19 Primary Tumors of the Thoracic Spinal Column

19.1 Introduction

Only 7,500 primary vertebral column tumors are seen each year,³ constituting less than 10% of all spinal column neoplasms.^4,5 These tumors can be divided into malignant tumors, which account for 62% of all cases⁶ and benign neoplasms or hamartomas, which account for the remainder. Malignant tumors are the chief concern of the spine surgeon due to their poor prognosis, but many benign lesions also require surgical intervention. This chapter discusses spine tumor staging, typing, and treatment, with a focus on tumors of the thoracic region.

19.2 Staging of Primary Tumors of the Spinal Column

Currently, there are three main staging systems for primary spinal column tumors—the Enneking system,^7,8 the Weinstein–Boriani–Biagini (WBB) system⁹ ( Fig. 19.1), and the Tomita system¹⁰ ( Fig. 19.2). They are summarized in Table 19.1 and discussed below.

19.2.1 The Enneking System

Though developed for appendicular musculoskeletal tumors,⁷ the Enneking system is now widely used to classify spinal column lesions^11,12,13 based on surgical grade, local extent, and the presence of metastases. Different scales are used for benign and malignant lesions,^{1,7,8,14,15,16,17} but both use clinical, histological, and radiographic evidence^8,17 and are guided by the principle that the tumor should never be entered during resection.⁴

Benign tumors are broken into three grades based on their aggressiveness and degree of circumscription.¹⁴ Grade I (latent) lesions are generally asymptomatic, well-circumscribed, monostotic, and display contact-dependent growth inhibition.^8,14 Grade II (active) lesions possess thinner, irregular borders,^8,14 and are generally symptomatic, expansile, and histologically well-differentiated,⁸ with a constant cell-to-matrix ratio throughout and an enhancing neovascular rim on computed tomography (CT).⁸ Last is grade III (aggressive) lesions, which are poorly circumscribed, symptomatic, hyperplastic.⁸ Unlike grade I or II lesions,^8,14 they expand extracompartmentally, and may form benign metastases.⁸ Current Enneking principles allow stage I lesions to be treated with intralesional excision due to their low propensity to recur.⁸ However, stage II lesions should be treated with marginal en bloc resection, unless the associated morbidity is unacceptable.^8,9 Lastly, stage III tumors require wide en bloc resection due to their tendency to recur.^8,9

Unlike benign lesions, osseous malignancies are graded on differentiation and compromise of vertebral cortical bone—A-type lesions remain intracompartmental, whereas B-type lesions breach cortical bone.^7,8,14 Grade I (low-grade) malignancies, unlike grade III benign lesions, are necrotic, highly vascular, and hemorrhagic.⁸ High-grade (grade II) malignancies are differentiated from low-grade lesions by more extensive proliferation, dedifferentiation, and nuclear atypia.^7,8,14 All malignancies with metastases are grade III, though they are generally not subdivided by degree of extracompartmental expansion.^{1,7,8,14,15,16,17} Current treatment standards suggest that stage I and II lesions be treated with wide en bloc resection, despite the sacrifice of significant neurovascular structures often required in treatment of IB and IIB lesions.^8,9 It has been suggested that stage III lesions be treated with wide resection plus adjuvant radiotherapy (RT) or chemotherapy,⁸ but systemic therapy and palliative care are preferable in cases where en bloc morbidity would be high.

Fig. 19.1 The Weinstein–Boriani–Biagini staging system divides the vertebrae into 12 sectors and 5 tissue layers—(A) paraspinal, (B) superficial vertebral bone, (C) deep vertebral bone, (D) intradural, extramedullary space, (E) intramedullary space. (a) Shows the sector and (b) shows a labeled thoracic vertebra for reference.

Fig. 19.2 The Tomita system assesses the feasibility of en bloc spondylectomy for a tumor based on the portions of the vertebra it involves, the extracompartmental invasion, and the presence of skip lesions. (Adapted from Tomita et al, 1994.³²)

Table 19.1 Classification systems for primary spinal tumors

Several studies have shown the Enneking system to have good interobserver and intraobserver reliability,¹¹ and have shown its use to decrease local recurrence and increase overall survival.⁴

19.2.2 The Weinstein–Boriani–Biagini System

The WBB classification differs from the Enneking staging in that it is designed to incorporate the more complex spinal anatomy^11,17,18 and seeks to describe the optimal surgical approach, not the surgical margin.^19,20,21,22 The WBB system acknowledges that true radical resection is impossible in nearly all symptomatic spinal malignancies^7,8,9 and so vertebrae are treated as the oncological compartments.

Staging begins by superimposing a clock face over a horizontal section of the vertebra so that the 12 and 1 o’clock sectors straddle the spinous process, and the 10 and 3 o’clock positions overlie the pedicles.²⁰ The tumor is then classified by (1) its angular position—the sectors of the clock face that it occupies, and (2) its radial position—whether it involves paraspinal musculature (A), cortical bone (B), medullary bone (C), epidural space (D), or intradural space (E).^11,20 Like the Enneking system, it has extremely high intraobserver and interobserver reliability,¹¹ and the two are often used together during surgical planning.^19,20,21,22

19.2.3 The Tomita System

Like the WBB system, the Tomita system assesses spinal malignancies based on anatomical location.^10,13 However, unlike the former, its purpose is to evaluate the feasibility of resection by en bloc spondylectomy. Tumors are divided into seven numbered, increasingly inclusive classes based on location within the spinal column: (1) the vertebral body, (2) the pedicle, (3) posterior elements, (4) the spinal canal, (5) the paravertebral area, (6) adjacent vertebrae, and (7) nonconsecutive vertebrae.^{1,10,13,23,24} Tomita et al recommend wide-margin en bloc spondylectomy for type III lesions and marginal en bloc spondylectomy for type IV and V lesions.²⁴ They recommend against en bloc spondylectomy for type VII lesions, and leave selection of treatment type I, II, and VI lesions to the individual surgeon, as type I and II lesions do not require en bloc spondylectomy to prevent recurrence, and type VI lesions often recur, even with en bloc spondylectomy.²⁴

