Management of Primary Malignant Tumors of the Osseous Spine

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Chapter 190 Management of Primary Malignant Tumors of the Osseous Spine

Alessandro Gasbarrini, Stefano Bandiera, Luca Amendola, Joseph Schwab, Stefano Boriani

Primary tumors of the spine are exceedingly rare. Owing to their rarity, few surgeons had gained enough experience and insight into their management until the 1970s when B. Stener first applied oncologic criteria in resecting spine tumors, previously submitted only to intralesional excisions (curettage). Stener ¹ was the first to plan and perform en bloc resections as they were already being performed in tumors of the gastrointestinal tract. His works are still unsurpassed examples of adapting surgery to tumor expansion and anatomic constraints to achieve a tumor-free margin by en bloc resection.

Later, R. Roy-Camille ² popularized a technique to standardize en bloc resection in the thoracic spine by the posterior approach and in the lumbar spine by a combined posterior and anterior approach. Some years later, K. Tomita³ proposed a similar technique, characterized by the use of a saw thinner than the Gigli saw, proposing to remove en bloc also the posterior arch. However, what is missing in these capital contributions—which represent the foundations upon which other surgeons have further advanced—is any consideration of the margins to be achieved, thus reducing the oncologic interest. These concepts were first applied to bone tumor by Enneking⁴ and more specifically to bone tumors of the spine by Campanacci and colleagues⁵ and by Talac and colleagues.⁶

Many examples are reported in the most recent literature of highly technically demanding surgical procedures performed either in tumors of the cervical or cervicothoracic spine,⁷^–¹¹ including in the resection functionally relevant structures with the purpose of achieving tumor-free margins.¹²^–¹³

Several different techniques are therefore described and detailed in this chapter together with the basic principles of surgical staging and planning, in order to individualize the surgical technique to the tumor extension. Tips to help avoid problems and reduce morbidity are also included.

Classification

Less than 5% of the 2500 primary malignant bone tumors that are found each year in the United States occur in the spine.¹⁴ For that reason, few centers can achieve a critical level of experience in the management of these tumors. The terminology used to describe these tumors has tended to vary considerably from one region to the next. In addition, there were no staging systems that helped one decide which type of surgery to perform. All of these reasons entered into our decision to help develop the Weinstein, Boriani, Biagini (WBB) surgical staging system.¹⁵ This system is designed to unify the ways tumors are described in order to facilitate communication between physicians. Once a common descriptive language is accepted, it also helps to facilitate research efforts. The WBB system helps guide the surgeon with regard to what type of resection is possible.

The WBB system divides the axial presentation of the vertebrae involved with tumor into 12 zones similar to a clock face (Fig. 190-1). Position number 1 begins at the left half of the spinous process and position 12 ends at the right half of the spinous process. Zones 4 and 9 are particularly important to know because they define respectively the left and the right pedicle. Vertebrectomy with adequate surgical margins depends upon one of these two zones to be free of tumor. The vertebra is further divided into radial zones. The radial zones define the depth of tumor invasion. For instance, zone A represents a soft tissue mass extending beyond the confines of the bony cortex. Zone B describes tumor within the superifical bony vertebrae, and zone C defines tumor within the deep bony vertebrae. Zone D describes epidural tumor involvement and zone E is intradural. It is also important to describe the longitudinal extend of the tumor.

FIGURE 190-1 WBB staging system. The transverse extension of the tumor is described with reference to 12 radiating zones (numbered 1 to 12 in a counterclockwise direction starting from the left half of the spinous process) and to 5 concentric layers (A to E).

As an example, a tumor of a lumbar vertebra involving the left pedicle and the vertebral body, extending in the psoas and the epidural space can be described based on the distribution within the WBB staging system as involving zones 4 through 8 with extension into zones A and D.

