Concepts in Primary Benign, Primary Malignant, and Metastatic Tumors of the Spine

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Arya Nick Shamie, MD

Francis John Hornicek, MD, PhD

Dr. Shamie or an immediate family member has received royalties from Seaspine and Stryker; is a member of a speakers’ bureau or has made paid presentations on behalf of SI Bone, Stryker, and Vertiflex; serves as a paid consultant to or is an employee of Stryker and Vertiflex; has stock or stock options held in Providence, SI Bone, and Vertiflex; has received research or institutional support from Pfizer; and serves as a board member, owner, officer, or committee member of the American College of Spine Surgery. Dr. Hornicek or an immediate family member serves as a paid consultant to or is an employee of Globus Medical and Stryker; has stock or stock options held in Biome AI, Inc. and Bone Solutions, Inc.; has received research or institutional support from Stryker; has received nonincome support (such as equipment or services), commercially derived honoraria, or other non-research-related funding (such as paid travel) from Biomet; and serves as a board member, owner, officer, or committee member of the American Association of Tissue Banks, FDA, ISOLS, and the Musculoskeletal Tumor Society.

Tumors involving the spine comprise various types and subtypes which require meticulous evaluation and diagnosis of the lesion to arrive at the best nonsurgical and/or surgical treatment for the patient. One of the most important steps prior to arriving at the correct diagnosis is to obtain adequate tissue biopsy. Some pathologic conditions have similar clinical presentations and appearances on radiographic and advance study imaging. Therefore, core or open biopsy of the suspicious lesion is critical to arrive at the best treatment for the patient. Some tumors can be treated medically and others require extensive en bloc resections with major reconstruction of the involved anatomic structures. Taking into account the biology of the tumor cells and the overall physiologic status of each individual patient will allow the surgeon and the multidisciplinary team to devise the best plan of care for each patient.

Keywords: chordoma, metastatic spine tumors, primary spine tumors, radiation therapy, surgical treatment of spine tumors

Introduction

Cancers involving the spine are encountered either as primary lesions or more commonly metastatic lesions from a remote location through hematogenous spread. Understanding the disease process is critically important as one devises the proper medical or surgical treatment for the patient. Primary tumors of the spine, although rare, are best treated aggressively with en bloc resection to decrease the risk of local recurrence or distant metastasis. In contrast, metastatic disease needs to be studied to understand the systemic burden on an individual patient before the proper medical or surgical treatment plan is devised.

Background

National Institutes of Health (NIH) and National Cancer Institute estimated that in 2018, more than 1.7 million new cases of cancer will be diagnosed in the United States and over 600,000 people will die from the disease.¹ The most common cancers (listed in descending order according to estimated new cases in 2018) are breast cancer, lung and bronchus cancer, prostate cancer, colon and rectum cancer, melanoma of the skin, bladder cancer, non-Hodgkin lymphoma, kidney and renal pelvis cancer, endometrial cancer, leukemia, pancreatic cancer, thyroid cancer, and liver cancer.

In 2016, there were an estimated 15.5 million cancer survivors in the United States. The number of cancer survivors is expected to rise to 20.3 million by 2026
partly due to aging population and improved detection. This increase in overall numbers of people living with cancer will also increase the prevalence of patients with metastatic disease. Approximately, one-third of men and women will be diagnosed with cancer at some point during their lifetimes (based on 2013-2015 data). Estimated national expenditures for cancer care in the United States in 2017 was over $140 billion. In future years, costs are likely to increase as the population ages and cancer prevalence increases. Costs are also likely to increase as more advanced and costly treatments are developed and utilized as standards of care.

In the United States, approximately 1.2 million people are diagnosed with cancer each year, making this disease category the second most common cause of death in the country. Autopsy studies have shown that more than 60% of patients with cancer have evidence of spinal metastasis. Spine tumors can be classified as primary spine tumors, which originate in the spinal elements, or metastatic tumors, which spread from some other location or organ in the body. Further classifications, like all tumors, are made designating a tumor malignant or benign. Metastatic disease substantial enough to cause spinal cord compression occurs in approximately 5% to 14% of patients with metastatic cancer, resulting in approximately 20,000 new instances of tumor-induced myelopathy per year. Approximately half of these patients will lose the ability to ambulate.

Primary benign tumors of the spine, such as hemangioma of bone, are present in up to 10% of the normal population and are often discovered incidentally. Primary malignant spine tumors, by contrast, are exceedingly rare and account for less than 3% of all malignant spine tumors.

Table 1 Anatomic Locations of Most Common Primary Tumors of Spine and Metastases

Vertebral Locations	Benign Tumors	Malignant Tumors
Anterior elements	Eosinophilic granuloma	Chordoma
	Giant cell tumor	Multiple myeloma
	Hemangioma	Metastasis
	Aneurysmal bone cyst
Posterior elements	Osteoblastoma Osteoid osteoma Osteochondroma
Adjacent levels	Aneurysmal bone cyst Osteoblastoma
Multiple noncontiguous levels		Metastasis
Reprinted with permission from Scott DL, Pedlow FX, Hecht AC, Hornicek FJ: Primary benign and malignant extradural spine tumors, in Frymoyer JW, Wiesel SW, eds: Adult and Pediatric Spine, ed 3. Philadelphia, PA, Lippincott Williams and Wilkins, 2004, p 192.

