Surgical Management of Chordomas and Chondrosarcomas of the Cervical Spine

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Introduction

Chordomas are rare primary bony tumors that arise from embryonic remnants of the notochord. They are low-grade malignant tumors that make up 1%–4% of all primary malignant bone tumors and can occur throughout the spinal column from the clivus to coccyx, but are most common in the clivus and sacrum. In addition to plasmacytomas, they are the most common primary malignant tumors of the mobile spine. Chordomas of the mobile spine originate in ectopic chordal rests within the vertebral body. They are infiltrative and can occupy most of the vertebral body by invading cancellous bone, but tend to spare intervertebral discs. Although they are slow-growing lesions, recurrence is inevitable if they are not treated appropriately. They often recur locally and can metastasize in late stages, most commonly to the lungs, liver, brain, bone, skin, and soft tissues. In general, treatment of chordomas consists of en bloc resection, surgery with radiation, or palliative radiation alone. Chordomas have a unique tendency to recur after intralesional excision or biopsy tract contamination, seeding of tumor along the wound tract, or intradural spread. Therefore, tumors should be excised with wide margins and, if a previous biopsy tract exists, it should be included in the resection.

Chondrosarcomas are the second most common primary malignancy of bone and arise from cells of chondroid origin throughout the axial and appendicular skeleton. Like most primary bony tumors, they are locally aggressive, but unlike other sarcomas, the histologic grade has prognostic significance. As such, preoperative biopsy provides important prognostic information about the lesion’s growth potential. Definitive treatment of these lesions consists of en bloc resection since conventional chemotherapy and radiation alone are relatively ineffective. Chordomas and chondrosarcomas often require high doses of radiation that exceed the tolerance of the spinal cord, which is generally estimated at 50 Gy.

Surgical Management

In general, treatment of cervical chordomas and chondrosarcomas consists of en bloc resection, resection with radiation, or palliative radiation alone. They must be approached carefully since they have the potential to recur locally after intralesional excision, biopsy tract contamination, seeding along the wound, or intradural spread. Tumors should be resected with wide margins and prior biopsy tracts, particularly in the case of chordomas, must be included in the resection. In one institutional series, local recurrence rates for complete en bloc resection without contamination of the surgical wound were 28%, while in cases in which the tumor capsule was entered, the recurrence rate was more than double, at 64%. This type of wide en bloc resection or radical extralesional surgery provides an opportunity for durable treatment, particularly when combined with adjuvant radiation. Recurrence-free survival is also associated with extent of resection; mean time from surgery to local recurrence after radical resection was over 2 years compared to 8 months in those undergoing subtotal resection.

Since chordomas and chondrosarcomas are relatively resistant to medical management, including radiation therapy and chemotherapy alone, en bloc resection with clear margins yields optimal survival. However, in the cervical spine, en bloc resection requires special preoperative considerations, the most important of which is determination of the extent of tumor invasion into adjacent anatomic structures. Vascular imaging such as CT angiography, MR angiography, and digital subtraction angiography assess the involvement of key vascular structures, specifically the vertebral and carotid arteries. In the event of vertebral artery involvement, balloon test occlusion is used to determine the viability of vertebral artery sacrifice, which can usually be performed to aid in complete en bloc resection. If vertebral arteries cannot be sacrificed, it is important to involve vascular surgeons to aid in reconstruction of the artery with a bypass graft, however such aggressive approaches are generally reserved for tumor recurrence.

When planning the surgical approach, it is important to consider involvement of adjacent structures. The Weinstein-Boriani-Biagini (WBB) staging system aids preoperative planning. It involves analysis of the spine in the axial plane with the patient prone. The spine is separated into 12 segments, similar to the numbers on a clock, and five levels of depth, from superficial to deep: A (extraosseous soft tissue), B (intraosseous/superficial), C (intraosseous/deep), D (extraosseous/extradural), and E (extraosseous/intradural). Although small case numbers preclude use of this system for analyzing surgical outcomes, it is useful for planning en bloc resections, particularly when assessing areas of planned marginal transgressions.