This system has been submitted to intra- and interobserver reliability assessment ¹⁶ by a group of spine tumor experts

Indications for En Bloc Resection

The goal of en bloc surgery is to remove the whole tumor with a continuous shell of normal tissue, the margin. Often the tissues surrounding spine tumors are functionally very important and even unresectable. Sometimes nerve root resection leads to significant motor deficit; sometimes a situation arises where a meaningful surgical margin is not possible without transection of the dura or even the spinal cord. These options should be first weighted considering the long-term outcome of oncologically appropriate surgery versus intralesional surgery in each specific conditions.^6,¹⁷^–²⁰ A 2009 systematic review of the literature²² offered evidence (low quality due to the small number of cases reported) that for thoracic and lumbar spine aggressive osteoblastoma, giant cell tumor (Enneking 3), en bloc resection—when anatomically feasible—can be recommended to minimize the risk of local recurrence. En bloc resection should be undertaken for chordoma and chondrosarcoma of the spine, provided wide or marginal margins can be achieved, because it is related to a reduced rate of local control and mortality. In osteosarcomas and Ewing sarcomas of the spine, en bloc resection is associated with better local control and overall survival if associated with a full course of chemotherapy.

The margins are a valid predictor of local and systemic prognosis,^6,^12,^13,¹⁷^–²¹ but the possibility to compensate intentional margin transgression with multimodal treatments should be carefully considered. The option of relevant functional sacrifices to target better systemic prognosis must be discussed with the patient. For some patients, the idea of paralysis is not worth considering. Conversely, others might wish to accept paralysis in exchange for possible cure. This is clearly a decision that only the patient should make in conjunction with the counsel of the surgeon. En bloc resections are sometimes proposed also in the treatment of bone metastases in the spine. This indication is open to discussion because the criterion to plan the treatment of metastatic disease is palliation, and risk-to-benefit ratio should always be carefully considered. However, when local control is the primary issue—in solitary metastases from clear cell tumor or colon carcinoma—en bloc resection, if feasible with acceptable risk, may be an option. Bilsky et al.,²³ however, in a 2009 systematic literature review, concluded that stereotactic radiosurgery is better than en bloc resection in the treatment of solitary metastases from clear cell carcinoma without epidural extension.

Finally, the specific morbidity of en bloc resections should always be carefully considered.²⁴

Preoperative Planning

The WBB system was designed to plan surgery. Preoperative MRI and CT scan are required to provide the details of tumor extension and normal tissue reactions necessary for the WBB staging system. Because the goal of surgery is to obtain a negative margin, the surgical planning should include in the specimen at least one sector and one layer outside the tumor border. In particular, the en bloc resection of the vertebral body will result in a tumor-free margin when the tumor spares at least one pedicle (zones 4 or 9). Extension into zone D can preclude one from obtaining a negative margin unless a layer of healthy tissue (pseudocapsule) exists between the tumor and the dura. It is not always possible to know this until the time of surgery. Close attention should be paid to zone A extension. The anterior approach should be directed toward the side with maximum zone A involvement to allow best visualization. In addition to these, one must pay close attention to the cephalocaudal extent of the tumor. This will help determine whether the transverse cuts should be made through a disc or vertebral body. If a foramen is involved, then the nerve root in that foramen needs to be taken with the tumor to obtain a tumor-free margin. It may be necessary to remove a nerve root to facilitate tumor exposure even on the nontumor side of the vertebra. This is easily accepted as connected with low morbidity in the thoracic spine.

It is imperative to plan ahead when en bloc resection is entertained. Sometimes a multidisciplinary team of surgeons must be assembled to perform this procedure. This team may include a thoracic surgeon, vascular surgeon, and/or abdominal surgeon, among others. Skilled anesthesia is critical, and postoperative intensive care should be anticipated. Blood products must be at the ready in case rapid infusion is necessary to counteract hypovolemia.

According to WBB planning system, four general types of en bloc resection in the thoracic and lumbar spine can be identified:

• A posterior resection (Fig. 190-2A) for posteriorly occurring tumor (Fig. 190-2B)

• A posterior-only approach (Fig. 190-3A) for vertebral body tumors not expanding in layer A (Fig. 190-3B)

• A staged approach (see Fig. 190-5A) for vertebral body tumors expanding anteriorly in layer A (see Figure 190-5B).

