Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

primarily involve the vertebral body, 10% to 15% have concomitant involvement of the posterior elements.21 Multiple lesions are seen in 25% to 30% of patients.24

Osteoid Osteoma

This benign, osteoid-producing tumor, usually <1.5 cm in size, is often surrounded by a ring of sclerotic bone. Almost all of these lesions involve the neural arch, and most occur within the lumbar spine, followed by the cervical, thoracic, and sacral regions. Bone scintigraphy and CT are gener-

ally more helpful for detecting and characterizing these lesions than is MRI. The nidus is hypoor isointense on T1weighted images and varies from hypoto hyperintense on T2-weighted images, often with surrounding hyperintensity that likely is related to a local inflammatory response (Fig. 12.5).25 The rapid enhancement pattern, typically located within the nidus, is best seen on dynamic sequences (e.g., serial postcontrast images). The surrounding reactive zone enhances more slowly with such imaging. Of note, up to 70% of patients may present with scoliosis, related to muscle spasm, with concavity on the side of the tumor.26

Osteoblastoma

Osteoblastomas, also known as giant osteoid osteomas, are similar histologically to osteoid osteomas but are di erentiated from them largely by size (>1.5 cm). Clinical symptoms also can help to distinguish these lesions: osteoblastomas cause a dull pain as opposed to the intense night pain caused by osteoid osteomas. Occasionally, osteoblastomas possess atypical features and behave aggressively. Like osteoid osteomas, these lesions originate in the neural arch but exhibit

greater mass expansion.5 Thus, they may be centered in the pedicle, lamina, transverse or spinous process, articular pillar, or pars interarticularis, with extension into the vertebral body. The lesion is hypoor isointense on T1-weighted images and isoor hyperintense on T2-weighted images with extensive peritumoral edema (flare phenomenon); fluidfluid levels are often present within the lesion (Fig. 12.6). Contrast enhancement is variable.27 Unlike osteoid osteomas, scoliosis may occur convex toward the side of the tumor.

Giant Cell Tumor

Giant cell tumors are locally aggressive, lytic tumors in the vertebral body and sacrum and are named for the osteoclastlike giant cells that are present on histology. Hemorrhage is common secondary to the hypervascular stroma of these lesions. MRI shows expansile lesions with hypoto isointense signal on T1-weighted images and isoto hyperintense signal on T2-weighted images (Fig. 12.7). Contrast enhancement often is heterogeneous, commonly surrounding areas of necrosis, blood, blood degradation products, and/or cystic cavities with fluid–fluid levels.28 Such lesions can undergo sarcomatous transformation (10% of cases) to become malignant giant cell tumors,29 and thus patients with these tumors must be monitored with MRI or CT because of the risk of recurrence. It is important to note that the di erential diagnosis of midline tumors in the sacrum includes giant cell tumor, chordoma, aneurysmal bone cyst, plasmacytoma, and metastases in adults, and sacrococcygeal teratoma in children.9

Osteochondroma

Osteochondroma, also known as osteocartilaginous exostosis, consists of cartilage-covered osseous protuberances with a medullary cavity that is contiguous with the parent

bone. These lesions grossly appear to be caulifloweror mushroom-shaped lesions with cartilaginous caps. Only 5% of these growths occur within the spine (compared with 85% in long-bone metaphyses), but when they do, they are located mostly in the cervical spine, particularly at C2.9 These lesions most commonly arise from the spinous and transverse processes, but they also may arise from the vertebral body. On T1-weighted and T2-weighted images, they appear as central hyperintense lesions surrounded by hypointense calcified cortex. The cartilaginous cap is hypoto isointense on T1-weighted images and isoto hyperintense on T2weighted images and exhibits peripheral enhancement of cartilage (Fig. 12.8).30 MRI is the preferred imaging modality for measuring the cartilaginous cap and determining the status of regional neural and musculoskeletal tissue. Thickening of the cap (>1 cm) should raise concern for malignant transformation to chondrosarcoma. CT may be used for evaluating the osseous structure of the lesion, confirming the contiguity of the medullary cavity with the parent bone, and evaluating for fractures.

