Summary of Key Points
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Histopathologic diagnosis is critical to understanding the natural history, aggressiveness, and likelihood of the tumor to respond to chemotherapy, radiation, or other adjuvant treatments.
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Surgical planning requires knowledge of the tumor grade; its relationship with surrounding osseous, vascular, and neural structures; and the presence or absence of systemic metastasis.
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A multidisciplinary treatment team can create a definitive approach aiming for maximal oncologic control while preserving functional status and spinal stability.
With advancements in spinal imaging and reconstruction/stabilization techniques since the 1990s, surgical treatment of primary spine tumors has improved. These rare tumors constitute less than 5% of all spinal column neoplasms and represent a wide array of histologies. It is estimated that up to 11% of all primary bone tumors reside in the spinal column. Proper diagnosis and careful preoperative multidisciplinary planning are paramount when dealing with patients harboring these lesions. A patient-specific treatment strategy should be based on histology and spinal column location aiming to preserve as much neurologic function as possible, ensure spinal stability, and improve oncologic prognosis. This chapter attempts to define a strategy to stage, plan, and treat primary spine tumors based on histology and location.
Preoperative Planning
Clinical Features and Evaluation
Given the biologic behavior of primary spine tumors, they are typically diagnosed at an earlier age than metastatic tumors. The most common presenting symptoms are pain at night, unremitting pain at rest, and more ominously pain that accompany neurologic deficits. The characteristics of pain must be meticulously quantified and clinically correlated to help prompt diagnosis. One classic example is the nocturnal nagging pain of osteoid osteoma that is dramatically relieved with the use of salicylates. This tumor can also present with torticollis, scoliosis, or kyphosis. Due to the rarity and slow growth of these tumors, they can go undiagnosed and the initial axial pain can progress to radicular symptoms, or progressive neurologic deficits. More aggressive malignant primary spine tumors can cause cord compression, pathologic fractures, and spinal deformities.
Age is an important factor in the differential diagnosis of primary spine tumors. Benign lesions typically occur in younger individuals with an average age of 20 to 30 years old. Malignant tumors vary based on histology with osteogenic sarcoma and Ewing sarcoma occurring in younger patients, whereas chordoma and chondrosarcoma are more common after age 40. The thoracic spine is the most common site, followed by the lumbosacral and cervical spine. Boriani and colleagues reported that more than 80% of malignant primary spine tumors are located within the vertebral body in contrast to benign tumors that tend to occur often in the posterior elements.
Clinical suspicion of a spine tumor should prompt evaluation via diagnostic imaging. Plain radiographs have a low sensitivity, as visualization of the soft tumor is poor in the absence of blastic or lytic components. Computed tomography (CT) and magnetic resonance imaging (MRI) are the gold standards in the diagnosis and indispensable for proper treatment planning. CT scans are used to assess the bony architecture of the involved level and extension of the tumor into the adjacent vertebral bodies. CT scans are also useful for planning the complex osteotomies and reconstruction techniques frequently required in the surgical management of these lesions. MRI is superior in delineating soft tissue structures of both the tumor and the surrounding normal tissue. The addition of gadolinium helps in demarcating the extent of the tumor in relation to normal, nonenhancing tissue. Some tumors have typical imaging characteristics on MRI. For example, aneurysmal bone cysts often have a fluid-fluid level within cystic areas of the tumor as well as blood breakdown products such as hemosiderin. Osteoid osteoma/osteoblastoma frequently have T2 signal change and enhancement that extends far beyond the actual lesion due to inflammation.
Angiography can be an adjunct in the diagnosis as well as a therapeutic treatment of some primary spine tumors. Embolization can be utilized to treat hemangiomas and to decrease the blood supply and consequent intraoperative blood loss in highly vascular tumors such as aneurysmal bone cysts, giant cell tumors, sarcomas, and hemangiomas. Serial embolizations may also provide definitive treatment for aneurysmal bone cyst.
