Thoracic and Thoracolumbar Spinal Tumors: Regional Challenges

Surgical Margins

All discussions regarding the surgical resection of tumors, regardless of the surgical discipline, reference the type of margin that is achieved when the tumor is removed. Surgical resections may be defined as either intralesional or en bloc. An intralesional resection is, by definition, a surgical resection in which the tumor is removed in a piecemeal fashion. An en bloc resection is a tumor resection in which the capsule of tumor itself is not violated. Intralesional resections rarely offer the possibility of complete eradication of the tumor. The reliability of an en bloc resection to relieve the patient of tumor burden depends on the margins that are obtained during the surgical resection. These margins may be described as intralesional (if the tumor capsule is violated), marginal, wide, and radical. Intralesional resections are self-explanatory. Marginal resections imply that the entirety of the tumor burden is removed, but little or no normal tissue is resected along with the tumor. Wide resection, by definition, includes a component of normal tissue that is removed along with the tumor. By taking a wide en bloc resection, the tumor tissue is not visualized at the time of the resection, as it is completely encapsulated by a margin of normal tissue. A radical resection, by definition, removes the entire organ, along with the blood and lymph supply to the organ. In spine surgery, a true radical resection is rarely, if ever, possible. In the event that an en bloc resection can be performed, a wide resection often is the only possibility.

With respect to spinal tumor surgery, regional classification systems have been developed. Weinstein first popularized this type of classification system. In Weinstein’s classification system, tumors were defined as intraosseous (A), extraosseous (B), or distant spread (C) ( Fig. 157.2 ). The zones were further subdivided with respect to the tumor’s location on the vertebrae. Other groups have attempted to define spinal tumor location in a similar manner. The Spine Oncology Study Group examined observer reliability for two of these classification systems. The researchers found that there was moderate interobserver reliability and substantial intraobserver reliability. The Spinal Oncology Study Group thought that changing the orientation of the diagram of the zones to fit the convention of magnetic resonance imaging and computed tomography (CT) axial cuts made the system more user-friendly ( Fig. 157.3 ). With respect to the classification system described by Weinstein, tumors that have extraosseous extension are rarely resectable in an en bloc manner because of the risks posed to the vascular and visceral structures present in the thoracic and thoracolumbar regions.

For an isolated metastatic tumor, the extent of resection has been related to patient survival. Sundaresan and associates reported that gross total resection of spinal tumors leads to a median survival of more than 2 years, compared with a historic median survival of 6 months for less aggressive resections. Tomita and colleagues reported on 28 patients who had undergone en bloc vertebrectomy with a mean survival of 38.2 months. Babat and McLain recommended that isolated metastasis from less eminently lethal tumors, such as breast, prostate, and kidney tumors, should be managed similarly to primary tumors of the spine.

Spine Stability

One of the primary indications for surgery for tumors in the thoracic or thoracolumbar spine is the preservation of spinal stability. After tumor invades the spinal bone, growth factors that stimulate osteoblastic and osteolytic activities are upregulated, resulting in a cycle of bone destruction and local cancer cell proliferation that can cause symptomatic pain, mechanic instability, neurological dysfunction, sphincter control failure, hypercalcemia, and pathological fractures. Metastasis destroys the vertebral body by causing microfractures and compression fractures, resulting in spinal instability. Kostuik and coworkers developed a system to evaluate the stability of spinal tumors based on the three-column classification developed by Denis. Most spine surgeons are familiar with this model, which divides each vertebral segment into an anterior column, a middle column, and a posterior column. Unlike the Denis classification system, these columns are further divided in half in the sagittal plane to create six zones ( Fig. 157.4 ). Destruction of fewer than three of the six zones is considered to be stable. Further bony involvement, specifically three- and four-zone bone involvement, is considered relatively unstable. Five- to six-zone destruction is considered markedly unstable, potentially benefiting from surgical intervention (see Fig. 157.4 ). Other researchers have recommended that the destruction of more than 50% of the vertebral body warrants either prophylactic treatment or surgical stabilization. Other modalities have been reported in the literature to be potentially helpful in this region of the spine. Specifically, minimally invasive techniques, such as kyphoplasty or vertebroplasty, have been found to aid both pain relief and spinal stability in this region.

