INTRODUCTION

Epidural malignant tumors originate from the vertebral body, pedicle, and laminae. Most of these tumors grow from the vertebral body and are classified as primary and metastatic tumors according to the origin of the cells. Cells in the vertebral body, such as osteoblast, chondrocyte, fibroblast, and hematopoietic cells, can develop various kinds of primary malignant tumors. Lymphoma and plasmacytoma originate from hematopoietic cells in the bone. Lymphomas are lymphoreticular neoplasms with a wide variety of specific diseases and cellular differentiation. Plasmacytomas are solitary monoclonal plasma cell tumors of bone and soft tissue.

Osteosarcomas are high-grade spindle cell neoplasms that form matrix filled with immature, woven osteoid. Ewing’s sarcoma is one of the “small round cell” sarcomas. Chondrosarcomas are malignant tumors of connective tissue, specified by formation of cartilage matrix by tumor cells. Chordomas are malignant tumors arising from notochordal remnants. Their pathological appearance is similar to that of chondrosarcomas.

Malignant fibrous histiocytomas arise from primitive mesenchymal cells capable of multidirectional differentiation. Fibrosarcomas are rare tumors of the soft tissue that can be associated with the adjacent fascia or periosteum.

The spine is the most commonly involved site for bone metastasis of cancer. The configuration of the metastasis is osteolytic or osteoblastic.

LYMPHOMA

EPIDEMIOLOGY

• Primary central nervous system lymphomas in immunocompetent individuals occur slightly more commonly in males than females with a peak incidence in the six and seventh decades of life.¹

• Of these primary central nervous system lymphomas, only 1% present within the spinal cord.

• The dura, skull, and vertebrae may be involved in patients with disseminated lymphomas.

DISTRIBUTION

There are no reported segmental differences in the occurrence of lymphomas in the spine.

RADIOLOGY

• Simple radiography may show no cortical destruction even in case of osseous lymphoma.

• Compression fracture may be present.

• Lymphoma can show osseous involvement, epidural mass with or without vertebral involvement, leptomeningitic mass, and intramedullary lesions.

Magnetic Resonance Imaging

In osseous lymphoma, low to normal marrow signal is seen on T1-weighted images (T1WI) and iso-signal to high signal is demonstrated on T2-weighted images (T2WI). On enhancement, diffuse uniform enhancement is observed (Fig. 3-5).

Fig. 3-5 In osseous lymphoma, the signal on T2WI is iso-signal or high signal (left). That of T1WI is low signal to iso-signal (right). The normal marrow signal is spotted under the background of the changed marrow signal.

OSTEOSARCOMA

EPIDEMIOLOGY

• Osteosarcomas most commonly develop in the appendicular skeletons of young males.

• Primary vertebral osteosarcomas are unusual and account for less than 5% of all osteosarcomas.

• In the largest series of primary vertebral osteosarcomas reported,² the median age of the 198 patients was 34 years, and there were slightly more females than males.

• Osteosarcomas may also develop within previous radiation fields or in the setting of Paget’s disease.

DISTRIBUTION

In the series just described, 14% of the primary osteosarcomas developed in the cervical segment, followed by 33% in the thoracic, 32% in the lumbar, and 21% in the sacral segments.

HISTOLOGY/GRADING

• Osteosarcomas are high-grade spindle cell neoplasms that form osteoid (Fig. 3-6) and often have associated giant cells.

• Tumor cells may be spindle or round, and size varies from small to giant (Fig. 3-7).

• Conventional osteosarcomas are subtyped based on the nature of the matrix (e.g., osteoblastic, fibroblastic, chondroblastic) (Figs. 3-7 and 3-8).

• Careful radiological correlation with the pathologic findings is required.

Fig. 3-6 Osteoblastic osteosarcoma. There are numerous osteoid and bone (calcified osteoid) depositions between the tumor cells. Reactive bone appears on the left (hematoxylin–eosin stain, ×40).

Fig. 3-7 Anaplastic features of conventional high-grade osteosarcoma and their direct production of osteoid materials (hematoxylin–eosin stain, ×200).

Fig. 3-8 Relatively low-grade fibroblastic osteosarcoma. The osteoid looks benign but is a tumor osteoid (hematoxylin–eosin stain, ×40).

RADIOLOGY

• Most vertebral osteosarcomas develop in posterior elements (80%).

• They show cortical destruction and soft tissue mass formation. Bone matrix produced by the malignant cells can be seen on simple radiographs in most cases (Fig. 3-9).

