Epidural Malignant Tumors

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Chapter 3 Epidural Malignant Tumors

Jae-Soo Koh, Ung-Kyu Chang, Se-Hoon Kim, Terri Haddix

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.

Computed Tomography

• Lytic, bone destructive lesion is shown (Fig. 3-3).

• Commonly, lymphoma presents as paraspinal mass (Fig. 3-4).

Fig. 3-3 CT of T3 lymphoma patient. Lytic bone destruction is seen in the marrow space, but the cortex is well maintained on axial cut (left). On sagittal view, central osteolytic lesion is surrounded by a somewhat osteosclerotic lesion in the vertebral body of T3 (middle and right).

Fig. 3-4 Paraspinal lymphoma is seen along the right side of the thoracic spine (left). After thoracotomy, the mass was excised en bloc (right). The mass was reddish and soft.

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.

DISTRIBUTION

Combining the results of the series just described, chondrosarcomas arose most commonly in the thoracic segment (51%), followed by the cervical (35%) and lumbar (14%) segments.

HISTOLOGY/GRADING

• Grade I chondrosarcomas are mild to moderately cellular neoplasms composed of neoplastic chondrocytes within lacunae in a chondroid matrix (Fig. 3-15).

• With increasing grade, there is greater nuclear atypia and cellularity and often necrosis. If there is a coexistent spindled morphologic pattern, a diagnosis of another more highly malignant tumor (e.g., dedifferentiated chondrosarcoma) is likely.²

• The histologic differential of low-grade chondrosarcomas includes chordoma. Even though the growth patterns of these two lesions are often evident with sufficient sampling, immunohistochemical staining also can differentiate the lesions; chondrosarcomas demonstrate immunoreactivity for S100 protein (Fig. 3-16) but not keratin (Fig. 3-17), whereas chordomas are immunoreactive for both.

Fig. 3-15 Low-grade chondrosarcoma. The tumor is of modestly increased cellularity composed of chondrocytes with enlarged, hyperchromatic nuclei and occasional binucleation (hematoxylin–eosin stain, ×200).

Fig. 3-16 Diffuse, strong S100 protein immunoreactivity (×200).

Fig. 3-17 Absence of pankeratin immunoreactivity (×200).

RADIOLOGY

• Chondrosarcoma is a malignant tumor of connective tissue characterized by formation of cartilage matrix by tumor cells.

• This tumor is composed of two parts: chondroid matrix mineralization of ring and arcs and a non-mineralized portion of hyaline cartilage.

• T2WI MR: High signal area of hyaline cartilage and low signal area of mineralization part (Fig. 3-18).

• T1WI MR: Low to intermediate signal (Fig. 3-19).

• Contrast MR: Non-enhancing parts represent hyaline cartilage, cystic mucoid tissue, or necrosis.

• CT: Can show bone destruction, calcification, and tumor extent (Fig. 3-20).

Fig. 3-18 T2WI of sacral chondrosarcoma. High signal and low signal are mixed. High signal means hyaline cartilage and low signal means mineralization (left, sagittal view; right, coronal view). Epidural mass is formed along the posterior margin of the sacrum.

Fig. 3-19 T1-weighted MR image of sacral chondrosarcoma. Low signal lesion involves sacral body and right side ala area. It shows diffuse low signal intensity (left, sagittal view; right, coronal view).

Fig. 3-20 CT finding of sacral chondrosarcoma. High density mass is seen on right side ala area of the sacrum.

CHORDOMA

EPIDEMIOLOGY

• Chordomas only rarely occur in individuals younger than 40 years of age.⁸

• Chordomas develop in males nearly twice as often as in females.

DISTRIBUTION

• Chordomas arise in midline structures, including the base of the skull and throughout the spine.

• Within the spine, the sacrum is the most common region in which chordomas develop. The cervical spine, the next most common site in which chordomas develop, is affected approximately four times less often than the sacrum.

RADIOLOGY

• On plain films, most chordomas are shown as radiolucent lesions with a sclerotic margin.