Primary Tumors of the Spine

Primary malignant spine tumors are rare and constitute less than 5% of extradural tumors involving the axial skeleton (Table 1). Primary tumors of the spine originate mostly from either the bone or cartilage tissue but also from associated tissues like neural structures in or around the spine. The primary lesions that originate from the bony structures are generally extradural in contrast to the intradural nature of most primary tumors arising from neural elements. Intradural tumors may be further subdivided into intramedullary and extramedullary tumors, depending on whether they originate from the spinal cord itself or the nerve roots distal to the spinal cord, respectively. In individuals older than 20 years, majority of primary tumors of the spine are malignant. Proper treatment protocols for these tumors have evolved over the years requiring extensive research and discussions leading to a consensus and leading to well-developed and evidence-based position papers.² It is critically important to follow the best practices in treatment for these primary tumors of the spine to minimize local recurrence and provide best quality of life and survival rates for these patients. Typically, a well-planned and more technically challenging en bloc resection is the best approach for these patients with intralesional resection leading to a less favorable outcome for the patient.

Diagnosis and Staging

Patient with tumors involving the spine, typically present with axial pain that is chronic and progressive. They typically report pain that awakens them in the middle of the night and when recumbent, in contrast to degenerative conditions of the spine which are typically activity related. Oftentimes, the delay in diagnosis and severity of the pain results in these patients being placed on narcotic pain medications prior to seeing a surgeon. A minority of patients present with neurologic symptoms or deficits but these symptoms often present later in the disease process as the tumor expands compressing the neural elements.

The evaluation in a patient with a suspected spine tumor should begin with a complete history of symptoms including a familial history followed by observation of the patient’s sagittal and coronal balance to assess for signs of reflexive splinting or scoliosis. The posterior spine should be palpated for areas of focal tenderness or masses. Many primary tumors of the spine can be palpable on presentation. The thyroid, breast, and prostate should be palpated for enlargement or irregularities, with the lymph nodes in the neck, axilla, and the groin.

The physical examination should then focus on evaluating the neurologic function with signs of lower or upper motor neuron compression. Patients with upper motor neuron compression may exhibit pathologic reflexes such as the Hoffmann, inverted radial reflex (digit flexion when tapping the brachioradialis tendon) or generalized hyperreflexia. Patients may also walk with a wide-based gait and be unable to perform a tandem heel-to-toe walking.

For patients showing signs of upper motor neuron compression, a thorough cranial nerve evaluation should be performed to check for intracranial involvement.

Radiographs remain the primary imaging tool, but many primary lesions are initially undetected, as, 30% to 50% trabecular bone destruction is required before the lytic lesion appears on traditional radiography. Evaluation of radiographs may also be more challenging with underlying degenerative conditions or metabolic bone diseases. With a higher degree of suspicion, more advance imaging needs to be obtained to evaluate a patient with suspected primary tumor of the spine. CT and MRI are used to evaluate the entirety of the spine. Certain characteristics of various tumors can delineate the specific diagnoses; moth-eaten lesions are typically due to a permeative process in the trabecular bone like multiple myeloma. The intervertebral disks are usually resistant to tumor invasion unless the lesion is producing collagenase and proteinase which is more typically seen in pyogenic processes. CT scan is also an essential tool for staging of malignancies with the typical series of chest, abdomen, and pelvis but can also provide anatomic and bony details not visible on radiographs or MRI. When MRI is not possible, CT myelogram can be used to assess neurologic compression in the spine. MRI’s advantage is that it provides detailed imaging in multiple planes of the spine in the absence of ionizing radiation and provides a detailed view of neural elements and can detect small lesions even when they are missed by radiographs or CT scans. Tumor infiltration of the bone marrow decreases the signal on T1-weighted images by displacing the fatty marrow and increases the signal on T2-weighted images due to increase in edema in reactive bone. Technetium bone scan is a low-cost tool for diagnosis of bone metastasis and skip lesions, but it has lower utility in detection of spine tumors when compared with CT and MRI. Recent literature suggests the use of a combination of positron emission tomography (PET) with MRI for earlier detection of disease and for differentiation of tumor versus radiation necrosis.³ But more investigation is necessary before this positron emission tomography (PET)/MRI or PET/CT modality is standardized and used routinely for evaluation of patients with spine tumors.

When encountering a patient with suspected tumor of the spine, it is critically important to distinguish the suspected disease from other differential diagnoses like trauma and infection and misleading processes like fibrous dysplasia, metabolic bone diseases, and bone islands. Comprehensive evaluation of routine labs, radiographs of involved areas and chest, CT of chest/abdomen/pelvis, and most often a biopsy are necessary to obtain the proper diagnosis. In addition to a complete blood count (CBC) and chemistry panel, serum electrophoresis (multiple myeloma), serum calcium, alkaline phosphatase, and prostate-specific antigen (PSA) (prostate cancer) should be considered.

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