chest imaging 1425 put your back into it: pathologic ......termed arachnoiditis ossificans....

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1425CHEST IMAGING

Cristopher A. Meyer, MD • Achala S. Vagal, MD • Danielle Seaman, MD

It is common to encounter pathologic processes of the lower cervical, thoracic, or upper lumbar spine in the course of routine computed tomography (CT) of the chest. Although magnetic resonance (MR) is the imaging modality of choice for evaluating known spinal disease, evaluation of the spine is an integral part of interpreting a chest CT study. Spinal diseases often have a characteristic CT appearance that allows the radiologist to make the diagnosis or provide a structured differential diagnosis. Pathologic conditions of the spine that can be identified at chest CT are categorized into benign or incidental find-ings, congenital anomalies, traumatic injuries, infectious spondylitis, primary or secondary neoplastic involvement, and associations with systemic disease. CT also provides information about bone mineral-ization and lesion calcification that complements the superior soft-tissue imaging capability of MR. In addition, chest CT data may be reformatted to create volumetric or multiplanar images of the spine to facilitate management decisions about spinal stabilization in symp-tomatic patients.©RSNA, 2011 • radiographics.rsna.org

Put Your Back into It: Pathologic Conditions of the Spine at Chest CT1

CME FEATURE

See www.rsna .org/education /rg_cme.html

LEARNING OBJECTIVES FOR TEST 5

After completing this journal-based CME activity, participants

will be able to:

■ List the spectrum of spinal diseases that can be identi-fied at chest CT.

■ Identify these enti-ties on the basis of their imaging mani-festations.

■ Discuss develop-ment of a structured differential diagnosis for common patho-logic processes in-volving the spine.

RadioGraphics 2011; 31:1425–1441 • Published online 10.1148/rg.315105229 • Content Codes: 1From the Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wis (C.A.M.); Department of Radiology, University of Cincinnati, 234 Goodman Ave, Cincinnati, OH 45267-0761 (A.S.V.); and Department of Radiology, Duke University Medical Center, Durham, NC (D.S.). Recipient of a Certificate of Merit award for an education exhibit at the 2009 RSNA Annual Meeting. Received November 23, 2010; revision requested February 2, 2011, and received March 16; accepted March 24. For this journal-based CME activity, the authors, editor, and reviewers have no relevant relationships to disclose. Address correspondence to A.S.V. (e-mail: [email protected]).

©RSNA, 2011

1426 September-October 2011 radiographics.rsna.org

IntroductionComputed tomography (CT) of the chest is often performed for evaluation of suspected infection or malignancy. Multidetector CT with subcentimeter reconstruction allows high-spatial-frequency evaluation of skeletal structures of the thorax, including the spine, and may be supplemented with sagittal and coronal multipla-nar reformation. For this reason, the incidental discovery of spinal disease at chest CT may be the first opportunity to provide diagnostic value during patient evaluation. Spinal disease can be categorized into benign or incidental findings, congenital malformations, traumatic abnormali-ties, infectious spondylitis, primary or secondary neoplastic involvement, and associations with systemic disease.

In this article, we consider each of these categories and describe several common entities within each category. Knowledge of the spinal pathologic conditions commonly encountered at chest CT will allow the radiologist to provide a confident diagnosis or structured differential diagnosis and guide additional work-up and man-agement decisions.

TechniqueWith the widespread availability of 16–320-row multidetector CT scanners, near-isotropic images can be obtained without additional radiation dose or scanning time. These volumetric techniques have reduced thoracic scanning times to less than 10 seconds, allowing all imaging to take place in a single breath hold. In a compliant patient, this eliminates most motion-related misregistration or step artifacts of the thoracic skeleton.

Our current thoracic imaging protocol uses a 64-row multidetector CT scanner with 0.6- or 0.625-mm detector collimation. The data are re-constructed into two sets, one with 5-mm section thickness and one with 1- or 1.25-mm section thickness and equivalent increments. For both sets, a high-spatial-frequency (lung) algorithm and a soft-tissue–mediastinal algorithm are used.

Alternatively, a single dataset with 2.5- or 3-mm section thickness can be used to achieve a com-promise between image resolution and the size of the dataset available for review.

