DOI:10.2214/AJR.05.0625
AJR 2006; 186:S227-S229
© American Roentgen Ray Society
AJR Teaching File: Progressive Myelopathy
Kent D. Nelson1 and
Catherine C. Roberts1
1 Both authors: Department of Radiology, Mayo Clinic College of Medicine, 13400
E Shea Blvd., Scottsdale, AZ 85259.
Received April 19, 2005;
accepted after revision August 18, 2005.
CONTINUING MEDICAL EDUCATION
The AJR Teaching File articles are available for .25 CME credit
for completing all three articles. They are free to ARRS members and may be
purchased by nonmembers for $10.00 each. Detailed information including
objectives, disclosure information, and how to obtain CME credit can be found
at
www.arrs.org
by selecting AJR Integrative Imaging.
Address correspondence to C. C. Roberts
(roberts.catherine{at}mayo.edu).
Keywords: MRI • myelopathy • neuroradiology • spine
Clinical History
A 55-year-old woman presents with a 3-year history of progressive lower
extremity numbness and weakness.
Radiologic Description
Sagittal T2-weighted MRI shows mild enlargement of the distal thoracic cord
with increased signal extending over a relatively long segment of the cord
(Fig. 1A). Enlargement of the
subarachnoid vessels on the surface of the cord is also suggested. On a
gadolinium-enhanced sagittal T1-weighted MR image, there is patchy central
enhancement of the abnormal segment of the cord
(Fig. 1B), and abnormally
dilated draining veins are better shown. A coronal MR angiogram shows a
markedly tortuous and dilated complex of vessels on the surface of the cord
(Fig. 1C). Anteroposterior
(Fig. 1D) and lateral
(Fig. 1E) views from a spinal
angiogram show a small branch of the left L2 lumbar artery filling a
collection of tortuous veins. The vessels have the same appearance on MR
angiography.
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Fig. 1A —55-year-old woman with 3-year history of progressive lower extremity
numbness and weakness. Sagittal T2-weighted MR image (TR/TE, 3,500/110) of
lower thoracic spine and upper lumbar spine shows increased signal in enlarged
lower thoracic spinal cord and conus medullaris (arrows) and numerous
flow voids along dorsal surface of cord (arrowheads).
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Fig. 1B —55-year-old woman with 3-year history of progressive lower extremity
numbness and weakness. Sagittal T1-weighted gadolinium-enhanced MR image
(600/8.3) shows patchy enhancement of conus medullaris (arrows) and
dilated dorsal draining veins (arrowheads).
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Fig. 1C —55-year-old woman with 3-year history of progressive lower extremity
numbness and weakness. Coronal MR angiogram, obtained using gadolinium bolus
technique (4-sec delay), of lower thoracic spine shows enlarged, tortuous
draining veins (arrowheads) along surface of spinal cord.
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Fig. 1D —55-year-old woman with 3-year history of progressive lower extremity
numbness and weakness. Anteroposterior (D) and lateral (E) views
of digital subtraction spinal angiogram obtained with injection of left L2
lumbar artery (arrow) show opacified fistula (asterisk) and
collection of abnormal draining veins (arrowheads).
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Fig. 1E —55-year-old woman with 3-year history of progressive lower extremity
numbness and weakness. Anteroposterior (D) and lateral (E) views
of digital subtraction spinal angiogram obtained with injection of left L2
lumbar artery (arrow) show opacified fistula (asterisk) and
collection of abnormal draining veins (arrowheads).
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Diagnosis
Spinal dural arteriovenous fistula (DAVF) is the best diagnosis for this
case because of the abnormal increased T2-weighted signal and enhancement of
the spinal cord combined with dilated draining veins.
Commentary
Spinal DAVF is a treatable cause of progressive myelopathy and is
frequently misdiagnosed [1]. An
abnormal arteriovenous connection in the dura supplied by the small radicular
branch vessel causes formation of arterialized draining veins that compete
with the normal veins that drain the cord. This is thought to result in venous
stasis and eventually in gliosis in the cord. There is a breakdown of the
blood-brain barrier and edema of the cord. The abnormal segment of cord
extends over time if the condition remains undiagnosed. This entity is most
common in middle-aged men. The time from onset of symptoms to diagnosis and
treatment averages 23-27 months
[1,
2].