• A posterior-only or staged sagittal resection (see Fig. 190-6A) for eccentrically located tumors (see Fig. 190-6B).

FIGURE 190-2 A, Schematic diagram of a posterior en bloc resection for a posteriorly occurring tumor. B, WBB rendering of criteria for achieving appropriate margin in a posteriorly located tumor: Sectors 4 and 9 must not be affected by tumor.

FIGURE 190-3 A, En bloc resection of the vertebral body by only a posterior approach. B, This technique is appropriate only if vertebral body tumors are not expanding in layer A, because digital blunt dissection is required, provoking violation of the margin if the tumor grows outside the anterior and lateral vertebral body cortex. An oncologically appropriate margin can be achieved if at least one between sector 4 or 9 is not invaded by the tumor. C, After removing the posterior arch and ligating the roots corresponding to the vertebra (or vertebrae) affected by the tumor, the dural sac must be completely released from the longitudinal ligament, cutting the Hoffmann ligament, which could prevent the removal of the vertebral body and is a possible cause of traction on the cord. D, Malleable retractors are positioned around the vertebral body. E, Stability of the spine is ensured by positioning pedicle screws in the adjacent monolateral cranial and caudal vertebrae. One rod is fixed, preferably the one on the side opposite to the determined side of tumor removal. F, A device specifically designed to protect the dural sac is modeled according to the vertebral contour and positioned between the neural structures and the posterior portion of the vertebral body. It is then firmly fixed, with a special instrument, to the rod. G, The Gigli saw is passed under the anterior face of the vertebral body and through the slots of the device specifically designed to protect the dural sac, which prevents it from slipping out of place, possibly damaging the dural sac. Vertebral osteotomy is then performed cranially and caudally and is complete when the Gigli saw touches the posterior portion of the device specifically designed to protect the dural sac. During the osteotomy it is advisable to irrigate the saw with water to allow it to slide more easily. (See the video.) H, The affected vertebra (or vertebrae) can then be removed. The Gigli saw has provided an ideal surface for implanting the vertebral reconstruction device.

En bloc excision from a posterior-only approach is possible for vertebral body or eccentric tumors, but it provides an adequate oncologic margin only for tumors without extension into zone A. For all tumors that extend into zone A we recommend a staged posterior and anterior procedure, the anterior release being the first step. It is our opinion that the staged approaches are safer and allow the best oncologic margins.

The techniques of en bloc resections are based on experience collected since 1991, applying and modifying the original techniques by Stener and Roy-Camille.^1,²

Operative Techniques

Vertebrectomy

Posterior Approach for Vertebral Body En Bloc Resection

The patient is placed in the prone position with both the hips and the knees flexed. Care is taken to avoid compressing the abdominal compartment. The shoulders and iliac crests must be protected to avoid skin breakdown.

A standard midline incision is used to elevate the paraspinal muscles for at least two levels above and below the site of the tumor. For low lumbar tumors this includes exposing the sacrum.

First, spinal instrumentation is implanted. We recommend inserting pedicle screws two levels above and two below, but there are exceptions to this rule: The sagittal alignment should be respected, avoiding ending the construct at the apex of a curve. In this case, one more level should be instrumented. The apex must be assessed on preoperative standing radiographs. Hooks may also be used. One of the advantages of pedicle screws, aside from providing more rigid fixation to the vertebral body, is that the pedicle screws can be used to connect the rod to the anterior construct. This is particularly interesting when carbon fiber cages are used. Another advantage is positioning before any tumor resection, making possible a fast conclusion of the procedure after tumor excision.