From the thin-section dataset, standard coronal and sagittal reformatted images can be created by using the high-spatial-frequency algorithm with edge enhancement to evaluate the lung parenchyma, bones, and soft tissue and with a smoothing algorithm for evaluation of the me-diastinum or paraspinal structures. These refor-matted images can be created by the technologist at the scanner console and stored in the picture archiving and communication system (PACS) or directly created on many PACS workstations or freestanding postprocessing workstations. The vertebral column should be routinely reviewed on sagittal images as a component of a complete thoracic CT evaluation to improve sensitivity for fracture detection (1).

Incidental Findings

Dural CalcificationSmall calcified plaques of the dura mater are of-ten encountered at surgery and autopsy and are usually asymptomatic (Fig 1a). Advanced calcifi-cation of the tentorium and spinal dura mater has been described in chronic renal failure and tertiary hyperparathyroidism (2). Such calcifica-tion needs to be differentiated from dural os-sification due to chronic arachnoiditis, an entity termed arachnoiditis ossificans. Arachnoiditis ossificans is frequently associated with a signifi-cant, often progressive neurologic deficit and is associated with trauma, surgery, subarachnoid hemorrhage, or myelography (particularly with oil-based contrast agents) (3).

Dural calcification has been reported in patients with ankylosing spondylitis; such cal-cification is thought to be due to ligamentous inflammation with contiguous inflammation of the meninges and dorsal bone elements. Involve-ment of the lumbar spine with associated cauda equina syndrome has also been reported (4). Although most of the thin linear dural calcifica-tions are incidental, extensive dural calcifications

RG • Volume 31 Number 5 Meyer et al 1427

Figure 1. Calcifications of the dura mater and ligamentum flavum. (a) Sagittal reformatted image from contrast material–enhanced CT shows linear calcifications (arrows) along the posterior dura mater. (b) Axial CT image, obtained in another patient, shows coarse calcification of the ligamentum flavum (arrowhead). There is encroachment into the neural canal and posterior compression of the spinal cord. On axial images, dural calcifications appear rounded while ligamentum flavum calcifications are classically V-shaped.

that reduce the anteroposterior dimension of the spinal canal to less than 1.0 cm should prompt the radiologist to recommend correlation for symptoms of spinal stenosis and consideration of magnetic resonance (MR) imaging to evaluate for cord impingement (5).

Ligamentum Flavum CalcificationDegenerative spinal stenosis results from a combi-nation of posterior osteophytes and disk herniation anteriorly and ligamentum flavum hypertrophy and facet disease posteriorly. Although calcifica-tion and ossification of vertebral ligaments are common, it is difficult to make a clear distinction between these two processes.

Calcification of the ligamentum flavum is a manifestation of calcium pyrophosphate dihydrate deposition disease. Osteophytes, facet hypertrophy, and ligamentous calcification are common find-ings at chest CT. If these findings encroach on the neural canal, its anteroposterior dimension is less than 1 cm, or neurologic symptoms are present, compression must be suspected (6) (Fig 1b).

Another entity, ossification of the ligamen-tum flavum, has been reported primarily in the Japanese literature. This is a metaplastic process in which enchondral ossification leads to bone formation and spinal cord compression with my-elopathy or paraplegia (7).

Extradural Arachnoid CystExtradural arachnoid cysts are focal outpouch-ings of the arachnoid that protrude through a dural defect and are filled with cerebrospinal fluid (Fig 2). These typically occur in the mid to lower thoracic spine (80% of cases), either pos-teriorly or posterolaterally, and average a cranio-caudal extension of 3.7 vertebral bodies (8). They usually occur in the 2nd decade of life and are more common in males (9). Associated imaging findings include scalloping of the vertebral body, thinning or erosion of the pedicles, and widening of the interpeduncular distance.


Figure 2. Extradural arachnoid cyst in a 27-year-old man. (a) Axial nonenhanced CT image shows a fluid-attenuation lesion that expands the spinal canal (arrow), displacing the spinal cord to the right. (b) On an axial T2-weighted MR image, the lesion has cerebrospinal fluid signal intensity and causes vertebral body scalloping, findings indicative of an extradural arachnoid cyst.

Arachnoid cysts may be symptomatic as a result of spinal cord or nerve root compression. They may be congenital, posttraumatic, postin-fectious, or idiopathic in origin. The differential diagnosis includes traumatic and lateral thoracic meningoceles (6). Once these cysts are identi-fied, MR imaging is the preferred modality for radiologic assessment.

