Pathophysiology:

Primary sources for spinal metastatic disease include the following: Lung (31%),  Breast (24%), GI (9%),  Prostate (8%),  Lymphoma (6%),  Melanoma (4%),  Unknown (2%),  Kidney (1%),  Others including multiple myeloma (13%). Time relation between primary and spinal metastases vary according to the site and nature of the primary.

Spread from primary tumors is mainly by the arterial route via nutrient artery. Retrograde spread through the Batson plexus during Valsalva maneuver has been postulated. Direct invasion through the intervertebral foramina also can occur.

About 70% of symptomatic lesions are found in the thoracic spinal region, 20% in the lumbar region, and 10% in the cervical spine. Over 50% of patients with spinal metastasis have multiple level involvement. About 10-38% of patients have multiple noncontiguous segment involvement. 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 small percentage of patients have disease in both posterior and anterior parts of the spine.

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. Epidural metastasis is the most ominous complication of bone metastasis to the vertebral spine and is a medical emergency. The tumor enters the-epidural space by contiguous spread from adjacent vertebral metastasis in the vast majority of cases. The remaining cases arise from the direct invasion of retroperitoneal tumor or tumor located in the posterior thorax through adjacent intervertebral foramina or, rarely, from bloodborne seeding of the epidural space.

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. The relative importance of vascular factors as opposed to purely mechanical ones has been a subject of controversy for many years. The tempo of development of spinal compression is, perhaps, impossible to generalize. Once neurological symptoms become manifest, the condition is a neurological emergency.

Clinical presentation:

Bone pain at night in a patient with cancer is always an ominous symptom. The majority of the patients present with radicular pain. The pain is usually midline, but patients whose tumor involves nerve roots have sharp or shooting pain in a radicular distribution. Untreated, the pain slowly intensifies with a mean duration of 7 weeks from the onset of pain to the onset of neurological deficits due to spinal cord compression. Half of these patients have sensory and motor dysfunction and over 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.

Diagnosis:

Plain x-ray is used to show erosion of the pedicles or the vertebral body. More than 70 percent of patients with spinal cord compression have an abnormal plain radiograph in the region of pain (compression fracture, plastic, or lyric metastasis). Owl eye erosion of the pedicles in the anteroposterior (AP) view of lumbar spine is characteristic of metastatic disease and is observed in 90% of symptomatic patients. Osteoblastic or osteosclerotic changes are common in prostate cancer and Hodgkin disease; occasionally, they also are seen in breast cancer and lymphoma. CT scan is useful in determining the integrity of the vertebral column, especially when surgery is anticipated. CT myelogram is

used if MRI is not available.

Osteolytic metastasis   Osteoblastic metastasis

MRI scan is the choice of imaging. MRI sagittal scout film is used for rapid screening of the surrounding soft tissues. Patients with persistent back pain in the region of abnormality on plain spine radiograph, with or without neurological deficits, should undergo evaluation with MRI. Patients with progressive back or neck pain whose plain radiograph is normal should also undergo an imaging study of the epidural space, even if their neurological examination is normal.

D2 met-MRI-sag	D2 met-MRI axial	D2 -met -CT	D8 hyperostotic met-MRI sag	D8 hyperostotic met-MRI axial

Emergency myelogram still is used in situations where MRI is not available. Myelograms, allow for cerebrospinal fluid (CSF) sampling. CSF sampling should be deferred if evidence of near/complete spinal block is noted. The risk of having neurological deterioration after myelogram is about 14%. Neurological deterioration is less likely with C1-2 puncture.

Bone scan findings are positive in 60% of cases.

Needle or open biopsy will establish the diagnosis.

A thorough metastatic workup is paramount in patients with spinal metastasis. This helps to delineate the nature and the extensiveness of the systemic disease; however, the appropriateness of diagnostic tests depends on the amount of time available. In patients with rapidly progressing symptoms, chest x-ray and physical examination is all that is permitted. The patient should then have a plain x-ray of the entire spine, followed by MRI with and without contrast.

Management:

Medical therapy: Immediate treatment is high-dose dexamethasone and analgesics. The optimal dexamethasone dose has not been established, but in practice the usual dose is 4 mg hourly after a loading dose of 24mg. Of all the corticosteroids, dexamethasone has the least mineralocorticoid effect and is least likely to be associated with infection or cognitive dysfunction, although it does increase the risk of myopathy. The frequency of complications from steroid therapy is dependent on the duration of the treatment and is associated with hypoalbuminemia. Treatment lasting more than 3 weeks is more likely to be associated with complications. Hypoalbuminemia appears to increase the risks of adverse effects associated with steroid treatment.