• On CT scan, a soft tissue mass is commonly associated with the osteolytic lesion.

• On T2WI MR, high signal change is as usual. However, in some cases, low signal change can be seen if the tumor mass is rich in fibrous component (Fig. 3-24).

• On T1WI MR, either hypo-signal or iso-signal change is possible (Fig. 3-25). With gadolinium (Gd) use, the enhancement pattern is variable (Figs. 3-26 and 3-27).

Fig. 3-24 Recurrent chordoma at C1–3. On T2WI MR, 2- × 1.5-cm low signal mass involving left C2 body is seen.

Fig. 3-25 On T1WI, low signal mass is shown along the posterior margin of C1–2 junction.

Fig. 3-26 Faint enhancement is seen with gadolinium use.

Fig. 3-27 On axial image, posterior protruding mass causes epidural compression.

SACROCOCCYGEAL TERATOMA

EPIDEMIOLOGY

• Sacrococcygeal teratomas (SCTs) are identified in approximately 1 in 35,000 live births and represent the most common extragonadal germ cell tumor in neonates and young children.⁹

• In two large studies ^9,¹⁰ composed of 126 and 51 patients, females accounted for 74% and 80% of the study populations, respectively.

• This tumor may be associated with other malformations of the central nervous, musculoskeletal, cardiovascular, or gastrointestinal system.¹¹

DISTRIBUTION

• SCTs are graded along a continuum based on the degree of external and presacral components, with Grade I tumors having a primarily external location and minimal, if any, presacral component, whereas Grade IV tumors are completely presacral.¹²

• The relative abundance of each SCT grade is: Grade I, 46.7%; Grade II, 34.7%; Grade III, 8.8%; and Grade IV, 9.8%.¹³

MALIGNANT FIBROUS HISTIOCYTOMA

EPIDEMIOLOGY

• Malignant fibrous histiocytoma (MFH) occurs preponderantly in soft tissues but also occasionally in bone. It is now established that MFH represents a rare primary spinal tumor.

• It is not clear whether this tumor represents a homogeneous entity or a collection of sarcomas of diverse type. It has been suggested that MFH arises from primitive mesenchymal cells capable of multidirectional differentiation.¹⁴ Four histologic subtypes of MFH have been described. The most common is the storiform-pleomorphic MFH.

DISTRIBUTION

The vast majority of osseous MFHs occur in long bones, with the femur, tibia, and humerus accounting for approximately 75% of all cases.¹⁵

HISTOLOGY

• MFH is a pleomorphic tumor that is primarily composed of pleomorphic mesenchymal cells and shows storiform arrangement (Fig. 3-30).

• The pleomorphic mesenchymal cells are composed of atypical giant cells and fibroblastic cells with frequent mitosis (Fig. 3-31).

Fig. 3-30 Low-power photomicrographs of malignant fibrous histiocytoma show storiform arrangement of spindle to pleomorphic cells with large hyperchromatic nuclei, many of which show irregular contours and multinucleation (hematoxylin–eosin stain, ×40).

Fig. 3-31 High-power photomicrographs of malignant fibrous histiocytoma (hematoxylin–eosin stain, ×400).

RADIOLOGY

• The plain radiographic and CT findings in osseous MFH include aggressive signs such as lysis and a permeative or moth-eaten pattern.

• Low signal on T2WI and intermediate signal intensity on T1WI MR (Fig. 3-32).

• After administration of contrast medium, the lesion shows intense enhancement.

• Because of involvement of contiguous vertebral bodies and discs, tuberculous spondylitis should be differentially diagnosed.

• The low signal intensity on T2WI and the rich enhancement correlate well with the histologic findings of fibroblasts and vascularization, respectively (Fig. 3-33).¹⁴

Fig. 3-32 Sagittal MRI. T1WI of the thoracic spine shows a low signal intensity lesion in the anterior epidural space displacing the cord posteriorly. There also is infiltration of the T8 vertebral bodies (left). The lesion also is seen to be low signal on T2WI (middle). With gadolinium, the epidural mass is strongly enhanced (right).