Methyl Methacrylate EmbolusMethyl methacrylate from intramedullary injection may leak into paravertebral veins in 30%–72% of cases, with pulmonary emboli occurring in up to 6.8%. Limited methyl methacrylate pulmonary emboli may be asymptomatic; in more severe cases, hypotension, arrhythmia, heart failure, pul-monary hypertension, respiratory distress, or death may result. Detection of methyl methacrylate em-boli at contrast-enhanced chest CT is optimized by using bone window settings (10) (Fig 3).

Congenital Anomalies

Neurenteric CystDuplication cysts are developmental lesions that can be classified as bronchogenic, esophageal, or neurenteric, according to the type of epithe-lial lining. Neurenteric cysts result from dis-placed alimentary elements. They are commonly encountered in the posterior mediastinum (Fig 4), most often in the lower cervical or upper thoracic region.

Figure 3. Methyl methacrylate embolus. Sagittal CT image shows a vertebroplasty per-formed for compression fractures of T6 and T7. Methyl methacrylate is seen in an adjacent paraspinal vein (arrow).


Figure 5. Diastematomyelia. Axial CT image shows a sagittal osseous bar (arrow) that bisects the spinal canal. Also note the dysplasia of the laminae and ribs with ab-sence of the spinous process.

Figure 4. Neurenteric cyst. (a) Axial nonen-hanced CT image of the chest shows a fluid-attenuation lesion (arrow) in the left paraspinal region. (b) Sagittal T2-weighted MR image shows the fluid intensity lesion (arrow), which did not en-hance, findings consistent with a neurenteric cyst.

The lesions may be intra- or extraspinal or both and may be connected through a vertebral body defect, anterior spina bifida, hemivertebra, or butterfly vertebra (11). Although these lesions are typically asymptomatic, they may cause

symptoms because of extrinsic compression. Imaging is most useful in demonstrating mass effect or complications, such as hemorrhage, rupture, or infection (12).

DiastematomyeliaDiastematomyelia consists of sagittal division of the spinal cord, resulting in two hemicords. This entity is more common in women and can become symptomatic anytime during life. Neurologic symptoms are nonspecific and indistinguishable from those of other causes of cord tethering.

Although clefts are most common in the thoracolumbar spine, unusual cases occur in the thoracic spine. Associations with other spinal dys-raphisms include myelomeningocele, meningo-cele, lipoma, neurenteric cyst, and dermal sinus (13,14). Associated bone anomalies of the spinal column are almost always present (15) (Fig 5).

Trauma

Insufficiency FractureWhile wedge compression deformities are the hallmark of osteoporosis, in a study of 323 patients by Bartalena et al (16), only 15% of such fractures were identified at multidetector CT. At 5 years, these fractures have associated morbidity and mortality equivalent to those of proximal femur fractures (17). Routine review of sagittal reformat-ted images is useful in improving detection (1).


Figure 6. Spinal trauma in a 35-year-old man after a high-speed motor vehicle accident. (a) Axial CT image shows subtle high attenuation due to blood in the spinal canal (arrowhead) and a paraspinal hema-toma (arrow). (b) Sagittal CT image shows a burst fracture of T4 with retropulsion into the spinal canal (arrow). This is an important finding because it can be associated with spinal cord compression. Review of sagittal images is critical in detection of subtle compression deformities.

Biyani et al (18) evaluated the distribution of the three most common causes of compression fractures in patients older than 50 years. A signifi-cantly higher prevalence of pathologic fractures was found in the upper thoracic spine, whereas osteoporosis and trauma predominated in the lower thoracic spine.

Traumatic FractureFractures of the thoracolumbar spine are pres-ent in 4%–5% of patients with blunt trauma (1). Fractures of the upper thoracic spinal levels (T1–T7) are often associated with sternal injuries (19). Although thoracic fractures are typically stabilized by the sternum and rib cage, it is important to rec-ognize CT findings that suggest associated spinal cord injury, such as retropulsion or malalignment (Fig 6). Hemorrhage, traumatic disk herniation, and spinal cord or ligamentous injury are best depicted with MR imaging (6).

