Multimodality imaging features of hereditary multiple exostoses

Abstract

Hereditary multiple exostoses (HME) or diaphyseal aclasis is an inherited disorder characterised by the formation of multiple osteochondromas, which are cartilage-capped osseous outgrowths, and the development of associated osseous deformities. Individuals with HME may be asymptomatic or develop clinical symptoms, which prompt imaging studies. Different modalities ranging from plain radiographs to cross-sectional and nuclear medicine imaging studies can be helpful in the diagnosis and detection of complications in HME, including chondrosarcomatous transformation. We review the role and imaging features of these different modalities in HME.

Figure 1.

Forearm radiographs showing a pseudo-Madelung deformity as a result of ulnar foreshortening with bowing of the radius.

Figure 2.

Knee radiographs of a young patient with hereditary multiple exostoses showing multiple exostoses in the distal femur and proximal tibia and fibula, which typically point away from the joint. There is an associated widening of the diametaphysis resulting in an Erlenmeyer flask deformity.

Figure 3.

(a) Anteroposterior and (b) lateral radiographs demonstrating an exostosis in the proximal left fibula. The cartilage cap is usually not seen on radiographs but can be detected using (c) ultrasound or MRI. A thickness of >2 cm in a skeletally mature patient may be suspected for transformation to a chondrosarcoma.

Figure 4.

Exostosis (black arrow) in the proximal right tibia causing compression and lateral bowing of the adjacent fibula.

Figure 5.

Coxa valga in a patient with hereditary multiple exostoses showing bilaterally increased femoral angles resulting in a more vertical orientation of the femoral neck.

Figure 6.

Frontal knee radiographs in a 15-year-old male patient (a) at the time of diagnosis of hereditary multiple exostoses demonstrating an exostosis at the distal right femur. (b) Radiograph taken after 3 years because of symptoms at the site of exostosis, showing interval growth of the exostosis after skeletal maturity. Ongoing growth raises suspicion of malignant transformation, and further evaluation using MRI should be performed.

Figure 7.

Male patient with known hereditary multiple exostoses presenting with left deltoid pain and swelling. (a) Radiograph of the left humerus demonstrating two exostoses in the proximal diaphyseal region. Prominent ring and arc calcification and thickening of the cartilage cap is seen in the lateral exostosis. (b) Coronal CT confirms thickening of the cartilage cap suggestive of malignant chondrosarcomatous transformation. (c) Axial T₂ weighted MRI showing a hyperintense thick multilobulated lesion in the proximal humerus because of an enlargement of the hyaline cartilage component that is highly suggestive of malignant transformation. (d) Radionuclide bone scintigram showing high radiotracer uptake in the proximal lateral left humerus corresponding to the site of malignant transformation.

Figure 8.

(a) Large right scapular osteochondroma in a patient with hereditary multiple exostoses presenting with increasing pain and swelling (black arrow) showing a chondroid matrix throughout the lesion. (b) Fused axial 18-fludeoxyglucose (¹⁸FDG)-positron emission tomography-CT image demonstrating ¹⁸FDG-avid hypermetabolic foci in the right scapula concerning for chondrosarcoma.

Figure 9.

(a) Axial CT, (b) 18-fludeoxyglucose (¹⁸FDG)-positron emission tomography (PET) and (c) fused ¹⁸FDG-PET-CT images through the pelvis, in a patient with hereditary multiple exostoses presenting with worsening right hip pain. The right iliac bone is involved by an aggressive process with avid ¹⁸FDG uptake compatible with a chondrosarcoma.

Figure 10.

Axial CT thorax image showing an exostosis involving the first right rib adjacent to the brachiocephalic artery. Direct compression or entrapment of neighbouring vessels can result in vascular compromise and distal ischaemic symptoms.

Figure 11.

Axial T₂ weighted MRI of the distal femur in a patient with pain and swelling in the thigh. A high-signal fluid collection is seen between the exostosis and vastus lateralis muscle (white arrow), where associated soft-tissue oedema is present, consistent with bursa formation and inflammation (bursitis).