Introduction

Spinal cancer is primarily a metastatic disease with >90% having originated from another source. ^, In addition, osseous spread is the third most common form of metastasis with 30%–70% of cancer patients encountering spinal metastasis. Many primary tumors affect persons of advanced age, with more than 60% of cancer patients being older than 65 years. Consequently, particular consideration for comorbidities, fitness for therapy, and patient preference are fundamental in guiding management plans to provide holistic care.

Surgery for Spinal Metastases

Indications include mechanical instability, neurologic compression, debilitating pain, and removal of local disease to enable the use of other modalities. Most patients have a life expectancy of <1–2 years, and a balance exists between the risks and benefits of surgery. It is generally accepted that surgery might be considered in a patient with a life expectancy >3 months, with goals to optimize quality of life. ^,

Staging and Scoring Systems

Various classification systems aid surgical decisions based on the stage of the disease. The Global Spine Tumor Study Group (GSTSG) recommends the use of the Tomita and Tokuhashi staging systems. The Tomita score incorporates the rate of growth of the primary tumor, the number of bone metastases, and the number of visceral metastases. The Tokuhashi score includes the general condition of the patient, the primary site of the cancer, and the presence of palsy and metastasis ( Table 20.1 ). The use of the Spinal Instability Neoplastic Score (SINS) aids clinical diagnosis of spinal instability associated with cancer ( Table 20.2 ). Mechanical instability is an indication for surgical intervention. There are six parameters, including location, pain, alignment, osteolysis, vertebral body collapse, and posterior element involvement. A score of 13–18 indicates the need for surgical stabilization. Additionally, the use of quality of life scores, such as the Euroquol EQ5D, is encouraged by the GSTSG. Scoring systems can aid management plans. If no encroachment of the canal is evident and the vertebral column is stable, surgical intervention is not required.

Hematologic Malignancies

For myeloma, plasmacytoma, and lymphoma, there is a shifting treatment paradigm away from surgery. For myeloma, the mainstay of treatment is systemic chemotherapy, bisphosphonates, and pain control. For spinal involvement, methods including bracing and cement augmentation, radiotherapy or surgery may be used. Patients can develop rapidly progressive, lytic lesions that can cause spinal instability; however, treatment with instrumented stabilization may fail due to poor bone quality and infection. Bracing can provide pain relief and manage fractures. A case report noted successful management of an unstable myelomatous vertebral fracture without neurologic deficit using a thoracolumbar sacral orthosis for 3 months. Thoracic and cervical fractures with and without deficits were also effectively managed conservatively in this report. Such approaches restore stability without the risks of surgery. Patients with multiple myeloma and back pain, or an early clinical spine deformity, must still be screened urgently for spinal lesions.

Most patients with solitary bone plasmacytoma (SBP) develop multiple myeloma. The spine is the main site of SBP, and radical radiotherapy is the treatment of choice. Multiple solitary plasmacytomas are treated with radiotherapy in the absence of systemic disease. However, patients with extensive disease or early relapse may benefit from systemic therapy +/– autologous stem cell transplantation. Surgical intervention is not recommended first-line.

Regarding lymphoma, the National Institute for Health and Care Excellence (NICE) recommends management strategies, including radiotherapy, immunotherapy, chemotherapy, immunochemotherapy, and stem cell transplantation, with no role for surgery. These malignancies should be managed nonoperatively, similar to plasmacytoma and multiple myeloma, with surgery reserved for cases resistant to nonoperative treatment and progressive neurologic compression.

Cement Augmentation, Kyphoplasty, Vertebroplasty

Cement augmentation using balloon kyphoplasty (BKP) and percutaneous vertebroplasty (PV) is useful in reducing pain and restoring strength. It is indicated for patients who are nonambulatory and unable to engage in physical therapy, and patients who cannot tolerate analgesia side effects. Benefits include shorter operative times and hospital stays, and reduced blood loss and postoperative pain. PV and BKP involve the injection of cement under fluoroscopic guidance. The cement stabilizes the fracture and preserves stability. Some rare complications include cement embolus and neurologic dysfunction. Leaking of cement into the intervertebral disc is less rare and can cause fractures of other vertebral bodies. In BKP, a similar approach is taken; however, a balloon is inflated first to restore the vertebral height. BKP reports a lower cement leakage rate. This is performed for osteoporotic fractures; however, it is also a therapeutic option in pathologic fractures. Patients require careful clinical assessment, magnetic resonance imaging (MRI), and computed tomography (CT) in combination with a SINS score. Cement augmentation may be used to decrease pain and enhance stability following a fracture or prophylactically, if a fracture is likely.