19.3 Surgery for Thoracic Spinal Tumors

All surgical intervention begins by deciding the goal of surgery, which for most primary tumors is to attempt cure.²⁵ Curative treatment starts by imaging the affected region, using CT to assess bony destruction, and magnetic resonance imaging (MRI) to evaluate for spinal canal and paraspinal soft tissue invasion.²⁶ If imaging and clinical findings are definitive, the tumor is staged using the Enneking and WBB systems in order to determine proper margins and proper approach, respectively.^9,27 Otherwise, a biopsy should be performed to allow for definitive diagnosis prior to staging and surgical planning.^3,28,29 This definitive diagnosis allows for selection of treatment that minimizes complications, and maximizes the chance of cure. CT-guided biopsy is preferred by many,³ as the biopsy tract can be placed in the future surgical field, which decreases recurrence.^9,30

One of the more popular techniques for en bloc excision of thoracic tumors is the en bloc spondylectomy first described by Tomita et al.³¹ The procedure involves a posterior-only approach and makes use of a specially designed T-saw, which has been shown to reduce seeding of the surgical site.³² The procedure begins with a posterior midline incision and subperiosteal dissection encompassing three levels above and below the lesion.^{10,31,33,34,35} Next, the inferior facets and spinous process of the level proximal to the specimen are osteotomized to expose the superior articular processes of the uppermost involved vertebra. Dissection continues laterally over the ribs, which are cut 3 to 4 cm lateral to the costotransverse joint. As a guideline, the dissection field must be wide enough to clear the tumor borders and allow dissection underneath the transverse processes. The pleura is then bluntly dissected from the ribs and vertebrae, and the intercostal vessels are ligated. Soft tissue around the intervertebral foramina is removed, taking care to avoid damage to the nerve roots during cervicothoracic or thoracolumbar procedures. A T-wire is then looped around the pedicle in the cephalocaudad direction using a C-shaped T-saw guide. The guide is removed and a T-saw is used to divide the pedicle. This is repeated bilaterally at each level to be resected and the posterior column is removed en bloc. The cut pedicle surfaces are sealed with bone wax to minimize bleeding and seeding of tumor cells into surgical field. Bilateral pedicle screws are placed two levels above and below the involved segments, and a temporary rod is installed on one side to maintain distraction during the corpectomy.¹⁰ The intercostal nerves are sacrificed contralateral to the rod and blunt dissection is used to free the aorta and great vessels from anterior faces of the vertebrae.^{10,31,33,34,35} Care must be taken during this step to avoid injuring the azygos system or inferior vena cava (IVC).³¹ Vertebral protectors are then inserted bilaterally to create a plane between mediastinal organs and the vertebrae. The thecal sac is freed from the posterior longitudinal ligament (PLL) and vertebral body, and a cord protector is inserted in the plane between the vertebrae and thecal sac. T wires are inserted in the plane of the vertebral protectors at the levels of the vertebral discs bounding the involved segments. The anterior longitudinal ligament (ALL), discs, and PLL are then transected; the cord protector must be firmly in place during this step to avoid cord injury. Additionally, shallow grooves may be formed in the sides of the discs prior to discotomies to ensure that transection occurs in the desired plane. Following the discotomies, the specimen is rotated around the long axis of the cord and removed en bloc from the side contralateral to the rod.^{10,31,33,34,35} Hemostasis is achieved and the wound may be washed with water and cisplatin to kill tumor cells that have seeded the area.²⁴ A bony strut or autograft-filled cage is then inserted into the anterior column defect. Permanent rods are installed, drains are inserted, and the wound is closed. The patient may also be given an orthosis to wear during the recovery period.^{10,31,33,34,35}

The above procedure is modified slightly for those tumors involving the great vessels and for tumors at the cervicothoracic and thoracolumbar junctions. In these cases, a combined approach may be preferred.^24,33 For a cervicothoracic tumor, the procedure begins with a transmanubrial approach.^36,37 An osteomuscular flap containing the sternoclavicular joint, entire clavicle, and cervical musculature is formed and reflected.³⁶ The medial portion of the first rib, and occasionally the second and third ribs, is resected. An upper lobectomy is also performed if the lung is involved.³⁶ Dissection continues by freeing the esophagus, trachea, and mediastinal vasculature from the anterior surface of the vertebrae.³⁷ The anterior wound is then closed and the patient is rotated to the prone position, where the procedure proceeds in a fashion similar to that described for the posterior-only approach.^36,37,38 During the posterior procedure, care should be taken to dissociate the cervical and upper thoracic nerve roots from the tumor,³⁷ as damage to these structures is associated with significant neurological dysfunction.

