Benign Spinal Tumors

Manish K. Kasliwal, Lee A. Tan, Carter S. Gerard, John E. O’Toole, and Richard G. Fessler

Abstract

Primary benign tumors of the spinal column are much less common compared to other spinal neoplasms such as metastases, multiple myeloma, or lymphoma. These tumors often affect a younger age group, with back pain being the most common presentation. Considering the ubiquitous nature of back pain and rarity of these benign spinal tumors, the potential for missed diagnosis, if not appropriately suspected, remains high. The differential diagnosis of these lesions is fairly broad and often requires appropriate recognition on initial radiology and subsequent complete workup to formulate the best treatment strategy. There has been significant progress in the treatment options available to treat these tumors that allow safer and more effective treatment with decreased overall morbidity. This chapter provides a brief overview of the presentation, radiology, and management of various benign spinal cord tumors in the light of most recent literature.

Keywords: benign, clinical, diagnosis, spine, tumor, neoplasm, radiology, management

46.1 Introduction

Primary benign tumors of the spine are much less common lesions compared to other spinal neoplasms such as metastases, multiple myeloma, or lymphoma.¹ Hemangioma, enostosis, osteochondroma, osteoid osteoma, osteoblastoma, giant cell tumor, aneurysmal bone cyst (ABC), and eosinophilic granuloma (EG) are the various subtypes of benign spinal tumors. All together, they account for only less than 5% of all spinal neoplasms.² They tend to occur in younger patients, in contrast to metastases, multiple myeloma, or lymphoma, which usually affect older age groups.¹^,²^,³^,⁴ Some of these benign tumors arise from the posterior elements of the spine, while others mainly originate from the vertebral body.²

Back pain is the most common presenting symptom for patients with benign spinal tumors,⁵ although sensorimotor deficit can also be present depending on the size and location of the lesion. Many of these lesions have characteristic clinical and radiographic features that can help clinicians to make the correct diagnosis. In contrast to primary malignant lesions that often require en bloc resection for best chance of cure, symptomatic benign primary tumors can often be safely treated with intralesional resection.⁴ Primary benign spine tumors are classified using the Enneking system ( Table 46.1), and generally stage II and III lesions require treatment.

Table 46.1 Enneking classification of benign spine tumors

Stage	Description
1	Latent, asymptomatic, incidentally found
2	Active, symptomatic lesion
3	Aggressive, can metastasize

In this chapter, we attempt to provide an overview of current minimally invasive techniques along with general principles of utilizing these minimally invasive surgery (MIS) approaches in treating benign spinal tumors. By having a solid understanding of tumor pathophysiology, local anatomy, and spinal biomechanics, spine surgeons can utilize MIS techniques to successfully treat benign spinal tumors with good clinical outcome. A brief overview of clinical and radiological features of primary benign spinal tumors is presented in the following sections.

46.2 Types of Tumors

46.2.1 Hemangioma

Vertebral hemangiomas are vascular malformations consisting of thin-walled blood vessels that usually affect the vertebral body with occasional extension into the posterior elements. They most commonly occur in the thoracic and upper lumbar spine. Classic imaging features include vertical striations on spinal radiographs known as the “corduroy sign,” and “polka-dot” appearance on axial CT images ( Fig. 46.1). Vertebral hemangiomas are often asymptomatic and only discovered incidentally. However, those with extension into the posterior elements and with paraspinal involvement are more likely to cause compressive symptoms. Large hemangiomas can also compromise the vertebral body’s ability to bear axial load and can result in vertebral fractures. Treatment options for symptomatic vertebral hemangiomas include sclerotherapy, vertebroplasty, endovascular embolization, and vertebrectomy.⁶^,⁷^,⁸

Fig. 46.1 Hemangioma with “polka-dot” appearance on axial computed tomography.

Fig. 46.2 Enostosis on radiograph showing a sclerotic lesion in the cervical spine. (a) MRI demonstrating hypointense signals on both T1-weighted (b) and T2-weighted (c) images.

46.2.2 Enostosis

Enostosis is a benign hamartomatous lesion consisting of cortical bone with irregular margins within the medullary bone, which is also known as “bone island.”⁹^,¹⁰ It typically has a round or oval appearance and is up to 2 cm in size. Imaging features include sclerotic appearance on radiographs, hyperdense on CT, and hypointense on both T1- and T2-weighted MRI images ( Fig. 46.2). Enostoses are usually asymptomatic solitary lesions that do not enlarge over time. However, biopsy may be considered if there is an increase in size to rule out other possible osteoblastic lesions.

