Aneurysmal Bone Cyst (C2)

1. Give a differential diagnosis based on the axial CT (C2 level) findings and on the axial T2W (C3–C4 level), midsagittal T2W, and coronal postcontrast T1W MR imaging findings for this 5-year-old boy.

2. Which finding is highly suggestive of the diagnosis of aneurysmal bone cyst (ABC) but is not pathognomonic?

3. Which finding has been proposed as a sign that is useful to differentiate ABCs from other cystic masses, especially neoplasms?

4. ABC most frequently involves which part of the vertebra and which region of the spine?

ANSWERS

Reference

Chan MS, Wong YC, Yuen MK, et al. Spinal aneurysmal bone cyst causing acute cord compression without vertebral collapse: CT and MRI findings. Pediatr Radiol. 2002;32:601-604.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, p 829.

Comment

Aneurysmal bone cyst is a benign, highly vascular osseous lesion of unknown origin. It accounts for approximately 1% to 2% of primary bone tumors, and 3% to 20% of ABCs involve the spine. Upper cervical lesions are rare. Patients with ABC are usually in the second decade of life. The pedicles and posterior elements are involved in most cases. In this C2 lesion, the bilateral pars interarticularis, facets, and posterior arch are involved by the expansile lesion, resulting in a kyphosis at C2–C3 (see midsagittal image). Cord compression at C2–C3 (shown on CT and midsagittal MR images) is likely due to vertebral expansion as well as epidural extension of the cystic components of the lesion through minor fractures in the thin cortical bone. Histologically, the interior of the ABC can be solid and vascular and/or cystic and hemorrhagic (surrounded by a thin bony rim). CT demonstrates the osseous expansion and can detect the multiple small fluid levels, although these are more evident on axial and sagittal T2W MR images. Within the cysts, the dependent fluid is hypointense, whereas the nondependent fluid is hyperintense as a result of the different sedimentation properties and composition of blood products in the two components. The internal septations and the peripheral tissue of the ABC are reported to enhance smoothly on postcontrast T1W images (see coronal image), potentially distinguishing ABC from neoplastic lesions, which are more likely to exhibit nodular enhancement.

Notes

Dural Arteriovenous Fistula

CASE 63

1. List at least four nonneoplastic, nondegenerative causes of myelopathy.

2. Which of these causes is favored based on the T2W and postcontrast T1W images?

3. How does this cause account for spinal cord enhancement on the T1W image?

4. Which MR imaging finding is key to narrowing the differential diagnosis?

ANSWERS

CASE 63

1. Multiple sclerosis, intramedullary (viral or postviral myelitis) or extramedullary (epidural abscess) infection, syringomyelia, trauma, toxins (contrast and anesthetic agents, intrathecal chemotherapy), physical agents (irradiation, electrical injury), metabolic factors (chronic liver disease, vitamin B₁₂ deficiency), and vascular disease (vascular malformations, infarction, hematoma).

2. The findings of abnormal signal and postcontrast enhancement within an unenlarged cord and the presence of prominent perimedullary “flow voids” suggest vascular disease, such as the presence of a spinal vascular malformation.

3. Retained contrast material within spinal cord veins, which are engorged as a result of retrograde intradural venous drainage of the fistula (located at T11), and possibly venous infarction with blood-cord barrier breakdown.

4. The enlarged intradural vessels with “flow voids.”

References

Burtis MT, Ulmer JL, Miller GA, et al. Intradural spinal vein enlargement in craniospinal hypotension. AJNR Am J Neuroradiol. 2005;26:34-38.

Gilbertson JR, Miller JR, Goldman MS, Marsh WR. Spinal dural arteriovenous fistulas: MR and myelographic findings. AJNR Am J Neuroradiol. 1995;16:2049-2057.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 832–836.

