| | Neoplastic Disease of the Vertebral Column: Radiologic-Pathologic CorrelationSpine imaging is frequently performed in daily practice. Due to the high frequency of spine examinations and the multiple modalities (ie, radiography, computed tomography, magnetic resonance imaging, positron emission tomography/computed tomography, single-photon emission computed tomography/computed tomography) used for imaging, neoplastic disease of the vertebral column will occasionally be encountered by practicing radiologists. When a lesion in the spine is encountered, it is helpful to have an understanding of the general types of pathology and key differentiating features that may aid in guiding appropriate workup (eg, no follow-up required, short-term follow-up, or directed biopsy). This article aims to provide a framework for characterizing neoplastic disease in the spine and allows the practicing radiologist an opportunity to develop a more concise and accurate differential diagnosis with which to guide clinical management. Spine imaging is frequently performed in daily practice. Given the high frequency of spine examinations and the multiple modalities (ie, radiography, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography/CT, single-photon emission computed tomography (SPECT/CT) used for imaging, neoplastic disease of the vertebral column will occasionally be encountered by practicing radiologists. This article aims to provide a framework for which to characterize these lesions. Examples of both more common and less commonly encountered lesions are used to provide a framework for which to create an appropriate differential diagnosis. Following the presentation of each entity, there is a brief discussion, which includes a discussion of demographics, pathology, radiology, and/or key differentiating features. Approach to Diagnosis  When a lesion is encountered in the spine, it is helpful to have a specific approach to guide characterization. Deciding whether a lesion is sclerotic or lytic is a helpful first step in creating a differential diagnosis. Next, the patient's age should be considered. Many differential considerations can be excluded based simply on the patient's age. Following patient age, both sclerotic and lytic lesions can be further differentiated by knowing a few key features of each entity as described below. A helpful way to remember the diagnostic considerations for spine lesions is based on the tissue of origin. A helpful table borrowed from a review article by Rodallec et al classifies spinal tumors into tissue of origin (Table 1). In addition to primary neoplastic disease, metastasis should always be considered as a differential possibility. | ⁎ Extremely rare in the spine. (Reprinted with permission from Rodallec et al.7) |
Sclerotic Bone Lesions When a sclerotic lesion is encountered, the patient's age should first be assessed (Table 2). Following patient age, sclerotic lesions can be further differentiated by knowing a few key features of each entity. Chronic osteomyelitis can mimic a neoplastic process and appear sclerotic on imaging. Other less common mimics include osteopoikilosis, an asymptomatic osteosclerotic dysplasia.1 Osteopoikilotic lesions resemble multiple bone islands, are typically symmetrical and periarticular, and demonstrate no increased uptake on bone scan. Some lesions can have a mixed lytic and sclerotic appearance due to the presence of coarsened trabeculae or internal matrix, but these can be considered as primarily lytic lesions and are assessed using that algorithm. Finally, reviewing old comparison studies can be helpful to demonstrate lesion stability. Following are several common and less commonly encountered entities. Bone Island The bone island is the most common lesion to involve the spine based on cadaveric studies.2 Bone islands have a propensity for the axial skeleton and can be considered hamartomas.3 Histologically, bone islands represent lamellar compact bone with a haversian system, which are embedded within the medullary canal (Fig 1A).3 They are typically seen to lie just beneath the cortex with radiating spicules at their periphery extending into the adjacent normal trabecular, medullary bone. This appearance has been described as representing “thorny radiations” or a “brush border.”4 Scintigraphy is typically normal (Fig 1B); however, giant bone islands (>2 cm) can display mildly increased radiotracer uptake on bone scan. Most bone islands remain stable in appearance; however, some may slowly increase or decrease in size.5 Vertebral biopsy should be considered if the lesion increases in diameter