Metastatic Tumors of the Spine

Presentation

The most common presenting symptom for spinal metastases is back pain, present in up to 80% of patients. Most patients will present with pain that localizes to the back or with radicular pain. Pain is divided into three categories: local, radicular, and/or mechanical. Local pain from spinal metastases is often considered tumor-related and, classically, is worse in the morning and improves throughout the day with activity. The pain responds to nonsteroidal antiinflammatory drugs and steroids. Mechanical pain, on the other hand, is worsened with movement and relieved with recumbency. It occurs secondary to bony, ligamentous, and/or muscular damage associated with the tumor and may be related to spinal instability. This pain is relieved by spinal stabilization. Radicular pain occurs secondary to compression of a nerve root; it can be constant or exacerbated with movement and is eliminated by treatment of the mass or bone causing compression with surgery, radiation, or chemotherapy. In general, a patient with a history of cancer and new onset back pain should be considered to have a spinal metastasis until proven otherwise.

Neurological decline is the next most common presentation for patients with metastatic spine disease. This occurs secondary to epidural cord or nerve root compression. The most common complaint is gait abnormality followed by a feeling of heaviness in the legs or leg weakness; patients present with bowel or bladder incontinence less frequently, and the degree of bladder dysfunction frequently correlates with the degree of motor dysfunction. ^, Weakness can manifest as a myelopathy, radiculopathy, or myeloradiculopathy. Sensory disturbances can also occur, manifesting as numbness, hypaesthesia, or parasthesias—frequently in a band-like distribution when the metastasis appears in the thoracic spine. The disturbance has been likened to a corset or a tight shirt.

Imaging Findings

Plain films are still routinely obtained for the work-up of back pain. Metastatic spinal lesions can be either osteolytic (most commonly) or osteoblastic; the most common osteoblastic lesions are from breast and prostate cancer. The most commonly seen findings in spine radiographs are loss of vertebral body height, absence of pedicles, and dislocation of bones with an intact disc space. Plain radiographs have significant limitations, the most important being a high false negative rate (10%–17%), as they are only able to see bony anatomy and are unable to see soft tissue extension to the spinal canal or neuroforamina. More than 50% of the bone must be destroyed by a lytic lesion to be visualized on x-ray. ^,

There are numerous studies available that investigate the cellular metabolism and provide a highly sensitive picture to aid in localization of bony metastases. Radionucleotide scintigraphy can detect increased metabolic activity with a higher sensitivity relative to plain films; however, this modality has low specificity, as increased metabolism can be seen in infection and other inflammatory conditions. 18-fluoro-deoxyglucose positron emission tomography (PET) is also used frequently in cancer staging to detect the location of metastasis with high sensitivity based on the fact that cancer cells with high turnover use glucose at a very high rate. Neither modality, even when PET is combined with computed tomography (CT) scan, provides the spatial resolution provided by magnetic resonance imaging (MRI).

CT can provide a high level of detail of the bony anatomy and is invaluable for assessing bony involvement of tumor, as well as the presence of pathological fractures. When combined with myelography, it provides a high-resolution picture of the epidural space and possible neural compression. The combination of CT with myelography is frequently used for radiation planning after the placement of spinal hardware. CT-angiography is also useful for imaging vascular anatomy such as the vertebral arteries, which may be distorted by tumor, and for investigating the vascular supply of a vertebral metastasis itself. PET scanning using fluorodeoxyglucose or sodium fluoride with CT have become highly sensitive tools for the identification and localization of tumors in the spine and in the body overall.

MRI provides the highest sensitivity and specificity of all imaging modalities for detecting metastatic spinal disease and is considered the gold standard. A systemic review of the diagnosis and management of epidural spinal cord compression (ESCC) supported the use of full-spine MRI to detect spinal metastases in patients with a history of cancer and concern for cord compression. Overall, MRI provides a superior picture of the soft tissue elements of the spine, including nerve roots, intervertebral discs, and ligaments, which is invaluable for surgical planning. Standard MRI of patients with suspected metastatic disease should include T1, T2, and postgadolinium sequences with axial, sagittal, and coronal images; fat suppression sequences such as short tau inversion recovery may help reveal additional osseous metastasis through suppression of the normal high T1 intensity of bone marrow fat.

Angiography can also be a valuable adjunct in investigating metastatic spinal disease, especially if there is concern for a highly vascular metastasis. Highly vascular primary malignancies such as renal cell, thyroid, angiosarcoma, leiomyosarcoma, and hepatocellular carcinoma have metastases which demonstrate prominent vascularity with angiography and may be amenable to preoperative embolization. For example, preoperative embolization of highly vascular renal cell carcinoma metastases has been shown to dramatically reduce intraoperative blood loss and operative times and prevent postoperative complications such as hematomas. ^,

Evaluation

The evaluation and treatment of metastatic spine disease is a multidisciplinary effort involving oncologists, radiation oncologists, and frequently interventional radiology and pain specialists, in addition to surgical subspecialists. The goals of treatment are not curative, but rather palliative. As such, a thorough understanding of the extent of the patient’s disease and medical fitness, prognosis and neurological function and the stability of the spine metastasis is necessary for optimal treatment.

Multiple models have been developed to provide a decision-making framework regarding the evaluation and management of metastatic spine disease. The neurological, oncological, mechanical, and systemic (NOMS) framework ( Fig. 47.1 ) was developed to incorporate the neurological status of the patient and risk for decline, the oncological pathology affecting the patient, the mechanical instability associated with the spine disease, and the overall systemic health and prognosis of the patients.

Neurological Function

The neurological function of the patient in the NOMS framework is assessed by incorporating the patient’s neurological symptoms, which include radiculopathy and myelopathy, as well as the degree of radiographic ESCC. As mentioned previously, weakness as a result of radiculopathy or myelopathy is an indication for intervention in the appropriately selected patient with the presence of ESCC.

The Spine Oncology Study Group (SOSG) has developed a grading system to evaluate the degree of ESCC in response to a need for consensus on the definition of “high-grade” ESCC. This scale uses T2 axial images and had a high inter- and intrarater reliability for determining the degree of ESCC, based on a 6-point grading system. Grade 0 ESCC represents disease limited to bone.

Grade 1 ESCC is divided into three subclasses (1a, 1b, 1c) to help make a decision regarding treatment with stereotactic radiosurgery (SRS). Grade 1a represents epidural impingement, grade 1b has deformation of the thecal sac without abutment of the spinal cord, and grade 1c has deformation of the thecal sac with deformation of the spinal cord without cord compression. Grade 1a and 1b may be appropriately treated with SRS, whereas grade 1c may be too close to the spinal cord to prevent radiation toxicity. Grade 2 compression occurs with compression of the spinal cord with cerebrospinal fluid (CSF) visible around the cord. Grade 3 compression is defined as compression of the spinal cord without visible CSF.