Comment

The findings of cord signal abnormality and enhancement are nonspecific and may result from neoplastic, inflammatory, or vascular conditions. Cord enlargement usually favors neoplasm although any intramedullary process that produces edema and breakdown of the blood-cord barrier may mimic neoplasm. The finding of multiple “flow voids” is the key to narrowing the differential diagnosis. Their presence favors a diagnosis of vascular malformation or vascular tumor although craniospinal hypotension or collateral venous drainage secondary to inferior vena cava occlusion can produce enlargement of intradural veins. In this case, no intramedullary tangle of vessels was identified. Thus, an intramedullary arteriovenous (AV) malformation causing the perimedullary flow voids was considered less likely than a dural AV fistula. Vascular tumor, such as hemangioblastoma, was also unlikely, since no focal nodular or mass-like enhancement and no associated cord cyst were detected.

For dural AV fistulas, abnormal MR findings are observed with approximately the following frequency: cord hyperintensity on T2W images, 90% to 100%; cord enlargement, 60% to 70%; cord enhancement (patchy or diffuse) with gadolinium, 60% to 90%; and abnormal intradural (subarachnoid) vessels, 40% to 80%. Cord enhancement results initially from spinal venous hypertension caused by the retrograde flow of blood from the fistula into the veins surrounding and within the cord. Without treatment, venous infarction develops over time.

Notes

Sickle Cell Disease with Osteomyelitis and Epidural Abscess, Lumbar

CASE 64

1. Name two potential causes of bone pain and tenderness at L4 in this febrile 57-year-old black woman.

2. Name two infectious agents that are more likely to affect this patient than the general population.

3. List five conditions in which vertebral biconcavity has been reported.

4. List four potential causes of myelopathy in patients with the disorder illustrated by this case.

ANSWERS

Reference

Martino AM, Winfield JA. Salmonella osteomyelitis with epidural abscess: a case report with review of osteomyelitis in children with sickle cell anemia. Pediatr Neurosurg. 1990;16:321-325.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 795–798.

Comment

Sickle cell patients are more prone than others to certain infections, including pneumococcal and Salmonella infections, as a result of decreased phagocytic ability of the reticuloendothelial system. This patient had Streptococcus pneumoniae sepsis and meningitis. She had been treated with antibiotics for 12 days when MR images were obtained because of persistent fever and back pain. The sagittal proton density FSE image, covering the T12–L1 to L4–L5 disk spaces, shows diffusely decreased signal intensity within the vertebral bodies relative to the disk spaces, consistent with bone marrow hyperplasia. The body of L4 is slightly hyperintense in comparison with the other vertebral bodies, and its inferior endplate is indistinct—features suggestive of osteomyelitis. The adjacent disk space had a normal appearance on all other sequences. A variably hyperintense anterior epidural collection extends from L3 through L5, with marked compression of the thecal sac and cauda equina at L4. The postcontrast, fat-saturated T1W axial image at L4 demonstrates heterogeneous enhancement within the L4 body and in the paravertebral and epidural spaces. An anterior epidural abscess was confirmed at surgery.

The skeletal imaging findings in sickle cell disease are due to (1) bone marrow hyperplasia secondary to anemia and (2) bone and marrow ischemia and infarction secondary to sickling episodes. In the spine the vertebral bodies have been described as having an H shape and/or a smoothly curved endplate depression. The H vertebral body shape has been attributed to a growth disturbance of the central area secondary to ischemia/infarction. Some authors distinguish this shape from a smoothly curved endplate depression attributed to osteoporosis secondary to bone marrow hyperplasia. Other authors use the general term biconcave to refer to the vertebral endplate contour abnormalities.

Notes

Chordoma, Sacral

CASE 65

1. List five tumors that may have the appearance shown on the axial T1W and sagittal T2W MR images, and on the noncontrast CT image.

2. Which of these tumors favors a midline location?

3. Which joint is most commonly invaded by tumor—discovertebral or sacroiliac?

4. What percentage of chordomas originates in the sacrococcygeal region?

ANSWERS

Reference

Sung MS, Lee GK, Kang HS, et al. Sacrococcygeal chordoma: MR imaging in 30 patients. Skeletal Radiol. 2005;34:87-94.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 828–829.