About 70-80% of patients experience improvement of symptoms within 48 hours of treatment. Approximately 64% of patients report alleviation of pain within 24-48 hours of starting steroid therapy and 57% show improvement in their motor function. In most cases steroid use needs to be continued until the completion of radiotherapy. 

Radiotherapy: Radiotherapy remains the mainstay of treatment for spinal metastatic disease. Most of the lymphoreticular tumors and prostate carcinoma are radiosensitive; lung and breast are less sensitive. Tumors of the gastrointestinal system and kidney are resistant to radiotherapy, as are melanomas.  

Nevertheless, radiotherapy has been offered to the latter group of patients and has demonstrated some response. The radiation port normally includes 2 vertebral bodies above and below the diseased segment. 1000-1200 rads a week in divided doses for 3-4 weeks, for an average total of 3200 rads is the usual dose. About 80% of patients with pretreatment pain have symptomatic relief; 48% of patients with motor or sphincter dysfunction respond to treatment.

Surgical therapy: Most often surgery is indicated only as a stabilization procedure or for tissue diagnosis. It is employed in patients who have disease progression despite radiotherapy and in those with known radiotherapy-resistant tumors.

The patient should be suitable for adjuvant therapy.

The results of surgery are superior to those of irradiation alone. Relief of pain and restoration of neurological deficit are respectively 82% and 70% after the surgery, and 56% and 55% after the irradiation. The duration of survival following surgery tended to be related to primary tumor. Minimal survival is achieved in lung carcinoma, and maximum survival is achieved with prostate carcinoma. Although the surgery of bone metastasis does not necessarily affect the life expectancies of the patients, adequate surgery is often able to provide a patient with several years of pain-free, mobile and useful life.

Neurological deficit and back pain are caused not only by cord or root compression, but also by skeletal instability. Therefore, the surgical results after the decompression and stabilization were superior to those after the decompression alone when they were evaluated on the basis of pain relief and restoration of neurological deficit. 

The selection of a surgical approach is influenced by the primary site and extent of osseous and neural involvement and the patient's preoperative neurological and clinical status. The current trend is to decompress anteriorly (vertebrectomy, corpectomy) for anteriorly placed lesions. It is always combined with reconstruction and  and stabilization with instrumentation. Laminectomy is indicated less commonly than these other procedures, because most of the lesions are anteriorly based, and posterior decompression may further destabilize the spine. In a potentially curable lesion, a combined anterior and posterior decompression may be indicated.                        Titanium cage & compression screws- AP         Titanium cage & compression screws- Lat

Stabilization with instruementation

Surgical decompression and stabilization together with radiotherapy is promising.

This offers stabilization of the diseased bone and allows ambulation together with pain relief. Patients with nonambulatory status at diagnosis do poorly, as do patients with more than one vertebra involved.

In selected cases, chemotherapy helps as an adjuvant to surgery and radiation. Hormone therapy, as in secondaries due to prostatic carcinomas,  give good palliation.

Conclusion:

The outcome of metastatic disease to the spine and associated structures is uniformly bleak.

The median survival duration for patients with spinal metastatic disease is 10 months.

The morbidity of spinal metastatic disease is of significance, 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 the caregiver.

The ultimate goals are to maintain the independence and dignity of the patient and to optimize his or her comfort level.

No treatment has been proven to increase the life expectancy of patients with spinal metastasis. The goals of therapy are pain control and functional preservation. The most important prognostic indicator for spinal metastases is the initial functional score. The ability to ambulate at the time of presentation is a favorable prognostic sign. Loss of sphincter control is a poor prognostic feature and is mostly irreversible.

Radiation therapy is more effective in achieving pain control (67%) than surgery (36%). Notably, surgery alone is the least effective way to treat spinal metastases. About 20-26% of patients who undergo surgery experience further deterioration in terms of either mobility or sphincter control while only 17% in the radiation therapy group experience further deterioration.

Surgical intervention with extensive reconstruction should be employed only after thorough evaluation of the extent of the systemic disease and with a clear understanding of the realistic expectation of the patients and their caretakers.