Preoperative Assessment

Initially, plain spine radiographs (anteroposterior and lateral) are used to determine the level and extent of tumor involvement. The spinal alignment can also be observed from these films. A CT scan without intravenous contrast at the appropriate spinal levels allows better definition of the degree of bony destruction of the spinal column. Although MRI is less precise than CT in outlining bony destruction, it provides the most precise means for illustrating the site and degree of spinal cord compression by tumor or soft tissues (Fig. 50-1). Myelography and postmyelography CT scan can be used when MRI is contraindicated or unavailable. The use of contrast for determining the degree of vascularity of the tumor with either CT scan or MRI is still at the research level. CT angiographies are becoming more useful in the spine as their resolution is increasing.

FIGURE 50-1 A, Proton density and T2-weighted sagittal MRI of metastatic carcinoma of the breast to the T12 vertebral body with angulation and severe spinal cord compression. B and C, Postoperative lateral and anteroposterior radiographs after T12 vertebral body resection showing the placement of a rib bone graft, methylmethacrylate, and Kaneda instrumentation. (Arrow in C indicates spinal canal.) Postoperatively, the patient recovered full neurologic function and was pain free. In view of the isolated vertebral body involvement, it was believed that good long-term survival was possible (thus the use of additional bone graft in the reconstruction). The patient, however, died of systemic metastatic cancer 8 months postoperatively. D, Sagittal reconstruction CT scan and corresponding axial image of (E) a patient with plasmacytoma involving the L1 vertebral body. T2-weighted sagittal (F) and axial (G) MRIs of the same case. Images of the CT scan illustrate the bony destruction, whereas the MRIs show the spinal cord compression more accurately. H, Preembolization angiogram showing the vascular supply of the L1 lesion with a tumor blush. I, Postembolization angiogram with a significant reduction in tumor blush in the same case.

To avoid complications from intraoperative and postoperative instability of the spinal column, it is important to assess the spinal stability before performing a vertebral decompression. Stability can be considered in terms of the three-column theory, after the extent of bony destruction produced by tumor has been determined from imaging.^15,16 Single-column involvement can be considered relatively stable. The additive destabilizing effects of decompression, however, must factor into the decision-making process.

Anterior column and middle column involvement is the most common finding in symptomatic patients with spinal tumors and is frequently associated with some degree of vertebral body collapse and bony retropulsion into the spinal canal (see Fig. 50-1A). If these conditions are treated by corpectomy, with a strut graft used for fusion (see Figs. 50-1B and C), stability of the spinal column can be achieved.

Careful review of the degree of involvement of the dorsal elements is required. The need for augmentation of ventral fixation with dorsal instrumentation will be based on the integrity of the laminae, lateral masses, pars interarticularis, and facets. Corpectomy and vertebral replacement techniques can result in persistent dorsal element instability if overdistraction and opening of the facets are achieved. This instability can prevent subsequent fusion and result in failure of the ventral fixation. The ease with which distraction can be obtained following decompression can also provide the surgeon with information regarding the degree of dorsal instability. Intraoperative radiographs can be taken to ensure the proper amount of distraction. In cases when the dorsal instability is deemed significant, dorsal stabilization should be undertaken. Discretion of the surgeon will be used to decide if and when the dorsal stabilization procedure is required.

When planning surgery for spinal tumors, an assessment of stability must also take into account angulation and alignment.¹⁶ Higher failure rates will be observed with a poorly aligned construct. It is also important to consider the nature of the tumor in terms of its capacity to infiltrate and destroy bony tissue and its response to RT or chemotherapy.

Preoperative Angiography and Embolization

Angiography, with a view to embolization, is recommended for patients with known vascular tumors (e.g., melanoma, renal cell carcinoma, metastatic thyroid tumor, primary giant cell tumor) or in patients in whom imaging suggests a relatively vascular tumor. If these tumors are amenable to embolization, it should be performed no more than 48 hours before surgery. Waiting too long after embolization may result in recanalization. The expertise of the interventional neuroradiologist will influence greatly the impact of presurgical embolization by reducing intraoperative blood loss. Additional information concerning the vascular supply of the spinal cord can also be obtained. Performing a spinal angiogram, however, for the sole purpose of defining the anatomy is unwarranted.