Percutaneous vertebroplasty (PVP) was first applied in the treatment of spinal metastases in 1989 by Kaemmerlen and colleagues, and since that time good results have been achieved in China and elsewhere. Until recently, its application in the treatment of multiple thoracic metastases had not been reported. Liu and associates retrospectively reviewed 28 patients with multiple thoracic metastases involving 104 vertebrae treated with PVP and its clinical implications through assessment of pain relief, improvement of activities of daily living (ADLs), and postoperative vertebral body height. This study showed that PVP quickly relieved thoracolumbar and back pain in patients with multiple thoracic metastases when assessed at 1 week and 3, 6, and 12 months, with response rates of 82.1%, 89.3%, 81.5%, and 88.5%, respectively. In addition, the ADL scores were significantly improved ( P < .01) compared with preoperative baseline. One year after PVP, the heights of the anterior border, center, and posterior border were not significantly different from those before PVP ( P > .05). The authors concluded that PVP not only significantly improves the patient’s quality of life, but also prevents further vertebral collapse and the invasiveness of intraspinal tumors, avoiding the nerve dysfunction caused by spinal cord compression.

Although PVP has been shown to be effective, it is not without complications, which will be discussed in further detail later is this chapter. However, PVP is not always an option in all patients with instability without changes in neurological function (e.g., erosion of the posterior wall of vertebral body). In this subset of patients, there could be a potential role for stabilization with minimally invasive percutaneous pedicle screw placement. Bernard and colleagues suggested a role for percutaneously placed long segment pedicle screw constructs in patients with contraindications to a major decompressive and reconstruction surgery. They retrospectively reviewed a prospectively collected subset of 17 patients. All these patients underwent percutaneous pedicle screw fixation followed by radiation treatment postoperatively. With regard to improvement in pain, there was a statistically significant improvement in the visual analog scale (VAS) score at 3 days, 3 weeks, 6 weeks, 3 months, 6 months, and 1 year after surgery. The Oswestry Disability Index scores significantly improved for the first 45 days postoperatively. All patients were ambulatory immediately after surgery, and in the five patients who could ambulate preoperatively, their walking tolerance significantly improved. In terms of complications, there were no reported wound complications, which is often a major complication reported with major open decompressive surgeries in these medically compromised patients. There were no adjacent level fractures, screw pullout, or progression of the disease requiring decompression surgery. There were two instances of disease progression requiring further radiation treatment.

Radiofrequency ablation (RFA) has been combined with percutaneous kyphoplasty (PKP) in the treatment of thoracolumbar vertebral metastasis. RFA is a minimally invasive treatment developed for treating vertebral tumors using image-guided positioning of an electrode in the lesion to kill malignant cells percutaneously with minimal damage to adjacent healthy tissue. Its use with PKP as opposed to PVP is more appealing because of the reduced risk of complications associated with cement leakage with the use of balloon dilatation as compared with PVP. Zheng and coworkers retrospectively reviewed the efficacy and safety of PKP in 26 patients with thoracolumbar vertebral metastatic disease, including 38 vertebral metastases ranging from T11 to S1. In this study there were no major adverse events or complications reported, and no recurrence or secondary surgical intervention occurred during follow-up. Pain peaked at 3 days after RFA with PKP intervention and was then relieved because no VAS score above 5 was reported by 6 months. These outcomes were more positive than those previously reported in a study by Nakatsuka et al., which stated that RFA treatment of vertebral metastases produced notable complications in almost one-fourth of patients, including nerve damage, sciatica, and high postoperative pain. Zheng and coworkers believe that their more favorable results were achieved because of careful positioning of the needle, with an optimal placement of 1 cm from any important nerves or blood vessels, as well as an optimal temperature of at 42° C (never exceeding 43° C), thus allowing the protective posterior cortex to form a natural thermal insulator crucial for the protection of the structure around the vertebral body.

An evidence-based process using expert opinion consensus was used to develop the Spine Instability Neoplastic Score (SINS). In this classification system, tumor-related instability is assessed by adding six individual component scores: spine location, pain, lesion bone quality, radiographic spinal alignment, vertebral body collapse, and posterolateral involvement of the spinal elements. The minimum score is 0, and the maximum is 18. A score of 0 to 6 denotes stability, 7 to 12 denotes indeterminate (possibly impending) stability, and 13 to 18 denotes instability. A surgical consultation is recommended for patients with SINS scores greater than 7. Although this classification has been found to be reliable, its ability to improve patient outcomes by changing surgeon decision making has yet to be proven.

Dimar and colleagues used a cadaveric model of bone destruction to examine pathological thoracic vertebral fracture risk. This group found that the force required to cause a vertebral fracture correlated with a value they termed the vertebral strength index, which is equivalent to the product of the remaining intact vertebral body and bone mineral density. Despite these guidelines, there is no consensus with respect to the absolute amount of bony destruction that would compel a spine surgeon to stabilize a threatened thoracic or thoracolumbar spine. Surgeons are again reminded to consider the patient and his or her disease state as a whole.