Fig. 3-33 Axial MRI of malignant fibrous histiocytoma. Low signal mass is seen in the epidural space on T1WI (left) and T2WI (middle). The mass infiltrates the vertebral body. With contrast, a homogeneous enhancement pattern is shown (right).

OSTEOLYTIC METASTASIS

EPIDEMIOLOGY

• Vertebral metastases are more common in the adult population, particularly in patients with advanced disease.

• Most vertebral metastases are from prostate, lung, breast, renal, and hematopoietic malignancies.¹⁶

• Osteolytic lesions develop where bone destruction exceeds bone production.

DISTRIBUTION

• Lytic metastases include breast, lung, kidney, and thyroid cancers.

• Metastatic nodules are seeded in the basivertebral plexus, therefore destroying the posterior half of vertebral body first. Then osseous destruction proceeds to the pedicle and anterior vertebral body.

HISTOLOGY

• Metastatic carcinomas are histologically discrete aggregates of neoplastic cells (Figs. 3-34 and 3-35).

• The metastatic tumor may or may not share identical cytoarchitectural features with the primary tumor. However, when presented with a metastatic lesion, efforts should be made to concurrently review a patient’s prior relevant pathology specimens.

• For metastatic lesions of unknown primary tumor, immunohistochemical panels can be diagnostic or help narrow the possible primary sites (Fig. 3-36).

Fig. 3-34 Metastatic renal cell carcinoma with near totally destroyed bone trabeculae; focally remaining calcified bony spicule is identified (hematoxylin–eosin stain, ×100).

Fig. 3-35 High-power view of metastatic clear cell renal cell carcinoma with acinar pattern (hematoxylin–eosin stain, ×200).

Fig. 3-36 Osteolytic metastatic renal cell carcinoma shows CD10 immunoreactivity in tumor cells (×200).

RADIOLOGY

• On radiography, osteolytic metastasis can be detected as absent pedicles, disappearance of cortical line, or compression fractures (Fig. 3-37).

• Bone destruction is best diagnosed with CT scan. Usually posterior cortical destruction is seen, and paraspinal or epidural soft tissue mass formation is observed (Fig. 3-38).

• MRI shows low signal change on T1WI and high signal change on T2WI. In most cases, a diffuse enhancement pattern is shown. The necrotic part of the tumor mass is not enhanced (Fig. 3-39). The extent of soft tissue mass is best diagnosed with MRI.

Fig. 3-37 Radiography of osteolytic metastasis (renal cell carcinoma). Right cortical margin of L2 vertebra is not seen (right). On lateral view of lumbar spine, double margins are seen on the upper endplate of L2 vertebra (left). Because of a compression fracture of the right half of the vertebral body, the upper margin is seen with dual image.

Fig. 3-38 CT finding of osteolytic metastasis (renal cell carcinoma). Bony density disappeared and soft tissue density mass replaced the vertebral body and right pedicle (left, regular window setting; right, bone setting image).

Fig. 3-39 MRI finding of osteolytic metastasis (renal cell carcinoma). T2WI shows high signal change of L2 vertebral body, vertebral body height decrease (compression fracture), and posterior cortical bulging (left image). T1WI shows diffuse low signal change of vertebral body marrow (middle image). With enhancement, a diffuse enhancement pattern is seen with a focal necrotic portion (right image).

OSTEOBLASTIC METASTASIS

EPIDEMIOLOGY

• Primary tumors that cause osteoblastic metastasis are composed of prostate, carcinoid, and bladder cancers.

• Mixed lytic and blastic primary tumors include lung, breast, cervix, and ovary cancers.

• The most common osteoblastic metastasis is from prostate. Bone metastasis is observed in 90% of prostate cancer patients, which is highest compared with other visceral organs (lung, 46%; liver, 25%; pleura, 21%; and adrenals, 13%).¹⁷

DISTRIBUTION

• Backward pathway through veins from the prostate to the spine has been proposed for the metastatic mechanism of prostate cancer.

