(Radiographics. 1999;19:1397-1400.)
© RSNA, 1999
Neuroradiology Case of the Day1
Francis G. Greiner, MD and
Deepak Takhtani, MD
1 From the Department of Radiology, University of South Alabama Medical Center, Mobile (F.G.G., D.T.), and the Department of Radiology, University of South Alabama School of Medicine, 2451 Fillingim St, Mastin Bldg 301, Mobile, AL 36617 (F.G.G.). From the 1998 RSNA scientific assembly. Received February 15, 1999; revision requested March 5 and received March 31; accepted April 1. Address reprint requests to F.G.G.
Index Terms: Lipoma and lipomatosis, 353.319, 353.64 • Spinal cord, compression, 351.64, 353.319 • Spine, diseases, 35.64, 353.319 • Steroids, complications, 353.319
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HISTORY
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A 44-year-old woman with systemic lupus erythematosus presented with weakness and inability to stand or walk. She reported mild back pain with symmetric weakness in the thighs, calves, and ankles of several weeks duration. Deep tendon reflexes were reduced in both legs. A vague sensory deficit was reported at the T7–T8 distribution. The patient's sedimentation rate and white cell count were elevated. Myelography was performed to evaluate for spinal cord compression. Computed tomography (CT) was also performed.
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FINDINGS
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Myelography revealed reduction in the size of the dural sac at the upper thoracic level (Figs 1, 2). There was posterior scalloping of the dura mater but only a minimal posterior defect in the spinal cord. CT revealed an area of soft-tissue attenuation posterior to the cord and dural sac (Fig 3) that measured nearly 17 mm in thickness from the dura mater to the posterior aspects of the spinal column in some places. There was no evidence of fracture or large osteophytes. The disk spaces were essentially normal, as were the vertebral bodies, bone of the posterior spinal column, and ligamentous structures. A subcutaneous chest port was used for immunosuppressive therapy, which included treatment with steroids. Prone cross-table imaging could not be performed because it caused respiratory distress.
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Figures 1, 2. (1) Prone myelograms depict the free flow of contrast material to the thoracic spine. An extradural defect from T3 to T5 is also seen (arrows). (2) Left lateral (a) and supine (b, c) myelograms of the thoracic spine also demonstrate the extradural defect (arrowhead) (cf Fig 1). The lateral view in a clearly depicts the defect as mostly posterior to the spinal canal.
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Figures 1, 2. (1) Prone myelograms depict the free flow of contrast material to the thoracic spine. An extradural defect from T3 to T5 is also seen (arrows). (2) Left lateral (a) and supine (b, c) myelograms of the thoracic spine also demonstrate the extradural defect (arrowhead) (cf Fig 1). The lateral view in a clearly depicts the defect as mostly posterior to the spinal canal.
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Figures 1, 2. (1) Prone myelograms depict the free flow of contrast material to the thoracic spine. An extradural defect from T3 to T5 is also seen (arrows). (2) Left lateral (a) and supine (b, c) myelograms of the thoracic spine also demonstrate the extradural defect (arrowhead) (cf Fig 1). The lateral view in a clearly depicts the defect as mostly posterior to the spinal canal.
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Figures 1, 2. (1) Prone myelograms depict the free flow of contrast material to the thoracic spine. An extradural defect from T3 to T5 is also seen (arrows). (2) Left lateral (a) and supine (b, c) myelograms of the thoracic spine also demonstrate the extradural defect (arrowhead) (cf Fig 1). The lateral view in a clearly depicts the defect as mostly posterior to the spinal canal.
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DIAGNOSIS: Extradural lipomatosis.
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DISCUSSION
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Magnetic resonance (MR) imaging could not be performed in this case due to the patient's large size; however, MR imaging would normally be the modality of choice in the evaluation of spinal cord compression. On T1-weighted images that demonstrate cord compression, the high signal intensity of epidural fat is generally diagnostic for epidural lipomatosis (Fig 4). Because our patient was too large for the existing MR imagers, myelography was performed instead. Findings at myelography may be normal in cases of epidural lipomatosis (1). At CT, the increased epidural fat usually manifests posterior to the dura mater and may compress the cord anteriorly (Fig 5a). Because of its low attenuation, the increased fat is usually easily identified on the basis of its negative HU values (Fig 5b) (2).
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Figure 4a. (a) Sagittal T1-weighted MR image obtained in a different patient reveals increased fat posterior to the dural sac (arrows). The fat is slightly more than 8 mm thick at the T6 level. (b) Axial T1-weighted MR image obtained at the T7 level reveals increased epidural fat but no scalloping of the dural sac (arrowhead). The fat is slightly more than 7 mm thick, a finding that is consistent with epidural lipomatosis.