• For MR findings, the mineralized portion of the tumor mass is seen as low signal on T1WI and T2WI. Soft portion of the tumor mass is seen as low signal on T1WI and high on T2WI (Fig. 3-10). With contrast, the mass shows a moderate enhancement pattern.

Fig. 3-9 Radiology of primary osteosarcoma in lumbar spine. Osteolytic mass lesion is seen at the right side of the L4 vertebral body. The right L4 pedicle is eroded (left). On lateral view, the radiolucent area is located at the posterior half of the vertebral body (middle). The high density area is included in the tumor mass, which is indicative of bone matrix produced by tumor mass (right).

Fig. 3-10 MRI of primary osteosarcoma in lumbar spine. Low to intermediate signal change is seen at L4 vertebral body on T2WI (A) and low signal change on T1WI (B). With gadolinium, a moderate enhancement pattern is shown (C). On axial view, soft tissue mass is accompanied with intraosseous mass through cortical breakage (D).

EWING SARCOMA

EPIDEMIOLOGY

• Ewing sarcoma typically involves the long bones of young males.

• Primary vertebral Ewing sarcoma is unusual and accounts for slightly less than 10% of all cases of this neoplasm.

• In the largest published series of primary vertebral Ewing sarcoma,³ the average patient age was 19 years and there was a definite male predominance (62%).

DISTRIBUTION

• More than one-half of all cases of primary vertebral Ewing sarcoma in the series just described arose in the sacrum. Another one-quarter of the cases were located in the lumbar segment, with approximately 10% in the thoracic region. The cervical segment was very rarely involved.

• Ewing sarcoma also has been reported to arise in the paravertebral soft tissues and secondarily involve the extradural space. Primary intradural involvement (with or without an intramedullary component) has been the subject of rare case reports.⁴

• Ewing sarcoma is one of the “small round blue cell” tumors (Fig. 3-11). The histologic differential is broad, but can usually be clarified through the use of immunohistochemical stains. This differential diagnosis includes, but is not limited to:

• Metastatic lesions (particularly neuroblastoma in the pediatric age group and small cell carcinomas in adults)

• Hematopoietic malignancies

• Ewing sarcoma demonstrates a honeycomb pattern of membranous CD99 immunoreactivity (Fig. 3-12). Definite diagnosis, however, requires cytogenetic or molecular genetic studies for the +(11; 22)(q24; q12) translocation, which is found in more than 95% of cases.⁵

Fig. 3-11 Uniform round cells with uniform round nuclei and scanty cytoplasm (hematoxylin–eosin stain, ×400).

Fig. 3-12 Immunohistochemical expression of CD99 showing characteristic reactivity on the cell membrane (×400).

RADIOLOGY

• This tumor shows a moth-eaten bone destruction pattern. It usually starts from the vertebral body or sacrum.

• The vertebral body destruction pattern is not extensive, so tiny perforation of the bony cortex is more common rather than wide loss of the cortical bone. Extraosseous soft tissue mass is often accompanied with the vertebral body mass (Fig. 3-13).

• The signal change in magnetic resonance imaging (MRI) is variable. On T1WI, the signal is intermediate to low, and on T2WI an intermediate to high signal change is a usual finding (Fig. 3-14). A moderate enhancement pattern is common. A necrotic area is commonly seen in the tumor mass.

Fig. 3-13 MR sagittal images of sacral Ewing sarcoma. On T2WI, high signal mass is seen to protrude to presacral area at S4 level (left). Higher signal epidural mass is in the spinal canal. In the mass, the signal is not homogeneous. On T1WI, a high signal epidural mass is seen in the spinal canal. The signal of the mass is not homogenous, but of mixed feature (middle). With contrast, a moderate enhancement pattern is seen, including a necrosis area (right).

Fig. 3-14 Axial MRI of Ewing sarcoma. On T1WI, a low signal mass is seen at S4 vertebral body. In the mass, a slightly high signal area is included (left). On T2WI, the high signal intensity lesion is observed. In the middle of the mass, a higher signal area is included (right).

CHONDROSARCOMA

EPIDEMIOLOGY

• Primary chondrosarcomas of the mobile spine are rare lesions. Two reviews ^6,⁷ document 22 and 21 patients for the two institutions (Istituto Rizzoli and University of Texas M. D. Anderson Cancer Center) in 59 and 43 years, respectively.

• Although chondrosarcomas overall demonstrate a male predilection, in the two series just described, there was only a marginally greater number of males than females. The average age of the patients at the time of diagnosis in the series was 33 and 51 years, respectively.