Dedifferentiated chordomas are biphasic malignant tumors composed of notochordal and high-grade sarcomatous components.
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Epidemiology
Dedifferentiated chordomas are very rare tumors that might be seen in recurrences or after radiotherapy 1-3.
Diagnosis
The diagnosis is based on typical imaging features of a bone tumor and the presence of biphasic histology of a conventional chordoma and high-grade sarcoma 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
bone tumor on imaging
known or histologically confirmed chordoma confirmed with additional high-grade sarcoma
Clinical presentation
Clinical signs and symptoms include pain and neurological symptoms related to the tumor site and are similar to those of chordoma. They might present at a site of a previously excised chordoma and progress faster 1.
Pathology
Dedifferentiated chordomas are biphasic tumors with a chordoma and high-grade sarcoma component 1-6 most commonly undifferentiated sarcoma less frequent osteosarcoma and rarely rhabdomyosarcoma 1-3.
Etiology
The etiology of dedifferentiated chordomas is unknown 1.
Location
Dedifferentiated chordomas predominantly arise from the sacrococcygeal area but can also grow in other areas of the axial skeleton 1.
Macroscopic appearance
Dedifferentiated chordomas will have the features of sarcoma with a solid cut surface on one hand and a gelatinous appearance on the other 1.
Microscopic appearance
Dedifferentiated chordomas are characterized by the histological features of both conventional chordomas and high-grade sarcomas with either separated or mixed components 1,2:
epithelioid cells with bubbly eosinophilic cytoplasm (physaliphorous cells) in a myxoid matrix
atypical cells with pleomorphic nuclei and frequent mitosis
Immunophenotype
On immunohistochemistry dedifferentiated chordomas are usually positive for cytokeratin but not for brachyury, depending on the sarcoma type they might express desmin or myogenin 1.
Radiographic features
Plain radiograph
Plain films might show a destructive osteolytic bone tumor.
CT
On CT dedifferentiated chordomas cannot be distinguished from other aggressive bone tumors with an expansile destructive lytic appearance and associated soft tissue component 1,4.
MRI
On MRI the biphasic nature of the tumor might be appreciated with hyperintense tumor components on fluid-sensitive and/or T2 weighted images featuring areas of chordoma and the dedifferentiated solid relatively hypointense tumor components 1,2.
Signal characteristics
T1: heterogeneous
T2: hypointense and hyperintense areas
T1C+ (Gd): heterogeneous enhancement
Radiology report
The radiological report should include a description of the following:
form and location
tumor margins and transition zone
cortical destruction
extension into the adjacent structures
associated complications
Treatment and prognosis
The prognosis is poor with frequent metastasis and a high mortality rate 1. Management relies on the success of surgery since the response to radiotherapy and chemotherapy is poor 1.
History and etymology
Dedifferentiated chordomas were first defined by American pathologist Jeanne M Meis and her colleagues in 1987 5,6. However, there have been previous descriptions of chordomas with biphasic tumor morphology such as one from the Japanese pathologists Hideki Kishikawa and Kenzö Tanaka in 1974 5,7.
Differential diagnosis
Condition or tumors that might mimic the imaging appearance of dedifferentiated chordomas include the following 1,2:
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