Aneurysmal Bone Cyst

These lesions are expansile benign neoplasms containing thin-walled cavities filled with blood and blood products

Fig. 12.8 Thoracic osteochondroma. (A) An axial CT image showing the characteristic “mushroom” appearance of the lesion (arrow) extending into the spinal canal. (B) A sagittal T2-weighted image show-

that occur most commonly in patients less than 20 years old. A substantial proportion of aneurysmal bone cysts are associated with preexisting osseous lesions, such as an osteoblastoma, giant cell tumor, chondroblastoma, nonossifying fibroma, or fibrous dysplasia.31 They arise in the neural arch, but most extend into the vertebral body. The classic presentation is a balloon-like expansile remodeling of bone,

ing a region of high signal intensity around the osteochondroma, which likely represents a cartilaginous cap (arrow).

leaving a thinned “eggshell” cortex. On T1-weighted and T2weighted images, the lesions appear as lobulated neural arch masses, commonly with extension into the vertebral body, epidural space, and adjacent vertebral bodies and ribs.32 Intratumoral cysts contain fluid-fluid levels secondary to blood breakdown products (Fig. 12.9), although visualization of these levels often requires the patient to be motionless for

A

Fig. 12.9 Aneurysmal bone cyst. (A) An axial CT image of the lumbar spine shows a lytic lesion (arrows) expanding the posterior elements and surrounded by a thin rim of bone resembling an eggshell. (B) An

B

axial T2-weighted image of the same patient shows a cystic lesion (arrows) within the posterior elements with fluid–fluid levels.

Fig. 12.10 A sagittal T2-weighted image of an eosinophilic granuloma showing the typical finding of a vertebra plana. In this case, there is also an epidural mass that displaces the spinal cord. Note the associated kyphotic deformity.

a few minutes before imaging. Contrast enhancement may be present at the periphery of the tumor and in the septations. Vertebral body collapse may occur secondary to the extensive vertebral body destruction associated with such lesions.

Eosinophilic Granuloma

This lytic lesion of the vertebral body classically presents with a single collapsed vertebral body (vertebra plana) in patients less than 10 years old (Fig. 12.10) and consists of a benign proliferation of Langerhans cell histiocytes. The lesions are hyperintense on T2-weighted images but present with variable intensity on T1-weighted images. Contrast enhancement is robust.5

Primary Malignant Tumors

Multiple Myeloma

Multiple myeloma is the multifocal, metastatic, and systemic presentation of a solitary bone plasmacytoma (see next

paragraph). Like solitary bone plasmacytomas, focal lesions appear in the vertebral bodies with low to intermediate signal intensity on T1-weighted images compared with normal bone marrow, and they appear hyperintense on T2-weighted images. Postgadolinium enhancement is often present (Fig. 12.11). Multiple myeloma also is revealed on MRI by di use marrow involvement at multiple spinal levels.33 Compared with other metastatic lesions that usually have early pedicle involvement, multiple myeloma usually involves the pedicle late in the course of disease.9

Solitary Bone Plasmacytoma

This tumor, a malignant tumor presenting as a mass of monoclonal plasma cells from bone or soft tissue, is the solitary form of multiple myeloma and may precede it by several years. Clinical di erentiation from multiple myeloma requires a biopsy-proven solitary lesion, the absence of other such lesions in the skeleton, and the absence of anemia, hypercalcemia, and renal involvement suggesting systemic myeloma.34 Such lesions are lytic, destructive, and often accompanied by compression fractures associated with soft-tissue masses and fractures that may lead to severe collapse (vertebra plana). T1-weighted images reveal a solitary lesion centered in the vertebral body that is hypoor isointense compared with muscle and can show curvilinear low signal areas and/ or cortical infolding caused by end-plate fractures. In most cases, the posterior elements are involved and neural compression is varied. T2-weighted images reveal heterogeneous signal within the lesion with focal hyperintensities. Mild to moderate di use contrast enhancement is common and peripheral (rim) contrast enhancement is rare.35 Scanning of the entire skeleton is mandatory to identify a secondary lesion, which occurs in the spine in one third of patients.9