by greater than 25% within 6 months, or 50% within 1 year.6 The appearance on CT is characteristic and demonstrates a densely sclerotic lesion equal in density and frequently adjacent to normal cortical bone. There will also be an abrupt transition to normal bone where the compact lamellar bone meets the trabecular, medullary bone. Given the lack of mobile protons, MRI not surprisingly will show decreased signal on all pulse sequences. Other characteristic features including the “thorny radiations” and close proximity to cortical bone described above can still be seen (Fig 1C). Metastasis Blastic metastases may also be frequently encountered in a busy practice. Blastic metastases are most frequently secondary to prostate cancer in older men and breast cancer in women.7 Other osteoblastic metastases include lymphoma, carcinoid tumors, mucinous adenocarcinoma of the gastrointestinal tract, pancreatic adenocarcinoma, and bladder carcinoma. In children, neuroblastoma and medulloblastoma should be considered.7 Imaging will typically reveal multiple sclerotic densities on CT or conventional radiography. These lesions show marked avidity for technetium-99m-methylene diphosphonate on bone scan due to their high osteoblastic activity (Fig 2A and B). Blastic metastases do not necessarily abut the cortical surface (Fig 2C) as commonly seen in bone islands, are frequently not homogeneously dense and equal in density to cortical bone, and do not typically demonstrate spiculated borders with abrupt transition to normal medullary bone. On MRI (Fig 2C), the decreased signal intensity on all pulses is similar to bone islands; however, other characteristic features of bone islands are typically absent. If there is any difficulty in differentiating metastases from bone islands or other benign conditions (ie, osteopoikilosis), a bone scan is warranted. POEMS Syndrome POEMS syndrome is a rare multisystemic disorder characterized by sclerotic bone lesions in addition to other clinical manifestations (ie, Polyneuropathy, Organomegaly, Endocrinopathy, M-protein, and Skin changes). Patients have a plasma cell dyscrasia that is difficult to classify into multiple myeloma or plasmacytoma (Fig 3A).8 In addition, they tend to be younger than typically seen with myeloma and the paraproteinemia is more likely to involve IgG or IgA and lambda chains.9, 10, 11 Clinically, there are proposed diagnostic criteria.12 Major criteria include polyneuropathy and a monoclonal plasma proliferative disorder. Minor criteria include sclerotic bone lesions, organomegaly, edema, skin changes, endocrinopathy, and Castleman's disease. Based on this system, 2 major and 1 minor criteria are required for diagnosis. Radiographically, sclerotic lesions are typically characterized as well defined or fluffy with lytic lesions demonstrating peripheral sclerosis (Fig 3B).9 Brandon et al13 characterized the lesions as having a “mulberry” appearance and scintigraphically found no increased uptake on bone scan (Fig 3B and C). MRI will demonstrate the characteristic decreased T1 and T2 signal seen with -blastic lesions (Fig 3D). Resnick and coworkers8 described areas of osseous proliferation, especially at the posterior spinal elements as more unique to POEMS syndrome. Lytic Bone Lesions Lytic lesions are more numerous and require more discriminators (Table 3). Often, these discriminating features are not pathognomonic, but suggestive, and can be used to create a more focused differential diagnosis. In patients under 30 years old, lytic lesions can be further differentiated based on whether there is predominant involvement in the posterior elements. That is not to say that the vertebral body cannot be involved by extension, but the lesion characteristically is centered within the posterior elements. In patients over 30 years old, it is helpful to determine whether tumor matrix is present. Paget disease and hemangiomas do not have true matrix, but the thickened and coarsened trabeculae may mimic matrix or result in a mixed appearance and these lesions are included in the matrix category. Osteoid Osteoma Osteoid osteoma only involves the axial skeleton in 10% of cases and of these most frequently involve the posterior elements (Fig 4A and B).14 The classic clinical presentation is a child with painful scoliosis, where the pain is worse at night and relieved by nonsteroidal anti-inflammatory drugs. Patients typically present between 10 and 20 years of age.4 The nidus is the center of the lesion, which can incite adjacent cortical bone, resulting in reactive sclerosis. Pathologically, the nidus represents