Extradural Benign Tumors

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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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Fig. 1-7 MR axial images of L1 hemangioma. The signal change is the same as in sagittal images. The extent of tumor involvement is confined to the vertebral body and pedicle.

OSTEOID OSTEOMA/OSTEOBLASTOMA

EPIDEMIOLOGY

• Both osteoid osteoma and osteoblastoma have a strong predilection for young males.
• Osteoid osteomas are approximately four times as common as osteoblastomas.

DISTRIBUTION

Osteoid osteomas typically affect long bones, whereas osteoblastomas often involve the spine.

HISTOLOGY/GRADING

• Osteoid osteomas and benign osteoblastomas share the same histologic features and are distinguished only by size with the latter neoplasm measuring greater than 1.5 cm.7
• The nidus of these neoplasms is composed of anastomosing bony trabeculae with intervening vascular loose tissue (Fig. 1-8). There may be a sclerotic rim.
• Although both of these lesions are considered to be benign tumors, rare osteoblastomas may develop more aggressive clinical behavior and histologic appearances.
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Fig. 1-8 Nidus of an osteoid osteoma. Irregular woven bone and numerous osteoblasts are seen with increased vascularity (hematoxylin-eosin stain, ×100).

RADIOLOGY

Radiography

• Small, central, lucent nidus often obscured by reactive sclerosis.
• Focal scoliosis concave on side of tumor.
• Typically involving neural arch.
• Reactive zone on T1WI, variable signal intensity of nidus on T2WI.
• Cortical thickening.

CT

• Central nidus contains variable amount of ossification, and wide peripheral zone of reactive sclerosis surrounds nidus.
• More easily diagnosed with CT than with MR.

MR

• Low signal intensity in the nidus and surrounding reactive zone on T1WI.
• Variable signal change on T2WI.
• Rapid enhancement pattern in the nidus with contrast.

OSTEOCHONDROMA

EPIDEMIOLOGY

• Osteochondromas are the most common benign bone tumor.
• These tumors are often solitary but can be numerous in multiple hereditary exostoses.
• Osteochondromas have a strong male predilection and are generally found in young adults and teens. Patients with multiple hereditary exostoses present earlier than patients with sporadically occurring tumors.

DISTRIBUTION

• Osteochondromas most often affect long bones but rarely involve the spine. A review of the literature found that up to 4% of solitary osteochondromas arose in the spine and that 9% of patients with multiple hereditary exostoses had lesions in the spine.8
• In the same review just described, cervical lesions overall (multiple and solitary lesions) were found in 49% of the patients, thoracic lesions in 30%, and lumbar lesions in 20%.

HISTOLOGY/GRADING

• Osteochondromas are low-grade lesions, which may best be considered hamartomatous.
• These lesions consist of thin fibrous capsule, a cap of benign cartilage (chondrocytes in an orderly columnar arrangement), and maturing bone (Figs. 1-9 and 1-10).
• The presence of a thicker cartilaginous cap, irregularity of the cartilaginous surface, or spindle cell proliferation at the cartilage-bone interface raises the possibility of malignant transformation.7
• On gross finding, the tumor capsule is smooth and glistening. The consistency is very hard (Fig. 1-11).
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Fig. 1-9 Low power view (×40) of an osteochondroma composed of fibrous capsule, cartilage cap, and mature bony stalk.

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Fig. 1-10 Higher power view (×200) of an osteochondroma. Low cellularity is shown without cytologic atypia.

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Fig. 1-11 After surgical resection, the surface of the tumor mass is glistening and smooth. On palpation, the consistency is very hard.

RADIOLOGY

X-Ray and CT

• Pedunculated osseous protuberance is connected with parental vertebra without cortical discontinuity. Chondroid matrix can be added (Fig. 1-12).
• Most common site is cervical spine (especially C2) and posterior elements are more often involved than vertebral body (Fig. 1-13). Tumor mass originates from the posterior element of C2 and grows downward to C3 level (Fig. 1-14).
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Fig. 1-12 Another case of osteochondroma that originated from the transverse process of the thoracic spine. Cortical continuity is maintained.

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Fig. 1-13 On simple radiograph, the high density mass is shown around the C1 lamina and spinous process area.

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Fig. 1-14 On CT scan, the mass is of high density and has a pedunculated appearance.

MR

• Central high signal mass surrounded by low signal cortex on T1WI (Fig. 1-15).
• Central high signal mass surrounded by low signal cortex on T2WI, high signal hyaline cartilage cap (Fig. 1-16).
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Fig. 1-15 Central high signal mass is surrounded by a low signal rim on T1WI.

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Fig. 1-16 Diffuse high signal mass on T2WI.

