Preoperative Evaluation of Patients With Tumors Affecting the Spine

Classification of Spinal Tumors

Spinal tumors are categorized depending upon their anatomical location into intradural-intramedullary, intradural-extramedullary, or extradural tumors. Generally, extradural lesions are the most common (60% of all spinal tumors), followed by extramedullary (30% of all spinal tumors) and intramedullary tumors (10% of all spinal tumors).

Spinal tumors are further categorized as primary tumors, which originate from the spine and its adjacent structures, and secondary (metastatic) tumors of distant organs, which spread hematogenously and lymphatically. Primary spinal column tumors arising from the bony elements of the spine include chordoma, chondrosarcoma, osteoblastoma, osteosarcoma, giant cell tumor, and aneurysmal bone cyst, to name a few.

Primary spinal tumors arising from the nervous system consist of intradural tumors, which are further classified by the tissue of origination: spinal cord, dura, or nerve root. Intradural intramedullary tumors, or tumors arising from the intrinsic neural tissue of the spinal cord, include ependymomas, astrocytomas, and hemangioblastomas, among others. Intradural tumors arising from the dura or nerve roots include meningiomas, schwannomas, and neurofibromas.

Metastatic tumors are the most common type (97%) of spinal tumors. The spine is generally susceptible to metastases because of its high vascularization and close relationship with regional lymphatic and venous drainage systems, such as Baston’s venous plexus. The thoracic and lumbar spine regions are the most common spinal segments affected by metastatic tumors. Thoracic tumors represent approximately 70% of cases, followed by the lumbar spine with 20%, with the remaining 10% being divided between the cervical spine and sacrum.

A detailed discussion regarding each of these specific tumor types is beyond the scope of this chapter, but pertinent themes regarding the preoperative evaluation of these tumors will be emphasized broadly in this chapter, with particular focus on spinal metastases, the most common tumors encountered in clinical practice.

Diagnostic Imaging

The preoperative assessment of patients with spinal tumors starts with the history and physical. However, a thorough diagnostic evaluation is also critical to further evaluate suspected spinal tumors. This is particularly the case with metastatic spinal tumors, where one imaging modality alone is not sufficient to fully assess or characterize these lesions.

Plain Radiographs

Plain radiographs (x-rays) are a common screening modality for patients with spinal disorders because they are easily available, accessible, and inexpensive. Although x-rays cannot provide detailed assessments of the bone marrow or dura, they can provide valuable information regarding the structural alignment of the spine and alert to the presence of pathological fracture. Often used as a screening tool upon the initial complaint of pain, it has been demonstrated that at least 50% of the vertebral body must be compromised by an osteolytic lesion (the most common type of metastatic tumor) before the abnormality can be identified on plain x-ray films. Although of limited use in advanced metastatic spinal disease, radiographs may provide evidence of pathological fractures, spinal deformity, and paraspinal masses. The radiographic characteristics of metastatic lesions can be osteoblastic, osteolytic, or mixed. Spinal metastases of prostate and breast carcinomas are generally osteoblastic or mixed-type lesions, but lung, thyroid, and renal cell carcinomas are usually lytic metastatic lesions.

Extension of a radioopaque lesion outside the boundaries of the vertebral body may indicate primary malignant lesions of the spine, like osteosarcoma or chondrosarcoma. However, definitive diagnosis in these situations is not possible without additional studies like magnetic resonance imaging (MRI), computed tomography (CT), and tissue biopsy because such imaging characteristics are not specific to tumor type. A faint shadow obscuring the visibility of one pedicle on the anteroposterior radiograph known as the “winking owl sign” indicates extension of tumor from the vertebral body and is an early radiographic sign of metastatic lesion ( Fig. 70.1 ). This suggests destruction of a pedicle and the posterior aspect of the vertebral body, and further study with CT and MRI is needed to assess the extent of vertebral bone marrow involvement, epidural extension if any, and presence of pathological fracture. Lytic lesions indicate bone destruction, and this pattern prompts further investigation. However, it is difficult to differentiate pathological compression fracture from benign osteoporotic fracture by x-ray alone ^, ( Fig. 70.2 ).

Plain x-rays are also helpful to the surgeon when assessing the local, regional, and global spinal alignment. Spinal alignment, particularly with respect to spinopelvic parameters, is highly correlated with morbidity and health-related quality-of-life outcomes after spine surgery. Although the importance of spinal alignment has been emphasized in the deformity literature, spinopelvic parameters have not been extensively studied in the context of spinal tumors. Because the goal of spine surgery is mostly palliative in this setting, consideration of spinopelvic parameters in surgical planning could improve postoperative outcomes by taking these alignment considerations into account.

Region-specific films, such as cervical or lumbar x-rays taken before surgery, can provide the surgeon with a sense of the structural integrity and the spinal alignment. In the lumbar spine, spinopelvic parameters, such as the pelvic incidence, lumbar lordosis, and pelvic tilt, can be readily calculated, providing the surgeon with a sense of any lumbar-pelvic mismatch that could be factored into surgical planning. Similarly, for the cervical spine, the presence of vertebral subluxation, facet dislocations, kyphosis, and scoliosis are useful information before surgery. X-rays performed while upright––standing or sitting––are helpful when considering stabilization surgery, so as to not instrument the patient into kyphosis or a flat back. Long cassette 3-foot scoliosis films can also be helpful to assess the global sagittal alignment, particularly when instrumenting across junction zones such as the cervicothoracic and thoracolumbar regions.

Bone Scan

The bone scan is a nuclear imaging method that is also frequently used as a screening tool for identifying metastatic bony disease in patients with cancer. A bone scan is capable of revealing spinal lesions in an earlier stage when compared with plain radiographs. By demonstrating an increased uptake of the intravenously injected radiotracer, bone scan images correlate with increased metabolic activity in the skeletal system. However, bone scans have low specificity for cancer, and, as increased metabolic activity may also be caused by inflammation or infection, these must be considered as possible diagnoses. Furthermore, the degree of detail in bone scans is low, and for purposes of diagnosis exclusion or surgical planning, correlation with CT or MRI is needed. Currently, in most centers, positron emission tomography (PET) scans with ¹⁸ F-fluorodeoxyglucose has replaced bone scan for purposes of whole-body screening and metastasis staging.

Technological advancements have integrated various imaging modalities to create hybrid imaging studies such as single-photon emission CT (SPECT)/CT, PET/CT, and PET/MRI. The advantage with these hybrid studies is combining the anatomical data from CT and MRI imaging and superimposing functional data from the nuclear medicine studies to increase diagnostic confidence. SPECT imaging of the skeleton using 99mTc-methylene diphosphonate can provide better localization of abnormal radionuclide uptake with a sensitivity and specificity for detection of bone metastases of 87% and 91%, respectively.