Chordoma

Chordoma is a rare malignant tumor that arises from notochord remnants. Chordomas account for 1 to 4% of all bone tumors.l They occur in older adults with the highest prevalence in the fifth to seventh decade. The ratio of male to female is two to one. Due to their origin in the notochord, chordomas occur in the mid-line of the axial skeleton. One half of cases occur in the sacrococcygeal region and one third occur at the base of the skull. Other rare sites include transverse processes of vertebrae and the paranasal sinuses.

The clinical presentation depends on the location of the tumor. Sacrococcygeal tumors often present as low back pain with no characteristic pattern or time course. Sacrococcygeal tumors can also present as bowel and bladder dysfunction. Presacral tumors can sometimes be palpated on rectal exam. Sacral tumors are often large at presentation as a large volume of tumor can be accommodated within the pelvis. Anterior cervical tumors can present as dysphagia and posterior cervical tumors can cause neurological deficits. Tumors at the base of the skull may present with headaches.

On plain x-ray, chordomas appear as a solitary mid-line lesion with bony destruction. There is often an accompanying soft tissue mass. Approximately half of the time focal calcifications are present. CT and MRI scans help demonstrate the soft tissue component, calcifications and epidural extension. MRI is helpful in identifying local recurrences. Chordomas have reduced uptake on bone scan.

On gross examination, chordomas are soft, blue-gray, lobulated tumors. There are gelatinous translucent areas and often a capsule is present. The lesion often tracks along nerve roots in the sacral plexus or out the sciatic notch in planes of least resistance.

Under the microscope, the chordomas are characterized by lobules and fibrous septa. The malignant cell has eosinophilic cytoplasm. Prominent vacuoles of mucus push the nuclei to the side resulting in "physaliphorous" cells from the Greek word for bubble or drop.
During the fourth to sixth week of fetal development mesenchymal cells from individual sclerotomes merge to surround the notochord and form the vertebral bodies. The notochord normally degenerates and remnants form the nucleus pulposus of the vertebral disc. The prevailing theory is that in chordomas the notochord fails to degenerate and then undergoes malignant transformation. The major failing of this theory is that normal notochord remnants have never been observed.

The treatment of chordomas is difficult. Wide surgical excision is desirable but rarely feasible based on the anatomic location of the tumor. With sacrococcygeal tumors, sexual function and sphincter control may be compromised after surgery. Radiation is used if complete resection is impossible. Chordomas metastasize to lymph nodes, lungs, liver and bone. Chemotherapy can be used for late stage disease.


References
l Healey, JH and JM Lane, Chordoma: A Critical Review of Diagnosis and Treatment, Orthopedic Clinics of North America, 20(3):417-425, July, 1989.

Bullough, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders. Co., 1991.

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