Once the screws are positioned, before excising the posterior elements, the lateral side of the vertebra is approached. This step is best and most safely performed before the laminectomy to avoid accidental digital pressure on the dural sac during the blunt dissection. In the thoracic spine, ribs are removed one level above and one level below the tumor. The ribs are also removed from the level of the tumor if they are not involved by tumor. Usually a 10- to 15-cm segment of the rib is removed from the rib head laterally. The pleura is carefully dissected and pushed anteriorly. The lateral aspects of the vertebral bodies are bluntly dissected, and segmental blood vessels are identified and ligated. These vessels run along the sides of the vertebral body toward the neuroforamina.

Next, all the posterior elements not involved by tumor are removed (see Fig. 190-3C). This is necessary to allow visualization of the structures anterior to the spinal cord. Obviously, if tumor involves a portion of the posterior elements such as a pedicle, this is left untouched to be removed during the anterior approach. If both pedicles are involved by tumor, it is still possible to remove the tumor en bloc, but it is less likely that an appropriate margin will be achieved. The uninvolved pedicle is removed with a rongeur or high-speed burr.

The dura must be circumferentially released (see Fig. 190-3C), with particular care to section the Hoffman ligament connecting its anterior surface to the posterior longitudinal ligament (PLL). This is a very difficult step when the tumor expands into the epidural space, with a high risk of tumor spread or dural tear.

If the tumor is not expanding in layer A, the en bloc resection may be finalized by a posterior approach, according to the technique proposed by Roy-Camille ² and by Tomita.³ The blunt finger dissection carefully separates the vertebral body from all the anterior elements. The insertion of the diaphragm at T12–L1 and, caudally, the psoas muscle are a difficult obstacle to this release. Once the dissection is performed, malleable elevators replace the fingers (see Fig. 190-3D) and the final step of the en bloc resection can start.

Before beginning the osteotomy, a rod must be secured to the screws on the side opposite to which the vertebra is expected to be removed. This is to prevent any sudden movement if the spine were to fracture through the osteotomy. The resection can be finalized through the disc or through the bone, depending on the tumor extension and the margin required. Roy-Camille proposed to start with a Gigli saw and then conclude with osteotomes; Tomita proposed a thinner saw and designed special tools to protect the dura and the neural elements to be held by the assistant surgeon. One of us (AG) has developed a special device safely connected to one of the rods (Fig. 190-3F and G), facilitating a complete osteotomy by Gigli saw (see Fig. 190-3H) and fully protecting the dura until the specimen is removed (Fig. 190-4).

FIGURE 190-4 Detail of the resected specimen with the perfect surface of cutting.

The surgical procedure should include an anterior release (Fig. 190-5A) when the tumor is located at the cervicothoracic, thoracolumbar, or lumbosacral junction or if the tumor mass is expanding anteriorly in layer A (Fig. 190-5B). In the junctional area the anterior release by posterior approach is difficult and risky; if the tumor grows anteriorly, the finger dissection by posterior approach is at high risk of opening the tumor capsule and contaminating the area, preventing local and systemic control. In these cases, the posterior approach ends with the blunt dissection of the lateral aspect of the vertebral body not involved by tumor, if it exists.

FIGURE 190-5 A, Staged approach for vertebral body tumors expanding anteriorly in layer A, as detailed by WBB. B, Only the visual control allows leaving a sheet of normal tissue over the tumor. C, Retroperitoneal approach on a patient lying on one side. The contralateral vertebral body has been released and some material has been left. D, Under visual control, once the segmental vessels are ligated and sectioned, a cuff of normal tissue is left as a margin over the tumor. E, The en bloc resection is finalized through the anterior approach.

Before concluding the posterior step in a staged approach, the PLL must be transected at the level of the osteotomy or the posterior part of the disc must be completely excised. In this case it is particularly important to remove as circumferentially as possible the annulus fibrosis, particularly at the side opposite to the anterior approach.

At this point, the rods are connected with the screws and the screw caps are positioned and hand tightened. They are not tightened with the torque wrench because the rods might be modified during the anterior approach. The wound is closed loosely.