Stereotactic Radiosurgery and Intensity-Modulated Radiotherapy

Stereotactic radiosurgery (SRS) and intensity-modulated radiotherapy (IMRT) target radiation precisely to the cancer to reduce injury to normal tissue. They allow for noninvasive, specific, and efficacious treatment. SRS targets a treatment site with multiple radiation beams of equal intensity. IMRT allows for variation of the intensity of each beam. It may be used solitarily or as an adjunct to surgery reducing the need for large resections. Evidence for these modalities is sparse due to small case series and limited follow-up periods. It has been shown to be a safe intervention; however, it has not been compared with existing techniques. Currently it is used for patients with recurrent disease for whom surgery is not available and is only accessible in centers with the appropriate technology and expertise.

Separation Surgery

Spinal surgery aims to achieve circumferential cord decompression. Separation surgery involves a posterolateral approach to obtain ventrolateral access to nerve roots, the posterior longitudinal ligament, and ventral epidural disease. It allows for rapid decompression, stabilization, and postoperative continuation of treatment. The goal is to create a space between the tumor and the spinal cord that enables safe postoperative delivery of SRS. This technique is useful to prepare patients with epidural disease that is too advanced for radiotherapy. This combined approach is also referred to as a “hybrid therapy.”

Decompressive and Stabilization Surgery

Decompression is indicated emergently for spinal cord compression and is commonly achieved with laminectomy. Posterior approaches are the most common and enable multilevel vertebral decompression resulting in effective symptom relief. However, complications associated with this are apparent, including the acceleration of instability and wound complications. Anterior approaches are seen more frequently in the cervical spine. Regardless of approach, posterior spinal stabilization is often needed to avoid instability. It is commonly accepted that at least two levels of fixation above and below the affected vertebrae are necessary to achieve adequate stability.

En Bloc Resection

En bloc resection is considered the gold standard in treatment of solitary spinal metastasis confined to the vertebral body. Unfortunately, patients with spinal metastases are frequently referred late and are not candidates. These surgeries have largely fallen out of favor due to the significant complications associated with an aggressive approach. These complications are divided into surgical (wound infections, cerebrospinal fluid [CSF] fistulas), hardware related (broken, migrated), medical (pneumonia), and neurologic (new deficit). As a result, it should be reserved for curative, as opposed to palliative, therapy.

Prognosis

The primary cancer is the key determinant in predicting survival. Median survival time is highest for breast and renal, and lowest for prostate and lung cancers, respectively. Additionally, factors such as having multiple metastases, cervical metastasis, and pathologic fractures have no significant influence on survival. Evidence supports surgery to enhance quality of life in these cases, and it may be used first-line to reduce pain, preserve neurologic function, prevent pathologic fractures, and correct spinal instability.

Anesthetic Considerations

Anesthesia for cancer patients undergoing spinal tumor surgery (STS) can be challenging. As mentioned above, the majority of this patient cohort is elderly (60% are aged >65 years), and preoperative evaluation may identify multiple organ impairment, which can occur in these patients through metastases, comorbid disease, and metabolic derangements, as well as immunosuppression due to chemo/radiotherapy. In addition, surgery can be extensive, involve special positioning, and have the potential for major hemorrhage. Airway management can be difficult both at intubation and extubation, which is compounded by the need for rapid emergence to facilitate neurologic examination. Postoperatively these patients pose challenges in terms of thromboprophylaxis and analgesia management.

Preoperative Evaluation

The challenge with preoperative evaluation for this patient cohort is that it must be comprehensive, with consideration of the patient’s comorbidities and disease burden, while also respecting the urgent nature of this surgery. These patients may present with mechanical instability or neurologic symptoms; therefore preoperative assessment should be focused.

Airway evaluation is crucial as patients presenting for spinal surgery may be challenging to intubate, particularly for surgeries involving the upper thoracic or cervical spine. Patient factors may include pathology that distorts the normal airway anatomy, or they may have reduced movement of their jaw or neck secondary to radiotherapy. This patient cohort may also have cervical spine instability. Airway examination should be paired with a full evaluation of preoperative imaging of the cervical spine, thoracic spine, and airway and a discussion with the surgical team about the degree of instability, all of which serves to guide perioperative airway management.

Evaluation of a patient’s respiratory function preoperatively is important, particularly in those cases of complex thoracic spine surgery where one-lung ventilation may be required. It is also important to remember that patients with mechanical instability may have been kept lying supine in bed preoperatively for spinal precautions. This may negatively affect the patient’s respiratory function. A chest x-ray, careful assessment of the patient’s CT images of the thorax, and arterial blood gas are useful adjuncts to a full respiratory examination. Liaising with physiotherapists for assessment of the patient’s cough, FEV1 (forced expiratory volume in the first second of expiration), and vital capacity can also be helpful. For scheduled, complex thoracic surgeries, formal pulmonary function tests may also be beneficial. It is worth undertaking these tests in the supine position, as this will give a more accurate reflection of the patient’s respiratory physiology in the perioperative period.

