Thoracic and Thoracolumbar Spinal Tumors: Regional Challenges

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Chapter 113 Thoracic and Thoracolumbar Spinal Tumors

Regional Challenges

The treatment of spinal column tumors is evolving steadily. Tumors of the thoracic and thoracolumbar regions of the spine represent a unique challenge to the spine surgeon because of the dangers posed by the surrounding neurologic and vascular structures. Each individual patient also represents a unique set of anatomic and physiologic characteristics that must be considered before the spinal tumor can be treated. Spinal tumors may be either primary or metastatic. Primary spinal tumors in the thoracic and thoracolumbar regions are uncommon, but they are tumors that may have the potential for a cure. Metastatic tumors in this region, on the other hand, represent an advanced stage of a primary cancer that may now be incurable and ultimately fatal. Any decision to perform surgery for a tumor-related condition in the thoracic or thoracolumbar spine must be carefully weighed in light of the patient’s projected life-span and the morbidity associated with the surgical approach required for treating the tumor. These and related issues are discussed in this chapter.

Primary Spinal Tumors

Primary spinal tumors are an uncommon subset of the tumors affecting the thoracic and lumbar spine. A review of data from the Leeds Tumor Registry shows that 2.8% of patients had tumors of the spine.1 In the United States, the incidence of primary tumors of the spine per 100,000 person years is estimated at 2.5 to 8.5.2 According to the series published by Weinstein and McLain, which reviewed 82 primary neoplasms of the spine over a 50-year period, nearly two thirds of all thoracic, lumbar, and sacral tumors were malignant.3 Rarely, these tumors present the possibility of a cure via surgical resection. A full description of primary spinal tumors is presented in Chapter 106.

Metastatic Spinal Tumors

Metastatic spinal tumors are the most common spinal tumors treated by the spine surgeon. At autopsy, 70% of patients who died of cancer have some form of vertebral metastasis.4 Spine surgeons, therefore, must have a clear understanding of the behavior of the primary tumor. Close consultation with medical oncologists and other specialists, however, is critical. Medical and adjunctive treatments have improved the quality of life and lengthened the survival of cancer patients.

There are two primary indications for surgery in patients with metastatic disease to the spine: (1) neurologic compromise or threatened neurologic compromise, and (2) spinal instability. Surgery also may reduce pain and may aid in establishing a tissue diagnosis when other attempts at obtaining one have failed.

Tumor type has been found to correlate with outcome. More aggressive primary tumors portend a worse long-term prognosis. Wise et al. reported that the longest mean survival times after the diagnosis of spinal metastasis were for myeloma (40.3 months), breast cancer (32.3 months), and prostate cancer (26.9 months), and shortest for lung cancer (12.3 months) and adenocarcinoma.5 The patient’s neurologic status, extent of disease, nutrition, overall health, and expected length of survival are other important considerations when deciding whether the patient is a candidate for extensive spine surgery. Most surgeons agree that metastatic spinal tumor surgery should be limited to patients who have an estimated life expectancy greater than 3 months. In an effort to better determine a patent’s life expectancy, Tokuhashi et al. presented a scoring system to be used in the preoperative evaluation of patients with metastatic spinal tumors.6 Scores of 0 to 2 points are assigned for each of six parameters (Table 113-1). The patient’s general health, the number of extraspinal skeletal metastases, the number of metastases to the spine, the status of metastases to internal organs, the site of the primary tumor, and the patient’s neurologic status are all weighted parameters in this scoring system. In addition to using this scoring system, spine surgeons are encouraged to consult with the patient’s medical and radiation oncologists, because multimodal treatment may offer the patient an even longer survival than otherwise predicted.

Table 113-1 Tokuhashi Scoring System for Preoperative Evaluation of Patients with Metastatic Spinal Tumors

Parameter Score
General Condition
Poor 0
Moderate 1
Good 2
No. of Extraspinal Bone Metastases
>3 0
1 or 2 1
0 2
No. of Metastases in the Spine
>3 0
2 1
1 2
Metastases to Major Internal Organs
Irremovable 0
Removable 1
None 2
Primary Site of Cancer
Lung, stomach 0
Kidney, liver, uterus, other 1
Thyroid, prostate, breast, rectum 2
Myelopathy
Complete 0
Incomplete 1
None 2

Data from Tokuhashi Y, Matsuzaki H, Toriyama S, et al: Scoring system for the preoperative evaluation of metastatic spine tumor prognosis. Spine (Phila Pa 1976) 15:1110-1113, 1990.

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 the 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 even 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), and distant spread (C).7 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. Most recently, the Spine Oncology Study Group examined observer reliability for two of these classification systems. They 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 MRI and CT axial cuts made the system more user friendly (Fig. 113-1). With respect to the classification system described by Weinstein, tumors that have extraosseous extension rarely are resectable in an en bloc manner due to the risks posed to the vascular and visceral structures present in the thoracic and thoracolumbar regions.8

image

FIGURE 113-1 This classification system divides tumors by vertebral location.

(From Chan P, Boriani S, Fourney DR, et al: An assessment of the reliability of the Enneking and Weinstein-Boriani-Biagini classifications for staging of primary spinal tumors by the Spine Oncology Study Group. Spine [Phila Pa 1976] 34:384–391, 2009.)

For an isolated metastatic tumor, the extent of resection has been related to patient survival. Sundaresan et al. 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.9 Tomita et al. reported on 28 patients who had undergone en bloc vertebrectomy with a mean survival of 38.2 months.10 Babat and McLain recommend that isolated metastases from less eminently lethal tumors such as breast, prostate, and kidney tumors should be managed similarly to primary tumors of the spine.11

Spinal Stability

One of the primary indications for surgery for tumors in the thoracic or thoracolumbar spine is the preservation of spinal stability. Kostuik et al. developed a system to evaluate the stability of spinal tumors based on the three-column classification of Denis.12 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 Dennis classification system, these columns are further divided in half in the sagittal plane to create six zones (Fig. 113-2). 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. 113-2). Other researchers have recommended that the destruction of more than 50% of the vertebral body warrants either prophylactic treatment or surgical stabilization.13 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.14

image

FIGURE 113-2 Regions of bony destruction described by Kostuik and Errico.12 This classification system divides tumors by the extent of vertebral involvement. The more zones occupied by tumor, the less stable the vertebral segment.

Dimar et al.15 used a cadaveric model of bone destruction to examine pathologic thoracic vertebral fracture risk. This group found that the force required to cause a vertebral fracture correlated with a value they called the vertebral strength index, which is equivalent to the product of the remaining intact vertebral body and the 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.