Management of Spinal Metastatic Tumors

Introduction

In postmortem dissections, up to 70% of cancer patients were found to have skeletal metastasis, and spinal bone metastatic lesions are the most common bone metastasis, occurring in 30% to 90% of bone lesions and expected to increase further with greater overall survival and diagnosis.

The most common primary tumors associated with spinal bone metastasis are breast, lung, and prostate cancers in descending order. There are various mechanisms of spread whether direct spread (eg, from the chest/abdominal/pelvic cavity or from a paraspinal muscle metastasis) or, more commonly, hematogenous spread (due to abundant blood supply and Batson's valveless venous system). Spinal metastases to the vertebral column are epidural, with extension into the vertebral bodies, the posterior elements, and possibly the paraspinal musculature, whether anterior (psoas/diaphragm) or posterior (multifidus), or into the central canal and neuroforamina. Their incidence is highest in the thoracic spine (70%), followed by lumbar (20%), cervical, and sacral spine, which is likely related to the relative bone mass of each section.

It is worth mentioning intramural metastases (whether extraaxial or intraaxial). These are the result of CSF spread and are thus drop metastases reflecting leptomeningeal spread. They originate from either a brain metastasis or primary tumors of the brain (eg, glioblastoma multiforme/ependymoma) and are spontaneously occurring or may follow manipulation in cranial surgery. Management is categorically different from that of bone metastatic tumors and is addressed elsewhere in this book, grouped with spinal cord neoplasms.

Spinal bone metastasis mandates a multidisciplinary approach, involving surgeons (spine surgeon, plastic surgeon, ear, nose, and throat [ENT] surgeon, cardiothoracic and vascular surgeon), radiation oncologist, oncologist, and interventional radiologist. Patients are stage 4 cancer patients with poor systemic disease control, and management is aimed at palliation rather than complete cure. Various options exist, and management is tailored according to the general condition of the patient, systemic disease, and life expectancy, as well as presentation, tumor extent, and histology.

Presentation

The spinal column provides for mechanical support of the body in addition to protecting the spinal cord and nerve roots. Metastasis to the spine presents with disturbances to either of those two functions. General systemic symptoms caused by the primary tumor, such as fatigue, weight loss, and cachexia, may be present. Asymptomatic lesions would also be detected through screening studies for known cancer patients. In addition, the compromise of the vertebral artery in cervical spine tumors may lead to vascular symptoms related to the posterior circulation insufficiency, depending on the caliber of the contralateral vertebral artery.

From 83% to 95% of patients present with pain, rendering it the most common presenting symptom for spine metastasis. It is imperative to fully evaluate cancer patients with new onset spine pain in order to rule out metastasis prior to an ensuing neurologic compromise. The type and origin of pain also factor into the management algorithm.

Nerve root compromise will cause radicular pain that could be sharp/shooting or neuropathic/burning in nature and may be due to epidural compression or neuroforaminal stenosis following collapse of the vertebral body. Biologic pain is a persistent deep ache that is stable with positional change, worsens at night, and improves with steroids or nonsteroidal antiinflammatory drugs (NSAIDs). This pain is likely due to periosteal stretch and inflammation by tumor, or paraspinal muscle infiltration, and may improve with radiation or vertebroplasty. The third type of pain is mechanical pain that worsens with upright posture and loading of the spine and does not resolve with NSAIDs. This may be due to associated fractures, deformity, or instability. The latter pain dictates a more proactive surgical intervention or bracing if the patient is not a suitable candidate for surgery.

The second most common presenting symptom in patients with spinal metastasis is neurologic dysfunction. Whether in the form of radiculopathy, myelopathy, or caudal equina, this results from either epidural tumor spread or associated fracture with bone compression.

It is important to recognize that there may be a potential for compromise of iliopsoas muscle, lumbar plexus, or pelvic nerves by metastatic tumor spread or by the primary tumor itself, presenting as weakness in the lower extremities or autonomic dysfunction. The prognosis for neurologic recovery after surgery is directly related to the degree and duration of neurologic compromise.

Imaging and Workup

Magnetic resonance imaging (MRI) with contrast is the gold standard for detection and follow-up of spinal metastatic lesions. Epidural spread, as well as soft tissue infiltration and age determination of fractures, is assessed. The degree of spinal cord compression and signal change within the spinal cord is also evaluated. Newer MRI protocols have been enacted to minimize ferromagnetic artifacts. Computed tomography (CT) myelograms are the scans of choice in case of inability to obtain an MRI and for follow-up with titanium hardware.

CT scan of the spine is of value in treatment planning, assessment of bone, and stability. Sclerotic/lytic/mixed lesions would be delineated, along with degrees of fractures and deformity, planning for instrumentation in surgery (screw dimension and trajectory), neuronavigation guidance intraoperatively, and stereotactic radiosurgery, especially with prior hardware placement. It is also invaluable in the postoperative assessment of fusion/hardware.

A newly discovered spine metastatic lesion in a known cancer patient, whether through MRI screen after presenting with symptoms or positron emission tomography (PET) scan routine screen in asymptomatic patients, warrants a complete MRI with contrast of the whole spine as well as systemic imaging to detect other metastatic lesions given the uncontrolled systemic disease. A patient presenting for the first time with a metastatic mass in the spine will need a CT of the chest, abdomen, and pelvis to locate the primary. In these de novo patients, a CT-guided biopsy of the primary is needed to plan the appropriate treatment.

In 10% to 20% of de novo patients, a primary is never found, and biopsy is warranted instead of the spine lesion. The same could be said for patients with a distant history of cancer that had been treated and was under control, to rule out a second malignancy. It is pertinent to avoid steroids prior to the biopsy if there is a high level of suspicion for a hemopoietic-based neoplasm (eg, lymphoma, chloroma [leukemic deposit] or multiple myeloma). It is also advisable to repeat negative biopsies of sclerotic/blastic lesions given their acellular nature. In case a diagnostic biopsy is not achieved, follow-up with serial MRI may be a reasonable venue.

Computed tomography angiography (CTA) of the neck is of extreme importance when dealing with a cervical spine metastatic mass in order to identify the calibers of both vertebral arteries and potential areas of compression and when anticipating the potential sacrifice of either vessel. Angiography is important to identify arterial feeders in more vascular tumors and to perform preoperative embolization to minimize blood loss (renal cell, thyroid carcinoma, hepatocellular and near endocrine tumors).

Nuclear studies are generally utilized for body screening purposes in asymptomatic patients at the time of cancer diagnosis or during a follow-up screen, or in those with a newly discovered metastasis. They are not specific to neoplastic lesions, and it is difficult to differentiate them from infections/inflammation. Bone scans provide 62% to 89% sensitivity for the detection of spinal metastasis, with limitations in the detection of sclerosing tumors. Single photon emission computed tomography (SPECT) offers a higher specificity for detecting metabolic activity, whereas PET offers a sensitive screening test given its detection of metabolic activity. Flouride-18 (F-PET) and fluorodeoxy glucose (FDG-PET) pick up skeletal remodeling and hypermetabolic lesions, respectively. Higher-yield biopsies are obtained from the more metabolic lesions.