For thoracolumbar tumors, a combined approach facilitates dissection of aorta branches from the vertebrae and preservation of the upper lumbar nerve roots. Whether the two approaches are performed simultaneously with posterior delivery of the tumor³⁹ or sequentially with delivery of the tumor through the anterior approach⁴⁰ is largely up to the individual surgeon. As with the combined approach for cervicothoracic tumors, the anterior approach is used to clear the anterior face of the spinal column—this includes taking down the diaphragm and releasing the major vessels. For posterior delivery of the specimen, the procedure is like that described for the posterior-only approach, with the exception that release of the ALL and anterior disc is done via the anterior approach.³⁹ However, for procedures with anterior delivery, posterior instrumentation and wound closure are performed first, followed by completion of tumor resection, tumor delivery, and reconstruction of the anterior column through the anterior approach.⁴⁰

19.3.1 Surgical Margins

Enneking originally described four types of surgical margins⁷—intralesional, marginal, wide, and radical—but only intralesional, marginal, and wide margins are feasible in the spine due to its complex anatomy^7,8,9,27. Intralesional resection—dissection along the tumor pseudocapsule—can be applied to the Enneking grade I benign tumors^8,41 but grade II tumors require marginal margins, or resection within the reactive tissue surrounding the tumor pseudocapsule.^8,41 Lastly, wide margins—resection of the tumor with a layer of healthy tissue—are prescribed for grade III benign lesions and all vertebral malignancies as they improve local control.^25,42,43 This improved control is the single strongest predictor of overall survival in spinal malignancies.^{15,17,21,42,43,44,45}

19.3.2 Resection Technique

The last consideration in surgical planning is the resection technique. En bloc excision—removal of the entire tumor in one piece with wide margins^9,41,46—is the only way to achieve tumor-free margins. It has the advantage of significantly improving patient’s overall survival and recurrence-free survival,^{4,17,23,25,41,46,47,48,49,50} and is the Enneking-appropriate approach for grade III benign lesions and all malignancies.⁸ However, it has higher intraoperative mortality and morbidity, and postoperative morbidity relative to piecemeal resection.^{4,10,23,41,48,51,52} This increased complication rate,²¹ reported as 10 to 35% in some series,^41,46,53 and en bloc’s steep learning curve led many practitioners to favor piecemeal resection. However, it is important to weigh these sequelae, the potential survival benefit,^25,41,46 and patient preference before selecting a resection technique. Current consensus holds that the risks of en bloc resection generally outweigh the benefits in benign lesions, whereas the reverse is true for localized malignancies.^17,23,30,46

19.4 Overview of Different Lesion Types

The remainder of the chapter focuses on the main tumor types that afflict the spine, as well as the rate at which they appear in the thoracic spine. Tumor types are coarsely divided into benign lesions, which can be treated nonsurgically in some cases, and primary spinal malignancies, which are almost uniformly treated with surgery. Epidemiology and basic imaging findings are summarized in Table 19.2 and Table 19.3.

19.5 Benign Tumors and Hamartomas

19.5.1 Aneurysmal Bone Cyst

Description

Aneurysmal bone cysts are highly vascular, locally aggressive cyst-like lesions^{5,54,55,56,57} characterized by significant bony destruction.^57,58,59 Two-thirds of cases are secondary to a giant cell tumor (GCT), osteoblastoma (OB), chondroblastoma, or osteosarcoma,^{21,55,57,59,60,61,62,63} and nearly all affect the posterior elements. As much as 90% also involve the vertebral body,^{26,55,57,58,61,62,64,65} creating three-column involvement and cord compression.⁶⁶ Histologically, they are characterized by a series of blood-filled channels lined with an abundant, fibrous stroma of spindle cells and osteoclast-like cells^{26,57,58,59,61,62,66} occasionally showing intralesional ossification.⁵⁷

Diagnosis

Patients often present with localized pain that worsens with activity and which has been present for 8 to 12 months.^{54,55,56,58,59,60,67,68,69,70} Pain is often worse at night²⁶ and may present along with a palpable mass.^62,67 Neurological involvement, pathologic fracture, and spinal instability are relatively rare, but have been noted.^54,62,66,69

On plain radiography, the lesion is expansile, well-circumscribed, and radiolucent⁶⁹ and on CT, it is expansile, eccentric, multilobulated, and osteolytic.^55,57,58,66 ABCs are often said to have a soap bubble appearance on CT,⁶² with an eggshell-like capsule and visible fluid–fluid level created by previous hemorrhage.^26,62,65,69 This fluid–fluid level is best visualized on MRI, which also shows the intralesional septation.^{26,55,57,59,60,62,70} Because of the abundant fluid, the lesion is generally hypointense on T1 and hyperintense on T2 MR.⁶⁹

Treatment

ABCs generally require treatment,^55,59 though no consensus exists regarding standard of care.⁷¹ Surgery has historically been front-line treatment, but results in the past decade have suggested that selective arterial embolization (SAE) may be equally effective in patients free of neurological dysfunction or spinal instability.^{54,60,62,72,73} Additionally, SAE has lower morbidity^54,60 and reduces intraoperative blood loss in patients who crossover to surgery.^{5,55,62,69,72} However, surgery, not SAE should be used in cases where the tumor shares a blood supply with the cord,^61,70 causes spinal instability, or creates rapidly progressive neurological dysfunction.

For surgical candidates, complete surgical resection is the goal, as it prevents recurrence.^{5,55,60,62,63,70,72,74,75} This local control is readily achieved through en bloc resection, but many report satisfactory results with intralesional curettage of grade I or II tumors.^{5,26,63,69,73,75,76} Adjuvant RT is contraindicated due to the risk of osteosarcoma induction.^{54,55,56,59,60,65,70}

Prognosis

Recurrence is observed in 10 to 44% of cases and generally occurs within the first 2 years of follow-up.^{56,66,68,73,75} Compared to those treated with en bloc resection, local recurrence is higher in patients treated with subtotal resection,^61,65,66 but not for those treated with SAE.^70,73

19.5.2 Benign Fibrous Lesion

Description

Benign fibrous lesions are a class of osteolytic lesions that includes fibrous dysplasia, chondromyxoid fibroma, benign fibrous histiocytoma, and nonossifying fibroma.^14,62,77 Despite their different origins, they all feature a collagenous stroma with cytologically normal, spindle-shaped fibroblasts arranged in fascicles or storiform patterns. The stroma may also contain woven bone, foamy macrophages, or multinucleated giant cells.^{29,62,77,78,79,80,81,82,83}

