Primary tumors of the spine are rare and make up only a small percentage of patients seen by the community orthopedic surgeon. Primary tumors of the spine represent less than 10% of all primary bone tumors. Most malignant spinal tumors are caused by metastatic spread from another primary source. Diagnosing a primary spinal tumor requires understanding of the epidemiology and presentation of these tumors. While approximately 70% of primary spinal tumors in children and adolescents are benign, this figure drops to 20% in older age groups. Furthermore, the location of a tumor (i.e., levels, anterior vs. posterior, bony vs. neural involvement) may point to its identity.

Advances in medical imaging, operative techniques, and multimodal treatment allow for both earlier and more precise diagnosis as well as improvements in both short- and long-term outcomes in tumor patients. The clinician must be aware of the patient goals in the treatment of both benign and malignant tumors. The spine represents unique anatomical challenges due to the proximity of osseous elements to vital functional neural structures; therefore, classic principles of orthopedic oncology as applied to the extremities (i.e., en bloc resection to achieve wide resection) often must be modified for primary spinal malignancies if the morbidity of the procedure would result in an unacceptable quality of life for the patient.

Understanding the anatomy and embryologic origins of the spinal cord are required to diagnose and treat both benign and malignant tumors of the spine.

The early precursor of the spinal cord is the neural plate, a layer of ectoderm on the dorsal surface of the early embryo. The notochord lies within the mesoderm and runs the full length of the developing embryo. It secretes sonic hedgehog protein which differentially affects cell migration and development in the embryo as it forms a rostral to caudal gradient, and acts as an initial “axial skeleton” before other structural elements are formed. During the third week postconception, the neural plate begins to invaginate upon itself to form the neural groove, and subsequently the neural crest. This overlaps with the paraxial mesoderm surrounding the developing neural tube, forming 42 pairs of somites: occipital, cervical, thoracic, lumbar, sacral, and coccygeal. These somites will eventually differentiate to form the bony spinal column as well as associated muscles, tendons, and ligamentous structures. The notochord itself ossifies within the vertebral bodies, and remnants are found only within the nucleus pulposus in the formed axial skeleton, and occasionally at the most rostral and caudal limits of the bony spinal column.

The fully developed spine comprised 7 cervical, 12 thoracic, 5 lumbar, and 5 fused sacral vertebral segments, as well as the coccyx. Vertebrae are separated by intervertebral disks, characterized by a firm annulus fibrosis surrounding a spongy nucleus pulposus. From dorsal to ventral, there are several important ligaments contributing to the structure of the spinal column. Dorsally and supralaminar, the supraspinous and intraspinous ligaments stabilize the posterior elements. The ligamentum flavum (yellow ligament) is found sublaminar and adjacent to the dura. Along the posterior edge of the vertebral body (adjacent to dura) lies the posterior longitudinal ligament (PLL), and along the anterior edge (adjacent to the retroperitoneal space) the anterior longitudinal ligament (ALL). The spinal cord begins upon exiting the brainstem and terminates at the L1–L2 region, after which point the cauda equina exists. The spinal cord itself is encased
in three layers of meningeal tissue. Immediately adherent to the cord is the pia mater, followed by arachnoid mater and dura mater. The pia mater acts to protect and stabilize the spinal cord within the intradural space. It covers and contains vascular supply to the cord, and passes through the arachnoid mater, attaching to the dura mater via denticulate ligaments which somewhat anchor the cord in place preventing microtrauma with movement. At the termination of the spinal cord, the conus medullaris, the pia mater becomes the filum terminale and is eventually confluent with the dura mater, and the periosteum in the lower coccygeal segments. Cerebrospinal fluid, secreted by choroid plexus, resides between the pia mater, and the arachnoid mater.

The vascular supply to the anterior 2/3 of the spinal cord is from the anterior spinal artery, and runs from its origin down the entire length of the cord to the filum terminale. In the region of C1–C6, the vertebral arteries, which also give rise to the posterior inferior cerebellar arteries, each contribute to give rise to the anterior spinal artery. The posterior 1/3 of the spinal cord is fed by the paired posterolateral spinal arteries. The anterior and posterior spinal arteries form frequent anastomosis called arterial vasocorona which supply the far lateral aspects of the cord. Segmental arteries branching from the aorta supply both the anterior and posterior spinal arteries. The dominant segmental artery is the artery of Adamkiewicz which has a variable course and laterality. It originates on the left side of the aorta between the T8 and L1 vertebral segments in 75% of individuals and variably contributes to the anterior spinal artery. The venous drainage of the spinal cord is segmental, and drains to a valveless venous plexus surrounding the cord.

The most common presenting symptom of a primary spinal tumor is pain, and less commonly neurologic deficit, kyphoscoliosis, or palpable mass. The reader should ensure that they are comfortable with the anatomy and physical examination of the spinal cord and cauda equina, as well as the peripheral nerve exam as a detailed physical examination will often be instrumental in locating the lesion and ordering appropriate investigations. Although there are exceptions, the location of tumors can strongly suggest their identity.

Posterior elements (spinous process, lamina)

Anterior elements (vertebral body)

Malignant

Intradural extramedullary

Malignant

Intradural intramedullary

Back pain is one of the most common complaints in individuals with spinal tumors presenting to primary or subspecialty care. Approximately 85% of patients will complain of focal back pain, and possible radicular pain depending on the location of the lesion. Patients will often associate the onset of their pain with a minor trauma, which can be either a spurious temporal association or pathologic fracture. Neurologic symptoms are far less common, with only 10% of patients presenting with focal motor loss, myelopathy, or cauda equina syndrome. Approximately 5% of patients are incidentally diagnosed with spinal tumors on other imaging.