Chordoma

These malignant tumors arising from notochord remnants typically present in one of two histologic patterns. The more common type, known as a typical chordoma, is composed of lobules and sheets of physaliphorous cells, which contain intracytoplasmic vacuoles and abundant mucin. The less common type contains cartilaginous foci and is termed chondroid chordoma.5 Chordomas present as lytic, destructive lesions arising in the midline of the spinal column at any location from clivus to coccyx, but they are found more commonly at the sacrococcygeal (50%) and sphenooccipital (clival) (35%) areas and less commonly in the vertebral body (15%).9 For lesions within the vertebral bodies, a cervical location (particularly at C2) is most common, followed by lumbar and thoracic areas. Chordomas often are several centimeters in size at discovery, usually involve two or more adjacent vertebrae, and extend into the intervertebral discs, surrounding paravertebral soft tissues, and spi-

Fig. 12.12 An axial fat-suppressed T2-weighted image of a right-side sacral chordoma revealing a hyperintense lesion between the ilia that has extended into the pelvis and right gluteal muscles (between arrows).

These malignant, lytic tumors of chondrocytes are characterized by the formation of cartilaginous matrix, can occur as primary tumors or as malignant degeneration of

Fig. 12.13 An axial T2-weighted image of a hyperintense, exophytic, cauliflower-shaped lesion, found to be a chondrosarcoma, arising from the left anterior vertebral body (arrow).

osteochondromas and enchondromas, can cause cortical disruption, and can extend into surrounding soft tissues. Chondrosarcomas can occur wherever cartilage exists,38 and approximately 5% occur in the spine.39 T2-weighted images reveal high signal intensity in areas of hyaline cartilage and low intensity in areas of mineralized matrix. T1-weighted images are helpful in delineating soft-tissue invasion. Contrast-enhanced images show strong enhancement of the septa with “ring and arc” patterns that de-

lineate areas of hyaline cartilage, cystic mucoid tissue, and necrosis, all of which do not enhance with contrast (Fig. 12.13).40

Osteosarcoma/Osteogenic Sarcoma

Of all primary osteogenic sarcomas, 4% occur in the spine and sacrum, primarily in the posterior spinal elements.41 These malignant, lytic tumors of osteoblasts are characterized by the formation of immature, woven osteoid and can occur as primary tumors or as malignant degeneration in individuals with Paget disease, irradiated bone, or bone infarcts. These tumors present primarily in the vertebral bodies, commonly with extension into the posterior elements, and typically have focal areas of low signal on all pulse sequences secondary to matrix mineralization (Fig. 12.14).42 In the telangiectatic form, T2-weighted images may show fluid–fluid levels.

Ewing Sarcoma

The spine is a rare site for Ewing sarcoma. When it does occur, it usually represents a metastatic tumor from another site of origin.26 Usually centered in the vertebral body or sacrum, Ewing sarcoma often causes a “moth-eaten” or permeative type of bone destruction rather than extensive bone loss. Fifty percent of these lesions have an extraosseous, noncalcified, soft-tissue mass.43 On T1-weighted images, these lesions are hypoto isointense compared with surrounding bone marrow, and the cortex usually is preserved despite extraosseous tumor spread. On T2-weighted images,

A

Fig. 12.14 Osteosarcoma. (A) An axial postgadolinium T1-weighted image of a right-side osteosarcoma at the cervicothoracic junction showing enhancement around a central hypointense cystic/necrotic area (arrow). (B) An axial postgadolinium T1-weighted image of a

B

lumbar osteosarcoma, in a di erent patient, showing increased signal within the vertebral body (white arrow) and in the epidural space (black arrow). Both diagnoses were made via percutaneous biopsy.