Diagnosis

Benign fibrous lesions most commonly present with chronic nonspecific back pain,^{29,79,80,82,83,84,85} but in rare cases may present with neurological symptoms of insidious onset.^29,77,81,85 Because of these nonspecific symptoms, diagnosis relies heavily on CT and MRI imaging.²⁹ CT demonstrates an expansile, blown-out lesion with ground-glass stroma and sclerotic cortex.^62,77,82

Treatment and Prognosis

Preliminary treatment is bisphosphonates to relieve pain,^62,86 but patients with spinal instability or neurological dysfunction may require surgery.^62,87 The goal of surgery is complete resection of the tumor^29,62,77,82 as a subset of these lesions recur following subtotal resection.²⁹ En bloc excision is unnecessary, as piecemeal gross total resection achieves 100% local control in many cases.^{29,77,78,80,82,85}

19.5.3 Chondroblastoma

Description

Chondroblastomas are extremely rare tumors derived from immature cartilage that grossly appear pink to beige, are lobulated by fibrous septa, and display multifocal calcification.^{88,89,90,91,92,93,94} Histologically, they possess a high density of polygonal, chondroblast-like cells in an eosinophilic chondroid matrix with giant cells and “chicken wire” calcification.^{62,88,90,91,92,94,95,96,97}

Diagnosis

The majority of patients have presented with localized pain as their chief complaint,^{88,89,90,92,94,97,98,99} though a fraction also have radicular pain and/or paresis.^{3,92,93,94,95,97,99,100} Furthermore, some thoracic lesions compress lung parenchyma and cause dyspnea.^93,94,97

Chondroblastomas are aggressive, eccentric, osteolytic lesions on radiograph, with marginal sclerosis, cortical bone involvement, and occasional multifocal intralesional calcification.^{88,89,90,91,92,96,97,100} The intralesional calcifications are best visualized on CT^93,97,100 and soft tissue invasion is best demonstrated as a hyperintense mass on T2-weighted MRI.^{92,93,94,95,97,99,101} Because these features are nonspecific, biopsy is generally necessary for diagnosis.^3,92,97

Treatment and Prognosis

Because of the small number of documented cases (≈30), no guidelines exist for treatment. Surgery has been the method of choice, with the goal of complete resection of the tumor,^{89,90,94,98,99} as 30% of vertebral chondroblastomas have locally recurred.^94,100 Both en bloc^89,93,94,97 and curettage have been used with high success,^{89,92,94,96,98,100,101} and neither is currently preferred.

19.5.4 Enostosis

Enostoses, or bone islands, are hamartomas^{26,102,103,104,105} less than 2 cm in diameter composed of intramedullary cortical bone.^{26,104,106,107} They are histologically identical to normal lamellar bone, possess a complete haversian system,^{102,104,105,108} and have an irregular or spiculated margin where they blend with surrounding cancellous bone.^102,104,105

Diagnosis

Enostoses are generally discovered as incidental findings on imaging studies^102,104,105 and are asymptomatic in nearly 100% of cases.^105,107 Radiographically, they are identical to cortical bone and have a “cumulus cloud”¹⁰⁴ appearance. On CT, they are round osteoblastic lesions within normal cancellous bone characterized by an irregular or spiculated border.^{102,103,104,105,106} They are hypointense on both T1- and T2-weighted MRI^{26,102,103,105} and are distinguished from metastases on bone scintigraphy, as they do not show elevated levels of tracer uptake.^{102,103,105,107,108}

Treatment and Prognosis

The majority of enostoses remain constant in size^103,104,105 and so do not require treatment. However, the 31.9% that do change in size can become symptomatic.^{103,104,105,106,107,109} Accordingly, patients with neurological symptoms and a history of enostosis may require removal of the lesion.

19.5.5 Eosinophilic Granuloma

Description

Eosinophilic granuloma (EG) is the most benign^22,62,110 and most common^22,110,111 type of Langerhans’ cell histiocytosis. It arises from the clonal expansion of Langerhans’ histiocytes^{62,111,112,113,114,115}—antigen-presenting cells found predominately in the skin^62,110,115—and typically presents as a solitary bone lesion^110,111 in the vertebral body.^116,117 EG is histologically characterized by abundant Langerhans cells^69,118 with variable numbers of eosinophils, multinucleated giant cells, lymphocytes, and other leukocytes.^113,118,119

Diagnosis

EG often shows an insidious onset with progressive osteolytic destruction leading to vertebrae plana in children and asymmetrical vertebral collapse in adults.^22,116,118 Patients commonly complain of local pain and spine stiffness, and less commonly present with spinal deformity, gait ataxia,^110,120 or other neurological impairment.^{62,69,110,112,116,118,120,121,122,123,124} Said impairment may result from direct invasion of the tumor into the spinal canal or from vertebral collapse,^110,120 an event most commonly seen with thoracic and lumbar lesions.¹²⁵

In up to 84% of thoracic lesions, EG presents as a vertebra plana with intact endplates and discs on CT or MRI.^{26,62,119,122,123,125,126,127,128} Intact vertebrae contain intramedullary lytic lesions on CT, with irregular margins^69,116,124 that appear hyperintense on T2- and hypointense on T1-weighted MR.^{26,62,116,121,122,125,126} Though vertebrae plana are highly characteristic of EG, they are not pathognomic. Biopsy allows for definitive diagnosis in 70 to 100% of cases though,^{22,112,113,120,124} as EG show Birbeck granules and strong CD1a staining.^{62,113,115,120,121,123,129}