A full cardiovascular examination may be challenging in this patient cohort as many of these patients have reduced mobility, making it more difficult to evaluate exercise tolerance. Nonetheless, a full history should be sought, with particular attention to congestive cardiac failure and pulmonary hypertension, both of which have been shown to be associated with perioperative adverse events after spine surgery. Useful investigations which may assist in a patient’s cardiovascular evaluation include a 12-lead electrocardiogram (ECG) and echocardiography. Stress testing should be performed only if it is indicated in the absence of the proposed spine surgery. There is no current evidence that further diagnostic evaluation will improve surgical outcomes.

As mentioned above, patients presenting for STS may have symptoms of mechanical instability or neurologic compression; therefore assessment and recording of neurologic function preoperatively is essential to ensure accurate surveillance and diagnosis of new postoperative deficits should they occur.

As well as the system-specific investigations suggested above, patients should have a comprehensive set of blood tests undertaken prior to surgery. This should include a full blood count, urea and electrolytes, calcium, and a type and screen with cross match. A full blood count is particularly useful in patients on chemotherapy to assess for anemia, leukopenia, or thrombocytopenia. Serum calcium levels are important to consider, as these may be elevated in the setting of malignant disease. Cross matching of blood will depend on the extent of the surgery and the patient’s individual risk of blood loss and coagulopathy; however, the risk of significant bleeding and need for transfusion in this patient population are significant.

Anesthetic Technique

Standard monitoring for general anesthesia (pulse oximetry, ECG, end expired carbon dioxide, blood pressure, and temperature) is used for spinal surgery patients. STS may result in significant blood loss with the need for rapid infusion of fluids. Two-wide bore IV cannulae should be placed and attached to fluid warming devices. Central venous access is placed if (a) the patient has difficult peripheral IV access, (b) if a need for vasoactive medications is anticipated, or (c) a volatile sparing anesthetic (total intravenous anaesthesia [TIVA]) technique is to be used intraoperatively. We also recommend the use of an invasive arterial pressure monitor, as this facilitates intraoperative blood sampling and rapid assessment of blood pressure, particularly in the setting of hemorrhage. Urinary catheterization and urine output monitoring would allow accurate assessment of fluid balance intraoperatively. For patients receiving a TIVA technique, processed electromyography (EMG) monitoring is recommended.

Intraoperative spinal cord monitoring should be considered in any case where the spinal cord is at risk. Multimodal intraoperative neuromonitoring (IONM), including motor evoked potential (MEP), somatosensory evoked potential (SSEP), and EMG, are often used to monitor spinal cord function during surgery on the cord or the vertebral column. While neurologic injury can cause changes in recorded potentials, other factors can interfere with their interpretation such as the use of inhalational anesthetics, hypothermia, hypoxia, hypotension, anemia, and preexisting neurologic lesions. Inhaled anesthetics, such as sevoflurane, isoflurane, and nitrous oxide, can suppress MEPs completely and diminish the amplitude and extend the latency of SSEPs. Neuromuscular blocking agents (NMBAs) also terminate MEPs and cannot be used when monitoring. Intravenous anesthetics, such as propofol, barbiturates, and opioids, have less of an effect on monitoring, though very deep anesthesia, with propofol, can have dose-dependent effects. Therefore, a TIVA technique is used for patients in whom neuromonitoring is undertaken. Tongue and lip biting injuries are the most common reported complications during MEP monitoring (incidence 0.2%–0.63%). Risk factors for tongue injury during MEP monitoring include C3–4 stimulation that directly activates the temporalis muscle and prone position, as it predisposes to tongue swelling.

Airway Management

Airway management in these patients can prove challenging, particularly in those with cervical spine instability. A suggested airway management algorithm for these patients is shown in Fig. 20.1 . Reinforced endotracheal tubes (ETT) are most commonly used in patients undergoing major spinal surgery. For most patients, a single-lumen ETT will be used; however, the lateral approach to the thoracic spine may require lung isolation with a double-lumen ETT. When a double-lumen ETT is used, it may be replaced by a single-lumen ETT if postoperative ventilation is required. Airway edema can be a significant problem on extubation. The incidence of airway compromise requiring reintubation after anterior cervical spine procedures has been reported as up to 1.9%. Risk factors include multiple level surgery, blood loss of >300 mL, duration >5 h, combined anterior and posterior approach, and previous cervical surgery. Hematoma formation or supraglottic edema as a result of venous and lymphatic obstruction may contribute to the development of airway compromise. Symptoms include neck swelling, change in voice, agitation, and signs of respiratory distress that usually develop within 6–36 h postoperatively. Tracheal deviation may occur, and compression of the carotid sinus can cause bradycardia and hypotension. High-risk patients should be monitored in a critical care setting with consideration for a staged extubation using an airway exchange catheter.

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