osteochondroma - NCBI Bookshelf
• Medscape - Osteochondroma
• Merck Manuals - Osteochondroma
• UpToDate - Osteochondroma