Treatment

General practice involves lesion biopsy and conservative management with nonsteroidal anti-inflammatory drugs (NSAIDs) and bracing,^{62,69,113,116,120,121,123,127} as many pediatric cases resolve spontaneously.^124,126,127 Those patients with pain refractory to NSAIDs may get relief with methylprednisolone injection,^112,124 but for cases characterized by cord compression, deformity, or severe neurological dysfunction, surgery is preferred.^{22,26,62,69,110,113,123,126} The goal of this surgery is to relieve neurological symptoms and address spinal instability, not to achieve gross total resection.¹¹⁷ This is most easily accomplished via a posterior approach in thoracic regions^22,121,123 and may involve resection of the affected vertebra.^120,121

Prognosis

Patients generally have excellent outcomes,^{62,110,119,124,125} as recurrence occurs in less than 20% of solitary pediatric^112,124 and adult EG.¹³⁰ Survival rate at both five years^121,126,129 and 10 years for monostotic disease is 100%,¹²¹ and the 5-year survival for polyostotic disease is similar.¹²¹

19.5.6 Giant Cell Tumor (Formerly Osteoclastoma)

Description

GCTs are highly vascularized,^5,131 expansile, osteolytic tumors^5,6,26,74 capable of producing spinal column instability¹³¹. They are considered to be the most aggressive benign primary spine tumor¹³² and are thought to arise from osteoclasts.^74,133 Histologically, they are characterized by multinucleate giant cells with abundant eosinophilic cytoplasm, monocytes, and spindle-shaped stromal cells in a collagen-rich matrix.^{3,5,14,26,62,74,134,135,136} GCTs most frequently involve the vertebral body, but may also involve the posterior elements.^{5,137,138,139}

Diagnosis

Patients generally present with focal back pain that overlies the lesion persisting for 6 to 12 months.^{5,14,21,69,136,137,138,139,140,141} Neurological deficits, radicular pain, and pathologic fracture are also seen in highly aggressive lesions.^{5,14,136,137,139,140,142}

Radiographically, GCTs have a “moth-eaten” or “soap bubble” appearance in a blown-out vertebral body.^{5,6,7,132,134,138,141} CT demonstrates a contrast-enhancing, expansive, osteolytic lesion commonly compromising the vertebral cortex.¹⁴³ MR shows a contrast-enhancing lesion with similar features, commonly accompanied by invasion of paraspinal tissue.¹⁴³ Because these features are common to many other pathologies,^{6,14,132,136,141,144} definitive diagnosis requires biopsy.^{6,131,132,138,145}

Treatment

As most spinal GCTs are Enneking grade II or III,^{140,141,146,147} the treatment of choice is gross total resection via a wide en bloc technique. This is associated with the lowest rate of recurrence and the highest rate of long-term cure.^{3,6,13,21,69,72,131,134,135,137,141,142,145,148,149,150} In cases where the tumor abuts neural elements^{5,13,132,147,150} and en bloc resection is not be possible, piecemeal gross total resection may be employed.^{5,69,134,140,141,145,146,150} In such cases, complete resection is essential, as it drastically reduces the rate of recurrence.^21,148,149

Preoperative arterial embolization is highly recommended in the treatment of this highly vascular lesion,^{3,5,72,74,131,132,141} as it improves visualization during resection and reduces intraoperative morbidity.^{3,72,74,84,131,132,141} Despite this effectiveness as a neoadjuvant therapy, selective arterial embolization is not currently recommended as a monotherapy.⁷²

The literature in support of other adjuvant therapies is insufficient to recommend their use.^{6,21,134,137,140,141,146,147,149} Specifically, radiotherapy is contraindicated due to its association with iatrogenic osteosarcoma^{5,14,132,134,137,139,140,146,149,150,151} and an eightfold increase in the odds of instrumentation failure.¹³ The use of denosumab is similarly questionable, though several recent studies suggest that it improves the rate of surgical success¹⁵² by preoperatively ossifying^74,135,152 or shrinking the tumor.^69,153 Lastly, the use of bisphosphonates is not supported, though some suggest they may help to prevent recurrence.^21,148

Prognosis

GCT prognosis has improved significantly over the past two decades.^148,149 Recurrence occurs in 46 to 80% of cases treated with subtotal resection^{3,6,69,133,134,141,147,149} and 25 to 50%^{74,142,146,148,149} of cases treated with piecemeal gross total resection. Local control afforded by en bloc resection is superior to these two methods and approaches 100% in some series.^{3,131,134,148,149} Recurrences for all interventions occur at a mean of 19 to 21 months, with 63 to 96% occurring within the first 2 years of follow-up.^{14,21,134,137,142,148,149} Predictors of improved recurrence-free survival are en bloc resection, univertebral involvement, lower Enneking grade, and younger age.^21,149 Most patients show improvement of pain^74,137,146 and neurological symptoms^74,150 following surgical treatment.

19.5.7 Osteoid Osteoma

Description

Osteoid osteomas (OOs) arise from cancellous bone^3,154 and are characterized by a small, osteolytic nidus, circumscribed by a thick sclerosis of reactive bone.^{26,62,154,155,156} Histologically, the nidus is highly vascularized¹⁵⁷ and contains osteoblasts, osteoid, and woven bone.^154,157 Nidal size traditionally distinguishes OOs (< 2 cm) from OB (> 2 cm).^{3,26,69,155,157,158,159} OOs are most commonly found in the pedicles and lamina,^160,161,162 and localize to the posterior elements in 70 to 100% of cases.^{26,69,155,156,159,160,163,164,165,166,167,168,169,170,171}