Subarachnoid HemorrhageAt nonenhanced CT, the spinal canal is typically of uniform low attenuation without clear delinea-tion of the spinal cord. Entities that increase the attenuation of subarachnoid fluid include hemor-rhage, proteinaceous or purulent cerebrospinal fluid, and intrathecal contrast material. Visualiza-tion of a hyperattenuating ring surrounding the spinal cord at nonenhanced CT should initiate a search for a hemorrhagic source (Fig 7).

PneumorrhachisAir in the spinal epidural space is known as pneu-morrhachis or epidural emphysema. It is almost always found in association with air in adjacent compartments, either pneumothorax or pneumo-

Figure 7. Subarachnoid hemorrhage. Axial CT image of the chest shows high attenuation in the subarachnoid space surrounding the spinal cord (ar-row), a finding consistent with subarachnoid hemor-rhage. In this case, the hemorrhage was the result of a ruptured vertebrobasilar junction aneurysm. Visualization of a hyperattenuating ring surrounding the spinal cord at nonenhanced CT should initiate a search for a hemorrhagic source.


Figure 9. Diskitis and osteomyelitis. (a) Axial CT image shows heterogeneous paraspinal soft-tissue attenuation with epidural extension (arrow). (b) Sagittal CT image shows disk space loss and endplate destruction (arrow). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the bone and affected disk space with an epidural phlegmon (arrowhead).

Figure 8. Epidural pneumorrha-chis after a motor vehicle collision. Axial CT image shows pneumo-mediastinum (white arrow) and subcutaneous emphysema (black arrows). There is extension of gas into the spinal epidural space (arrowhead).

mediastinum (Fig 8). Although usually asympto-matic, pneumorrhachis can cause symptoms of neurologic compression in rare cases (20).

Although most often related to trauma, pneu-morrhachis has been reported in association with epidural anesthesia, radiation therapy, thoracic surgery, bronchial asthma, and malignancy (21–23). Traumatic epidural pneumorrhachis is generally asymptomatic and resolves spontane-ously; if it is symptomatic, then treatment should address the cause (20).

Infection

Osteomyelitis and DiskitisPyogenic spinal infections occur by means of hematogenous, contiguous, or direct inoculation and are the most common spine infection in adults

(24). Staphylococcous aureus is the most common pathogen, followed by Escherichia coli and Strepto-coccus viridans (25). Risk factors include diabetes, autoimmune disease, cancer, compromised im-munity, and intravenous drug use.

The diagnosis is often delayed due to the non-specific symptoms of back pain, fever, and mal-aise; furthermore, disk space narrowing and bone destruction may take weeks to develop (26). CT is more sensitive in demonstrating the early findings of paravertebral fat infiltration and interverte-bral disk hypoattenuation (26). CT is also useful for assessment of bone destruction, sequestrum formation, and epidural granulation tissue (24). Typically, infection involves the disk space and the adjacent vertebral body endplates (Fig 9).


Metastatic disease rarely involves the disk space and frequently demonstrates associated extraosseous soft-tissue masses. Skip lesions are common in metastatic disease and rare in pyo-genic infection (27). Exudative pleural effusions may be a presenting finding in pyogenic verte-bral osteomyelitis (28). Furthermore, in a study of 50 patients with streptococcal or enterococcal spondylodiskitis, one-fourth had concomitant infectious endocarditis (29).

Medical management is the mainstay of therapy for pyogenic vertebral osteomyelitis. However, it has been suggested that MR imaging may be

useful in predicting which patients are likely to require surgical treatment, according to the percentage of segmental involvement (30). In one large study, pyogenic infection was more common in the lumbar spine, while neurologic complica-tions were more frequent in cervical and thoracic spondylodiskitis.

Pott DiseaseApproximately 3% of human immunodeficiency virus (HIV)–negative patients with tuberculosis have skeletal involvement, whereas up to 60% of HIV-positive patients with tuberculosis have skeletal involvement (31). The spine is the most common site involved in approximately 50% of cases (32).

Figure 10. Pott disease. (a) Coronal CT image shows a paraspinal abscess with calci-fication (arrow). (b) Sagittal CT image (bone window) shows anterior compression deformity with kyphotic angulation and associated scle-rosis (arrowhead). (c) Contrast-enhanced T1-weighted MR image shows the subligamentous abscess (white arrow) and posterior epidural extension (black arrow). There is contiguous involvement of four thoracic vertebral bodies with contrast enhancement. Note the relative sparing of the intervertebral disks. Anterior compression fractures are seen at T7 and T8 with kyphotic angulation (arrowhead).