Intraoperative Monitoring and Anesthetic Management

The authors recommend electrophysiologic monitoring, if available, including somatosensory and motor evoked potentials, at all vertebral levels involving the spinal cord. Electromyography (EMG) monitoring is also useful in the lumbar region, if segmental pedicular fixation is contemplated. Monitoring setup time and cost are definite drawbacks to this type of technology, although its use is generally supported in the literature.^12,17–19 In approaches of the upper and middle thoracic spine, a double-lumen endotracheal tube allows the lung in the operative field to be deflated, improving the surgical exposure. In lesions of the lower thoracic and thoracolumbar regions, the lung can be retracted easily. Invasive arterial pressure monitoring and central venous pressure (CVP) monitoring and access are recommended in order to address any blood loss during the surgery.

Positioning

Patients are positioned in the full lateral decubitus position (Fig. 50-2) with an axillary roll placed under the dependent axilla to prevent neurovascular compromise. A mild flexion in the hip will assist mobilization of the psoas muscle should the exposure require it.

FIGURE 50-2 Patient is in the lateral position, and a dorsolateral thoracotomy skin incision is placed below the scapula.

Incision and Exposure

The side of approach and the level of the spine that is involved are important factors in determining where to make the incision. To maximize resection, the decision to perform a right-sided or left-sided skin incision and approach should be determined by the side of the spine with greater tumor involvement. If neither side is predominantly involved by tumor, the spine is generally approached from the right side, at or above the T5 vertebral segment, to avoid the arch of the aorta. Below T5, the spine is generally approached from the left side to minimize retraction on the liver. Careful review of the axial images in order to appreciate the corridor of access between the great vessels and the lateral aspect of the spine is essential. This information may, in fact, push a surgeon to the other side and to tolerate the liver retraction.

Lesions involving the cervicothoracic (C7-T1), upper thoracic (T1-5), lower thoracic (T6-11), thoracolumbar (T12 and L1), and lumbar and sacral (L2 to sacrum) segments require specific approaches (see Table 50-1) and considerations that have been described in other chapters of this text.

Exposure

The pleura is sharply incised and reflected. A rib that overlies the level of the pathology in the midaxillary level is resected. The appropriate rib is identified using intraoperative imaging. The segmental vessels at the level of the pathology and of the vertebral bodies above and below the lesion (Fig. 50-3) are ligated and divided. Division of segmental vessels over the vertebral body in the middle of the body reduces the risk of vascular compromise of the spinal cord by taking advantage of collateral vessels from adjacent levels. The periosteum is reflected medially, and the anterior longitudinal ligament is identified.

FIGURE 50-3 Exposure of the thoracic spine after entry into the thoracic cavity and placement of a self-retaining chest retractor. The parietal pleura has been separated from the ribs and spinal column with the segmental vessels along the side of the vertebrae identified.

Vertebral Body Decompression

The intervertebral discs above and below the involved vertebral body are identified and resected initially by sharp dissection (Fig. 50-4). Disc material is cleared with curettes and pituitary rongeurs. Removing the rib head will allow identification of the ipsilateral pedicle and its continuation into the vertebral body. The pedicle is an important marker for the orientation and position of the spinal canal. Using sharp curettes, rongeurs, and a high-speed drill, the vertebral body is resected ventrally to dorsally, except for a rim of the ventral portion of the vertebral body. This rim protects the aorta and inferior vena cava from accidental trauma. Resection of the vertebral body can progress as far as the opposite pedicle (Figs. 50-5 and 50-6), and the entire dorsal aspect of the vertebral body can be removed. Sufficient bone needs to be removed to clear the posterior longitudinal ligament of any compression of the dura. The dissection can also be continued dorsolaterally to allow decompression of the spinal nerve roots. The tumor involvement and the quality of the residual bone for instrumentation will determine the extent of bony removal. Techniques to augment the strength of the purchase into the bone are discussed in subsequent paragraphs.