Diagnosis

Painful scoliosis is a near-pathognomic finding and may occur in up to 70% of cases.^{154,155,156,157,160,162,164,168,172,173,174} It is most common in thoracic lesions and lesions localized to the lateral aspect of the vertebra.^174,175 It is thought to result when nidus-produced PGE₂^{157,160,171,176} causes inflammation and contraction of paraspinal muscles, which flexes the spine away from the lesion.^{154,155,173,174} This theory is supported by the fact that tumors usually localize to the concave aspect of the scoliotic apex^{154,155,168,174} and rarely produce scoliosis when localized to the spinous process.¹⁵⁵ OO also classically produces focal pain that worsens at night, improves with NSAID use,^{26,62,69,154,157,159,161,162,163,164,167,168,169,170,173,177} and has been present for 11 to 22 months at presentation.^{62,154,166,168,170,174,177,178} It infrequently produces neurological dysfunction or radicular pain.^69,157,171

On plain radiograph, the lesion is round and radiolucent with surrounding sclerosis^{3,26,69,154,155,157,162,172} and intranidal calcification.^26,69 Small lesions may be difficult to detect on radiograph,^{26,162,172,173} but are easily visualized on Tc⁹⁹ bone scans.^{62,156,160,162,179} MR also helps to visualize tumors, which are contrast-enhancing,^26,154 low-to-intermediate signal on T1, and high signal on T2.^{26,69,164,170} They may also be surrounded by edema^{26,154,157,166} resulting from nidal COX2 activity.¹⁵⁷

Treatment

OO is a self-limiting tumor that occasionally regresses over time.^{69,157,163,164,172} As such, NSAIDs are first-line therapy in most cases.^{3,62,154,156,157,160,171,177} Failure of conservative therapy, development of neurological dysfunction, or onset of spinal instability recommend the patient for surgical intervention.^{62,69,154,157,170,171,177} The goal of surgery is gross total resection,^{3,154,157,169,179} though many groups achieve good results with only resection of the nidus.^{154,160,162,173,176} En bloc resection is not required and curettage is the standard of care at many centers.^{69,162,163,164,171,173,176} Though painful scoliosis resolves in 70 to 90% of cases following nidus resection^154,168,171 reconstruction is necessary in patients where the scoliosis has become structural.^69,160

For medically refractory patients presenting with pain alone, laser or radiofrequency ablation may serve as cost-effective alternatives¹⁷² offering quicker recovery, lower complication rates, and lower morbidity.^{72,159,161,177} Their use is contraindicated in OOs directly contacting the neural elements though,^{72,156,164,172} as a layer of cortical bone is necessary to act as an insulator and prevent thermal damaging to the cord or nerve roots.^{160,164,169,172} This risk has led many interventional radiologists to avoid radiofrequency ablation (RFA) in all cases of spinal OO.^{26,156,157,161,164,172,173,176}

Prognosis

Most patients experience good outcomes, with a 4.5 to 10% rate of recurrence in OO treated with intralesional resection and ≈ 0% rate of recurrence in those treated with wide-margin en bloc resection.^{69,154,161,162,178} The higher level of recurrence in intralesional cases is thought to result from failure to completely resect the tumor nidus.¹⁶² Symptomatic relief is also high, with greater than 90% of surgically treated patients achieving complete pain relief^154,171 and 70 to 90% of scoliotic patients showing improvement without reconstruction.^154,168,171

19.5.8 Osteoblastoma

Description

Previously called giant OO, osteoblastoma is a potentially aggressive osteolytic tumor^{5,26,62,157,180} that is grossly friable, blood-filled, and well circumscribed.^69,158,181 It most frequently affects the posterior column^{5,26,138,155,158,167,168,181,182,183,184} and is histologically characterized by extensive vascularization, osteoid production, and immature woven bone.^{181,183,184,185} Unlike OO, it contains large vascular spaces, giant cells,¹⁵⁴ and a nidus greater than 2 cm in diameter.^{3,5,26,154,155,158,161}

Diagnosis

Like OO, OB commonly produces local back pain^{26,154,157,158,178,185,186} that has been present for 12 to 20 months,^{62,154,158,166,168,170,174,178,182,183,187} although fewer OB patients get relief with NSAIDs.^{155,157,168,170,178,182,186} Neurological dysfunction is more common than in OO due to the larger lesion size,^{154,166,170,187} but painful scoliosis is less common.^{157,158,168,174}

Radiographic characteristics of lesions are similar to those of OO.^154,155,157 On CT, it has a ground-glass appearance due to multifocal mineralization within the lesion nidus.^{26,69,158,182,186} And on MR, it is hypointense on T1- and hyperintense on T2-weighted images,^158,186 and may demonstrate soft tissue involvement.^{5,26,157,182,185,186}

Treatment

Treatment begins with NSAID-mediated medical management of pain.¹⁵⁷ Those patients with neurological dysfunction or instability are treated surgically though,^170,183 as are patients who have failed conservative management.^{157,161,183,188} Gross total resection of the tumor nidus is considered front-line treatment^{3,161,183,188} and current recommendations suggest that this be achieved via wide en bloc excision in high-grade tumors,^{3,5,158,178,183,188,189} though lower-grade lesions can be treated with intralesional gross total resection.^{5,158,182,183,185,189} As with OO, current evidence does not support adjuvant radiotherapy for local control,^5,69,185,189 and surgery is first line for treatment of recurrences^5,157,183.