GIANT CELL TUMOR

EPIDEMIOLOGY

• Giant cell tumor (GCT) is a locally aggressive tumor composed of osteoclast-like giant cells and spindle to ovoid mononuclear stromal cells.
• Giant cell tumors of bone are rare in the vertebrae above the sacrum. On the other hand, the sacrum is one of the more commonly involved skeletal sites.
• GCT usually occurs in skeletally immature patients and is reported more commonly in younger patients than patients with lesions of long tubular bones.
• Generally GCTs comprise between 5–10% of all benign bone tumors, occurring most commonly in the third decade of life. They are more common in females than in males.9

DISTRIBUTION

• Spinal GCT is less than 10% of all GCTs. These tumors are equally distributed in the cervical, thoracic, and lumbar spines. One-half of spinal GCTs develop in the sacrum.
• The body of a vertebra is the most common site of the lesion in 54%, the vertebral arch in 17%, and both the body and arch in 29%.

HISTOLOGY

• The characteristic histologic appearance is of round to oval polygonal or elongated mononuclear cells evenly mixed with numerous osteoclast-like giant cells (Fig. 1-17).
• The cytoplasm is ill defined, and there is little intercellular collagen. Mitotic figures vary from 2 to 20 per 10 high power fields, but atypical mitoses are not seen and their presence should point to a diagnosis of a giant cell rich sarcoma (Fig. 1-18).
• It is now generally accepted that the mononuclear stromal cells represent neoplastic components and osteoclast-like giant cells are non-neoplastic reactive recruited components.
• Secondary degenerative changes, such as foam cell collection and aneurysmal bone cyst area, are not rare. Small foci of bone formation within the tumor and in the peripheral shell are found, and those findings are exaggerated in the case of soft tissue recurrence and lung metastasis.
• Malignancy in GCT is a high-grade sarcoma arising in a GCT or at the site of previously documented GCT.
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Fig. 1-17 GCT with oval or plump spindle mononuclear cells uniformly interspersed with multinucleated giant cells (×100). Empty lacunar spaces around giant cells represent commonly observed fixation artifacts.

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Fig. 1-18 High-power view (×400) shows multinucleated giant cells and oval or plump mononuclear cells. Mitotic figures are not rarely observed but nuclear atypism is minimal.

RADIOLOGY

• GCT appears as a radiolucent, expansile lesion on radiography (Fig. 1-19). The margin usually is not sclerotic.
• CT scan demonstrates a soft tissue attenuation with distinct margins and occasional surrounding sclerosis.
• Variable signal intensity is seen with a heterogeneous low-intensity image on T1- and T2-weighted sequences of MR imaging. Enhancement pattern is heterogeneous (Figs. 1-20, 1-21, 1-22, and 1-23), and sometimes necrosis can be found (see Figs. 1-21 and 1-23).
• Usually the vascularity of the tumor mass is very high from the neighboring segmental arteries (Fig. 1-24).
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Fig. 1-19 On lateral view of lumbar spine, osteolytic expansile lesion is seen in the vertebral body.

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Fig. 1-20 T1 sagittal MR image of L5 GCT. On precontrast scan, the mass is seen to be low signal (left). After gadolinium enhancement, the mass is homogeneously enhanced and a central necrosis area is seen (right).

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Fig. 1-21 T1-enhanced axial MR image of L5 GCT. The mass grew to the right side of the vertebral body and broke posterior cortex. Multiple necrotic areas are observed, and the dural sac is compressed.

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Fig. 1-22 Sagittal MR image of sacral GCT. Mixed signal change is seen on T2WI (left). Low signal change is observed on T1WI, and the mass shows a heterogeneous enhancement pattern, including necrosis portion.

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Fig. 1-23 Axial MR image of sacral GCT. On T2WI, iso-signal area and high signal area are mixed in the tumor mass. Tumor mass itself and necrosis area are included in the high signal area.

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Fig. 1-24 Angiographic finding of sacral GCT. The mass shows hypervascular staining from the branches from bilateral internal iliac arteries.

References

1 Acosta FLJr, Dowd CF, Chin C, Tihan T, Ames CP, Weinstein PR. Current treatment strategies and outcomes in the management of symptomatic vertebral hemangiomas. Neurosurgery. 2006;58:287-295. discussion 287–295

2 Redekop GJ, Del Maestro RF. Vertebral hemangioma causing spinal cord compression during pregnancy. Surg Neurol. 1992;38:210-215.

3 Osborn AG. Diagnostic Neuroradiology. St. Louis: Mosby, 1994;876-918.

4 Scott WA. Magnetic Resonance Imaging of the Brain and Spine, 3rd ed., Philadelphia: Lippincott Williams & Wilkins; 2002:1720.

5 Krueger EG, Sobel GL, Weinstein C. Vertebral hemangioma with compression of spinal cord. J Neurosurg. 1961;18:331-338.

6 Sainani NI, Pungavkar SA, Patkar DP, Lawande MA, Naik M. Multiple hemangiomas involving the vertebral column. Acta Radiol. 2005;46:510-513.

7 Inwards C, Unni K. Bone tumors. In: Mills SE, editor. Sternberg’s Diagnostic Surgical Pathology. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2004:265-320.

8 Albrecht S, Crutchfield J, SeGall G. On spinal osteochondromas. J Neurosurg. 1992;77:247-252.

9 Randall RL. Giant cell tumor of the sacrum. Neurosurg Focus. 2003;15:E13.

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