Comment

The CT and MR images show a soft tissue mass that appears to originate in the sacrum from S1 to S3, causing bone destruction. The mass is midline and extends into the sacral ala and the presacral region as well as the sacral canal. On the sagittal T2W image, the mass is hyperintense. The findings are typical for a destructive neoplasm but are not specific, and several tumors may be considered in the differential diagnosis. Two findings may help distinguish chordoma from other neoplasms: (1) a midline location (as shown here) and (2) the appearance on T2W images of hypointense septations separating hyperintense lobules that make up the bulk of the mass.

Because they originate from notochordal remnants, chordomas may involve any segment of the craniospinal axis from the sphenoid to the coccyx. The approximate frequency of involvement is as follows: sacrococcygeal, 50%; clival, 35%; remainder of the spine, 15%. Sacral chordomas usually extend anteriorly rather than posteriorly, so that they compress or invade the lower sacral nerves. Typical chordomas consist of mucin-containing physaliphorous cells and/or purely cystic mucinous pools. These account for the hyperintense lobulations of the mass that are seen on T2W images. Hypointense septations represent fibrous strands between the lobular components of the tumor. Sacral chordoma occurs with almost twice the frequency in men as in women. It is uncommon in individuals younger than 40 years of age. Chordomas are typically slow growing but are locally aggressive, and gluteal muscle infiltration due to lateral extension of tumor is common. Most sacral chordomas displace rather than invade the rectum. Metastasis is usually a late event. The presenting symptom in the vast majority of patients is local pain. Approximately one third of patients also have radiculopathy due to irritation of the sciatic nerve or iliolumbar trunk.

Notes

Multiple Sclerosis, Cervical

CASE 66

1. List at least three conditions that may produce the findings demonstrated on these T2W sagittal and axial (C5 level) images from a 13-year-old girl with a 9-day history of right hemiparesis.

2. Are the findings at C5 more likely due to anterior cord infarct or demyelinating disease?

3. Are the majority of spinal cord MS plaques detected in the cervical or thoracic cord?

4. In diffusion tensor imaging of the spinal cord, name two measurable properties of white matter that are likely to be altered when there is demyelination and axonal loss.

ANSWERS

CASE 66

1. Acute disseminated encephalomyelitis, multiple sclerosis, vasculitis, and possibly infarction.

2. Demyelinating disease.

3. Cervical cord.

4. Mean diffusivity and fractional anisotropy.

References

Clark CA, Werring DJ, Miller DH. Diffusion imaging of the spinal cord in vivo: estimation of the principal diffusivities and application to multiple sclerosis. Magn Reson Med. 2000;43:133-138.

Tartaglino LM, Friedman DP, Flanders AE, Lublin FD, Knobler RL, Liem M. Multiple sclerosis in the spinal cord: MR appearance and correlation with clinical parameters. Radiology. 1995;195:725-732.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 802–803.

Comment

The sagittal image demonstrates diffuse, heterogeneous hyperintensity and mild enlargement of the upper cervical cord, as well as anterior cord involvement at and below C4–C5. On the axial image, the anterior cord involvement appears to encompass the anterior median sulcus and the region of the anterior columns. Although there also appears to be some involvement of the central gray matter, raising the possibility of anterior spinal artery (and/or branches) ischemia/infarction, the characteristic findings of a double-dot or H-shaped hyperintensity in the central gray matter due to infarction are not observed. In a study of cervical and thoracic, predominantly short-segment MS plaques, each occupying less than 50% of the cord cross-sectional area, Tartaglino et al found that the epicenter for the plaques was anterior/anterolateral cord periphery in 20% and posterior/posterolateral cord periphery in 79%. Only 1% of plaques had a central location.