• There is a reported inverse relationship between spine and lung metastases, suggesting that metastasis to the spine is independent of lung metastasis.¹⁷

• The maximum frequency of spine involvement occurred in smaller tumors (4–6 cm) as compared with the maximum spread to lung (6–8 cm) and liver (>8 cm), suggesting that spine metastases precede lung and liver metastases in many prostate cancers. There is a gradual decrease in spine involvement from the lumbar to the cervical level (97% vs. 38%), which is consistent with a subsequent upward metastatic spread along spinal veins after initial lumbar metastasis.

HISTOLOGY

• Bone biopsy shows that tumor cells infiltrate intensive myelofibrosis and osteosclerosis.

• Bony trabeculae are thickened as a result of a new woven bone formation (Fig. 3-40).¹⁸

• Osteoblastic lesions are associated with higher serum levels of alkaline phosphatase and may produce hypocalcemia.

Fig. 3-40 Metastatic prostatic adenocarcinoma between bony trabeculae (hematoxylin–eosin stain, ×100).

RADIOLOGY

• On radiography, dense sclerotic foci involve the vertebral body, pedicle, and posterior element. Generally, a high density change of the vertebral body is seen (Fig. 3-41). Sometimes compression fracture is detected.

• With CT scan, the bone marrow is replaced with dense foci of sclerosis. When the sclerotic change appears in diffuse pattern, this phenomenon is called an ivory vertebra (Fig. 3-42).

• Generally MR signal change is low on T1WI and T2WI (Fig. 3-43).

Fig. 3-41 Radiography of osteoblastic metastasis (prostate cancer). Multiple dense foci are scattered throughout all vertebral bodies. Sclerotic change may be seen as small nodules or diffuse increased density areas. In the posterior element, small, high density nodules also are seen (right).

Fig. 3-42 CT finding of osteoblastic metastasis (prostate cancer metastasis). The bone marrow is replaced with high density nodules of various sizes (left).

Fig. 3-43 MRI finding of osteoblastic metastasis (prostate cancer metastasis). The bone marrow signal is generally low on T2WI (left). Diffuse involvement of low signal change is seen in the vertebral body on T1WI (middle). Vertebral body signal is lower than disc signal. With enhancement, lesions show a variable enhancement pattern depending on the degree of sclerosis (right).

SOLITARY BONE PLASMACYTOMA

EPIDEMIOLOGY

• Plasmacytoma means that bone marrow is infiltrated with neoplastic plasma cells.

• A solitary type of plasmacytoma represents only 2–10% of all plasma cell myelomas.¹⁹

• Solitary plasmacytoma occurs most commonly in the sixth decade of life. There is a male predominance, with a ratio of 2:1–3:1.

• Spinal plasmacytomas comprise 50% of all solitary plasmacytomas.

DISTRIBUTION

• Spinal plasmacytomas usually affect the vertebral bodies. They may cause epidural extension or pathologic fracture, resulting in spinal cord compression.

• The criteria for a diagnosis of solitary bone plasmacytoma include a solitary bone lesion, bone marrow plasmacytosis less than 10%, biopsy evidence of plasma cell neoplasm, and no evidence of other lesions based on the clinical examination or skeletal survey.¹⁹

HISTOLOGY

• Monotonous collection of neoplastic plasma cells; eccentric, round, moderately pleomorphic nuclei with a “clock face” chromatin; and rich basophilic cytoplasm (Fig. 3-44).

• Immunohistochemical staining is necessary to confirm plasma cell lineage and monoclonality (see Fig. 3-44, B, C, and D).

