Are bone islands raised and palpable?

Bone Islands: Radiographic Characteristics and Clinical Presentation

Bone islands (enostoses) are not raised and cannot be palpated as they are located within the bone rather than on its surface.

What Are Bone Islands?

Bone islands are benign, sclerotic foci of mature compact (cortical) bone located within cancellous bone. They represent either:

• A congenital or developmental anomaly 1
• Failure of resorption during endochondral ossification 1

Radiographic Characteristics

Bone islands have distinctive imaging features:

• Plain radiographs: Appear as homogeneously dense, sclerotic foci within cancellous bone with characteristic radiating bony streaks ("thorny radiation") that blend with surrounding trabeculae, creating a feathered or brush-like border 1

• CT scan: Show as low-attenuation foci 1

• MRI: Demonstrate low signal intensity similar to cortical bone on all sequences 1

• Bone scan: Typically "cold" (non-active) on skeletal scintigraphy, though some histologically confirmed bone islands can show activity 1

Anatomic Location

Bone islands can be found throughout the skeleton:

• Most commonly in the pelvis, femur, and other long bones 1
• Can occur in flat bones such as the pelvis, ribs, and scapula 2
• May be found in the spine and other locations 1

Size Classification

• Small bone islands: Measure 0.1 to 2.0 cm in diameter (most common) 3
• Giant bone islands: Measure greater than 2 cm in diameter (rare) 3

Clinical Significance

Symptomatology

• Typically asymptomatic: Most bone islands are incidental findings on imaging studies performed for other reasons 1
• Rarely symptomatic: Some cases of symptomatic bone islands have been reported:
  • Giant bone islands (>2 cm) may cause pain 3
  • Rarely, even small bone islands (<2 cm) can be symptomatic 4

Clinical Management

• Generally considered "do not touch" lesions 5
• No treatment is typically necessary for asymptomatic bone islands 4
• In rare symptomatic cases where all other causes of pain have been excluded, surgical resection may be considered 4

Differentiation from Other Conditions

Bone islands must be distinguished from more aggressive bone lesions such as:

• Osteoblastic metastases
• Osteosarcoma
• Other sclerotic bone tumors

The characteristic imaging features, particularly the thorny radiations and typically negative bone scan, help differentiate bone islands from these more concerning entities 1.

Key Points for Clinicians

• Bone islands are located within the bone and cannot be palpated externally
• They are not raised lesions on the bone surface
• Most are asymptomatic incidental findings
• The characteristic radiographic appearance allows confident diagnosis in most cases
• No intervention is typically required for asymptomatic lesions