Hereditary multiple exostoses

Last revised by Dr Henry Knipe on 15 Sep 2022

Hereditary multiple exostoses/osteochondromas, also known as diaphyseal aclasisosteochondromatosis, or simply multiple osteochondromas is an autosomal dominant condition, characterized by the development of multiple osteochondromas.

Hereditary multiple exostoses demonstrate an autosomal dominant inheritance pattern, with incomplete penetrance in females leading to a slightly male predominance. Prevalence is estimated in 1 in 50,000 people 6. The number of exostoses, the degree, and type of angular deformity, and even the rate of malignant transformation varies significantly, even within families.

Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 6:

  • essential: ≥2 radiological osteochondromas at the juxtaepiphyseal region of the long bones and positive family history and/or EXT gene germline mutation

Most patients are diagnosed by the age of 5 years, and virtually all are diagnosed by the age of 12 years. Patients may be asymptomatic with a few small lesions or may be significantly deformed by multiple large osteochondromas. 

Hereditary multiple exostoses can involve any bony in the body except for the calvarium 5. Common sites of involvement include the distal femur, proximal tibia, wrist and hands, humerus, ankle, pelvis, and ribs.

Hereditary multiple exostoses is thought to result from EXT1EXT2, or EXT3 gene mutations on chromosomes 8q24 (EXT1), 11p11-13 (EXT2), and 19p (EXT34,5.

Except that they are multiple, imaging features are identical to solitary osteochondromas. The skeletal distribution of lesions can significantly vary, with some authors noting that the typical distribution is bilateral and symmetric, whereas others report a strong unilateral predominance.

Often associated with a broadened shaft at the end of long bones, hence the term diaphyseal aclasis. 

Are also similar to those of solitary osteochondroma and include:

  • vascular impingement
  • neural impingement
  • fracture
  • bursitis
  • deformity and ankylosis
  • malignant transformation

Malignant transformation is more common than in sporadic cases, with transformation rates reported as high as 25% (lower rates of 3-5% have also been published) 3. The mnemonic GLAD PAST 1 lists the associations with sarcomatous transformation.

Refer to the generic osteochondroma article for more information.

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Figure 1: femoral osteochondroma
    Drag here to reorder.
  • Case 1
    Drag here to reorder.
  • Figure 2: osteochondroma typical appearances
    Drag here to reorder.
  • Case 2
    Drag here to reorder.
  • Case 3
    Drag here to reorder.
  • Case 4
    Drag here to reorder.
  • Case 5
    Drag here to reorder.
  • Case 6
    Drag here to reorder.
  •  Case 7
    Drag here to reorder.
  • Case 8: plain film and MRI
    Drag here to reorder.
  • Case 9
    Drag here to reorder.
  • Case 10
    Drag here to reorder.
  • Case 11
    Drag here to reorder.
  • Case 12
    Drag here to reorder.
  • Case 13
    Drag here to reorder.
  • Case 14
    Drag here to reorder.
  • Case 15
    Drag here to reorder.
  • Case 16
    Drag here to reorder.
  • Case 17
    Drag here to reorder.
  • Case 18
    Drag here to reorder.
  • Case 19
    Drag here to reorder.
  • Case 20
    Drag here to reorder.
  • Case 21
    Drag here to reorder.
  • Case 22
    Drag here to reorder.
  • Case 23
    Drag here to reorder.
  • Case 24
    Drag here to reorder.
  • Case 25
    Drag here to reorder.
  • Case 26
    Drag here to reorder.
  • Case 27
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.