Fig. 12.15 Left-side paraspinal ganglioneuroma. (A) A T2-weighted image showing a lesion adjacent to the vertebral body and anterior to the psoas muscle. The lesion (arrow) is hyperintense compared

lesions are hyperintense. MRI is the ideal imaging study for delineating extension of soft-tissue mass. Because Ewing sarcoma is histologically a small, round cell tumor, it can be radiographically identical to primitive neuroectodermal tumors, Langerhans cell histiocytosis, lymphoma, leukemia, myeloma, and metastatic neuroblastoma. Ewing sarcoma may also have imaging characteristics similar to those of osteomyelitis. In addition, like patients with Langerhans cell histiocytosis, patients with Ewing sarcoma may present with vertebral body collapse.44

Other Tumors

Neuroblastic Tumors

These embryonal tumors, which are derived from neural crest cells, exist as a spectrum ranging from the most benign ganglioneuromas, to intermediate-di erentiated ganglioneuroblastomas, to the most malignant neuroblastomas. These tumors present almost exclusively in patients less than 10 years old and almost exclusively as abdominal or thoracic paraspinal masses with intraspinal extension.5 The lesions are typically large and extend through a widened neural foramen, creating dumbbell-shaped morphologies and compressing the spinal cord (Fig. 12.15). The lesions are hypoto isointense on T1-weighted images and hypoto hyperintense on T2-weighted images. Although classically they present as paraspinal masses, they may appear as metastatic lesions within vertebral bodies. Contrast enhancement varies but often surrounds areas of internal hemorrhage or necrosis.45,46

Angiolipoma

These benign lesions of adipose and vascular elements present in the spine primarily as epidural masses; they rarely

with muscle. (B) A postgadolinium, T1-weighted image showing the lesion (arrow) to be isointense compared with muscle, with sparse intralesional and peripheral enhancement.

present in an intramedullary location. Because the lesions are composed of fat and vascular tissues, MRI shows heterogeneous signal intensity. On T1-weighted images, most lesions are hyperintense with isoto hypointense areas around prominent vascular components. The lesion may appear heterogeneous on T2-weighted images, but it generally has high signal intensity. Thus, fat-suppressed T1-weighted images with contrast are most useful for defining this lesion and often show heterogeneous enhancement. Interestingly, these lesions do not show vascular flow voids. These lesions may destroy adjacent bone in the anterior epidural space, although only rarely in the posterior epidural space.47

Lymphoma

Lymphoreticular neoplasms present with variable imaging manifestations within the spine. All locations of the spine may be a ected: epidural space (most common), osseous structures, lymphomatous meninges (within the subarachnoid space), and intramedullary (least common).9 Lymphomas of the spine are usually metastatic lesions, not primary lesions arising in the spine.48 Conversely, only 3% to 4% of all malignant bone tumors are primary osseous lymphoma. In the spine, non-Hodgkin lymphoma is far more common than Hodgkin disease, and more than 80% of such lesions are of B-cell origin.49

MRI is ideal for defining the spinal compartment within which the tumor resides. Epidural lesions are isointense on T1-weighted images and variable, but often isointense or hyperintense to spinal cord on T2-weighted images (Fig. 12.16). Osseous lesions are hypointense compared with normal marrow on T1-weighted images and isoto hyperintense on T2-weighted images. Leptomeningitic lymphomas result in thickening of the nerve roots, occasionally with focal nodules, which are isointense compared with the spinal cord on T1-weighted and T2-weighted images.

Fig. 12.16 Epidural B-cell lymphoma surrounding and compressing the thecal sac in the lumbar spine. (A) On a sagittal T2-weighted image, the lesion is isointense compared with the cord and fills the

Intramedullary masses show cord thickening that is isointense compared with the spinal cord on T1-weighted images and hyperintense with surrounding edema on T2-weighted images. Contrast-enhanced images show di use uniform enhancement regardless of the location, with a diagnostic accuracy of 99%.9

■ Intradural–Extramedullary Tumors

These lesions arise within the dura but not from within the spinal cord. Classic MRI findings include a widened ipsilateral subarachnoid space in which the cord and roots are displaced away from the mass (Fig. 12.17). Nerve sheath tumors (schwannomas and neurofibromas) and meningiomas account for more than 80% of such masses.50

Meningioma

Most of these tumors are slow growing, benign (>95%), and based on the dura mater.51 CT imaging may provide added

spinal canal with expansion of the canal at S1 (arrows). (B) On a sagittal postgadolinium T1-weighted image, the lesion shows robust enhancement.