Figure 11. Hemangioma with epidural extension. (a) Axial CT image shows a vertebral hemangioma with the classic polka-dot appearance (arrow), which results from thickening of the primary trabeculae. (b) Axial MR image obtained at the same level shows epidural extension of the hemangioma (arrow) with cord compression. Epidural extension is a rare complication of a vertebral hemangioma and may be symptomatic due to neural compression. It is difficult to visualize the associated epidural soft tissue on CT images.

Tuberculosis spreads to the spine via hematogenous dissemination, although rarely the spine is involved via direct extension or lymphatic drainage from adjacent affected areas such as the pleura (33).

The infection usually originates in the anterior vertebral body and propagates along the anterior or posterior longitudinal ligament. With disease progression, anterior vertebral body collapse occurs with resultant kyphotic angulation and gibbus deformity. The posterior elements may also be involved; when present, posterior involve-ment allows differentiation of tuberculous from pyogenic infection (33).

Paraspinal abscess is common; when calcifica-tion is present, a paraspinal abscess is virtually diagnostic of tuberculosis (34). Calcification in a large paraspinal abscess without new bone for-mation or sclerosis favors the diagnosis of tuber-culosis. Mycobacterium species do not produce proteolytic enzymes; therefore, destruction of the intervertebral disk is more suggestive of other in-fections (26). Note the relative preservation of the intervertebral disks in our case (34) (Fig 10).

A recent case report of fatal disseminated tu-berculosis mistaken for metastatic bronchogenic carcinoma emphasizes the importance of tissue confirmation in cases of a focal lung lesion asso-ciated with pathologic fractures of the spine (35).

Primary Neoplasms

HemangiomaHemangiomas of the vertebral body are benign hamartomas consisting of vascular tissue. These are extremely common lesions, reported in 10%–12% of spines at autopsy, and are usually an incidental finding (36). Symptomatic he-mangiomas are due to bone expansion, epidural extension of the tumor, epidural hemorrhage, or vertebral body compression fracture (37). The classic CT finding of a hemangioma is a polka-dot appearance caused by cystic vascular malfor-mations between the bony trabeculae (38).

Epidural extension of a hemangioma may produce symptoms of cord compression; 90% of cases of this complication occur in the thoracic spine (36). The onset is usually insidious, with progressive pain and neurologic deficits over weeks to months. MR imaging is most useful in evaluating the extraosseous extension (Fig 11). Small hemangiomas with the pathognomonic feature of intraosseous polka-dot appearance due to prominent trabeculae can be ignored as an incidental finding.


Figure 13. Ependymoma. (a) Axial contrast-enhanced CT image shows an enhancing lesion in the spinal canal (arrow). (b, c) Sagittal T2-weighted (b) and contrast-enhanced T1-weighted (c) MR images show the intra-medullary lesion in the thoracic spine. The lesion has mixed signal intensity (arrow in b) with a focus of gado-linium enhancement (arrow in c).

Figure 12. Osteochondroma in a 20-year-old man. Axial (a) and coronal (b) CT images show the classic appearance of an osteochondroma (arrow in a), which arises from a paravertebral rib with cortical and medul-lary continuity with underlying bone (arrow in b).

Six features predictive of increased likelihood of cord compression by a vertebral hemangioma are location between T3 and T9, complete verte-bral body involvement, extension into the neural arch, expanded and indistinct cortical margins, an irregular honeycomb pattern, and a soft-tissue mass (39). Symptomatic lesions may require surgical resection (38).

OsteochondromaOsteochondromas are the most common benign cartilaginous tumors and usually arise from the metaphysis of long bones. They rarely occur in a vertebra; when they do, they are almost always associated with the posterior elements (40) (Fig 12). Osteochondromas are usually solitary but can be multiple and hereditary, with an average age of 33 years at diagnosis. Solitary spinal osteo-chondromas occur in only 1%–4% of cases and rarely manifest with neurologic symptoms (36).

The risk of spinal canal extension of osteochon-dromas in patients with multiple hereditary exos-toses is reported to be as high as 27%, with men affected much more commonly than women (42% vs 6%, respectively) (41). MR imaging is use-

ful for evaluation of the cartilaginous cap. There is a 1%–2% risk of malignant transformation in patients with a solitary osteochondroma and an up to 25% risk in the hereditary form (42).

