Sunday 28 January 2007
Definition: Although chordoma may have a superficial similarity to a cartilage lesion, it is a neoplasm that arises from remnants of the notochord, and therefore, in almost all cases, it occurs in the midline of the axial skeleton.
About half the cases occur in the sacrococcygeal region, whereas one third are present at the base of the skull.
The remaining cases arise at different sites along the vertebral column, most commonly in the cervical region.
Chordoma is a slow-growing neoplasm, causing clinical symptoms that depend on its location.
Cranial lesions usually are smaller than sacrococcygeal lesions at the time of initial presentation.
Men are more frequently affected than women; the average age at diagnosis for sacral lesions is approximately 55 years and, for spheno-occipital lesions, somewhat younger.
On imaging studies, bone destruction is the hallmark of chordoma, and about half of the patients exhibit focal calcifications within the lesion.
Localization of the lesion has been greatly aided by the use of MRI, particularly in cases of intracranial chordoma.
When chordomas affect areas of the spine other than the two common sites (i.e., sacrococcygeal and cervical), the lesions are likely to be lytic, located centrally within the vertebral body, and slowly expansile.
When the cervical vertebrae are affected, extension anteriorly into the soft tissues may result in dysphagia, whereas posterior extension may lead to neurologic complications.
Since giant notochordal rests may also occur within the vertebral bodies, they need to be differentiated from chordoma.
Systemic metastases to the regional lymph nodes, lung, liver, and bone occur in up to 25% of cases.
On gross examination, chordomas are generally soft and appear to be well encapsulated.
Lobulations are apparent on cut section, and the tumor usually has a bluish gray color with extensive gelatinous translucent areas that are focally cystic and hemorrhagic.
Grossly, the tissue may suggest a chondrosarcoma or even a mucinous carcinoma.
Microscopic examination reveals a characteristic arrangement of tumor cells separated into lobules by fibrous septa of different thicknesses.
The tumor cells are of various sizes and shapes, arranged in both cords and sheets, with an eosinophilic cytoplasm associated with both extracellular and intracellular mucin that may be minimal or abundant.
The intracellular vacuoles may be very prominent and displace the nucleus to one edge, producing the so-called "physaliphorous cell".
characteristic lobulated, firm blue gray tissue mass, with focal hemorrhage and cystification
nests and cords of tumor cells with abundant eosinophilic cytoplasm separated by lakes of mucoid tissue.
large mucoid foci are present;
in these mucoid areas, cords of eosinophilic cells may be present
large variegated and vacuolated cells characteristic of chordoma (physaliphorous cells)
The tumor cells express both S-100 protein and epithelial markers.
- Approximately one third of spheno-occipital chordomas contain a significant chondroid component, and these lesions can easily be confused with chondrosarcomas, especially with chondrosarcomas having a predominantly myxoid structure.
- On occasion, a large notochordal rest in a vertebral body may be discovered as an incidental finding on MRI.
- In such a case, the differentiation from a chordoma may be a problem, although in a chordoma, there is generally a lytic lesion seen on radiographic imaging, whereas this has not been the case with the notochordal rests, which have been reported to be more often associated with bony sclerosis.
- Microscopically, notochordal rests lack myxoid extracellular material and their close resemblance to marrow fat makes them easy to overlook.
- Reactive bony sclerosis is often evident, and the lesions do not show extraosseous extension.
- Immunostains for cytokeratin and S-100 label the lesional cells.
Rarely, an associated malignant mesenchymal tumor has been described in association with a chordoma, either a malignant fibrous histiocytoma or another poorly differentiated sarcoma (i.e., dedifferentiated chordoma); at least some of these cases have been associated with a history of radiation therapy.
poorly differentiated chordoma