Spondylectomy for Spinal Tumors

Summary of Key Points

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In the cervical spine, the vertebral arteries must be carefully assessed for tumor involvement and to determine whether they can be sacrificed.
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T2-12 thoracic nerve roots can be sacrificed with minimal functional loss.
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The preparatory and delivery stages can all be done from a dorsal approach or from combined dorsal and ventral approaches depending on the tumor location and involvement of visceral structures ventral to the spinal column.
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If at least one S3 nerve root is preserved, there is a 67% chance that the patient will still have bowel/bladder function.
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Careful preoperative planning and consideration for postoperative adjuvant therapy are essential to optimize patient outcome.
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Spinal reconstruction should be designed to withstand the biomechanical stresses placed on the instrumentation, especially before complete bony fusion occurs.
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Plastic surgery closure should be considered in extensive dissections to optimize wound healing and reduce postoperative wound complications.

Spondylectomy involves the removal of an entire segment of the spine, including the vertebral body, pedicles, superior and inferior articulating processes, pars, transverse processes, lamina, and spinous process. En bloc resection of the entire spinal segment is possible only with sacrifice of the spinal cord or the cauda equina, as these two structures lie within the spinal canal and are surrounded by the spine. If the tumor is within the spine, it can be removed either in piecemeal fashion (intralesional) or en bloc (in one piece, without violation of the tumor margin). The technique of a total spondylectomy can be utilized to achieve an en bloc resection of the tumor ( Fig. 117-1 ). In such cases, the tumor is resected en bloc, but as a point of semantics, the spondylectomy is usually not an en bloc spondylectomy.

Techniques for en bloc tumor resection are complex and entail significant risk to the patient. These techniques are reserved for specific tumor pathologies that oncologically may benefit from such resection. In general, when such an operation is considered, the lesion should be a solitary tumor without evidence of metastasis. The most common indication for an en bloc resection is malignant primary bone tumors when resection may result in cure or long-term, tumor-free survival for the patient. Pathologies benefitting from en bloc tumor resection include chordoma, chondrosarcoma, and osteosarcoma. Less aggressive primary bone tumors for which en bloc resection is also contemplated include giant cell tumor, aneurysmal bone cyst, osteoid osteoma, and osteoblastoma. There are certain circumstances of solitary metastasis to the spine (such as renal cell carcinoma or breast cancer), in which some oncologists may advocate the use of this technique for local tumor control. This is a highly contentious area of debate, and the surgical approach to tumor resection is evolving, especially with the advent of other adjunctive therapies such as stereotactic radiosurgery for the spine.

General Concepts and Surgical Planning

The anatomic location and the particular vertebral level of the tumor to be removed will dictate the steps in achieving an en bloc resection via a spondylectomy. For simplicity, the surgical plan can be divided into two stages: a preparatory stage and a stage in which the tumor is delivered. Accomplishment of the first stage, the preparatory stage, may involve multiple procedures before the tumor is ready to be delivered.

The preparatory stage focuses on freeing the tumor from the surrounding structures so that it can be delivered while the spinal cord and critical nerves and blood vessels are protected with minimal functional sacrifice. In the delivery stage, the focus is on delivering the specimen in an en bloc fashion. As a general rule, the preparatory stage is performed on the side of the spinal cord, or thecal sac, opposite the tumor. A spinal segment can be thought of as a ring of bone that encases the spinal cord. For a portion of that ring to be delivered away from the spinal cord, an area of it has to be resected, creating a window that is at least as large as the diameter of the spinal canal. The vertebral segment around the tumor specimen is dissected as much as possible to mobilize the specimen during the preparatory stage so that it can be easily delivered in the final stage. This allows the spinal cord and dura mater to pass through this window as the remaining portion of the ring, with the specimen, is delivered away from the cord.

In certain instances, vascular and neurologic structures may need to be ligated and cut to free the en bloc specimen. The anticipated vascular complication and the neurologic deficit produced from doing so must be thoroughly understood and discussed with the patient before proceeding with the treatment. Some tumor architectures involve more aggressive sacrifice of vascular and neurologic structures that result in significant morbidity, the consequences of which must be balanced against the potential oncologic benefit and the patient’s acceptance of a life with the expected permanent handicap that may result.

The vascular structures involved in the tumor resection vary at different levels of the spine. In the cervical spine, a vertebral artery may need to be ligated and cut to achieve a resection; doing so might result in posterior fossa ischemia and stroke. When performing an en bloc tumor resection in the thoracic spine, multiple segmental vessels may need to be ligated, increasing the risk of ischemia to the spinal cord. In the lumbar spine, the iliac vessels may need to be manipulated or even bypassed, potentially resulting in ischemia to the bowel, kidneys, or lower extremities. Manipulation of the inferior vena cava and iliac vessels also increases the chance for thrombus formation and consequent pulmonary embolus.