The white matter tracts in the spinal cord are predominantly longitudinally oriented structures that more or less restrict the movement of water molecules depending on the direction of their average displacement. Thus, water molecules that diffuse parallel to the long axis of the tracts (i.e., in approximately the superior-inferior direction) essentially move without restriction, whereas molecules that diffuse perpendicular to the long axis (i.e., in the right-left or anteroposterior direction) have restricted motion. This phenomenon is referred to as diffusion anisotropy. If the fiber structure of the white matter is disrupted, for example, by demyelination and especially axonal loss, diffusion perpendicular to the long axis of the fibers becomes less restricted, and anisotropy is diminished. In addition, less restricted motion in the right-left and/or anteroposterior directions results in an increase in the mean diffusivity. Preliminary reports indicate that such changes are occurring in chronic MS plaques of the spinal cord. For acute inflammatory lesions, edema may contribute to the increased mean diffusivity and the loss of anisotropy. Measures of white matter integrity based on MR diffusion imaging may prove to be more sensitive than standard spin-echo imaging of cord morphology based on T1 and T2 relaxation times and spin density of water protons. Preliminary studies suggest that acute spinal cord infarction, like acute brain infarction, results in decreased mean diffusivity (equivalent to the trace of the apparent diffusion coefficient, or ADC).

Notes

Vertebral Lymphoma with Epidural Venous Enlargement

CASE 67

1. Identify the enhancing structures located anterolaterally in the canal on the postcontrast T1W axial image (T12 vertebral body level).

2. List the four major components of the vertebral venous plexus.

3. At the level of the disk space, are the anterior internal veins normally located anterior or posterior to the posterior longitudinal ligament (PLL)?

4. Is the spatial distribution of metastases in a vertebra determined by the mode of hematogenous (i.e., arterial versus venous) delivery?

ANSWERS

Reference

Yuh WT, Quets JP, Lee HJ, et al. Anatomic distribution of metastases in the vertebral body and modes of hematogenous spread. Spine. 1996;21:2243-2250.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 765, 824.

Comment

The left parasagittal fat-saturated T1W image demonstrates a pathologic fracture of T11 with abnormal enhancement posteriorly in the bodies of T10 and T11. Retropulsion of the T11 body was shown on adjacent images. The confluent epidural enhancement follows the course of the left anterior internal vertebral vein from T11 to the lumbar region. The axial image at the T12 level shows that both anterior internal epidural veins are enlarged. The venous engorgement may be explained as follows: (1) compression of the anterior venous plexus by tumor or displaced bone at T11 and/or (2) intravenous tumor or thrombosis at T11. Biopsy of T11 revealed B-cell lymphoma. The question then arises about whether the posteriorly located lesion in the body at T10 is the result of local spread of lymphoma from T11 via the vertebral venous plexuses.

The vertebral venous system is a valveless anastomotic system in which blood flows either cephalad or caudad, depending on changes in intrathoracic and intra-abdominal pressure and postural factors. The anterior internal vertebral venous plexus has a relatively constant morphologic pattern consisting of a pair of longitudinal trunks each located anterolaterally in the canal. The trunks deviate laterally at the level of the intervertebral disk and converge medially at the midpoint of the vertebral body, where they unite with the basivertebral vein. The trunks are located anterior to the PLL at the level of the vertebral body and then posterior to the PLL where it merges with the intervertebral disk. Compared with the anterior internal plexus, the posterior internal plexus is smaller, less constant, and more difficult to opacify on radiologic studies. Anastomoses exist between the anterior and posterior internal plexuses at each vertebral level and between the internal and external venous plexuses.

Notes

Intradural Lipoma, Lumbar

CASE 68

1. List three lesions that may have the appearance demonstrated by the mass at L1–L2 in this 53-year-old woman with chronic low back pain.

