One of the most common and dangerous complications of any cancer is spinal cord metastases, the spreading of cancer cells from elsewhere in the body to the spinal cord. In order to better understand this condition one must first have knowledge about the structures surrounding the spinal cord. The spinal cord is surrounded by three membranous layers collectively known as the meninges. The outermost layer is called the dura mater. Beneath the dura is the second layer, the arachnoid. This layer overlies the third layer, the pia mater, which intimately covers the spinal cord surface. Between the arachnoid and the pia mater is a space known as the subarachnoid space. Metastases can occur in the cord itself (intramedullary metastasis), in the subarachnoid space (leptomeningeal metastasis), or in the epidural space, a space external to the dura mater but internal to the bony vertebral column (epidural metastases). Epidural metastases are the most common form of spinal cord metastases, and typically result from tumor spread to the vertebral column with subsequent growth inward toward the spinal cord. Epidural metastatic compression of the spinal cord occurs in 5% of all people who die of cancer (20,000 people in the U.S. each year).
Patients initially present with pain due to cord compression. Such pain may be axial (if limited to the central parts of the body), referred (in which the pain seems to arise from a source different from its true origin), or radicular (a pain which "shoots" down a part of the body). After the initial period of pain, cancer patients experience three characteristic symptoms of metastatic epidural compression:
Magnetic resonance imaging of the spinal cord is the best way to diagnose the cause of spinal cord compression. An alternate method is contrast myelography, in which dye is injected into the spinal fluid and X-ray pictures are taken. However, this procedure is invasive and has risks that are not associated with MR imaging.
This condition is an emergency situation. Rapid and effective treatment is essential in preventing progressive and permanent paralysis and improving the long-term prognosis. There are two major therapies employed to treat patients with spinal cord compression due to epidural metastases:
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