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Figure 4b. (a) Sagittal T1-weighted MR image obtained in a different patient reveals increased fat posterior to the dural sac (arrows). The fat is slightly more than 8 mm thick at the T6 level. (b) Axial T1-weighted MR image obtained at the T7 level reveals increased epidural fat but no scalloping of the dural sac (arrowhead). The fat is slightly more than 7 mm thick, a finding that is consistent with epidural lipomatosis.
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Figure 5a. (a) Sagittal reconstructed CT scan demonstrates an extradural defect posterior to the spinal cord (black arrow) and displacing the dural sac anteriorly (white arrow). (b) Axial CT scan shows the mass with attenuation values between -60 and -100 HU, a finding that is consistent with fat. There is no evidence of septation or encapsulation to suggest a focal lipoma.
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Figure 5b. (a) Sagittal reconstructed CT scan demonstrates an extradural defect posterior to the spinal cord (black arrow) and displacing the dural sac anteriorly (white arrow). (b) Axial CT scan shows the mass with attenuation values between -60 and -100 HU, a finding that is consistent with fat. There is no evidence of septation or encapsulation to suggest a focal lipoma.
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Spinal cord compression is generally due to impingement by disk, bone, blood, tumor, or infection. In our case, the focality usually associated with disk or bone impingement was not seen; instead, narrowing extended the length of several vertebral body segments and was generally posterior and lateral to the cord and dural sac.
Hemorrhage, neoplasm, and infection would still be considered as possible diagnoses. The elevated sedimentation rate seen in this patient is nonspecific and could be seen with tumor or infection. It is also consistent with the patient's known history of systemic lupus erythematosus. CT revealed the extradural mass effect to have very low attenuation, a finding that would be inconsistent with these three causes of compressive myelopathy.
In addition to the common causes of cord compression listed earlier, there are other less common causes including synovial cysts, extramedullary hematopoiesis, arachnoid cysts, and lipomatosis (3–6). The low attenuation (-60 to -100 HU) of the compressing soft-tissue mass seen in our case was most consistent with epidural lipomatosis, and this diagnosis was confirmed with a decompressive surgical procedure. No focal encapsulation or indication of a lipoma, infection, cyst, or neoplasm was found.
Epidural lipomatosis is an unusual condition. Lipomatosis is more often seen in the mediastinum, kidneys, or pelvis (7,8). It is most often associated with Cushing syndrome and exogenous corticosteroid drug therapy. Patients with rheumatoid arthritis, systemic lupus erythematosus, asthma, and dermatomyositis as well as transplant recipients have all been reported to develop epidural lipomatosis after undergoing steroid therapy (9). Long-term steroid treatment is usually required to exacerbate lipomatosis, although symptoms may occur with doses as low as 10–20 mg/d after just 6 months. In a relatively large series, 68% of cases of steroid-induced epidural lipomatosis occurred in the thoracic spine and involved a mean dose of 40 mg/d administered over an average of 6.9 years (10). To our knowledge, there have been no reported cases of epidural lipomatosis in the cervical spine, probably due to the small amounts of epidural fat in this area (11). Idiopathic epidural lipomatosis is even less common and is found with equal frequency in the thoracic and lumbar spine (10, 12,13).
Although results of neurologic examination may be normal, patients with epidural lipomatosis usually present with weakness (72% of cases), decreased sensation and reflexes (50%), and mild back pain. Alterations in bowel and bladder function are seen less frequently (14).
The treatment of epidural lipomatosis often consists of reduction in steroid dose and prescribed weight loss. Patients who undergo surgery for decompression may have a mortality rate as high as 22% (13), probably due to the overall immunosuppressed status of affected patients.
The normal thickness of epidural fat at the T7 level is 3–6 mm (mean, 4.6 mm) on sagittal T1-weighted MR images. According to a study by Quint et al (1), epidural lipomatosis as a cause of myelopathy should be considered when (a) a complete posterior block is seen at myelography, (b) CT or MR imaging reveals only fat contiguous to a ventrally displaced dural sac, (c) there is a history of chronic steroid use, (d) there are myelopathic or radicular symptoms referable to the level of the abnormality, or (e) there are no other structural lesions that could help explain the symptoms and imaging findings.
Our patient was treated with laminectomy of the involved thoracic spine segments. No evidence of focal lipoma, infection, or neoplasm was identified. The posterior spinal canal had extensive fatty infiltration. Surgery produced only minimal improvement in symptoms. Follow-up myelography demonstrated reduced impression by the fatty mass at the surgical site and reduced dural sac compression.
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References
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Fessler RG, Johnson DL, Brown FD, Erickson RK, Reid SA, Kranzler L. Epidural lipomatosis in steroid-treated patients. Spine 1992; 17:183-188.[Medline]
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HISTORY
FINDINGS