2. Name at least three congenital abnormalities that occur with increased frequency in patients with spinal lipoma.

3. What clinical syndrome should be considered for this woman?

4. What two mechanisms have been proposed to explain the features of spinal lipomas?

ANSWERS

References

Emery JL, Lendon RG. Lipomas of the cauda equina and other fatty tumors related to neurospinal dysraphism. Dev Med Child Neurol Suppl. 1969;20:62-70.

Gupta SK, Khosla VK, Sharma BS, Mathuriya SN, Pathak A, Tewari MK. Tethered cord syndrome in adults. Surg Neurol. 1999;52:362-369.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, p 822.

Comment

The T1W and T2W images demonstrate an intradural lipoma at L1–L2, a cord that lacks normal tapering and appears posteriorly tethered, and an intramedullary cyst at T10–T11. Other findings detected on additional images in this case were filar lipoma (L5–S3), diastematomyelia at L1, and spina bifida occulta at L4 and L5. Gupta et al reported that the most frequent MR finding in patients with adult tethered cord syndrome was low-lying conus with an intradural and/or extradural lipoma. Spinal lipomas are usually considered in three groups: with intact dura, with deficient dura, and filar. The first two groups are hypothesized to occur owing to premature disjunction with subsequent “insertion” of fat in the dorsal surface of the neural plate. Lipomas with deficient dura are much more common than lipomas with intact dura (84% vs. 4% in one series), with the latter group predominantly involving the cervical and thoracic spinal cord. The third group of spinal lipomas represents a disorder of development of the lower conus and filum. This group accounts for the filar lipoma, and probably also the intradural lipoma at L1–L2, since published reports have noted an association between filar and conus lipomas.

Notes

Traumatic Disk Herniation, Cervical

CASE 69

1. Based on the sagittal T2W and axial T1W images, what is the most likely etiology of the isointense-to-hyperintense soft tissue mass posterior to the C6 vertebral body in this patient with acute spine trauma?

2. Is MR likely to be more or less sensitive than conventional radiography in the detection of (a) acute fracture, (b) acute facet subluxation or dislocation, and (c) canal stenosis?

3. What is the condition of the anterior longitudinal ligament?

4. What findings on a midsagittal MR image or on a lateral radiograph help differentiate bilateral from unilateral facet dislocation?

ANSWERS

References

Bucciero A, Carangelo B, Cerillo A, et al. Myeloradicular damage in traumatic cervical disc herniation. J Neurosurg Sci. 1998;42:203-211.

Katzberg RW, Benedetti PF, Drake CM, et al. Acute cervical spine injuries: prospective MR imaging assessment at a level 1 trauma center. Radiology. 1999;213:203-212.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 837–838.

Comment

On the sagittal T2W image, there is evidence of a ruptured disk at C6–C7. Mild hyperintensity posterior to the C6 body is due to fragmented disk material (on the basis of operative findings). Marked hyperintensity within the C6–C7 disk space is consistent with the presence of edema and provides evidence that the C6–C7 parent disk is the source of the disk fragment. The axial T1W image at C6–C7 demonstrates the herniation compressing the ventral cord and extending to the right neural foramen. The rounded low signal intensity posterior to the cord on the sagittal image was found at surgery to represent a small bony fragment arising from the facet complex.

In their prospective study comparing MR with conventional radiographs in the detection of acute cervical spine injuries, Katzberg et al found that 43% of acute fractures and 59% of acute facet subluxations/dislocations were detected on MR images compared to 48% and 72%, respectively, on conventional radiographs. MR was significantly better in demonstrating chronic, underlying canal stenosis in the population studied. In a study of pure traumatic cervical disk herniations in 41 patients, Bucciero et al found that the most common level was C5–C6 with 58.5%, compared with 19.5% at C6–C7, 17.1% at C4–C5, and 9.7% at C3–C4.

