Malignant transformation in an 11-year-old child with multiple hereditary exostosis
Keywords:multiple hereditary exostosis (MHE), chondrosarcoma, osteochondroma, malignant transformation
Background: Multiple hereditary exostosis (MHE) is a rare autosomal dominant disorder predisposing to the development of multiple osteochondromas. Malignant transformation is an uncommon complication of osteochondromas and is especially rare in the paediatric population. Making a diagnosis of malignant transformation is recognised as a challenge globally.
Methods: We obtained informed consent and ethics approval prior to reviewing the hospital file, radiology and pathology of our index patient, as well as conducting a directed literature search.
Results: An 11-year-old male with MHE presented with new onset pain in the right leg with an associated inability to weight bear. Plain radiographs and magnetic resonance imaging (MRI) showed features consistent with malignant transformation. The child underwent a Malawer 1 resection of the proximal fibula with no complications. The pathology confirmed a grade 1 secondary peripheral chondrosarcoma (CS) arising in an osteochondroma. The rate of malignant transformation in MHE is as high as 36.3% in select specialist tertiary centres. Ninety per cent of the resultant malignancies are chondrosarcomas. Malignant transformation before the age of 20 years is exceptional. Plain radiology is routinely used for monitoring of patients with MHE. Other modalities exist to assess for cartilage cap thickness, a much-debated criterion of malignant change. Pathology is essential for confirmation of malignant transformation as well as to exclude high grade lesions. Treatment is wide local excision (WLE) with limb-sparing surgery and long-term follow-up to detect for local recurrences.
Conclusion: The malignant transformation of osteochondromas occurs more frequently in individuals with MHE and may even arise in the paediatric population. In the presence of suspicious clinical or radiological features, en-bloc surgical resection and histopathological correlation is mandatory to make the diagnosis. We encourage a multidisciplinary team approach with collaboration between the orthopaedic surgeon, radiologist and pathologist.
Level of evidence: Level 5