Chordomas are very rare primary bone tumors that can arise at almost any point along the axis of the spine from the base of the skull to the sacrum and coccyx (tailbone). The incidence of chordoma in the general U.S. population is about 8 per 10,000,000 people. They occur somewhat more often in males than females and, for unknown reasons, are rare in African Americans. Under the microscope, chordoma cells appear to be benign, but because of their location, invasive nature, and recurrence rate, the tumors are considered to be malignant. They arise from cellular remnants of the primitive notochord, which is present in the early embryo. In normal mammalian development, the notochord and substances produced by it are involved in forming the tissues that give rise to vertebrae. Normally, the tissues derived from the notochord disappear after the vertebral bodies have begun forming. However, in a small percentage of people, some tissues from the notochord do not disappear. Rarely, these leftover tissues give rise to chordomas.
About one-third of chordomas are found in the region around the clivus. The clivus is a bone in the base of the skull. It is located in front of the brainstem and behind the back of the throat (nasopharynx). Chordomas occur with equal frequency in the skull base, the vertebrae and the sacrococcygeal area towards the bottom of the spine.
Symptoms of the presence of chordomas vary with their location and size. Most chordomas occur randomly among the population (sporadic). However, some people develop this tumor as a result of a mutation inherited as an autosomal dominant trait.