Although spinal DAVF is the most common spinal vascular malformation
[2], spinal DAVF is still
relatively a rare entity and is often not considered clinically. If these
lesions are identified early, the myelopathic changes can be reversible
[1]. Treatment consists of glue
embolization [3] or surgical
obliteration [4] of the fistula
and proximal draining vein. The patient in this case underwent surgical repair
with subsequent improvement in her clinical symptoms.
Patients with myelopathy often undergo MRI examinations of the spine for
evaluation of their symptoms. The findings of spinal DAVF are not always
obvious. The most common finding is increased T2-weighted signal within the
spinal cord, likely due to venous congestion
[2]. The spinal cord can be
enlarged and enhancing. Cord enlargement and enhancement can also be
suggestive of a neoplastic process. The cord changes seen in spinal DAVF,
however, extend over an average of seven levels
[2], whereas
"enhancing" neoplasm tends to be more focal. Frequently on
T2-weighted sequences, prominent flow voids are visualized in the high-signal
CSF surrounding the spinal cord. Sometimes the enlarged subarachnoid vessels
can be seen only on a sagittal gadolinium-enhanced T1-weighted series.
Spinal angiography is required to identify the site of the fistula. In this
case, a spinal angiogram was obtained at the onset of the patient's symptoms.
However, it included only neck vessels and segmental arteries from T5 to T12.
If a patient has imaging findings and presentation consistent with spinal
DAVF, a complete angiography examination must be performed from the neck to
the internal iliac arteries or to the point at which the offending fistula is
identified. Once found, several levels above and below the site of the fistula
should be injected to avoid missing a rare second fistula, which is usually at
an adjacent level. Mistakes are commonly made by misnumbering the vertebral
segments so that a segment is missed or by not including the intracranial or
sacral vessels in the angiography examination. Digital subtraction angiography
makes the abnormal vessels more easily identified during the examination.
Recently, MR angiography of the spinal canal has made it possible to narrow
the search for the fistula and frequently allows correct identification of the
actual level and side, resulting in a significant decrease in the length of
the angiography examination.
Objective
The educational objective of this article is to teach the imaging
appearance of spinal DAVFs, a frequently misdiagnosed cause of progressive
myelopathy.
Conclusion
Spinal DAVFs cause a progressive myelopathy that is challenging to
diagnose. This entity is often not clinically considered, and suggestive
imaging findings can be subtle. On MRI, the spinal cord has increased
T2-weighted signal and can be enlarged and enhancing, sometimes simulating a
neoplasm, demyelination, or infection. Prominent subarachnoid veins
surrounding the spinal cord can usually be seen, although they are sometimes
subtle. Spinal angiography is necessary to confirm the site of the fistula. MR
angiography has recently been helpful in verifying the presence of abnormal
veins and usually suggests the level of the site of the fistula, thereby
decreasing the search time, radiation exposure, and contrast load during
angiography. Myelopathic changes can be reversible if these lesions are
identified early.
References
- Atkinson JLD, Miller GM, Krauss WE, et al. Clinical and
radiographic features of dural arteriovenous fistula, a treatable cause of
myelopathy. Mayo Clin Proc 2001;76
: 1120-1130[Medline]
- Gilbertson JR, Miller GM, Goldman MS, Marsh WR. Spinal dural
arteriovenous fistulas: MR and myelographic findings.
AJNR 1995; 16:2049
-2057[Abstract]
- Jellema K, Sluzewski M, van Rooij WJ, Tijssen CC, Beute GN.
Embolization of spinal dural arteriovenous fistulas: importance of occlusion
of the draining vein. J Neurosurg Spine2005; 2:580
-583[Medline]
- Watson JC, Oldfield EH. The surgical management of spinal dural
vascular malformations. Neurosurg Clin N Am1999; 10:73
-87[Medline]
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