Metastatic Disease to the Spine and Related Structures

Introduction
Background
Spinal metastasis is common in patients with cancer. The spine is the third most common site for cancer cells to metastasize, following the lung and the liver. Approximately 60-70% of patients with systemic cancer will have spinal metastasis; fortunately, only 10% of these patients are symptomatic. Approximately 94-98% of these patients present with epidural and/or vertebral involvement. Intradural extramedullary and intramedullary seeding of systemic cancer is unusual; they account for 5-6% and 0.5-1% of spinal metastases, respectively.

Metastatic disease to the neuraxis other than the brain parenchyma and the spinal column is uncommon. The incidence of cancer cells invading the leptomeninges is as high as 8-13%. In autopsy studies, the rate has been estimated to be 25%.


Pathophysiology
Spread from primary tumors is mainly by the arterial route. Retrograde spread through the Batson plexus during Valsalva maneuver is postulated. Direct invasion through the intervertebral foramina also can occur. Besides mass effect, an epidural mass can cause cord distortion, resulting in demyelination or axonal destruction. Vascular compromise produces venous congestion and vasogenic edema of the spinal cord, resulting in venous infarction and hemorrhage.

About 70% of symptomatic lesions are found in the thoracic region of the spine, particularly at the level of T4-T7. Of the remainder, 20% are found in the lumbar region and 10% are found in the cervical spine. More than 50% of patients with spinal metastasis have several levels of involvement. About 10-38% of patients have involvement of several noncontiguous segments. Intramural and intramedullary metastases are not as common as those of the vertebral body and the epidural space. Isolated epidural involvement accounts for less than 10% of cases; it is particularly common in lymphoma and renal cell carcinoma. Most of the lesions are localized at the anterior portion of the vertebral body (60%). In 30% of cases, the lesion infiltrates the pedicle or lamina. A few patients have disease in both posterior and anterior parts of the spine.

Primary sources for spinal metastatic disease include the following:


•Lung - 31%
•Breast - 24%
•GI tract - 9%
•Prostate - 8%
•Lymphoma - 6%
•Melanoma - 4%
•Unknown - 2%
•Kidney - 1%
•Others including multiple myeloma - 13%

Frequency
United States
The spine is the most common site for metastatic disease. About 30-70% of patients with a primary tumor have spinal metastatic disease at autopsy. Spinal metastases are slightly more common in men than in women and adults aged 40-65 years than in others.

Mortality/Morbidity
•Median survival of patients with spinal metastatic disease is 10 months.
•The morbidity of spinal metastatic disease is important, especially in patients with paralysis and/or bowel and bladder involvement. The latter compromises the quality of life of patients with cancer and puts an additional burden on their caregivers. Cord compression is normally seen as preterminal event. Median survival at that stage is about 3 months.
Clinical
History
Spinal metastasis may be the initial presentation in 10% of patients with systemic cancer. About 2% of symptomatic patients have no identifiable systemic disease.

Approximately 90% of patients present with bone and/or back pain followed by radicular pain. About 50% of these patients have sensory and motor dysfunction, and more than 50% have bowel and bladder dysfunction.

About 5-10% of patients with cancer present with cord compression as their initial symptom. Among those who present with cord compression, 50% are nonambulatory at diagnosis, and 15% are paraplegic.

Bone pain at night in a patient with systemic cancer is always an ominous symptom. In fact, it is the most ominous symptom in patients with metastatic disease to the spine.