Biopsy for Histopathologic Diagnosis
Biopsy is one of the most important steps in the management of primary bone tumors. Although the radiologic evaluation can provide clues to the diagnosis, it is typically not definitive. Histopathologic diagnosis is critical to understanding the natural history, aggressiveness, and likelihood of the tumor to respond to chemotherapy, radiation, or other adjuvant treatments. Proper histopathologic diagnosis is paramount in the decision making and for the selection of surgical strategies and reconstruction techniques.
Tissue sampling for histopathologic analysis is usually obtained by fine-needle aspiration (FNA) and, preferably, by core needle or trocar biopsy. The core biopsy has the advantage over FNA of providing more tissue and better preserving the tissue architecture for the pathologists. The chosen method should limit the amount of normal tissue and compartments that are traversed to avoid seeding of the tumor along the biopsy path. Transvisceral (transoral, transrectal) biopsies are particularly discouraged. The clinician performing the biopsy, if not the spine surgeon, should discuss the planned site and trajectory with the spine surgeon to ensure the biopsy tract can be excised at the time of definitive surgery if at all possible. The most common biopsy method is CT-guided core needle biopsy. This technique has greater than 80% diagnostic accuracy with some reports upward of 93%, a low rate of morbidity, and the least likelihood of extralesional spread of tumor cells. Open biopsy is also discouraged, as it leads to contamination and violates oncologic principles of resection for primary bone tumors.
Oncologic Staging
Once the histologic diagnosis has been made, proper oncologic staging is the next step in the workup of primary spine tumors. The key components of staging are to (1) establish the tumor grade; (2) define the relationships between the tumor and surrounding osseous, vascular, and neural structures; and (3) evaluate the presence or absence of metastasis. Once the tumor is properly staged, a multidisciplinary treatment team can create a definitive approach aiming for maximal oncologic control while preserving functional status and spinal stability.
Enneking developed one of the first staging systems for primary bone tumors ( Table 113-1 ). This system was developed for musculoskeletal tumors and has proved effective in guiding surgical intervention for limb lesions. The system has been applied to primary tumors of the spine with oncologic success. Based on tumor grade (G), extent (T), and presence of metastases (M), tumors are staged. Benign tumors are divided into three stages: S1, S2, and S3. The S1 stage is a latent or inactive tumor that is surrounded by a sclerotic rim of bone within the vertebral body and causes no symptoms and needs no treatment. S2 lesions are active but slower-growing lesions that can cause mild symptoms and are typically surrounded by a thin rim of reactive tissue. An intralesional resection can be performed with a low rate of recurrence on these lesions. An S3 lesion is a more aggressive rapidly growing benign tumor (aggressive osteoblastoma, benign fibrous lesions, giant cell tumors) with a thin discontinuous capsule that invades surrounding compartments and creates a pseudocapsule. Intralesional resection of these lesions can lead to higher rates of recurrence, so wide margin or en bloc resection is the modality of choice provided the morbidity is acceptable.
| Tumor Behavior | Stage | Description | Resection Strategy | |
|---|---|---|---|---|
| B enign | Latent | S1 | Completely contained within a well-defined capsule, asymptomatic, no metastasis | No surgical management unless for decompression or stabilization |
| Slow growth | S2 | Thin pseudocapsule, confined to bone | Intralesional excision ± adjuvant therapy | |
| Aggressive growth | S3 | Incomplete or absent capsule, wide reactive extravertebral pseudocapsule | Marginal en bloc resection | |
| M alignant | Low grade, confined to vertebra | IA | Slow growth, thick pseudocapsule with microscopic islands of tumor invasion | Wide en bloc resection |
| Low grade, with paravertebral extension | IB | Slow growth, thin or incomplete pseudocapsule with microscopic islands of tumor invasion | Wide en bloc resection | |
| High grade, confined to vertebra | IIA | Rapid growth, no pseudocapsule, contained inside the vertebra, may have microscopic seeding in surrounding tissues | Wide en bloc resection + adjuvant therapy | |
| High grade, with paravertebral extension | IIB | Rapid growth, no pseudocapsule, direct extension to epidural, and paravertebral tissue with satellite nodules | Wide en bloc resection + adjuvant therapy | |
| Any grade with systemic metastasis, confined to vertebra | IIIA | Rapid growth, no pseudocapsule, contained within vertebra but may have microscopic seeding in surrounding tissues, with systemic metastasis | Palliative | |
| Any grade with systemic metastasis, with paravertebral extension | IIIB | Rapid growth, no pseudocapsule, direct extension to epidural, and paravertebral tissue with satellite nodules, with systemic metastases | Palliative |
Enneking’s system divides malignant tumors into three stages as well (see Table 113-1 ), with each stage further subdivided into type A lesions—where tumor remains within the confines of the vertebra—and type B lesions—where tumor extends beyond the vertebra into adjacent soft tissues. Stage I lesions are low-grade, slow-growing malignancies surrounded by a thick pseudocapsule, which contains microscopic rests of tumor tissue and should not be violated during an attempt at surgical resection. Preferably, these tumors are removed en bloc with as wide a surgical margin as possible, if surgical morbidity related to sacrifice of neurovascular structures permits a reasonable functional outcome. Stage II tumors are high-grade lesions whose rapid growth may preclude formation of a pseudocapsule. These are associated with seeding of the surrounding tissues, with satellite nodules, skip metastases, pathologic fractures, and epidural extension. Due to the higher grade, less-defined capsule and increased risk of spread beyond the primary mass, achieving en bloc resection with wide margins may be more difficult. Therefore, adjuvant chemotherapy or radiation is vital for both local control and to prevent distant metastases. Stage III lesions are similar to stage II tumors in their malignant growth pattern but distinct in having metastasized to regional lymph nodes or distant organs.
Surgical Staging
Once a primary spinal tumor has been staged using Enneking’s principles and an en bloc resection is recommended, a surgical staging system is useful to plan the complex vertebral osteotomies needed to remove the tumor intact while sparing the neurologic structures. Such a system was initially introduced by Weinstein and colleagues in 1987 and underwent subsequent revisions. It is now known as the Weinstein, Boriani, Biagini (WBB system) ( Fig. 113-1 ). The WBB system relates tumor location in the transverse plane of the vertebra into 12 radiating zones centered on the center of the spinal canal. These zones are numbered 1 through 12, and zone 12 is located at the spinous process. This system also divides the vertebra into five layers, named A to E, from the paravertebral compartment to the dura, respectively. By superimposing the tumor on the WBB vertebra, the location of the tumor can be described and the proposed osteotomies can be placed appropriately. The location of the tumor then determines the type of procedure that is performed. For example, tumors located in zones 4 to 8 or 5 to 9 are suitable for en bloc resection. These locations allow the surgeon to remove the noninvolved lamina and pedicle via a posterior approach, thus freeing the neural structures from the diseased vertebra. En bloc resection of the involved vertebra can then be performed by a second anterior approach or, if in the thoracic spine where nerve roots may be sacrificed, from the same posterior approach used to remove the lamina. Tumors that are located in zones 2 to 5 or 8 to 11 require the spine to be divided in the sagittal plane. These are typically approached from both a posterior and anterior staged or combined approach. The posterior approach allows the involved pedicle/facet/posterior vertebra to be separated and the spine to be stabilized. The simultaneous or staged anterior approach allows the remaining vertebra to be divided, the resection to be completed, and the anterior column to be reconstructed, if necessary ( Fig. 113-2 ).
Oncologic Surgical Approaches
As stated previously, the approach to primary bone tumors of the spine depends on the oncologic staging to determine the type of resection and margin, followed by the surgical staging to determine how best to achieve this margin. For benign tumors requiring an intralesional resection, the surgical approach is geared toward accessing the lesion and stabilizing the spine. It is not dissimilar from the approach to metastatic disease except that the excision must be complete in order to decrease the likelihood of recurrence. For aggressive benign or malignant tumors, the goal is en bloc resection with clear margins. In most cases, this will involve a posterior release (spinal canal opened in areas of normal and thecal sac protected) with spinal stabilization and an anterior or lateral approach to complete the osteotomies required to release the diseased vertebra and reconstruct the spine if necessary. The order of the approaches, whether they are staged or simultaneous or whether additional approaches are needed (i.e., opposite chest), depends on the anatomic distribution of the tumor and surgeon preference. The following sections review some of the regional approaches utilized to obtain the extensile exposures necessary for these complex surgical procedures.
Craniocervical Junction
The anatomic complexities of the craniocervical junction (CCJ) have historically given spine surgeons limited ability to perform complex tumor resections. Access is challenging particularly for en bloc resections that require access to the margins around the tumor. Utilizing collaborative approaches with our colleagues in head and neck surgery, and capitalizing on advances in image guidance and spinal stabilization, previously unresectable tumors can be safely removed.
There are five corridors to approach the CCJ: anterior, anterolateral, lateral, posterolateral, and posterior. All of these are utilized, both alone and in combination, to achieve access in this region. The posterior approach is the most commonly used. It is familiar to all spine surgeons, is the most straightforward route for locating and protecting the neurologic elements, and is the primary site for stabilization across the craniocervical junction. The occipital condyles and suboccipital region can all be accessed via this midline posterior approach.
The anterior approach, initially described by Fang and Ong in 1962 utilizing a transoral transpharyngeal route, has undergone significant improvement since its initial description. This surgical exposure allows access from the inferior third of the clivus down to the C2 vertebral body. Dividing the mandible provides further caudal exposure of the C3 vertebra. This can be coupled with LeFort maxillotomies or the transoral transpharyngeal extended maxillotomy approach to gain access from the entire clivus down to the upper cervical spine. These transoral approaches are limited in that they are transvisceral (contamination risk) and provide only a narrow width of exposure. They may be used for intralesional excision of small, benign lesions but are not useful for en bloc excision of aggressive benign or malignant histologies.
To access anterolateral lesions of the CCJ, one approach that has gained popularity is the high transcervical approach with mandibular swing. This offers excellent vascular control due to its wide exposure from as far cephalad as the infratemporal fossa to as caudal as the midcervical spine. The high transcervical approach can also be combined with a transmandibular lateral circumglossal approach to improve access to the upper midline structures. As entry into the pharynx is contraindicated with primary malignant bone tumors, a retropharyngeal exposure can be added. This provides a direct exposure of the lower clivus, foramen magnum, atlas, axis, and middle cervical spine and allows for arthrodesis if indicated. This approach has a risk of injury to the carotid sheath contents, laryngeal nerve and vessels, and the hypoglossal nerve, and we utilize the expertise of our head and neck surgeons to protect these structures. A more tangential approach to this area providing excellent vascular control and requiring dissection of only the spinal accessory nerve is the lateral transcervical approach; however, its utility is limited to only the most lateral lesions. In most cases, en bloc resection requires a combination of approaches based on surgical staging. The approaches must also account for management of the vertebral arteries.
Cervical Subaxial
There are two standard approaches to the subaxial cervical spine: the anterior cervical approach popularized in the 1950s commonly used for exposures of the anterior vertebral body and disc spaces from C3 to C7 and the posterior midline approach, which has been the mainstay of treating cervical spine pathologies for more than a century. These approaches can be combined to resect the majority of primary bone tumors in the subaxial cervical spine.
Depending on the location of the tumor and the surgical staging, the spinal cord, nerve roots, and vertebral arteries are typically separated from the tumor during the posterior approach. Nerve roots or a single vertebral artery that are within tumor must be considered for sacrifice. Stabilization is also performed during the posterior approach. With the spinal ring opened in areas of normal composition, and with these vital structures separated, the anterior approach may be used to complete the osteotomies necessary to free the diseased vertebra and resect it. Anterior column reconstruction can then be performed.
For tumors with major paravertebral extension, collaboration with head and neck surgeons can be helpful for protecting and preserving soft tissue structures within the neck including nerves, vessels, and viscera ( Fig. 113-3 ).
