Metastatic spine tumors

1

What is the most common tumor of the spine?

Metastatic lesions are the most common tumors of the spine. Metastatic lesions account for over 90% of all spinal column tumors. Spine metastases are the most common type of skeletal metastases.

2

What percentage of spinal metastases result in spinal cord compression?

Spinal cord compression occurs in 20% of patients who develop spinal metastases.

3

Which malignancies most commonly metastasize to the spine?

In descending order of frequency: breast (21%), lung (14%), prostate (7.5%), renal (5%), gastrointestinal (GI) (5%), and thyroid (2.5%).

A useful mnemonic to aid recall of common malignancies that metastasize to the spine is “P T Barnum Loves Kids” (prostate, thyroid, breast, lung, kidney).

4

Where are metastatic spinal lesions most commonly located?

• Within the vertebra , metastatic lesions first involve the vertebral body, followed by subsequent invasion of the pedicles and surrounding tissues. The disc space remains relatively uninvolved by metastatic tumor.

• Within the spinal column , metastatic lesions are found most commonly in the lumbar region, less commonly in the thoracic region, and least commonly in the cervical region.

• With respect to tumor type , breast and lung tumors most commonly metastasize to the thoracic spine. Prostate tumors tend to metastasize to the lumbar spine, pelvis, and sacrum.

5

What are the pathways by which metastatic disease spreads to the spine?

Potential pathways for spread of metastatic disease to the spinal column include:

• 1.

  Hematogenous spread (venous or arterial route)

• 2.

  Direct tumor extension

• 3.

  Lymphatic spread

The most common pathway for spread of metastatic disease is the hematogenous route. Batson plexus, a thin-walled system of veins that extend along the entire spinal column, provides a connection between the spinal column and the major organ systems and is a common pathway for tumor migration and metastases. Alternatively, tumor cells may spread via the segmental arteries to the vertebral body.

6

What is the most common presenting complaint of a patient with a metastatic spinal tumor?

Progressive and unrelenting pain is the most common presenting complaint. The pain is often unrelieved with rest and is worse at night. Constitutional symptoms may be present and include unintended weight loss, fatigue, and anorexia. Other presentations include mechanical pain, radicular pain, motor and/or sensory deficits, bladder dysfunction, sphincter dysfunction, and symptomatic spinal fracture. Occasionally patients may present with spinal deformity or a palpable mass.

7

What causes pain in patients with metastatic tumors of the spine?

Many causes of pain are possible: hyperemia and edema secondary to tumor, expansion of tumor into the periosteum of the vertebra and surrounding tissues, direct compression or invasion of nerve roots, spinal cord compression, and osseous destruction leading to segmental spinal instability or pathologic spinal fracture with associated mechanical pain.

8

What radiographic signs are suggestive of a metastatic spinal lesion?

Radiographic signs suggestive of a metastatic lesion include an absent pedicle, vertebral cortical erosion/expansion, and loss of vertebral body height.

9

When are metastatic spinal tumors detectable on plain radiographs?

Most tumors of the spine are osteolytic. They are not demonstrated on plain films until more than 30%–50% destruction of the vertebral body has occurred. An exception is prostate cancer, which tends to be osteoblastic.

10

What is the “winking owl” sign?

This sign refers to the loss of one of the pedicle shadows on an anteroposterior (AP) spine radiograph. The cause for this radiographic finding is most frequently a metastatic vertebral lesion that has extended into the pedicle region and caused destruction of the pedicle.

11

What are the steps in evaluating a patient with a suspected metastatic spinal lesion?

Evaluation should occur in an organized and comprehensive fashion, as outlined below:

• Patient history should assess the pain pattern, sphincter control, neurologic symptoms, and pertinent factors such as baseline and current ambulatory status, use of assistive devices, and ability to perform activities of daily living. Risk factors for pyogenic osteomyelitis should also be assessed as this condition is included on the initial list of differential diagnoses.

• Physical examination should be comprehensive and include a full neurologic assessment with rectal examinatio, as well as examination of the breasts, thyroid, abdomen, prostate, and regional lymph nodes.

• Laboratory studies should include routine tests such as complete blood count, erythrocyte sedimentation rate, C-reactive protein, electrolytes, calcium, phosphate, and liver function tests including alkaline phosphatase. Additional special tests such as prostate-specific antigen, serum and urine protein electrophoresis, thyroid function tests, and nutritional indices are obtained as indicated.

• Imaging studies are critical for diagnosis and planning treatment. AP and lateral spinal radiographs are used to assess spinal anatomy, bony destruction, and alignment. Magnetic resonance imaging (MRI) is the primary imaging study for defining the anatomic extent of metastatic spine tumors. Metastatic lesions generally demonstrate low signal intensity on T1 and high signal intensity on T2 and enhance when gadolinium contrast is administered. MRI also provides information on the extent of neurologic compression. As metastatic disease involving the spine may be multicentric, the entire spinal column should be evaluated with MRI. Radioisotope studies are valuable to survey the skeleton for metastatic lesions. Technetium total body bone scans are highly sensitive but nonspecific, and their ability to detect osseous metastases depends on tumor type. Osteoblastic metastases are readily detected on bone scans, whereas osteolytic lesions such as multiple myeloma and hypernephroma may not be detectable. Positron emission tomography is an alternative radioisotope study that is highly sensitive and specific for cancer cells. Fluorine-18-labeled fluorodeoxyglucose undergoes rapid uptake by tumor cells due to their increased metabolic activity. Computed tomography (CT) plays a role in the localization and quantification of bony vertebral destruction and allows for surgical planning in regard to fixation strategies. If the primary tumor remains unknown, CT scans with intravenous and oral contrast should be obtained to assess the chest, abdomen, and pelvis in an attempt to locate the primary tumor. Female patients may require mammography.

• Biopsy is performed if the diagnosis remains in question at this point. CT-guided biopsy is generally preferred. Thoracic and lumbar lesions are generally approached posterolaterally, cervical lesions are approached anterolaterally, and for sacral lesions a direct posterior approach is used. If there is a possibility of infection, cultures should be obtained at the time of biopsy. Bone marrow biopsy is performed if multiple myeloma is in the differential diagnosis.

12

What is the goal for treatment of a metastatic spinal lesion?

The goal of treatment is generally palliation and not cure. Metastasis indicates that regional disease has progressed to a systemic illness that is generally incurable. Treatment is directed toward maximizing quality of life by providing pain relief, structural stabilization, and maintaining or restoring neurologic function via adequate neural decompression. Accordingly, surgery generally involves intralesional tumor resection (piecemeal removal). An exception to this treatment strategy is the patient with a solitary metastasis and potential for long-term survival with en bloc spondylectomy (removal of tumor in a single, intact piece encased by a continuous shell of healthy tissue called a “margin”).