Multiple hereditary exostoses

Genetic disorder: multiple Osteochondromas throughout the skeleton

• Autosomal dominant (EXT1/EXT2 genes)`

Clinical Features

• Presents in childhood (often before age 10)
• Progressive, with increasing number/size of exostoses until skeletal maturity
• May cause limb length discrepancy, bowing, joint deformity
• Often painless, but can compress nerves/vessels, causing impingement

Common locations

• Metaphyses of long bones (femur, tibia, humerus most common)
• Also: pelvis, scapula, ribs
• Rarely in spine/skull

Complications

• Malignant transformation (~1–5%) to secondary Chondrosarcoma arising from its cartilaginous cap
  • Signs: new pain, rapid growth, thick cap
• Neurovascular impingement
• Bursitis (overlying prominent lesions)
• Pathological fracture (rare)

Imaging

• Multiple bony outgrowths—continuity of cortex and medullary cavity with parent bone
• Cartilage cap (best seen on MRI):
  • Thick cap (>1.5–2 cm in adult) = risk of malignant change
• Deformity: bowing, limb shortening, valgus/varus angulation

Pearls

• New pain or rapid growth in MHE = Chondrosarcoma until proven otherwise
• Deformities can be severe—refer to ortho early for surveillance
• Family screening is important