Fig. 3-44 An atypical plasma cell proliferation. A, Sheets of plasmacytoid cells with eccentrically positioned nuclei, “clock face” chromatin, and occasional perinuclear clearing (“hof”). Clinical correlation is necessary to determine whether such a proliferation is part of a disseminated process (e.g., multiple myeloma) or represents a solitary lesion (e.g., plasmacytoma) (hematoxylin–eosin stain, ×400). B, Diffuse CD138 immunoreactivity confirming plasma cell lineage (×200). C, Diffuse strong immunoreactivity for lambda light chain expression and no reactivity for kappa light chain (D) establishes monotypic nature of the proliferation (×200).

RADIOLOGY

• On radiography, the lesion is usually large, well defined, expanded and cystic-appearing, and may have permeative components.

• The CT appearance of plasmacytoma is that of lytic abnormalities with sclerotic margins without the usual focal punch-out appearance as in multiple myeloma.²⁰

• On MRI studies, the mass lesion is isointense or slightly hyperintense on T1WI and hypointense on T2WI, and shows weak homogeneous enhancement (Figs. 3-45 and 3-46).

Fig. 3-45 Sagittal MRI of T6 mass. The mass signal is isointense or slightly hyperintense on T1WI (left) and hypointense on T2WI (right).

Fig. 3-46 Enhanced MRI of plasmacytoma. The mass shows weak homogeneous enhancement (left). The axial image after enhancement shows that the tumor mainly invaded the posterior and middle elements of T6, compromising the spinal canal (right).

FIBROSARCOMA

EPIDEMIOLOGY

• Fibrosarcoma is a rare tumor of the soft tissue, occurring primarily in the deep musculature and commonly associated with the adjacent fascia or periosteum.²¹

• Low-grade fibrosarcomas mainly affect the extremities and trunk of adults of either sex.

DISTRIBUTION

Fibrosarcomas primarily affect the extremities, shoulder girdles, and trunk. Furthermore, they arise most commonly in the deep soft tissue of young and middle-aged adults of either sex, are slow growing, and may metastasize distantly.

HISTOLOGY

• Among malignant mesenchymal tumors, fibrosarcoma is one of the neoplasms with a well known histologic variability.

• Histologically low-grade fibromyxoid sarcoma, hyalinizing spindle cell tumor with giant collagen rosettes, and sclerosing epithelioid fibrosarcoma are well established entities.²²

• Recently fibrosarcoma of low-grade fibroblastic type, a new entity, is categorized as a diagnosis of exclusion.

• The individual tumor cell has a monotonous appearance, consisting of polygonal cells arranged in a herringbone pattern surrounded by dense collagenous stroma with areas of hyalinization (Fig. 3-47).

• The tumor infiltrates into the surrounding cortical lamellar bone. When tumor cells are observed under high-power magnification, they are rounded, oval, or polygonal; of small to medium size; and with clear or pale eosinophilic cytoplasm (Fig. 3-48).

• The nuclei of the tumor cells are small, ovoid, or angular and mostly pale or vesicular, with distinct nucleoli and little pleomorphism. Some of the tumor cells show clear or vacuolated cytoplasm, but they constitute less than 20% of the tumor.

• Differential diagnosis includes benign fibrous lesions, low-grade myofibroblastic sarcoma, and malignant peripheral nerve sheath tumor.

Fig. 3-47 Fibrosarcoma. Monotonous spindle cells are arranged in a herringbone pattern. Mitotic figures are frequently apparent (hematoxylin–eosin stain, ×100).

Fig. 3-48 Fibrosarcoma. Numerous, mainly regularly shaped fibroblasts with a storiform pattern. Such cell-rich areas are never seen in fibromatosis (hematoxylin–eosin stain, ×200).

RADIOLOGY

• On CT, the mass density is very low, and a typical osteolytic pattern is seen (Fig. 3-49).

• MRI shows heterogeneous intermediate signal intensity on T1WI.

• T2WI show a mass of heterogeneously low-to-high signal intensity.

• On Gd-enhanced MRI images, the mass shows strong enhancement (Figs. 3-50 and 3-51). With these findings, the radiological differential diagnoses includes plexiform neurofibroma, fibromatosis, and malignant neurogenic tumor.