Anterior Approach for Vertebral Body En Bloc Resection

The patient is placed on one side in a secure position. An anterolateral skin incision is made. Depending on the level, a thoracotomy, throracolumbar, or retroperitoneal approach (see Fig. 190-5C) is used. Segmental vessels are identified and ligated. A malleable retractor is place between the large vessels and the vertebral body. The tumor mass is identified and a cuff of soft tissue is left to cover it (see Fig. 190-5D), representing the oncologic margin. The posterior incision is reopened. Nearly two thirds of the vertebral body can now be visualized. The blind side is not visualized, but the dissection from the posterior approach has addressed this. The spinal cord is protected.

The remaining disc or bone can now be cut or removed. The osteotomy is finished with an osteotome or high-speed burr or Gigli saw. Copious bleeding should be anticipated during osteotomy. The tumor is now delivered en bloc (see Fig. 190-5E).

Reconstruction of the defect may now ensue. The size of the defect can be measured, and an appropriately sized cage may be inserted. Alternatively, a massive allograft (femoral shaft) may be used. The cage or the diaphyseal graft is preferably filled with autogenous bone obtained during the previous exposure. Connection of the anterior reconstructive device by screws to the posterior construct seems to enhance the stability of the whole construct. As a final step, the screw caps are tightened with a torque wrench.

High thoracic spine sternotomy can be considered, and L5 bilateral retroperitoneal or direct transperitoneal approach may be planned in selected cases. In these cases the anterior release is performed as the first step, with the patient supine. The release ends once all the anterior tumor surface, covered by a layer of normal tissue, is fully released. All other structures are removed by posterior approach performed as the second step in the prone position.

Sagittal Resection

Sagittal resection aims to achieve en bloc resection of a tumor that is growing eccentrically (see Fig. 190-6B). It consists of piecemeal removal of the uninvolved posterior elements to circumferentially release the dura and finalize the resection by a sagittal osteotomy (see Fig. 190-6A). An anterior approach is required when the tumor is growing anteriorly, and a margin of normal tissue must be left under visual control over the tumor, or vital structures must be protected. The dedicated region-specific anterior approach will be necessary to reach the anterior surface of the tumor.

FIGURE 190-6 A, Schematic of the steps required for sagittal resection. This technique may be performed by a posterior-only approach or by staged anterior and posterior approaches. The normal sectors of the posterior arch may be removed piecemeal to perform a circumferential dural release, with section of nerve root(s) or possibly with sacrifice of the area of the dural sac adherent to the tumor. B, WBB staging for eccentrically located tumors.

As an alternative, a T-shaped incision combining a posterior midline and a posterolateral incision may be made. In our experience, this second option has been abandoned because it is associated with a higher risk of local complications ²⁴

One or more neuroforamina are involved by tumor, and the corresponding nerve root(s) must be sacrificed to obtain an appropriate margin.

The posterior dissection is performed in the same way as the posterior step of the vertebrectomy, but a cuff of muscle must be left on the transverse process or ribs if a soft tissue mass extends posteriorly (Fig. 190-7A). The uninvolved posterior elements are removed piecemeal. The dura must be exposed on the side opposite the tumor, and the nerve root(s) entering the tumor must be ligated and sectioned. This allows the dural sac to be completely released from the tumor. In the thoracic spine, the rib above and the rib below are removed and the involved ribs are resected at least 2 cm laterally to the maximal tumor extension. In the lumbar spine the soft tissues are cut by cautery 2 cm from the periphery of the tumor mass.

FIGURE 190-7 A, The most critical step in performing en bloc sagittal resection is the release of the dural sac, allowing the surgeon to ligate and section the nerve root(s) entering the tumor. A cuff of normal tissue must be left around the tumor, and the anterior elements must be protected. In this case, resection of a rib segment allows the surgeon to visualize and protect the element. In many cases an anterior approach is necessary because of a large anterior extension of the tumor. B, The final step of the resection. In the artist’s rendering the action of the retractors is too strong, protecting the dura while the osteotome performs the sagittal section. It is mandatory to avoid overtraction, particularly in the thoracic spine. A malleable retractor is positioned to protect the anterior elements.