46.2.3 Osteochondroma

Osteochondroma is an abnormal outgrowth of bone capped by hyaline cartilage with its medullary part continuous with the parent bone. It usually affects the appendicular long bones such as the femur, tibia, and humerus, but posterior elements of the spine can also be involved occasionally. It is usually sporadic with a 3:1 gender predilection for males,² and often discovered during the third and fourth decades of life. Although vertebral osteochondromas can occur anywhere along the spine, they appear to have a predilection for the cervical spine, especially for the C2 vertebrae.²^,¹⁰ Radiographic features include a “cauliflower-like” mass capped by cartilages with its medullary component in continuity with medullary part of the parent bone on CT ( Fig. 46.3). The cartilaginous cap usually appears isointense or hypointense on T1 and hyperintense on T2-weighted MRI. A cartilage cap greater than 1.5 cm may be a red flag for malignant transformation to a chondrosarcoma in adults, which warrants further investigation. Symptoms include pain and neurological deficits, which are due to local mechanical effect or neurovascular compression. Lesions protruding into the spinal canal often present much earlier than those projecting posteriorly, given the limited space available in the spinal canal. Symptomatic lesions can often be cured with excision of the lesion at the point of cortical and marrow junction to the parent bone.

Fig. 46.3 Osteochondroma with a “cauliflower-like” mass capped by cartilages with its medullary component in continuity with medullary part of the vertebral body on CT.

46.2.4 Osteoid Osteoma

Osteoid osteoma is a benign bone tumor produced by osteoblasts consisting of osteoid and woven bone frequently surrounded by cortical thickening and bony sclerosis. Although it most commonly involves the posterior elements of the spine, it can rarely involve the vertebral body as well.¹¹ The lumbar spine is the most frequently affected, followed by cervical, thoracic, and sacral segments. It has a slight male predilection and most frequently affects patients in their second or third decades of life. The classic clinical feature is pain that worsens at night or with alcohol consumption, and improves with nonsteroidal anti-inflammatory drugs (NSAIDs). By definition, they are less than 2 cm in size. CT often demonstrates a radiolucent mass with cortical thickening and sclerosis in the posterior elements of the spine ( Fig. 46.4). The nidus can often have central calcification as well. It is usually isointense to hypointense on T1 and isointense to hyperintense on T2-weighted MRI. Radiofrequency ablation often provides symptomatic relief. Surgical excision is curative if the nidus is completely removed.

46.2.5 Osteoblastoma

Osteoblastoma is similar to osteoid osteoma histologically, but is greater than 2 cm in size by definition. It is also present in the second and third decades of life with male predilection. Similar to osteoid osteoma, it most frequently originates from the posterior elements but can often extend into the vertebral body. Osteoblastomas tend to have slow growth over time and can rarely have malignant transformation to osteosarcoma. The radiologic appearances are similar to osteoid osteomas, characterized by a radiolucent mass with cortical thickening and sclerosis and surrounding sclerosis with or without central calcifications, but they are by definition greater than 2 cm in diameter ( Fig. 46.5). The more aggressive subtype may demonstrate bony destruction and paravertebral extension; it may also include a component of ABC in a minority of cases.¹² Surgical resection is the treatment of choice, with 10 to 15% chance of recurrence.¹³^,¹⁴

46.2.6 Aneurysmal Bone Cyst

ABC is a benign lesion consisting of blood-filled spaces without endothelial lining within affected bone. About 10 to 30% of ABCs are located in the spine,¹⁵ with thoracic spine being the most frequently affected site, followed by lumbar, cervical, and sacral segment. It usually arises from the posterior elements but with frequent expansion into the vertebral body and paravertebral tissue. CT demonstrates an expansile osteolytic mass with a thin rim of sclerosis; MRI demonstrates the characteristic “fluid–fluid level” ( Fig. 46.6), which is due to repeated hemorrhage and resultant blood of various ages. Spinal ABCs can be effectively treated with intralesional resection, en bloc resection, or endovascular embolization.¹⁵ Preoperative embolization should be considered prior to intralesional resection to limit intraoperative blood loss.

46.2.7 Giant Cell Tumor

Giant cell tumors are expansile, lytic lesions consisting of osteoclast-like cells often containing thin-walled vascular channels, which predispose them to hemorrhage. Spinal giant cell tumors often present in the second to fourth decade of life with female predilection. The sacrum is most commonly affected, followed by the thoracic, cervical, and lumbar segments.¹⁶ It usually arises from the vertebral body with frequent extension into the posterior elements and paraspinal tissues. Vertebral fracture can often occur. CT demonstrates an expansile lytic lesion ( Fig. 46.7); MRI shows isointense to hypointense signals on T1-weighted images and variable appearance on T2-weighted images. Radicle resection with or without adjuvant radiation is usually the preferred treatment.¹⁷ New medical treatment with denosumab has been shown to be highly effective and has changed the treatment paradigm for giant cell tumor in recent years.

Fig. 46.4 A radiolucent lesion less than 2 cm in size affecting the posterior elements consistent with an osteoid osteoma (arrow).

Fig. 46.5 Osteoid blastoma manifesting as a lytic mass measuring greater than 2 cm affecting the posterior elements (arrow).

Fig. 46.6 (a) Axial and (b) sagittal T2-weighted showing “fluid–fluid” levels in a vertebral aneurysm bone cyst affecting the left lateral aspect of the vertebral body with extension into the posterior elements.