detail because these tumors can calcify; however, MRI is still the ideal imaging modality.51 Classically, the lesions are isointense compared with the spinal cord on T1-weighted images and isoto hyperintense on T2-weighted images (Fig. 12.18). Focal areas of hypointensity occur in the presence of calcifications or flow voids. Contrast-enhanced T1-weighted images show prominent enhancement, sometimes with a broad-based dural attachment (dural “tails”). Most lesions are solitary and occur most commonly in the thoracic spine (80%) followed by the cervical spine (16%) and lumbar spine (4%).52,53 Compared with nerve sheath tumors, which are usually anterolateral, meningiomas are usually located dorsal to the cord.52,53

Schwannoma

These benign neoplasms of the peripheral nerve sheaths are the most common intradural–extramedullary masses and appear as well-circumscribed lesions that may be intradu- ral–extramedullary (75%), completely extradural–paraspinal (15%), or intraand extradural (dumbbell-shaped).5 T1-

Spinal cord

Exiting nerve root

Tumor

Dura

12 Tumors of the Spine 329

have MRI characteristics similar to those of schwannomas (Fig. 12.20), but they often occur as multiple lesions in a patient with the stigmata, including the following:

•Vertebral anomalies

•Meningoceles

•Dural ectasia

•Intramedullary astrocytomas

•Short-segment thoracic scoliosis or kyphosis

•Axillary or inguinal freckling

•Café-au-lait spots

•Optic glioma

•Lisch nodules (hamartomas of the iris) of neurofibromatosis type 1

Therefore, if lesions that look like a schwannoma or neurofibroma on imaging occur in an individual with characteristics of neurofibromatosis type 1, the lesions are likely to be neurofibromas, not schwannomas. Even when isolated, these lesions are usually associated with neurofibromatosis type 1. Additionally, and unlike schwannomas, neurofibromas on T2-weighted images often have a peripheral area of high signal intensity surrounding a central area of low to intermediate signal intensity known as a target sign. Also unlike schwannomas, neurofibromas typically lack a cystic component.

Fig. 12.17 Artist’s sketch (dorsal view) depicting the imaging characteristics of an intradural–extramedullary mass.

weighted images often show an isoto hypointense lesion relative to the spinal cord that may be associated with adjacent osseous erosion, such as widening of the neural foramen or vertebral scalloping.54,55 In contrast to meningiomas, most schwannomas are hyperintense on T2-weighted images. Postgadolinium T1-weighted images show enhancement that may be homogeneous, heterogeneous, or rim-enhancing around cystic areas (Fig. 12.19). Hemorrhage and cystic degeneration are more common with schwannomas than with neurofibromas. Solitary lesions are usually sporadic, but when these lesions occur at multiple concurrent sites, the diagnosis of neurofibromatosis type 2 should be considered.

Malignant Peripheral Nerve Sheath Tumor

These malignant spindle-cell sarcomas of neural origin involve the spinal roots, neural plexuses, peripheral nerves, and end organs and are divided into malignant schwannomas and neurofibrosarcomas. Approximately 50% to 60% are associated with neurofibromatosis type 1. They most commonly present as large (>5 cm), infiltrative, hemorrhagic, soft-tissue masses.51 MRI is the preferred imaging modality. The lesions are hyperintense compared with surrounding fat on T2-weighted images and on STIR images, and isointense compared with muscle on T1-weighted images (Fig. 12.21). T1-weighted images with contrast show marked enhancement. Infiltration into surrounding soft tissue may lead to indistinct margins. Hemorrhage and necrosis within the mass may be seen, resulting in heterogeneous signal. Intra- dural–extramedullary masses often may show a dumbbell configuration with widening of the intervertebral foramina and erosion of the pedicles. Because of this characteristic, these lesions may be di cult to distinguish from benign spinal schwannomas. Thus, a malignant peripheral nerve sheath tumor should be suspected in the presence of sudden growth in a preexisting schwannoma or neurofibroma.

Neurofibroma

These benign neoplasms of the peripheral nerve sheaths can present as focal, di use, or plexiform lesions. They can undergo transformation to malignant tumors. Neurofibromas

Hemangiopericytoma

Although these dural-based lesions appear, radiographically, very similar to meningiomas, they are hypervascular, more