Pedicle screws should be implanted two levels above and below the tumor level(s). The sagittal osteotomy can be performed by high-speed burr or osteotomes between the tumor and the dura or on the other side of the dural sac. It is critical to remove the contralateral pedicle so that the dura is not retracted into its hard surface.

Once the vertical cut has been made, two horizontal cuts are made at each end of the vertical cut to complete the osteotomy. If a sheet of silicone plastic (Silastic) or other material has been left, this protectes the anterior structures. The tumor is finally removed in one piece (see Fig. 190-7B).

Reconstruction of the spine can be as simple as removing the remaining discs and placing interbody cages filled with bone, or a reconstructive cage may be used if more than one third of the vertebral body has been taken. When we use a cage that is not connected to the posterior hardware, we use a plate along the sides of the vertebrae for extra support. The rod is now placed back into the posterior screw heads, and the screw caps are tightened with a torque wrench.

Posterior Resection

The posterior resection (see Fig. 190-2A) requires that both pedicles be free of tumor to obtain an oncologically appropriate margin (see Fig. 190-2B). The patient is placed prone as described earlier. A cuff of normal tissue is left over the tumor in the posterior elements. The spine is exposed subperiosteally above and below this level. The spine must be exposed lateral to the end of the transverse processes in the lumbar spine and lateral to the angle of the ribs in the thoracic spine. The dura must be exposed above and below the level of the tumor. Both pedicles must be exposed without contaminating the field.

The pedicles are transected. There are several ways to do this. As described by Tomita,³ the T saw can be passed around the pedicle with the use of a guide. Once the saw is in place, the bone is cut by using a back and forth motion with the saw. Alternatively, a high-speed burr may be used. We prefer a diamond burr because it is less likely to injure the dura as long as it is kept cool with irrigation. Curve rongeurs may also be used to cut the pedicles. The tumor can be lifted away, and any further soft tissue attachments can be removed bluntly or sharply as required. The spine is reconstructed with posterior instrumentation.

Postoperative Care and Rehabilitation

Vertebrectomies and sagittal resections require a stay in the intensive care unit postoperatively. This is usually not the case for posterior-only resections. Once patients are out of the intensive care unit, we allow them to bear weight. In many cases we use a three-point orthosis. This is discontinued at about 2 months.

Complications

Complications are very common after en bloc surgery in the spine. We have a team dedicated to the management of spine tumors, and one of three patients in our series sustained a complication.²⁴ The rate of complication goes up with when surgery is for a recurrence or if more than one level is involved. Staged procedures had a higher rate of complication compared to single-stage approaches.²⁴ This likely correlates with the more technically challenging cases because they are most likely to require staged approaches.

The technical challenges of these procedures cannot be emphasized enough. Some of these tumors are quite adherent to the dura, making dural tear more likely. Previously irradiated tissues have a higher rate of complications. In this setting, a dural tear might not heal, even with primary closure of the durotomy. A lumbar drain is sometimes necessary to help with closure. A blood patch may also be used. Dural tears can lead to CSF leak and depletion with possible subdural hematoma. Infectious meningitis is another possible result.

Damage to the large vessels in the abdomen or chest can lead to rapid blood loss and death. It is wise to consider having a vascular surgeon available to help with large vessel management.

Infections are a problem in part due to the long operative times as well as to the tissue that is necessarily removed, leading to a potential dead space. This is made worse in patients who have been treated with chemotherapy or who are malnourished.

Nonunion and hardware failure are also problems. Again, large portions of bone are removed, making fusion more difficult. It is important to have very stable anterior and posterior stabilization to help mitigate the loss of bone.

Our mortality rate from these surgeries is 2%.¹³ Unfortunately, these tumors eventually cause the demise of most of these patients if they are not removed. This is a critical point to remember. Local recurrence, metastases, and death are all the enemies of these patients. The surgeon carries a large burden when attempting to remove a spine tumor en bloc. The surgery is morbid and death is a possibility from the surgery itself. The patient and the surgeon must understand this before engaging in these cases.