“Red flags” on history and physical examination include:

A thorough history and physical examination should be conducted. History should include onset of symptoms, temporal progression, aggravating and relieving factors, and red flags. Physical exam includes a full neurologic and rectal exam. Of note, over half of patients with a sacral chordoma have a palpable mass on rectal examination. The findings of physical examination will be used to order appropriate imaging studies. Small lesions may be asymptomatic or present with localized pain.

The spinal cord extends from the medulla to the conus medullaris and usually extends form C1 to L1/L2, although conus medullaris may be found lower in some people. Lesions causing spinal cord compression may present with myelopathic signs and symptoms which include gait ataxia, lower and upper extremity weakness, difficulty with fine motor activities, frequent dropping of objects, fecal incontinence, and urinary retention. On physical exam, Hoffman’s sign, Babinski sign, clonus, hyperreflexia, and decreased rectal tone may be present. Radicular pain or weakness may occur in cases where the tumor is compressing individual nerve roots and may be noted in conjunction with myelopathy or may serve as the sole presentation. Lesions around T1 (primary spinal malignancies or locally invasive mass, e.g., Pancoast tumor) may disrupt the sympathetic chain and result in Horner’s syndrome: meiosis, ptosis, anhydrosis on the side of the lesion.

Tumors below the conus medullaris may present with individual radicular signs and symptoms or as cauda equina syndrome which may include fecal incontinence, urinary retention, saddle anesthesia, sexual dysfunction, and lower extremity motor and sensory deficits.

Sacral tumors are often neurologically asymptomatic until they reach a large size and cause compression of bilateral sacral roots or invade individual foramina causing painful radicular symptoms. Wide resection of sacral masses is possible, often with only limited motor impairment (S1 nerve root sacrifice still allows patients to walk). Unilateral sacrectomy or low sacrectomy allows better preservation of function than bilateral high sacrectomy (Table 13.1).

Laboratory workup is recommended but may not definitively establish a diagnosis in the case of primary spinal tumors. The authors recommend a comprehensive blood draw, including ESR and CRP. In adult patients, SPEP (serum protein electrophoresis) should be obtained. If osteogenic or Ewing’s sarcoma are suspected, an alkaline phosphatase (AFP) and lactase dehydrogenase (LDH) should be ordered as they confer prognostic significance. For patients with a history of cancer, serum markers can be drawn when appropriate including a PSA, CEA, TSH, and AFP.

Plain radiographs of the affected area are a good initial screening tool in the workup of suspicious focal back pain. The affected area should be focally imaged, but total spine standing plain x-rays are useful to examine deformity associated with the lesion and to screen for other lesions. Small lesions, however, may be missed on plain radiographs. MRI with and without gadolinium is the imaging modality of choice to assess lesions with associated or predominant soft tissue component and their relationship to neural elements. In addition, diffusion-weighted MRI of the bone marrow may help to differentiate benign from pathologic vertebral compression fractures, and in some cases infection from malignancy. Malignant vertebral compression fractures are hyperintense, while benign compression fractures are isointense or hypointense on diffusion-weighted images. Infections have a propensity to start in the disk space and invade the adjacent superior and inferior endplates. In contrast, neoplasms generally begin in the vertebral body themselves. CT scan without contrast is preferred to examine bony architecture of the lesion or as an alternative to MRI if the patient cannot undergo the study. Bone scan is widely employed to assess bone turnover in the primary lesion as well as to screen for secondary lesions. Grossly destructive lesions such as multiple myeloma and renal cell carcinoma may appear cold on bone scan, limiting its utility in certain pathologies. Positron emission tomography (PET) scan can also be similarly employed. It provides information about soft tissue organs and does not require osseous remodeling in order yield a positive result.

The Enneking classification (Tables 13.2 and 13.3) is the staging system used by the Musculoskeletal Tumor
Society (MSTS) to guide treatment of benign and malignant limb tumors. This system was modified by Boriani et al. to apply to spinal tumors. Benign tumors are defined using Arabic numerals. Malignant tumors are defined using Roman numerals to denote the grade of the tumor and whether there are metastases present. The letters A and B are used to denote containment within a compartment. A compartment as defined in the spine is intraosseous versus extraosseous (i.e., within the vertebral body vs. paravertebral extension).

Awareness of the above-mentioned system for malignant tumors is instructive. However, it is somewhat oversimplified when spinal tumors are concerned. For any malignant tumor, a wide to radical resection is the goal from an oncologic standpoint. However, the concept of “wide resection” in the spine is challenging and often impossible without damage to the neural elements. The principles of resection of primary malignant tumors of the spine will be elaborated later in this chapter. The goal of treatment is to:

Radiotherapy is almost always used as an adjuvant to surgical resection, and chemotherapy is used when appropriate. The Tomita staging system is similar to the Enneking system, but more directly applicable to spinal tumors of metastatic origin. The principles of classification may be applied to the primary spinal lesion with caution. It describes the tumor’s intracompartmental involvement (lesion in situ, pedicle involvement, anterior to posterior involvement), extracompartmental involvement (epidural involvement, soft tissue extension, or invasion of adjacent vertebrae), and the presence or absence of skip metastasis

The Weinstein–Boriani–Biaginini classification divides the vertebrae into 12 radial zones (clockwise in the original description, counterclockwise in the Spine Oncology Study Group modification). The tissues are then labelled from soft tissue to intradural (A to E). Both of the above classifications may be used to guide surgical planning (Table 13.4).

Benign tumors of the spine can present with significant pain and occasional deformity. The Enneking classification of benign lesions can be applied to benign spine tumors, as described above.

The most common benign lesions of the spine are: