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



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


Gideon Blumstein, MD, MS

Matthew W. Colman, MD, FAAOS, FAOA


Dr. Colman or an immediate family member has received royalties from Alphatec Spine and Spinal Elements; is a member of a speakers’ bureau or has made paid presentations on behalf of DePuy, a Johnson & Johnson Company, K2M, and Orthofix, Inc.; serves as a paid consultant to or is an employee of Alphatec Spine, K2M/Stryker Spine, Orthofix, Spinal Elements, and Xenix Medical; has received research or institutional support from AO Spine North America and CSRS; and serves as a board member, owner, officer, or committee member of AO Spine North America, Cervical Spine Research Society, LSRS, Musculoskeletal Tumor Society, and North American Spine Society. Neither Dr. Blumstein nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.





ABSTRACT

The evaluation, diagnosis, and treatment of spinal tumors remains a challenging issue in orthopaedic surgery. Although ultimate management is typically carried out by highly specialized practitioners in the fields of orthopaedic spine surgery and orthopaedic oncology, a foundational understanding of the topic is required for all practitioners who may encounter and evaluate patients with suspected spinal tumors to avoid delays in treatment or inappropriate management that can lead to deleterious results. Most spinal column tumors are metastatic, and a thorough oncologic history is required of all patients who present with back pain, radicular symptoms, or myelopathy. Prior history of cancer must prompt early workup and imaging. Primary tumors of the spine are rare and often insidious in nature and present challenges to early diagnosis. Careful evaluation and early referral to specialized care improve treatment options and outcomes. Treatment of spinal tumors varies greatly depending on the biology, location, and extent of disease and may include surgical, pharmaceutical, or radiotherapeutic approaches. Surgical treatment may be curative in some cases but is also extensively used for palliation in tumors that are resistant to radiation or chemotherapy. Treatment of benign spinal tumors is at times equally challenging because of tumor location and potential compression of neural elements. Although appropriate evaluation, imaging, and referral must not be delayed, tissue biopsy should not be performed before discussion with the physician ultimately treating spinal tumors, as inappropriate biopsy may significantly limit treatment options.

Keywords: malignant; metastatic; multidisciplinary; reconstruction; spondylectomy


Introduction

Spinal tumors encompass a broad spectrum of benign and malignant processes, both primary and metastatic, with varying degrees of biologic activity. Because of the broad spectrum of biology and tissue origin of spinal tumors, treatment algorithms are varied and complex, and many do not currently have established evidence-based guidelines. Therefore, accurate, timely diagnosis and thoughtful, patient-specific, multidisciplinary evaluation, and treatment planning are paramount.


Current Staging of Spinal Tumors

Benign and malignant tumors of the spine continue to be staged in a manner similar to that of their appendicular counterparts via the Enneking benign and Enneking malignant staging systems (Table 1). The key determinants of stage for benign tumors include rapidity of
growth, lytic component, bone destruction, and expansion beyond cortical boundaries. For malignant bone tumors, key determinants of stage include presence of metastasis, size, depth, and histologic grade. The American Joint Commission on Cancer staging system for malignant bone tumors uses tumor grade (high or low), tumor size (larger or smaller than 8 cm), the presence of regional lymph node metastasis, and the presence and location of metastasis, with staging distinction between skip metastasis (separate lesions within the same bone), pulmonary metastasis, and nonpulmonary metastasis.1 A spine-specific staging system (Weinstein-Boriani-Biagini; Figure 1) for benign or malignant tumors continues to be the standard by which practitioners describe the anatomic distribution of spinal tumors. This system is based on a clock-face division of the vertebral axial view, with a radial depth modifier. This system is not only descriptive, but it also guides treatment, because it implies resection extent, surgical approach, feasibility of obtaining a wide margin, and other treatment-related factors. Also, a staging system originally described in 2010 describes the anatomic extent of cord-level tumor compression. Not only is this system descriptive, but it also helps guide treatment based on MRI, which can help predict which patients are candidates for stereotactic radiosurgery2 (Table 2).









Imaging

The initial standard of care in imaging spinal tumors is a plain radiograph series. Although abnormalities may be subtle or obscured by overlying visceral anatomy, plain radiographs are an excellent initial screening tool to diagnose lytic or blastic lesions and to determine the lesion aggressiveness by demonstrating bone destruction or periosteal reaction. The so-called winking owl sign of an obliterated en face pedicular cortical density is a late but important finding. When not otherwise contraindicated, standing weight-bearing radiographs should be obtained because they give an indication of mechanical deformity, instability, or fracture.

Contrast-enhanced MRI of the entire spinal column is an appropriate study when managing most tumors because multifocal disease is common in metastatic carcinoma and possible in primary bone tumors such as chordoma. This modality allows concurrent visualization of neoplastic tissue, neural structures, and other soft-tissues. CT allows excellent visualization of bony detail, which, in addition to demonstrating the pattern of bone destruction, may reveal characteristic findings that facilitate a diagnosis, such as the calcification patterns unique to chondrosarcoma and chordoma, the trabecular appearance of hemangioma, or the sclerotic bony reaction of osteoid osteoma or osteoblastoma. Aside from imaging of the spinal axis itself, it may be important to use systemic imaging such as technetium Tc-99 bone scintigraphy, body MRI, or positron emission tomography in circumstances such as staging or metastatic surveillance for spinal tumors. The role of these systemic modalities is not well defined for most histologies, and their use is currently center and physician specific.

One emerging imaging modality that deserves mention is intraoperative computerized navigation.

Based on either scanning fluoroscopy, CT, or MRI, this modality allows for the linking of two-dimensional and three-dimensional patient images with real-time intraoperative instrumentation and maneuvers such as bony cuts or instrumentation insertion. As in the extremities and pelvis, early experience with this modality seems to indicate improved accuracy of instrumentation and tumor resection along with lower levels of surgeon ionizing radiation exposure, as discussed in a 2019 study.3 However, no data exist regarding benefit in terms of local recurrence or other patient-related outcomes (Figure 2).














Anatomic Considerations in Spinal Tumor Management

Structural mobility and rigidity are key in evaluating spinal tumors. Junctional (occipitocervical, cervicothoracic, thoracolumbar, and lumbosacral) and mobile zones (cervical, lumbar) are areas of high stress that do not tolerate structural bone loss as well as the thoracic spine, which is protected by sternocostal architecture.4 Likewise, spinal cord-bearing levels (occiput-L1) are less tolerant to deformity or epidural encroachment than the spinal nerve root containing levels of the lumbosacral spine. The occipitocervical articulation is particularly unique and relies heavily on occipital-C1-C2 ligamentous support from the transverse and alar ligaments. Bony destruction from tumor or after resection of the dens, C2 lateral masses, C1 ring, or C1 lateral masses can result in the functional equivalent of a traumatic occipitocervical dissociation and requires careful reconstructive consideration. Likewise, resections of the sacrum that involve more than half of the L5-S1 articulation may create sacropelvic discontinuity in this high-stress zone.






Vascular anatomy in the spine has important considerations in spinal tumors. The spinal cord is nourished primarily by the anterior spinal artery via sporadic radiculomedullary vessels, including the thoracolumbar artery of Adamkiewicz, which do not occur at every spinal level. Although compensatory mechanisms exist and the authors of a 2020 study have described safe resection of up to three spinal levels,5 reports of paraparesis after key radiculomedullary vessel sacrifice have been described.6 Preoperative angiogram, risk discussions, and intraoperative maneuvers such as
temporary clamping before definitive vessel sacrifice are important. The cervical spine tends to have more vascular redundancy than the poorly collateralized thoracic spine,7 whereas vascular-related neurologic events are extremely rare in the lumbosacral region.


Primary Malignant Tumors

Primary malignant tumors of the spinal axis represent a challenging clinical problem. Aggressiveness and fastidiousness of disease, anatomic constraints, technical nature of surgery, and significant complication profiles are obstacles that can stand in the way of successful tumor eradication. The modern standard of care is adherence to Enneking-appropriate surgical oncology principles in the management of bone sarcoma. This encompasses multidisciplinary evaluation, appropriate use of adjuvants, meticulously planned biopsy technique, and margin-negative en bloc resection of tumors.


En Bloc Spondylectomy

Advances in surgical technique and a detailed understanding of spinal anatomy have allowed Enneking’s principles to be applied to tumors of the mobile spine. Tumor distribution according to the Weinstein-Boriani-Biagini classification dictates the extent of resection. For example, malignant tumors in the posterior elements may require a fairly straightforward en bloc removal of the lamina alone, whereas tumors that occupy the entire anterior body may require deletion of the entire spinal segment, termed total en bloc spondylectomy.

The technique of total en bloc spondylectomy began in the 1970s and is currently being used.8,9,10 There are many different approaches to performing en bloc spinal tumor resections, and the surgical strategy relies on recognition that the spinal canal is a bony ring that must be osteotomized before rotating the vertebral body away from the neural elements. This can be done with posterior, anterior, or combined approaches.11 For staged anterior/posterior procedures, the posterior ring is usually osteotomized in the first stage, with placement of stabilizing segmental instrumentation above and below the tumor segment. In the second stage, the tumor is accessed via retroperitoneal or thoracotomy approach, great vessels are mobilized, transdiskal or transosseous cuts are made, and the specimen is delivered via rotation away from the neural elements. Cuts are facilitated via the use of thread wire saws that may be passed ventral to the thecal sac, around the vertebral bodies, and dorsal to the great vessels. In all posterior technique, the same basic steps are accomplished, but the procedure is more technical, given blind passage of thread wire saws and vertebral body cuts made ventral to dorsal, toward the thecal sac.

The most likely location for a marginal or contaminated margin is the dural margin. This may be managed by dural resection en bloc with the specimen, but persistent cerebrospinal fluid leakage may be an issue, especially in radiated beds. Thus, intraoperative brachytherapy may be used to maintain and treat the dural layer where margins are anticipated to be close.12

If wide margins can be achieved via en bloc spondylectomy, the oncologic benefit in terms of local recurrence and overall survival has been demonstrated. Key factors in addition to margin status for the risk of local recurrence include the absence of adjuvant radiation therapy, large tumor size, and high tumor grade. Overall survival is dependent on a wider array of variables, but most authors have reported overall survival rates after wide margin en bloc spondylectomy for spine sarcoma that are similar to those for extremity sarcoma. There are, however, exceptions to this in higher grade diseases where spinal involvement itself is still a poor prognosticator. For example, spinal osteosarcoma carries a dismal prognosis even with successful wide margin resection and adjuvant chemotherapy.13,14,15

Complication rates following total en bloc spondylectomy are high. One study reported an overall perioperative complication rate of 42%, with potential risk factors being prior intralesional surgery, staged anterior-posterior surgery, higher number of total spondylectomy segments, and exposure to radiation therapy.16 Instrumentation failure because of cage subsidence and/or pseudarthrosis is the most common major complication event, reported in 3% to 40% of patients. Other significant issues include wound infections, neurologic decline, deep vein thrombosis/pulmonary embolism, massive blood loss, and pneumothorax.

Recently, patient-reported quality-of-life outcomes following en bloc spondylectomy have been studied. Despite the reasonable hypothesis that such an extended surgical procedure done for malignant tumors would lead to poor postoperative quality of life, disease-specific and general health metrics are comparable to those in other spine-related conditions such as postpseudoarthrosis repair and are not statistically different from those in patients treated for the same conditions with definitive radiation therapy and no surgery according to a 2019 study.17 Mental health scores may approach normal population means if patients are considered to be free of disease; conversely, local recurrence or metastasis affects both mental and physical summary scores, suggesting an interplay between psychological and physical factors.17



Reconstructive Issues Following Spondylectomy

The occipitocervical region of the spine has an especially unique articulation. Key ligamentous stabilizing structures include the transverse and alar ligaments, but in clinical situations where spinal tumors are involved, it is more frequently the bony columnar support that is compromised. Following C2 spondylectomy, posterior reconstruction alone appears to be insufficient, and central or lateral columnar reconstruction from the clivus or occiput to C3 provide equivalent stability.18,19

Reconstruction of the mobile spine following partial or total spondylectomy uses techniques borrowed from other clinical settings. Key concepts include the use of load-sharing rigid posterior segmental instrumentation and load-bearing anterior column reconstruction. Recent advances include recognition of the importance of biologic fusion, leading to use of microvascularized autograft, especially in settings where adjuvant radiation has been used. Cage subsidence, which leads to cyclical micromotion, appears to be the root cause of most episodes of implant failure,20 and advances to increase end plate surface area and structural rigidity of reconstruction cages may lead to improved outcomes.

The sacrospinal articulation provides further challenge in reconstruction following tumors. After partial or total sacrectomy, posterior spinopelvic instrumentation, even with multiple rod constructs, appears inferior to constructs that reconstruct the anterior spinopelvic columns via cathedral-type vascularized or nonvascularized supports.21


Chordoma

Chordoma is a rare (annual incidence of one per one million persons) slow-growing, low-grade neoplasm of the axial skeletal system with a prevalence in the sacrococcygeal area (50%), skull base (35%), and mobile spine (15%). Within the mobile spine, the cervical segments are the most common site. The cell of origin is thought to be a remnant of the primitive notochord, which becomes the nucleus pulposus for the intervertebral disk in developed humans. This explains the almost exclusively axial location, as well as possibly the rarely reported cases of multicentric chordoma. In addition, the notochordal cell of origin is thought to possibly implicate benign notochordal cell tissue as a precursor lesion, although according to a 2021 study, subsequent investigations have not definitively demonstrated progression to classic chordoma.22 The rate of metastasis is 30% to 40% and typically occurs late in the disease course, consistent with the low-grade nature of the lesion.

The imaging hallmark of a hyperintense, lobular, T2 bright axial lesion (Figure 3) with occasional calcifications on CT scan sometimes obviates the need for formal biopsy, especially in difficult-to-access areas and considering chordoma’s fastidious tendency to seed biopsy or needle tracts. When in doubt, histologic diagnosis via core needle biopsy placed in a resectable location along a proposed incision line is always preferable. Conventional chordoma displays the classic physaliferous cell, a foamy, vacuolated cell distributed in myxoid stroma. The hallmark of chordoma staining is brachyury positivity, a transcription factor for notochordal differentiation, but keratin positivity is an important factor that distinguishes chordoma from chondrosarcoma. This is especially relevant given the variants of chordoma that may include chondroid or even dedifferentiated histologic subtypes.

Given that chordoma is a low-grade lesion, the treatment of choice is wide en bloc excision, and the tumor is classically radioinsensitive and chemoinsensitive. However, modern treatment of chordoma usually involves an element of neoadjuvant and adjuvant radiation therapy, which allows for local control of macroscopic and
microscopic satellite lesions to which chordoma is prone. This adjuvant also helps marginate the tumor in cases where anything better than a marginal margin may not be possible. In addition, for sacral locations, the recognition that both radiation therapy and surgery should potentially involve the gluteus and piriformis musculature has enhanced successful local control. Using this methodology, one study reported only one local recurrence over 23 cases of primary chordoma,11 a rate much lower than that previously reported for this tumor.23,24 Prognostic factors for local recurrence are consistently large tumor size, previous tumor contamination, and intralesional resection, whereas predictors of poor survival include preoperative motor deficit and older age.25







Chondrosarcoma

Chondrosarcoma, like chordoma, is a fastidious, rare, predominantly low-grade, slow-growing neoplasm of cartilage cell lineage. It is even more rare in the spine, with only 10% to 12% of chondrosarcomas presenting in the axial skeleton, most commonly in the thoracic region.26 Most arise as spontaneous primary neoplasms, but secondary chondrosarcomas arising in the setting of multiple hereditary exostosis or one of several multiple enchondroma syndromes do occur.27 The lesion typically appears as an aggressive, T2 bright tumor with extraosseous component and intralesional calcifications. Survival mirrors that for other sarcomas, with most series reporting in the 60% to 70% survival range at 5 years, with an approximately 40% overall metastatic rate.28

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May 1, 2023 | Posted by in ORTHOPEDIC | Comments Off on Current Concepts in Primary Benign, Primary Malignant, and Metastatic Tumors of the Spine

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