Cervicothoracic Junction, Thoracic, and Lumbar Spine
Like the craniocervical junction, the cervicothoracic junction is another challenging spinal region in which to apply Enneking’s principles. Given the anatomic complexity, the spine surgeon needs to be familiar with anterior, lateral, and posterior exposures in order to treat primary spine tumors of this region. Furthermore, the surgeon must understand where the limits of each approach overlap, so that they can be combined effectively. In this region, it is useful to collaborate with the thoracic surgeons who are familiar with the various transthoracic routes to the apex of the chest.
The posterior approach is familiar to most surgeons and allows exposure of the posterior vertebral elements and the dorsal dural tube. If additional anterior exposure is needed, this approach can be extended to include resection of the transverse process, facet joints, and the head of the rib, allowing access to the posterior and lateral portions of the vertebral body. For lesions at T2 and below, the nerve roots can be sacrificed, dissection can be performed circumferentially around the vertebra, and the vertebra can be removed from an all posterior approach as described by Tomita. This strategy will not work at T1 where the nerve roots provide hand function and cannot be sacrificed. Moreover, for tumors with significant paravertebral extension, the blind dissection from a posterior approach increases the risk of inadvertent entry into the tumor. In these cases, a combined approach allowing for direct anterior visualization is preferred.
A standard low anterior cervical approach with a paramedian incision medial to the sternocleidomastoid down to the sternal notch usually allows access from C6 to T1-2. When necessary a supraclavicular extension will allow wider exposure with access to the lung apex, lower brachial plexus, and lateral body of T1.
Transsternal approaches can be added to the low anterior cervical approach in order to extend anterior access caudally from C4-T4. The limitation of these approaches is that they are narrow and become less effective for lesions that extend beyond the vertebra and into the chest. When combined with an anterior thoracotomy, this approach is termed the clamshell or trapdoor . These patients are intubated utilizing a double-lumen endotracheal tube to enable deflation of the ipsilateral lung. The “J” incision is carried out medial to the sternocleidomastoid muscle down to below the fourth intercostal space. The pectoralis is divided proximal to its insertion on the sternum for reapproximation. The sternum can then be split from the notch of the manubrium to the fourth intercostal space. The spine is most easily accessed from the right chest as the heart and great vessels are not in the way. Division of the azygos vein allows the posterior mediastinal structures to be elevated away from the spine. If necessary an interaortocaval subinnominate window can be created to facilitate placement of stabilizing devices onto the anterior aspect of T3-5.
For the remaining thoracic and lumbar spine, the posterior approach is the most commonly utilized surgical route. Benign lesions located in the posterior elements are directly accessed by a standard posterior midline approach. Extracavitary, transpedicular, or posterolateral techniques can allow for circumferential decompression of the spinal cord and a multitude of stabilization options. This is particularly true in the thoracic region where the nerve roots can be sacrificed. For aggressive benign or malignant primary tumors requiring en bloc resection, the posterior approach provides access to the spinal canal. Application of the WBB staging system to divide the spinal ring in areas of normal allows the planning of complex osteotomies aiming for en bloc removal of the diseased bone while avoiding excessive manipulation and trauma to the spinal cord. Circumferential extracavitary dissection around the vertebra can be performed in the thoracic and upper lumbar spine by ligating the nerve roots. The entire vertebra can be freed completely around its circumference and resected en bloc via the posterior approach. Stabilization and reconstruction can also be performed and the entire spondylectomy can be completed by a single posterior approach ( Fig. 113-4 ). Limitations to the all posterior en bloc resection include significant paraspinal extension or involvement of thoracic structures that must be freed or sacrificed under direct vision. Figure 113-5 shows an example of a tumor with significant paraspinal extension involving WBB zones 8 to 10. This tumor requires a sagittal osteotomy and chest wall resection. A staged posterior, followed by a combined posterior-anterior approach, is utilized to safely complete the osteotomy, mobilize the chest structures, and remove the tumor in one intact piece. Although this case could conceivably be performed via an all posterior approach, circumferential dissection would be challenging and risk injury to vital vascular and visceral structures, as well as inadvertent entry into the tumor mass.
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