Extradural Benign Tumors

Published on 02/04/2015 by admin

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Last modified 02/04/2015

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Chapter 1 Extradural Benign Tumors

Jae-Soo Koh, Ung-Kyu Chang, Terri Haddix

INTRODUCTION

Extradural benign tumors refer to the benign tumors arising from the vertebral body and neural arches. Benign tumors are not commonly found in the spinal column. The most common tumor is a vertebral hemangioma, a slow-growing skeletal and soft tissue tumor that is often encountered as an incidental finding. Hemangiomas are hamartomatous proliferations of vasogenic and endothelial tissue in the bone. They rarely grow out of the bony cortex and cause spinal axis pain.

Osteoid osteomas are benign osteoid-producing tumors that are identified pathologically as irregular woven bone and numerous osteoblasts with increased vascularity. Patients with osteoma suffer from aggravating pain at night that is relieved with aspirin medication.

Osteochondroma is the most common benign bone tumor, but it is rarely found in the spinal column. It is a cartilage-covered osseous mass connected with parent bone. These lesions consist of a thin fibrous capsule, a cap of benign cartilage, chondrocytes in an orderly columnar arrangement, and maturing bone. Some patients with these lesions show hereditary tendency and multiple occurrences.

Giant cell tumors are locally aggressive tumors composed of osteoclast-like giant cells and spindle to avoid mononuclear stromal cells. They are usually found in the sacrum. Because of the very high possibility of local recurrence, surgeons perform repeated operations and recommend adjuvant radiation therapy.

VERTEBRAL HEMANGIOMA

EPIDEMIOLOGY

• Hemangiomas are benign, slow-growing skeletal and soft tissue tumors that commonly involve the bony spine.
• The actual incidence of hemangiomas is uncertain as they are often discovered only incidentally in asymptomatic individuals. They account for approximately 2–3% of all spinal tumors and occur with an estimated incidence of 10–12% in the population as based on large autopsy series and review of plain spine radiographs.1
• These lesions are usually asymptomatic and often present as incidental findings on plain radiographs and on magnetic resonance (MR) images.
• Rarely, they may enlarge and cause pain or neurologic deficit because of spinal cord compression, vertebral body or arch expansion, or pathologic fracture.

DISTRIBUTION

• Vertebral hemangiomas are extremely vascular bone tumors. They commonly occur as incidental findings within the vertebral body.2
• Vertebral hemangiomas are the most common benign spinal neoplasms. The peak incidence is in the fourth to sixth decades, with a tendency to increase in size with age.3,4
• Asymptomatic hemangiomas occur equally in men and women, but there is a female predominance with symptomatic lesions. Symptomatic hemangiomas (about 1% of all hemangiomas) are usually observed during adult age and tend to occur in the thoracic region.5
• Pregnancy may exacerbate vertebral hemangiomas.2,3 Vertebral hemangiomas are solitary in 66% and multiple in 34% of cases.4
• These tumors have a predilection for the thoracic spine (60%) compared with the lumbar spine (29%), cervical spine (6%), and sacrum (5%).4 Concomitant posterior element involvement can be seen in 10–15% of cases.

HISTOLOGY

• Hemangiomas are composed of a collection of irregular vascular spaces lined by bland endothelial cells (Fig. 1-1).
• They are slow-growing hamartomatous proliferations of vasogenic and endothelial tissue in the bone and can be of capillary or cavernous type; the latter is a more common type (Fig. 1-2).6
• Vertebral hemangiomas vary predominantly from fatty lesions to those composed largely of vascular stroma with little or no fat tissue.3
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Fig. 1-1 Curettage specimen often shows collapsed vascular space without blood, which may be the processing artifact (hematoxylin–eosin stain, ×40).

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Fig. 1-2 Histologic pattern of cavernous hemangioma showing broad, thin-walled blood vessels lined by a single layer of flat endothelial cells and filled with blood (hematoxylin–eosin stain, ×100).

RADIOLOGY

• On plain films, the thickened vertical trabeculae of hemangiomas cause parallel linear densities described as having “jail bar” or “corduroy” appearance, or may show lytic foci with honeycomb trabeculations.3 The classic “honeycombing” or vertically oriented vertebral lucencies separated by thickened trabecular bone are indicative of a vertebral hemangioma (Fig. 1-3).
• On axial computed tomography (CT), these thickened trabeculae give a typical spotted or “polka dot” appearance to the vertebral body (Fig. 1-4).
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Fig. 1-3 L4 vertebral body hemangioma with coarse vertical trabeculae. Anteroposterior view (left), lateral view (middle), and CT (right).

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Fig. 1-4 Another case of vertebral body hemangioma. On plain radiography, multiple compression fractures are seen. On CT scan at L1 level, typical trabecular pattern of hemangioma is shown in right vertebral body and pedicle.

MR is extremely sensitive in detecting spinal hemangiomas. On both T1- and T2-weighted images, these lesions tend to have increased signal intensity, reflecting the adipose tissue rather than the hemorrhagic component. The hyperintense stroma surrounds foci of very low signal intensity, which represent the thickened vertical trabeculae (Fig. 1-5).3 In cases of hemangiomas that are rich in vascular element, the signal change is high on T2-weighted images (T2WI), low on T1-weighted images (T1WI), and shows homogenous enhancement with contrast (Figs. 1-6 and 1-7).

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Fig. 1-5 MR image of vertebral body hemangioma. High signal lesion is seen on T2 sagittal image (left), T1 sagittal image (middle), and T2 axial image (right).

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Fig. 1-6 MR sagittal images of L1 hemangioma. The signal is high on T2WI, low on T1WI, and demonstrates homogeneous enhancement with gadolinium. This hemangioma is rich in vascular element.

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