Introduction

Spinal metastases (SM) complicate the courses of 5 to 10% of cancer patients. The primary treatment modalities for metastatic spinal tumors are radiotherapy and surgery; the goals are palliative and include neurological preservation or improvement, mechanical spinal stability, and local tumor control. The treatment decision-making process can be broken down into four fundamental considerations referred to as NOMS: Neurological (N) includes the degree of myelopathy and the degree of radiographic spinal cord compression; Oncologic (O) primarily reflects the known radiosensitivity of the tumor; Mechanical instability (M) is broadly defined as movement-related pain and is level dependent; and Systemic disease (S) includes both the extent of disease and the medical comorbidities. Approximately 95% of the patients with SM will demonstrate epidural disease, mainly affecting the vertebral body and the pedicle regions. Symptomatic spinal cord compression occurs more frequently in the thoracic spine, followed by cervical and then lumbar. As chemotherapy is usually ineffective in providing local control in the spine, radiotherapy and/or surgery is most often used in the treatment of spinal tumors. The treatment of primary spinal tumors involves a similar decision process as well as considerations regarding curative resection that are pathology and case dependent. Preoperative embolization of hypervascular tumors significantly reduces intraoperative blood loss and improves the surgeon′s ability to decompress the spinal cord and maximize tumor resection. Furthermore, it also aims to reduce operative time and improve visualization of the operative field. Spinal tumors previously considered unresectable due to the potential for catastrophic blood loss can be effectively addressed following tumor embolization. Curative embolization is occasionally the goal in patients with certain benign primary tumors, such as giant cell tumors and aneurysmal bone cysts (▶ Fig. 71.1 ). Arterial embolization of bone tumors was first described in 1975. Since then, there have been several reports in the literature describing embolization of spinal tumors prior to surgical resection. With the advent of microcatheters, and new embolic agents, as well as advances in digital substraction imaging over the past two decades, embolization of spinal tumors has become a standard and safe procedure.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Whether or not treatment is indicated.

   
   
2. 
   

   Indications for diagnostic spinal angiography.

   
   
3. 
   

   Case selection for preoperative endovascular embolization and adequate timing for surgery after embolization.

   
   
4. 
   

   Potential complications of endovascular embolization and technical nuances.

Whether to Treat

The optimal clinical management of these patients requires integrated decisions by an interdisciplinary cancer team comprised medical and radiation oncologist and spine surgeons, as well as all other health care professionals and involved medical specialties. The decision to refer a patient for angiography and preoperative embolization is based on both tumor histology and magnetic resonance imaging (MRI) findings ( 1 , 2 in algorithm ). Traditional MRI criteria suggestive of tumor hypervascularity include flow voids, intratumoral hemorrhage, and diffuse contrast enhancement. The presence of these findings is an indication of hypervascularity; however, many tumors are hypervascular on angiogram even in the absence of these findings. Recently, dynamic contrast-enhanced MR (DCE-MR) imaging has been used to differentiate tumor vascularity and may be more accurate compared with standard MRI. Unfortunately, this is not currently a standard imaging sequence. Thus, tumor histology is used as an independent predictor of hypervascularity ( 2 in algorithm ). Tumor histologies that are commonly hypervascular and benefit from embolization include benign lesions such as hemangioma, aneurysmal bone cyst, and giant cell tumors; primary malignant tumors (Ewing′s sarcoma and hemangiopericytoma), metastatic tumors (renal cell carcinoma, papillary and follicular thyroid carcinoma, cholangiocarcinoma, and angiosarcoma), neuroendocrine tumors such as carcinoid, pheochromocytoma, and paraganglioma of the spine ( 3 in algorithm ). Most of the common solid tumor malignancies, such as breast, lung, and colon carcinoma are relatively avascular and do not require preoperative embolization. Conversely, multiple myeloma, melanoma, and hepatocellular carcinoma are potentially hypervascular, but do not typically benefit from embolization because the vascularity is derived from small capillary feeders, rather than major segmental arteries. In addition, any histology in which the word “angio” or “hemangio” is part of the tumor or if the organ of origin is vascular should also be evaluated with angiography (i.e., cholangiocarcinoma, angiosarcoma, and hemangioma). For this reason, it is critical to recognize that solitary fibrous tumor was initially called hemangiopericytoma, and is commonly found to be among the most hypervascular tumors ( 3 in algorithm ). MR characteristics for preoperative angiography and embolization include intratumoral flow voids, hemorrhage, and avid contrast enhancement ( 4 in algorithm ).

Anatomical Considerations

The arterial supply to the spinal column, spinal cord, dura, nerve roots, and the paraspinal soft tissues comes from the segmental arteries. The segmental arteries originate from the vertebral arteries and the thyrocervical or costocervical trunk in the cervical region, the aorta in the thoracic and upper lumbar spine, and the internal iliac or median sacral artery in the lower lumbar spine and the sacrum. The segmental arteries give rise to the radiculomeningeal arteries that supply the dura and nerve roots and the anterior and posterior radiculomedullary arteries that supply the anterior and posterior spinal arteries, respectively. The radiculomeningeal arteries exist at every vertebral level, but the radiculomedullary arteries exist only at some levels with great variability. The anterior spinal artery runs in the groove of the anterior median fissure from the level of the foramen magnum to the conus medullaris and supplies blood to the anterior two-thirds of the spinal cord. The two posterior spinal arteries run parallel to each other on the posterolateral surface of the spinal cord and supply blood to the posterior one-third of the spinal cord. The most cephalic portion of the anterior spinal artery is formed by small branches from one or both vertebral arteries. The blood supply to the most cephalad portion of the posterior spinal arteries arises from small branches of either the vertebral or the posterior inferior cerebellar arteries. There are 6 to 8 anterior radiculomedullary arteries that make functional connections to the anterior spinal artery and 11 to 16 posterior radiculomedullary arteries that supply the posterior spinal arteries. At the cervical level, the radiculomedullary arteries arise from the vertebral artery and the ascending and deep cervical arteries. At the thoracolumbar level, the radiculomedullary arteries arise from the supreme intercostal, posterior intercostal, and lumbar arteries. The great anterior radiculomedullary artery, better known as the artery of Adamkiewicz, is the largest radiculomedullary artery in the thoracolumbar region and is the major supplier of blood to the anterior spinal artery at the lower thoracic and upper lumbar levels. It characteristically makes a sharp hairpin turn caudally as it joins the anterior spinal artery (▶ Fig. 71.2 ). In 75% of individuals, it arises at the T9 to T12 vertebral level, most often on the left side. The blood supply of the sacrum and the cauda equina is via the lateral sacral and the iliolumbar arteries from the internal iliac artery, and the median sacral artery off the aorta. Each segmental artery is often connected to the neighboring segmental artery via intersegmental anastomoses along the anterolateral aspect of the vertebral body and adjacent to the transverse process. Thus, the anastomotic network around the spine needs investigation of the adjacent vertebral levels above and below the tumor to exclude a potential shunt between the segmental artery targeted for embolization and a spinal artery.

Classification

Vascularity can be graded as normal (0, same as the normal adjacent vertebral body), mildly increased (1, slightly more prominent than the normal vertebral body blush; Case illustration 1), moderately increased (2, considerable tumor blush without early arteriovenous shunting), or severely increased (3, intense tumor blush with early arteriovenous shunting; Case illustration 2). The degree of embolization is considered complete if there is grade 0 or less of residual vascularity, near-complete if there is grade 1 or residual vascularity, and partial when grade 2 or 3 residual vascularity.