well-organized, interconnected trabecular bone within a background of vascularized connective tissue (Fig 4C and D).14 Radiologically, CT demonstrates nicely the central lucent nidus, which should be <1.5 cm, with or without central calcification.4, 7 There is marked uptake by the nidus on bone scintigraphy.4 On MRI, the nidus is generally low-to-intermediate signal on T1 and intermediate-to-high signal on T2, likely reflecting the vascularized nature of the lesion. Chondrosarcoma Conventional intramedullary chondrosarcoma is the most common type of primary (de novo) chondrosarcoma and typically presents in the fourth or fifth decade of life.15 The spine represents only 7% of cases. Radiographically, a mixed sclerotic and lytic pattern is observed with mineralized chondroid matrix causing a ring-and-arc appearance (Fig 5A). The classic ring-and-arc appearance is due to endochondral ossification at the margins of the cartilagenous tumor lobules (Fig 5D).15 The thoracic spine is most commonly involved and involvement in the sacrum is rare.15 On MRI, increased T2 signal reflects the high-water content of these usually low-grade malignancies (when they occur in the spine) (Fig 5B). Soft-tissue involvement is typically present and crossing of the intervertebral disk occurs in 35% of cases.15 They most commonly are centered within the posterior elements and enhance in a peripheral and septal fashion (Fig 5C).15 Paget Disease Paget disease is common and affects 3%-4% of the population over 40 years of age.16 It is actually a metabolic bone disorder that can mimic neoplastic disease and can have a variety of appearances reflecting the 3 following discrete stages of involvement: lytic, mixed, and blastic. This entity can also be found in the Table 2 for a sclerotic lesion because the appearance can infrequently mimic blastic metastasis as an “ivory” vertebrae. Pathologically, the lytic stage is dominated by osteoclastic activity, while the mixed and blastic stage possess osteoblastic activity. Osteoblastic activity results in the hyperplastic bone with thickening of trabeculae seen in Paget bone (Fig 6A). Each stage of the disease can mimic metastasis and 1 defining feature seen in the later stages of the disease process is bony expansion. A second is cortical thickening, which in the spine results in the “picture frame” vertebral body where all sides of cortical bone are thickened. This can aid in differentiation from other conditions that can mimic cortical thickening such as osteopetrosis and hyperparathyroidism (ie, rugger Jersey spine). These conditions will only involve the endplates and not the anterior and posterior cortical margins of the vertebral body. Comparison with other studies may also be helpful to evaluate for characteristic features in other parts of the body such as thickening of the iliopectineal line with pelvic involvement. Bone scintigraphy typically reveals marked uptake of radionuclide in all phases of the disease process. This should aid in distinction from a compressive hemangioma (see following discussion), which can involve the entire vertebral body and mimic the appearance. Radiographs typically reveal a “picture frame” vertebrae with cortical thickening on all sides of the vertebral body. CT demonstrates the characteristic thickened cortical and trabecular bone with bony expansion (Fig 6B). Hemangioma Classically described in the radiologic and pathologic literature as vertebral hemangiomas, these lesions should more correctly be termed vertebral venous malformations.17 Prevalence increases after middle age and there is a slight female predilection.7 Pathologically, they are composed of thin-walled vessels lined by flat, quiescent endothelial cells.7, 18 The suffix -oma is best used to refer to lesions that exhibit cellular proliferation as seen in infantile or congenital hemangiomas.19 Radiologic-pathologic correlation demonstrates an association between the signal characteristics of the lesion and the proportion of adipocytes, vessels, and interstitial edema.18 Malformations with a higher proportion of intervening adipocytes have higher signal on T1 (Fig 7A), while those with a greater vascular component have more intermediate signal on T1 and higher signal on T2. Radiographically, they classically have a coarse “honeycomb” appearance secondary to reinforced trabeculae within the lesion (Fig 7B).7 Scintigraphy typically shows photopenia or mild increased uptake.7 Compressive vertebral hemangiomas have a much wider spectrum of appearances (Fig 8). There may be a stroma of soft-tissue density rather than the typical fat seen with asymptomatic