Prognosis

Local control is nearly 100% in cases treated with en bloc resection,^5,185,188 but only 85 to 90% in cases treated with subtotal resection.^{69,154,170,180,182,185,189} Aggressive-type lesions,^{158,186,188,189} higher Enneking grade lesions, larger lesions, and cases with less extensive resection^{5,166,187,188} have all been associated with higher rates of recurrence.^183,188 Both intralesional and en bloc resection create significant relief of pain in more than 90% of patients.^{154,157,158,161,166,176,186,187}

19.5.9 Osteochondroma

Description

Osteochondromas, also called osteocartilaginous exostoses, are the most common type of benign bone lesion.^{190,191,192,193,194} Though commonly treated as a tumor, they are actually hamartomas,^{13,190,193,194,195} as they form when growth plate cartilage fragments escape the physeal plate^{3,69,190,195,196,197} and produce a subperiosteal, cartilage-capped bony excrescence. This lesion then grows through endochondral ossification and creates symptoms by compressing neural elements.^{192,194,195,196,197,198,199,200,201,202} Exostoses can occur secondary to radiotherapy or a genetic condition,^3,197 and are commonly thought to cease growth at the time of epiphyseal plate closure.^{62,190,192,194,200,203,204}

Histologically, exostoses are characterized by a bony stalk with a core of pathologically normal bone and cap of hyaline cartilage.^{193,195,198,200,204} The cartilaginous cap resembles the physeal plate in structure¹⁹⁵ and is the point at which the lesion grows.^192,197,200 The majority of lesions are slow growing⁶⁹ and are found in the posterior column.^{13,69,190,194,196,197,198,203,205}

Diagnosis

The vast majority (99%) of spinal lesions are asymptomatic, as they grow away from the spinal canal.^{13,190,195,197,199,200,201,206,207} Symptomatic patients most commonly present with pain of gradual onset that has been present for years,^{194,197,208,209} but may also present with radiculopathy or myelopathy.^{3,13,192,194,197,207} Neurological symptoms are most commonly associated with thoracic lesions, which may present with neurological symptoms in as much as 85% of cases.¹⁹⁰ Lesions that lie in the posterior column may also present as a palpable mass.^{3,190,194,195}

Radiographically, lesions present as a sessile mass iso-radiolucent to and contiguous with the underlying vertebra.^{3,13,192,195,198,199,210} These features are considered pathognomic for exostosis,^195,200 but may be difficult to identify on plain radiograph due to the complex spinal anatomy.^{3,26,69,194,195,197,200,203,208} CT is therefore the modality of choice as it allows visualization of these pathognomic radiological features.]^{3,13,26,190,194,195,197,198,200,203,208} It can be complemented by MRI, which demonstrates a cartilaginous cap that is hypointense on T1 and hyperintense on T2.^{26,69,195,201} MRI also differentiates osteochondroma from chondrosarcoma, which is characterized by a cap thicker than 1.5 cm in adults and 3 cm in children.^{13,26,195,197,198,201,203}

Treatment

Asymptomatic exostoses are treated with observation, whereas symptomatic lesions are treated with gross total resection.^{3,26,69,192,193,197,198,205,206} Given the lesion’s benign nature, piecemeal resection of the cartilaginous cap is associated with extremely high rates of local control^{13,190,192,196,198} and is curative in the majority of cases.⁶⁹ Rapid progression of symptoms suggests malignant transformation^13,197 and said tumors should be treated en bloc.^3,190

Prognosis

Osteochondromas generally have a favorable prognosis, with 85% or more of patients showing symptomatic improvement^{190,197,199,203,204,207,209} and 96 to 98% showing long-term local control.^{13,193,195,203} Gross resection improves local control slightly,^190,194,197 but the difference is negligible if the cartilaginous cap is completely excised. Recurrences usually occur more than 2 years after surgery^190,197 and are rarely associated with transformation to chondrosarcoma.¹⁹⁷

19.6 Malignant Tumors

Malignant tumors of the spine occur at a rate of 1 to 2 per 100,000 person-years²¹¹ and account for less than 0.2% of all cancers.^212,213 The majority have relatively poor prognoses, though outcomes have begun to improve with the increased use of Enneking-appropriate en bloc resection.²¹⁴ Definitive diagnosis requires biopsy,^{215,216,217,218} which is generally done transpedicularly to reduce recurrence.

19.6.1 Chordoma

Description

Chordoma is one of the most common primary malignancies of the spine.^{3,4,19,143,212} Frequently, low grade and slow-growing,^{19,215,219,220} it arises from notochordal remnants^{3,26,69,143,212,217,220} and is locally aggressive, osteolytic, and often large at diagnosis.^{3,16,19,26,143,217,218,220} Histologically, chordoma is characterized by cords or sheets of spindle-shaped physaliphorous cells containing hyperchromatic nuclei, mildly eosinophilic cytoplasm, and abundant mucin-filled vacuoles.^{3,26,143,217,221} These cells may have indistinct borders and are surrounded by abundant myxoid matrix.^143,221 More aggressive lesions are hyperplastic,²²¹ possess abundant mitotic figures,²¹⁸ and demonstrate central necrosis.¹⁴³ Positive staining for the transcription factor Brachyury distinguishes chordoma from chondrosarcoma and other cartilaginous lesions.^{16,143,216,218} Metastasis occurs in 5 to 30% of cases,^{19,143,218,222,223,224,225} most commonly to the lungs or skeleton.^217,218

Diagnosis

Patients present with nonspecific symptoms that have been present for months or years.^16,216,218 Pain is the most common complaint, and may be accompanied by paresthesias, weakness, or incontinence.^{3,16,218,220,226} On radiograph and CT, chordomas are midline, osteolytic lesions of the vertebral body^217,218,220 with multiple septa, irregular shape, and amorphous intralesional calcification.^{3,26,69,143,218,221} Chordomas generally remain extradural,^217,218 but may invade epidural space²¹⁹ and adjacent disc space.²¹⁸ MRI is the modality of choice as it allows for good delineation of soft tissue components^69,219 and identification of spinal metastases.^217,226 The appearance on MRI is similar to that of the nucleus pulposus, in that it is hyperintense on T2 MRI, hypointense on T1,^3,26,143,218 and shows moderate contrast enhancement.²¹⁷