FIGURE 50-4 After a thoracotomy via resection of a rib located one level rostrally, the pleura is reflected off the ventral spine. The segmental vascular bundles are isolated and ligated as shown. Vertebral decompression of the tumor begins by the excision of intervertebral discs above and below the involved vertebra. Following this, 1 to 2 cm of the rib head is drilled down to expose the ipsilateral pedicle.

FIGURE 50-5 Axial section through vertebra involved with spinal tumor showing the extent of bony decompression necessary to allow adequate tumor resection.

FIGURE 50-6 Remaining vertebra after bony decompression and tumor removal showing that the decompression extends from the ipsilateral pedicle to the contralateral pedicle.

Rostrocaudal Dissection

Special care is afforded to the cartilaginous end plates and the central regions of cancellous bone of vertebral bodies adjacent to the corpectomy site. Removal is performed using a small high-speed bur or curette (Fig. 50-7) or osteotomes and rongeurs, depending on the bone consistency. This allows troughs to be created in the vertebral bodies above and below the corpectomy site to allow subsequent reconstruction with a bone graft, an implant, or an acrylic graft. Preparing the end plates to accommodate the construct requires special attention. When the construct involves bone, either autograft or allograft, an eventual fusion will be desired. In this circumstance the end plates require adequate vascular supply for achieving fusion. The structural integrity of the graft can also fail if it is suboptimal or radiated. Methylmethacrylate (MMA), on the other hand, will not fuse, and the overall construct strength can be weakened by aggressive removal of the end plates. The risk of telescoping and the graph imploding into the vertebral body can also occur when the end plates are destroyed. MMA, however, will tolerate radiation.

FIGURE 50-7 After tumor resection, the end plates and cancellous bone of adjacent vertebral bodies are removed to the degree shown (dotted line) using an angled high-speed drill or angled curettes.

Intraspinal Decompression

After adequate bony resection, decompression, and removal of all devitalized bone and tumor tissue, the posterior longitudinal ligament is resected to expose the dura mater that encloses the spinal cord and segmental nerve roots. Any tumor or bone impinging on the dural sac or nerve root is carefully removed to allow decompression of these structures. The goal of surgery should be radical tumor resection and decompression. In patients who have previously received RT, the posterior longitudinal ligament is frequently adherent to the dura mater and may be difficult to separate. In these cases, it may be advisable to leave it in situ. In most virgin cases the dissection plane between tumor and dura is easily exploited.

Complications Related to the Approach

A thoracotomy carries pulmonary risks such as atelectasis and pneumonia. The retroperitoneal exposure may injure the spleen, kidney, or ureter, and a prolonged postoperative ileus may occur. Any unrepaired defect in the abdominal wall or diaphragm may be the site of visceral herniation. Using vertebral body screws with manual confirmation of bicortical penetration requires considerable dissection of the contralateral aspect of the vertebral body, placing the aorta, inferior vena cava, and iliac vessels at risk if this is not done meticulously. Injury to the lumbar hypogastric plexus at L5 in males may be complicated by retrograde ejaculation. Chyle leak from damage to the thoracic duct is best managed with immediate repair.

Inadequate Spinal Decompression

Inadequate decompression or incomplete tumor resection reduces the chance of adequate neurologic recovery. It is important that the decompression be performed to the contralateral pedicle. Complete visualization of the dura mater and confirmation with intraoperative radiograph that the appropriate level has been decompressed are required.

Neurologic Injury

A carefully staged approach to spinal decompression with adequate exposure and identification of segmental vessels, nerve roots, and the dural tube markedly reduces the risk of nerve root and spinal cord injury. Nuwer²⁰ concluded that intraoperative neurophysiologic monitoring is a cost-effective way of reducing the potential for a neurologic deficit. Intraoperative information is valuable not only to the prognosis but also by altering intraoperative and postoperative management. Hardware revision and removal during the operation may be performed on the basis of intraoperative neurophysiologic changes.