Sacrifice of neurologic structures should be considered only if the deficit that will be produced is tolerable to the patient’s expectations and lifestyle acceptance. Transection of a certain root alone might not produce a significant deficit, but combinations of roots sacrificed may be crippling ( Table 117-1 ). C1-2 can be sacrificed without significant morbidity. Sacrifice of C3 and C4 together may weaken the diaphragm but individually will not likely have any deleterious effects. Cutting C5, C6, C7, C8, or T1 results in profound weakness in the muscle groups of the upper extremities. Sacrifice of the T2-12 thoracic nerve roots results in a bandlike distribution of numbness but usually has inconsequential motor loss. Sacrifice of L1 or L2 in isolation may produce hip weakness, but over time, patients usually are able to compensate for the loss. L3 loss results in quadriceps weakness and may require bracing of the knee to walk. L4 sacrifice may also result in quadriceps weakness, but the problem that is more commonly noted is proprioceptive difficulty of the knee joint. Without proper proprioception of the knee, a patient may find the knee weak and can complain of the knee buckling during ambulation. L5 loss results in footdrop. Sacrifice of S1 is usually well tolerated but does result in gastrocnemius weakness, which can make it difficult for a patient to stand on the toes. Loss of bilateral S2 and S3 nerve roots results in loss of bowel, bladder, and sexual function. Preservation of at least one S3 nerve root has been found to preserve bowel/bladder function in two thirds of patients. In regard to sexual function, similar trends have been observed where unilateral sacral resection still preserves overall function although there is numbness on the side of the resection. S4, S5, and the coccygeal nerves can be sacrificed without significant consequences.

TABLE 117-1

Deficits from Specific Nerve Root Sacrifice

Nerve Sacrifice	Deficit
C3 and C4	Possible diaphragm weakness
C5	Deltoid weakness
C6	Bicep weakness
C8 or T1	Hand intrinsic weakness
T2–T12	Dermatomal sensory loss
L1 or L2	Iliopsoas weakness, usually compensated over time
L3	Quadriceps weakness
L4	Quadriceps weakness, knee proprioceptive difficulty, and footdrop
L5	Footdrop
S1	Minimal deficit
Unilateral S2 and S3	Bowel/bladder/sexual function abnormal but functional
Bilateral S2 and S3	Loss of bowel/bladder/sexual function
Bilateral S3 with S2 sparing	Some bowel/bladder/sexual function
S4, S5, and coccygeal nerves	Dermatomal sensory loss

When contemplating a surgical approach, it is important to plan for adjunct therapies. Special considerations must be taken if there is a chance of requiring high-dose radiation therapy such as proton beam irradiation postoperatively. Structures at risk of injury from the radiation may benefit from repositioning or from protection with complex plastic surgery flaps. Certain approaches, such as the transoral and transmandibular approaches, which have considerable risk of postoperative pharyngeal dehiscence and mandibular pseudarthrosis may need to be avoided if there are plans to use adjuvant proton beam radiation therapy.

For simplicity, this chapter describes the technique for en bloc resection starting in the cervical and cervicothoracic spines, followed by the thoracic spine and then the lumbar and sacral spine. Nuances for each section of the spine will be discussed in more detail. This chapter does not describe the techniques of en bloc sacral resections.

Level-Specific Challenges

Cervical Spine and Cervicothoracic Junction (C2-T1)

Anatomic Considerations

The cervical region has complex anatomy that needs to be considered prior to the undertaking of a spondylectomy in that region. The key anatomic structures that determine the feasibility of en bloc tumor resection in the cervical spine are the vertebral arteries. En bloc resection of a tumor without causing neurologic devastation is only feasible if the tumor does not involve both vertebral arteries and if the vertebral artery that is preserved is able to provide sufficient blood supply to the posterior fossa after tumor resection. Studies thus need to be performed in the preoperative period to (1) determine the extent of tumor involvement with the vertebral arteries and (2) determine the extent that each vertebral artery supplies the posterior fossa circulation. The former can be determined with magnetic resonance angiography (MRA) or even with computed tomography angiography (CTA). If the tumor involves only one of the vertebral arteries ( Fig. 117-2 ) potentially requiring sacrifice of that vertebral artery, then it must be determined preoperatively whether the contralateral vertebral artery provides sufficient vascular supply to the brain. This can be undertaken by determining which artery is dominant by comparing the calibers of the vertebral arteries on CTA or MRA. If the tumor involves only the non-dominant vertebral artery, then no further investigation is usually required. If the dominant artery involved in the tumor or dominance is not clear, then ancillary testing should be utilized. A conventional four-vessel diagnostic cerebral angiogram is helpful in assessing the patency of the circle of Willis to determine whether the anterior circulation could possibly provide the blood supply to the posterior circulation. In addition, a vertebral artery balloon occlusion test can be performed to assess whether there is sufficient blood flow from the other blood vessels to the brain after occluding the vertebral artery that may be sacrificed in the operation. Even if the preoperative angiogram suggests that a patient may tolerate unilateral sacrifice of a vertebral artery, this must be undertaken with caution, and oftentimes a temporary clip is applied to the vertebral artery and signals (i.e., somatosensory evoked potentials, brain stem auditory evoked potentials) are monitored before the vertebral artery is ligated and transected. Other complications to be aware of postoperatively include vasospasm, emboli from the ligated vertebral artery, or thrombosis of the remaining vertebral artery.