EpendymomaEpendymomas are the most common primary spinal neoplasm, representing 60% of intramed-ullary tumors. These tumors occur most often in the cervical region, followed by the conus, filum terminale, and cauda equina. However, in pa-tients over 50 years of age, ependymomas make up 83% of tumors, with 55% being in a thoracic location (43).


Figure 15. Schwannoma. (a) Axial CT image shows a dumbbell-shaped extradural mass that ex-tends through the left neural foramen (arrow) with associated widening of the foramen. (b) On an axial T2-weighted MR image, the mass (arrow) has high signal intensity. In addition, the lesion dem-onstrated homogeneous enhancement that extended through the widened neural foramen.

Figure 14. Meningioma. Axial con-trast-enhanced CT image shows an enhancing mass (arrow) in the spinal canal. The findings were confirmed with MR imaging.

These tumors arise from the ependymal cells of the central canal and thus are typically in-tramedullary; rare cases of an intradural extra-medullary location have been reported, with the majority being thoracic in location (44). They typically span five vertebral body segments and are commonly associated with hemorrhage, cystic change, and contrast enhancement (Fig 13). The myxopapillary subtype typically arises from the filum terminale (45).

MeningiomaSpinal meningiomas are intradural extramedul-lary lesions and are usually located in the thoracic spine (80% of cases) (Fig 14). They are some-times difficult to distinguish from schwannomas (46). Meningiomas account for 25%–46% of primary spinal cord tumors (47).

Spinal meningiomas are found more commonly in women at a median age of 53 years (46). The

differential diagnosis for calcified masses in this lo-cation at CT includes meningioma, schwannoma, sequestered disk, and osteoma. Such lesions are best evaluated with MR imaging (48).

SchwannomaSchwannomas are benign, slow-growing, enhanc-ing tumors that originate from Schwann cells. They usually occur in adults and occur centrally in association with neurofibromatosis type 2. Cystic degeneration is common, but hemorrhage and calcification are rare (49).

Defining the local extent of the lesion is im-portant because nerve sheath tumors may extend in dumbbell fashion through the neural foramen and into the neural canal (Fig 15). MR imaging is superior to CT in demonstrating intraspinal extension (50).


Figure 16. Chondrosarcoma. Axial CT image shows a large right paraspinal soft-tissue mass with characteristic chondroid matrix calcification. There is erosion of the right lamina with extension through the neural foramen (arrow) into the epidural space.

ChondrosarcomaChondrosarcoma, the most common primary chest wall malignancy and the second most common malignant osseous lesion of the spine, occurs in patients 30–60 years of age. Spinal chondrosarcoma typically manifests as osseous destruction of both the vertebral body and pos-terior elements (45% of cases) or the posterior elements alone (40%). Chondroid matrix calcifi-cations occur in 70% of cases.

The osseous destruction and chondroid matrix calcifications are best seen with CT (51) (Fig 16). At MR imaging, chondrosarcoma has char-acteristic high signal intensity on T2-weighted images and demonstrates variable enhancement (51). In patients younger than 20 years of age, 6%–10% of chondrosarcomas originate in the spine and are often low grade (52). There are rare case reports of intradural chondrosarcomas (53).

Multiple MyelomaThe characteristic imaging features of multiple myeloma are osteoporosis or focal bone destruc-tion. Fractures can occur with minimal trauma, especially in the spine. Vertebral compression fractures occur in 55%–70% of patients and may be the presenting finding in 34%–64% (54). Ver-tebral body lesions can be difficult to differentiate from metastatic disease or osteoporotic insuffi-ciency fractures. Approximately 90% of vertebral compression fractures associated with multiple myeloma occur between T9 and L4 (54).

Characteristics that suggest multiple myeloma include sharply demarcated lytic lesions, scal-loping, marked osteoporosis, “cold” lesions on bone scans, and lack of a primary neoplasm (55). Rarely, patients with plasma cell dyscrasias may have sclerotic bone lesions as a clinical manifes-tation of POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) (56).

Imaging is crucial in staging and follow-up of multiple myeloma. Multidetector CT is more sensitive than plain radiography in assessment of anatomically complex regions such as the tho-racic spine (57). Multidetector CT and MR im-aging are complementary in initial evaluation of multiple myeloma, as MR imaging may result in understaging in 10%–20% of patients with stage III multiple myeloma and proved bone marrow infiltration (58).