Cervical anatomy poses unique challenges. To best achieve an en bloc resection, a two-stage anterior and posterior approach is often utilized. The first stage involves resection of posterior elements of the cervical spine and osteotomies through one or both pedicles. The second stage involves parasagittal osteotomies through the involved vertebral bodies or transverse foramina. High cervical lesions, for example those involving C2, pose a unique challenge. For lesions primarily based at C2, we prefer a mandibulotomy approach with midline glossotomy as needed, but for lesions based in the subaxial spine with significant C2 involvement, we use a transmandibular retropharyngeal circumglossal approach. For the majority of other lesions based in the subaxial spine, we use a standard transcervical approach, but if these lesions are large we utilize a bilateral transcervical approach and work through both exposures.

For resection of posterior elements, standard perioperative antibiotics and steroids are administered preoperatively. We follow somatosensory-evoked potentials, motor-evoked potentials, and electromyography throughout the case. Since most cervical chordomas and chondrosarcomas are ventrally based and adjacent to the trachea, pharynx, esophagus, and carotid sheath, a wide margin of excision from the biopsy tract is not always possible. Wide exposure of bilateral lamina and lateral masses is necessary, followed by posterior fixation three levels above and below the planned osteotomy. If required, fixation can extend to the occiput. In the upper cervical spine, we prefer C1 lateral mass screws and C2 pedicle screws if needed. Once fixation of uninvolved segments is complete, attention is turned to wide laminectomies through uninvolved bone. Inferior and superior articular processes are removed; pediculectomy through the uninvolved pedicles follows. For more lateralized tumors, the pediculectomy is performed on the side of ventral tumor involvement, and bilateral pediculectomies are performed for large midline tumors. In some cases, particularly in the upper cervical spine, nerve roots can be sacrificed to improve exposure prior to pediculectomy. At this point, after the vertebral artery is secured with Weck clips, it is divided to sacrifice. After removal of the posterior elements, posterior fixation is completed and a silicone rubber sheet is placed between the ventral tumor surface and the dura.

Attention is then turned to en bloc resection of the anterior column and tumor. We prefer to perform this in staged fashion on a separate operative day. Discectomies are performed above and below the planned resection and the posterior longitudinal ligament is resected. A parasagittal osteotomy is performed through the involved vertebral body down to the silicone rubber sheet. This technique preserves oncologic margins while removing multilevel chordomas en bloc. The location of the osteotomy depends on tumor location; osteotomy cuts are shown in Fig. 25.1 for lateralized tumors involving less than 50% of the vertebral body (line 1) or less than 75% of the vertebral body (line 2). For tumors involving greater than 75% of the vertebral body, the osteotomy cuts lie at the very edge of the vertebral body or, in cases of complete spondylectomy, on the transverse process at the foramen transversarium with associated mobilization of the vertebral artery (line 3). Once the vertebral artery is safely mobilized, the involved vertebral bodies are removed en bloc. In cases of obvious tumor transgression, dural sealant or bone wax can seal the area of unintentional contamination. Of note, chondrosarcomas have a greater propensity for dural invasion than do chordomas. Dura containing tumor should be resected with a dural substitute placed over the defect. These substitutes are relatively inexpensive, form a good barrier for tumor invasion, and have low antigenicity and toxicity. Additionally, they have a low propensity for forming adhesions to adjacent anatomic structures. When completing the en bloc vertebrectomy, a Caspar pin can be inserted into the specimen to help manipulate it as it is removed. Once the tumor has been resected, the anterior column is reconstructed with an expandable cage and anterior plating. In challenging cases, maxillofacial screws can fit through the titanium mesh cages and stabilize the cage directly to bone. For surgery of a tumor recurrent after radiation or for cases of pseudarthrosis, vascularized autograft fibula can be considered for fusion. This en bloc resection is associated with good outcomes in patients with cervical chordomas and chondromas; rates of disease-free survival are 88% and 74% at 1 and 5 years. Cervical chordomas of the upper cervical spine (C1 and C2) pose unique challenges compared to those of the subaxial cervical spine (C3 to C7). Comparisons of outcomes after attempted en bloc resection for upper cervical spine and subaxial spine chordomas found that although chordomas of the upper cervical spine were associated with less favorable margins, higher rates of complications (severe dysphagia, pharyngeal erosion or dehiscence, and implant failure), and increased tumor recurrence, there were no differences in overall survival.