vertebral hemangiomas. They may also exhibit extraosseous soft-tissue extension and cortical lysis, mimicking metastasis (Fig 8D).20 On CT, an intraosseous polka-dot pattern representing prominent trabeculae is helpful in making the diagnosis (Fig 8A).20 On MRI, hyperintensity on T1 (corresponding with the fatty component) is specific, but insensitive (50% of lesions), while the presence of signal voids representing coarsened trabeculae is a helpful secondary sign in those lesions that are hypointense on T1 (Fig 8C).20 It is important to think about compressive hemangioma in the differential when an isolated aggressive lesion is seen within a vertebral body. If there is any thought that the lesion could represent a hemangioma, nuclear medicine bone scan could be performed to assess the degree of radiotracer uptake (Fig 8B) (no significant uptake is expected in a hemangioma). Epithelioid Hemangioendothelioma Epithelioid hemangioendothelioma is a true vascular neoplasm that can occur at any age but most frequently during the second and third decades.21 It is defined as an intermediate-grade malignant vascular neoplasm that is less aggressive than an angiosarcoma.21 Epithelioid hemagioendothelioma is typically painful and, when involving bone, most frequently involves the calvarium, axial skeleton, and lower limbs.21 Multifocal disease is seen in over 50% of cases, and given the potential for visceral involvement, a CT examination of the chest, abdomen, and pelvis and a bone scan should be considered when the diagnosis is made.21 Pathologically, the tumor consists of solid nests and anastamosing cords of round, polygonal, or spindle-shaped cells with eosinophilic cytoplasm.21 Intracyoplasmic vacuolization is a characteristic feature indicative of primitive vascular channels.21 Radiographically, a lytic lesion without mineralized matrix is characteristic (Fig 9). Calcification and periosteal reaction are not typically seen and homogenous contrast enhancement is expected. Aneurysmal Bone Cyst Not a true cyst or an aneurysm, the name aneurysmal bone cyst was initially coined by Jaffe and Lichtenstein, owing to “aneurysmal” expansion of bone and the blood-filled cavity encountered on entering a thin shell of bone (Fig 10A).4 Aneurysmal bone cysts (ABC) typically present (80%) in patients under 20 years old and the spine accounts for approximately 12%-30% of cases.22 The exact etiology is still unclear; however, classically, they are divided into primary (no underlying neoplasm; trauma may result in a local vascular disturbance) or secondary (related to an underlying neoplasm; either by venous obstruction or by arteriovenous fistula).22 However, there is also evidence that there may be a hereditary component or predisposition to formation.23 Radiographically, these lesions characteristically arise within and expand the posterior elements; however, they can also commonly extend into the adjacent vertebral body.4, 22, 23 Fluid levels are characteristic on T2-weighted MRI sequences, but not pathognomonic (Fig 10B). Fluid levels may also be seen on CT, especially with appropriate windowing and use of the soft-tissue algorithm. Enhancement of thin septations about the blood-filled cavities is expected (Fig 10C). Enhancing solid portions should suggest that the ABC is actually secondary to a primary neoplasm. Bone scintigraphy classically shows peripheral uptake, the so-called “donut sign,” although this can also be seen in giant cell tumors.4 Plasmacytoma Thought to be a precursor to multiple myeloma, a plasmacytoma consists of a focal proliferation of malignant plasma cells without diffuse bone marrow involvement (Fig 11A).7 The majority (70%) of patients are over 60 years old and often manifest with a single collapsed vertebrae.7 Radiographically, the appearance is that of a purely lytic process replacing cancellous bone (Fig 11B). Compensatory hypertrophy of the remaining trabeculae results in cortical thickening and sometimes a “mini-brain” appearance, which has been suggested as nearly pathognomonic for plasmacytoma (Fig 11D).24 This appearance is distinct from Paget disease and “hemangioma,” which can also cause trabecular thickening. MRI often demonstrates a nonspecific pattern of decreased signal on T1- and increased signal on T2-weighted sequences (Fig 11C). Age is probably a more helpful differentiating feature than any particular internal signal characteristic. Giant Cell Tumor Giant cell tumor involves the spine in 7% of cases and typically affects a younger patient population (second to fourth decades).4 Like chordomas, spinal giant cell tumors