LymphomaThe differential diagnosis for a sclerotic (ivory) vertebral body includes lymphoma, metastatic disease, and Paget disease. Bone marrow in-volvement in lymphoma may manifest as lytic or sclerotic lesions and may also be associated with paraspinal and epidural soft tissue (Fig 17). CT is better for evaluation of cortical destruction, although MR imaging and positron emission tomography/CT are more sensitive overall (59). Lymphoma may also manifest as fever of un-known origin and vertebral compression deformi-ties in elderly patients (60).

Secondary Neoplasms: Metastatic Disease

The vertebral column is the most common site for bone metastases, with a prevalence of 30%–70% (61). Nearly half of all spinal metastases arise from breast, lung, or prostate cancer (62). Although spinal metastases may be extradural, in-tradural extramedullary, or intramedullary, 98% are extradural. Metastatic disease is the most common extradural malignant spine tumor; its distribution is based on the location of red mar-row, initially beginning in the vertebral body (61).

It is important to recognize metastatic exten-sion into the spinal canal, which can result in neurologic symptoms and paralysis (6) (Fig 18). Thoracic lesions are the most commonly symp-tomatic (70% of cases) (63). According to the staging system of the International Association


Figure 17. Spinal lymphoma. (a, b) Axial (a) and sagittal (b) CT images show a paraspinal soft-tissue mass (arrow in a) with sclerosis and pathologic fracture of the adjacent vertebral body (arrow in b). The sclerotic appearance may be accentuated by associated vertebral body compression. (c) Sagittal T1-weighted MR image shows involvement and collapse of the T10 vertebral body with epidural extension of the tumor and cord compression.

Figure 18. Metastatic disease from prostate cancer. (a) Axial CT image shows mixed lytic and sclerotic skeletal metastases with erosion through the posterior vertebral body at T5 and epidural extension (arrow). Erosion of the posterior vertebral cortex is an important finding and needs to be recognized at chest CT. (b) T2-weighted MR image shows tumor extension through the posterior vertebral body with resultant cord compression (arrow). Note the low signal intensity in multiple vertebrae, a finding consistent with diffuse sclerotic metastatic disease.

for the Study of Lung Cancer, direct invasion of a vertebral body by a primary lung cancer represents stage T4; however, it has been sug-gested that a tumor involving less than 30% of a vertebral body can be resected and clear margins achieved (64).

Impending vertebral body collapse is depen-dent on the percentage of involvement, with an odds ratio of 4.35 for every 10% of involve-ment. Collapse is dependent to a lesser extent


Figure 20. Lateral meningocele in a 23-year-old woman with neurofibromatosis and severe scoliosis. Axial CT image shows a left paraspinal lesion of fluid attenuation (arrow) that expands the neural foramen.

on pedicle involvement (65). This is important because vertebroplasty or kyphoplasty may pro-vide symptomatic relief in patients with spinal metastases before the occurrence of vertebral body collapse and neurologic deficit (66).

Systemic Disorders

Sickle Cell DiseaseSickle cell anemia results in increased destruc-tion of red blood cells and reactive expansion of the hematopoietic (red) marrow. As bone marrow expands the diploic space, cortical thinning and bone softening result in biconcave vertebral bodies (67). Rarely, extramedullary hematopoiesis has been described in sickle cell anemia (68). Sick-ling of red blood cells in the medullary space may result in stasis, hypoxemia, and bone infarction.

The centripetal vascular supply to the verte-bral body endplates results in central endplate necrosis and characteristic H-shaped vertebral bodies (67) (Fig 19). Other changes in vertebral body shape associated with sickle cell anemia in-clude anterior vertebral vascular notches, vanish-ing vertebra, and tower vertebra (69).

NeurofibromatosisType 1 neurofibromatosis is the most common of the phakomatoses, occurring in one in 3000 persons, with autosomal dominant inheritance. Thirteen percent to 35% of patients are found to

have asymptomatic spinal tumors (70). Plexi-form neurofibromas are pathognomonic for type 1 neurofibromatosis and have a 2%–6% risk of malignant transformation (70).