Notes

Metastasis Mimicking Diskitis/Osteomyelitis

CASE 70

1. Are the destructive changes at C5–C7 more likely due to infection or tumor?

2. In general, which two imaging findings favor metastasis over diskitis/osteomyelitis?

3. What are the most common granulomatous infections of the spine?

4. List three nonneoplastic conditions that can mimic diskitis/osteomyelitis.

ANSWERS

References

Gupta RK, Agarwal P, Rastogi H, et al. Problems in distinguishing spinal tuberculosis from neoplasia on MRI. Neuroradiology. 1996;38(Suppl 1):S97-S104.

Kim JK, Ryu KN, Choi WS, et al. Spinal involvement of hematopoietic malignancies and metastasis: differentiation using MR imaging. Clin Imaging. 1999;23:125-133.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 822, 824.

Comment

The MR images show destruction of C5 through C7, with epidural and prevertebral extension. The findings are compatible with diskitis/osteomyelitis: (1) confluent, decreased signal and an inability to discern a cortical margin between the endplates and the disk on the T1W image; (2) increased signal intensity within the presumed intervertebral disks and within the adjacent vertebral bodies on the T2W image; and (3) prominent paravertebral masses and prevertebral extension of disease. These findings are also compatible with a neoplastic process. The hyperintensity (radiation changes) in the intact cervical vertebrae on the T1W image, plus lesions involving the posterior elements of C5 through C7, support a diagnosis of neoplasm. In adults, extension of osteomyelitis from the vertebral bodies into the posterior neural arch occurs in ≤12% of cases. By comparison, Kim and colleagues found that the anterior and posterior elements were involved in 76% of patients with metastatic disease and in 100% of patients with hematopoietic malignancies (lymphoma, leukemia, multiple myeloma) involving the spine. Among tumors, metastases are the most common mimickers of diskitis/osteomyelitis. Less common are primary bone tumors, such as plasmacytoma, eosinophilic granuloma, aneurysmal bone cyst, giant cell tumor, and chordoma.

Notes

CNS Dissemination of Conus Ependymoma

CASE 71

1. List five nonneoplastic, noninfectious causes of leptomeningeal enhancement.

2. On the basis of the findings shown on the postcontrast T1W images, postulate a mechanism that relates the cervical enhancement to the appearance of the conus 1 year earlier.

3. Name three primary pigmented tumors of the leptomeninges.

4. Are intracranial ependymomas more likely than spinal ependymomas to disseminate?

ANSWERS

Reference

Friedman DP, Hollander MD. Neuroradiology case of the day: myxopapillary ependymoma of the conus medullaris or filum terminale resulting in superficial siderosis and dissemination of tumor along CSF pathways. Radiographics. 1998;18:794-798.

Cross-Reference

Neuroradiology: THE REQUISITES, 2nd ed, pp 277–279, 812–815.

Comment

The postcontrast image of the thoracolumbar spine shows evidence of surgery with laminectomies from T10–T11 to L1, inhomogeneous enhancement of the cauda equina and conus, and a residual conus mass (upper edge of the figure). The bodies of T11–L2 demonstrate marked hyperintensity, compatible with postradiation changes. The postcontrast image of the cervical spine, obtained 1 year later, demonstrates leptomeningeal enhancement, with multiple nodular foci extending from the cervical region to the basal cisterns of the posterior fossa and tonsillar ectopia. No irradiation changes are detected in the cervical vertebrae. The combination of findings on the two images suggests that this patient has leptomeningeal metastatic disease secondary to CSF spread of metastases from a conus tumor (most commonly an ependymoma) that was incompletely resected and that this patient received postoperative radiation therapy.

The incidence of dissemination of primary spinal ependymomas is 12.5%, versus 9.6% for primary intracranial ependymomas. Most of the disseminated tumors from primary spinal lesions are of the myxopapillary histologic subtype. This subtype is commonly found in primary ependymomas of the filum terminale, cauda equina, or conus (as in this case). The goal of surgical treatment of both intracranial and spinal ependymomas is gross total resection. The frequency of CNS dissemination following surgery is strongly dependent on the extent (total vs. subtotal) of the initial resection.

Notes

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