occur most frequently in the sacrum and may cross the sacroiliac joint; however, central calcification/matrix is not seen. Pathologically, abundant osteoclastic giant cells are seen intermixed throughout a spindle cell stroma (Fig 12A).4 Areas of fibrous tissue with abundant collagen content can also be seen, which may contribute to the low-to-intermediate signal often seen on T2-weighted MR sequences.4, 25 On imaging, an expansile lesion with bone lysis is typical. As mentioned above, mineralized matrix is not seen and the intermediate-to-low signal intensity frequently seen on T2 can help distinguish this neoplasm from other differential considerations such as myeloma, metastasis, lymphoma, and chordoma, which tend to have higher T2 signal (Fig 12B).4, 25 As previously mentioned, bone scintigraphy can demonstrate a “donut sign” as described in ABC (Fig 12C). Evaluation of involvement at the S1 vertebral body and sacroiliac can aid in presurgical evaluation to determine resectability. Recurrence is frequent, estimated at 40%-60%, and seen as new areas of bone destruction.4 Chordoma Chordomas arise from notochord remnants, which represent the earliest fetal axial skeleton.4 Normally, the notochord evolves into the nucleus pulposus; however, vestiges of notochordal tissue can persist and a chordoma can develop. They typically occur in middle-aged patients with a peak incidence in the fifth decade.4 Pathologically, physaliphorous (“bubble-like”) cells are seen, representing clear cells with intracytoplasmic vacuoles (Fig 13A). Both intra- and extracellular mucin is characteristic. On imaging, the characteristic appearance is a destructive lesion involving the midline of a vertebral body. The sacrococcygeal region is most frequently involved (50%), with calcification seen in up to 90% of cases.4 Calcification is less frequently observed above the sacrum (30% of cases).4 On MRI, these lesions are characteristically very bright on T2, similar in intensity to the nucleus pulposus. Epidural involvement was seen in 90% of cases in a series of cervical chordomas.21 They often extend over multiple levels and have an associated soft-tissue mass with a “collar button” or “mushroom” appearance (Fig 13B).26, 27 Enlargement of neural foramina was also frequently observed, which may mimic a schwannoma or even meningioma. Activity on nuclear medicine bone scintigraphy can be a helpful differentiating feature because, unlike many bone tumors, chordomas tend to show reduced uptake (Fig 13C).28 The exact reason is unknown but thought to relate to either interruption of the bone blood supply by the tumor with impedence of uptake of radiotracer or gross bone destruction and resultant lack of reactive bone tissue within the region of the tumor.28 Plasmacytomas may also demonstrate photopenia on bone scintigraphy. Chordomas, in addition to giant cell tumors and ABCs, may cross intervertebral disks, simulating infection. Last, a relatively new entity, the giant vertebral notochordal rest has been described, which can be easily confused with chordoma. This entity is thought to represent a macroscopic vertebral lesion composed of benign notochordal tissue.29 These lesions tend to be bright on T2 and low in signal on T1, similar to chordomas, and can mimic chordomas on histology. Radiologic criteria have been proposed to aid in distinction and include (1) confinement to the vertebral body; (2) conformity to the shape of vertebral body; (3) no lytic lesion, but often mild sclerosis; (4) no soft-issue extension; (5) no progression of growth.29 A lesion in a vertebral body with these imaging characteristics, but with histology raising the possibility of chordoma, may actually represent a giant notochordal rest. This is important because these 2 entities have vastly different management. Careful clinical and radiological follow-up is recommended for giant notochordal rests, while vertebrectomy is required with a diagnosis of chordoma.29 Conclusion Due to the large amount of spine imaging performed in a typical practice, lesions in the vertebral column are frequently encountered. 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a Department of Radiology, West Virginia University, Morgantown, WV b Department of Pathology, West Virginia University, Morgantown, WV  Reprint requests: Andrew M. Zbojniewicz, MD, Division of Radiology, Cincinnati Childrens Hospital Medical Center, 3333 Burnet Ave MLC 5031, Cincinnati, OH 45229-3039
PII: S0363-0188(09)00057-7 doi:10.1067/j.cpradiol.2009.07.004 © 2010 Mosby, Inc. All rights reserved. | |
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