Dural Tears

Dural tear from direct surgical trauma may occur while the tumor is being dissected or because of erosion of the dura caused by the tumor. In these cases, the precise site of dural tear should be identified and the tear repaired with a nonabsorbable suture (e.g., 4-0 Nurolon [Ethicon]). In less discrete or poorly visualized dural tears, fibrin glue can be layered over the cerebrospinal fluid leakage site and allowed to adhere to underlying dura mater. A lumbar drain should be placed for 5 days postoperatively to assist dural closure and reduce cerebrospinal fluid leaks.

Excessive Epidural Bleeding or Bleeding from Tumor

Preoperative angiography and embolization of vascular tumors reduce the risk of such intraoperative bleeding. After careful identification and mobilization, segmental vessels above and below the corpectomy site should be ligated and cut to avoid bleeding from these vessels when the vertebral bodies adjacent to the corpectomy site are spread apart. Other sites of epidural bleeding should be identified, and hemostasis should be attained with bipolar coagulation. Epidural bleeding can be particularly troublesome and require the use of various packing agents such as hemostatic gelatin (Gelfoam, Baxter Healthcare, Glendale, CA) and thrombin. Dealing with epidural vessels by coagulation before sharp dissection is the optimal strategy. Tumor bleeding can also be difficult to address. Remember to remove all visible tumor, because the most frequent site of bleeding is from the tumor bed. Preoperative planning and gross total resection of the lesion is the best strategy for tumor bleeding. Tumor bleeding can also be controlled using various packing material as described earlier. Polymethylmethacrylate (PMMA) in the resection cavity can be used. The primary function is to reconstruct, but one of the secondary benefits will be from the thermal reaction of the cement, which can cauterize the remaining tissues.

Graft Material

The appropriate type of material to use for spinal column reconstruction depends on the nature of the lesion and the patient’s life expectancy. In cases of trauma, for benign lesions, or for patients with malignant tumors who have a relatively long life expectancy (>2 years), reconstruction is best when using autogenous bone from the iliac crest or rib for single vertebral body defects. If two or more vertebral levels are involved with the neoplasm, an allograft (e.g., from the fibula or humerus) can be used. It is often useful to supplement the allograft strut with local autograft bone (Fig. 50-8).

FIGURE 50-8 A, Proton density sagittal MRI scan illustrating an L1 burst fracture with compression of the conus. B and C, Postoperative anteroposterior and lateral radiographs after anterior decompression and stabilization using bone graft (combination of humeral allograft and rib autograft) and Kaneda instrumentation. Coronal (D) and sagittal (E) CT scan images showing an expandable cage for the reconstruction of a two-level corpectomy. The Kaneda system is added to the construct for additional support to the anterior and middle column. The arrows in (E) identify the Kaneda screws into the body above and below the cage, while the arrow in (D) shows the connecting rods.

In patients with malignant disease and a short life expectancy, autogenous bone grafts have certain disadvantages: (1) If life expectancy is less than 1 year, solid bony fusion over the long term is unnecessary; (2) the use of adjunctive radiation and chemotherapy will slow or prevent the bony fusion needed for stability; (3) any remaining local tumors may infiltrate the bone graft and weaken the construct; and (4) autogenous donor sites may not be suitable because of tumor involvement.

For patients with an expected survival of 18 months or less, a synthetic construct using PMMA with or without titanium cages can be used. Expandable cages with only titanium construct have also been used to provide ventral support and reconstruction in difficult cases (see Fig. 50-8D and E). Biomechanical studies looking at intervertebral fixation have shown resistance of the implants to cyclical fatigue within typical normal physiologic loading and superior reduction of intervertebral motion and increased spinal stiffness.^11,21–27 The use of expandable vertebral protheses or cages is gaining popularity. An example of such a device can be found with the X-mesh cage (DePuy Spine, Raynham, MA).

Reconstruction Technique