Oncological Approaches, and Outcomes for Primary Spine Tumors

Clinical Features and Evaluation

Unlike metastatic tumors to the spine, primary spine tumors are typically diagnosed at an earlier age. The most common presenting symptoms are pain at night, unremitting pain at rest, and, more ominously, pain that accompanies neurological deficit. Patients can also present with radicular pain, sensorimotor dysfunction, or bowel/bladder dysfunction. ^, Malignant primary spine tumors can grow rapidly and can cause cord compression, pathological 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 of occurrence, followed by the lumbosacral and cervical spine. ^{, ,}

Clinical suspicion of a spine tumor should prompt evaluation via diagnostic imaging. Computed tomography (CT) and magnetic resonance imaging (MRI) are the gold standards in the diagnosis. CT is also useful for planning the complex osteotomies and reconstruction techniques frequently required in the surgical management of these lesions. MRI is superior in delineating neurovascular and soft tissue structures involved with, or adjacent to, tumor. The addition of gadolinium helps in demarcating the extent of the tumor in relation to normal, nonenhancing tissues.

CT-angiography, magnetic resonance angiography, or digital subtraction angiography can be used to determine tumor vascularity and surrounding important vasculature structures (such as vertebral arteries), and for endovascular embolization before surgical resection of some primary spine tumors, such as aneurysmal bone cysts, giant cell tumors (GCTs), sarcomas, and hemangiomas. Serial embolization may also provide definitive treatment for aneurysmal bone cysts.

Biopsy for Histopathological Diagnosis

Biopsy is one of the most important steps in the management of primary bone tumors. Although the radiological evaluation can provide clues to the diagnosis, it is typically not definitive. Histopathological diagnosis is critical to understanding the natural history, aggressiveness, and likelihood of the tumor to respond to chemotherapy, radiation, or other adjuvant treatments. The most common biopsy method is CT-guided core needle biopsy. This technique has greater than 80% diagnostic accuracy, ^, a low rate of morbidity, and the least likelihood of extralesional spread of tumor cells. Transvisceral (transoral, transrectal) and open biopsies are particularly discouraged. The biopsy tract should be marked so that it can be excised at the time of definitive surgery if possible.

Oncological Staging

Once the histological diagnosis has been made, proper oncological staging is the next step. The key components of staging are to: (1) establish 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.

Enneking developed one of the first staging systems for primary bone tumors ( Table 153.1 ). 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 oncological success. ^, Tumors are staged based on tumor grade, extent, and presence of metastases. S1 to S3 are benign tumors. The S1 stage is a latent or inactive tumor that is surrounded by a sclerotic rim of bone within the vertebral body. These tumors typically are asymptomatic, and require no initial intervention. 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, GCTs) 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. ^{, ,}

Malignant tumors are divided into three stages (see Table 153.1 ), 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 that 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, satellite nodules, skip metastases, pathological fractures, and epidural extension. Because of 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 both for 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 neurological 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. 153.1 ). 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, with zone 12 located at the spinous process. This system also divides the vertebra into five circumferential compartments, 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 osteotomies planned. 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 with a combined anterior-posterior approach, typically in a staged fashion ( Fig. 153.2 ).