Type 2 neurofibromatosis is characterized by bilateral acoustic neuromas and is much rarer, occurring in 1 in 37,000 persons. Spinal tumors occur in over 75% of cases and include ependy-momas, meningiomas, schwannomas, and neu-rofibromas (71). Nerve sheath tumors character-istically have low attenuation at CT and may be mistaken for congenital cysts. Posterior scalloping, neural foraminal widening, and pressure erosion are characteristic vertebral body changes (72).

Figure 19. Sickle cell anemia. (a) Sagittal CT image shows diffuse osseous sclerosis with characteristic central endplate depression. (b) Sagittal T2-weighted fat-suppressed MR image shows areas of high signal intensity in the vertebral bodies (arrow). This finding represents regions of bone in-farction surrounded by areas of intermediate-signal-intensity red marrow.


Lateral meningoceles result from herniation of the leptomeninges through a defect in the ver-tebral body or the neural foramen. Most lateral meningoceles, up to 85%, are associated with neurofibromatosis. In some studies of neurofi-bromatosis, lateral meningoceles are reported to be the most common cause of a paraspinal mass (72). They are right-sided in 70% of cases (72).

As demonstrated in our case, CT shows a homogeneous low-attenuation mass, often con-tiguous with the neural foramen and associated with anomalies of the vertebral bodies and ribs or scoliosis (Fig 20). The lesion should opacify with intrathecal contrast material, a finding that allows confirmation of the diagnosis (72).

Epidural LipomatosisEpidural lipomatosis, which was described by Lee et al (73) in 1975, is an uncommon condition characterized by deposition of unencapsulated fat in the epidural space. Associations include endogenous steroids (Cushing syndrome), exog-enous steroid use, and obesity; 55.3% of reported cases are associated with exogenous steroid use, typically long-term (74). Patients may present with chronic back pain and lower limb weakness.

Quint et al (75) report a mean sagittal fat thickness of 4.6 mm, with a range of 3–6 mm. Epidural fat thicker than 6 mm is suggestive of this condition. Isolated thoracic involvement is seen in 46% of cases, while 11% have combined thoracic and lumbar spine involvement (74). Fat deposition at the thoracic level is usually dorsal to the spinal cord (76).

MR imaging is the modality of choice for dem-onstrating the craniocaudal extent of fat deposi-tion and the associated compressive effects on the spinal cord and nerve roots (Fig 21). Treatment

may include weight reduction, steroid dose re-duction, or decompressive laminectomy, accord-ing to the severity of the symptoms (77).

ConclusionsPathologic processes are commonly imaged in the course of performing routine chest CT. While MR imaging is often the modality of choice for evaluating neurologic symptoms of the spine, chest CT may precede this evaluation owing to nonspecific chest and back pain symptoms. CT provides information about bone mineralization and lesion calcification that complements the superior soft-tissue imaging capability of MR.

Many spinal diseases have a characteristic CT appearance that allows confident diagnosis or development of a structured differential diagnosis. In addition, chest CT data may be reformatted to create volumetric or multiplanar images of the spine to better inform management decisions about spinal stabilization in symptomatic patients.

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This journal-based CME activity has been approved for AMA PRA Category 1 CreditTM. See www.rsna.org/education/rg_cme.html.

Teaching Points September-October Issue 2011

Put Your Back into It: Pathologic Conditions of the Spine at Chest CT1

Cristopher A. Meyer, MD • Achala S. Vagal, MD • Danielle Seaman, MD

RadioGraphics 2011; 31:1425–1441 • Published online 10.1148/rg.315105229 • Content Codes:

Page 1428 (Figure on page 1428)Detection of methyl methacrylate emboli at contrast-enhanced chest CT is optimized by using bone win-dow settings (10) (Fig 3).

Page 1430 (Figure on page 1430)Although thoracic fractures are typically stabilized by the sternum and rib cage, it is important to recognize CT findings that suggest associated spinal cord injury, such as retropulsion or malalignment (Fig 6).

Page 1433Calcification in a large paraspinal abscess without new bone formation or sclerosis favors the diagnosis of tuberculosis.

Page 1436Characteristics that suggest multiple myeloma include sharply demarcated lytic lesions, scalloping, marked osteoporosis, “cold” lesions on bone scans, and lack of a primary neoplasm (55).

Page 1436 (Figure on page 1437)It is important to recognize metastatic extension into the spinal canal, which can result in neurologic symptoms and paralysis (6) (Fig 18).

chest imaging 1425 put your back into it: pathologic ......termed arachnoiditis ossificans....

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