Treatment

Treatment of chordoma should involve a multidisciplinary team^217,226 and revolves around wide en bloc resection of the tumor.^{3,16,19,69,215,217,218,219,223,225,226,227,228,229} Though associated with increased complication rates,^19,219,224 en bloc resection significantly improves overall survival and local control.²¹⁵ When en bloc resection is not possible or not accepted by the patient,^217,224 every effort should be made to achieve negative margins through piecemeal resection.^{217,219,220,226,229}

Chordomas are resistant to chemotherapy and radiotherapy,^{4,16,19,215,223,224,225,226,227,230} but adjuvant radiotherapy greater than 60 Gy^218,227,231 may be useful in cases where only positive or marginal margins are achieved.^{217,218,227,229,232} The major disadvantage of such high-dose RT is that it can damage the spinal cord.^218,227 Recent advances in hypofractionated stereotactic radiosurgery and charged particle RT^227,229,232 have reduced this risk, as they allow higher doses of radiation to be delivered to the tumor while maintaining extralesional doses below the safety limit of 50 Gy.^218,227 These newer radiosurgery techniques are not supported as monotherapy, except in cases of inoperable lesions, where they are the standard of care.^{217,219,224,229,231,233,234,235} Unlike radiotherapy, chemotherapy is not currently supported as an adjuvant.^217,218

Prognosis

Recurrence is incredibly common,^{16,19,26,215,217,218,220,222,223,226} occurring in more than 50% of patients treated with gross total resection.^217,226 En bloc resection provides significantly better local control,^{19,23,49,219,223} as high as 83 to 95% in some series.²²³ The current median overall survival for isolated, surgically treated chordoma is 84 to 104 months,^{16,19,23,212,213,215,220,228,229} with 5-year, 10-year, and 20-year overall survivals of 50 to 97%, 33 to 84%,^{3,16,19,23,69,212,213,215,217,219,220,223,226,228,229,231,235} and 13.1%,^23,215,228 respectively. In the few series examining mobile spine lesions, local recurrence-free survival is reported to be 55 to 67.6%,^{19,23,223,226} with recurrence in 25 to 48% of cases, median time to recurrence of 37 to 64 months,^{19,215,219,232} and median recurrence-free survival of 37 months.¹⁹ Positive predictors of overall survival are younger age,^226,228 smaller tumor burden,^215,225,226 use of en bloc resection,^{16,19,215,219,223,225,226,229,232,235} index versus revision surgery,^{16,219,220,223,225,229,235} isolated lesion,^19,212 and adjuvant radiotherapy.^3,224,227 En bloc resection with negative margins is the greatest determinant of long-term outcome though.^217,223

19.6.2 Chondrosarcoma

Description

Chondrosarcomas are slow-growing,^21,42 low-grade^44,143,236 connective tissue sarcomas that constitute the second most common primary tumor of vertebrae.^3,4,26 They can occur as either a primary tumor or as a malignant transformation of an osteochondroma,^26,216 and are broken into four main types based on histology: conventional (classical), dedifferentiated, mesenchymal, and clear cell chondrosarcomas.⁴⁵ Conventional chondrosarcomas account for 80 to 90% of all cases and appear grossly as lobulated lesions that destroy surrounding bone.^{45,71,211,237} They share radiographic features with chondromas,⁴⁵ but are distinguished by greater invasion of surrounding bone and more abundant mucoid matrix.²³⁷ Microscopically, they are hyperplastic with pleomorphic nuclei and a matrix possessing a mixture of myxoid and hyaline features.²³⁷ Degeneration of these conventional chondrosarcomas produces dedifferentiated chondrosarcomas, which account for 10% of all lesions.^71,238 They have the poorest prognosis, with a 5-year survival rate less than 10%,⁴⁵ and are histologically characterized by a central cartilaginous component surrounded by a peripheral sarcomatous component.²³⁹ Mesenchymal chondrosarcomas are the next most common, accounting for 3 to 10% of all chondrosarcomas, and possess a mixture of low-grade chondrocytes and undifferentiated spindle-shaped neoplastic cells.^45,71 Clear cell chondrosarcomas account for the remaining 2% of cases.⁷¹ They are hyperplastic, with cells featuring round, centrally placed nuclei and abundant, clear cytoplasm^45,71,238 in a matrix lacking cartilaginous features.²³⁸

Diagnosis

Symptoms show insidious onset and include nonfocal pain, which persists for months prior to presentation,^{42,43,71,216,236,240,241} a palpable mass,^71,236,241 or neurological impairment.^43,45,240 Up to 50% of patients present with a neurological deficit.^45,236

Radiographically, chondrosarcoma is an expansive, osteolytic lesion involving the vertebral body with or without posterior column involvement.^3,26,143,238 Low-grade tumors are circumscribed by reactive cortical bone,^143,240 but high-grade tumors usually breach the cortex.^28,236 The chondroid matrix of the tumor usually demonstrates mineralization in a “ring-and-arc” pattern on radiograph and CT.^26,45,71,242 Lesions are also generally lateralized within the vertebrae, distinguishing them from the centrally placed chordoma. On MRI, chondrosarcomas appear heterogeneously hypointense on T1, hyperintense on T2,^43,47,71 and demonstrate “rings-and-arcs” enhancement with gadolinium contrast.^{26,143,238,243} MRI also allows delineation of soft tissue invasion,^{3,71,143,216,238,240} and differentiation from osteochondroma.

Treatment

At present, surgery is the standard of care in treating chondrosarcoma,^212,240,242 as it is the only therapy with documented efficacy.^{42,43,211,216} Resection should be executed en bloc with negative margins ( Fig. 19.3, Fig. 19.4), as this significantly reduces the rate of recurrence.^{3,26,28,43,44,45,195,216,236,238,240,244} Piecemeal gross total resection is employed where en bloc excision is infeasible,^43,45,242 but virtually assures recurrence of the lesion.^43,45,240

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