Customer Testimonial :

“The MRA was incredible helpful in this patient. T2W MRI had clearly demonstrated the diagnosis of dural AVF. Angiography in this condition continues, injecting each intercostal and lumbar artery, (as well as the external carotids, vertebrals, and internal iliacs), until the fistula is found. This particular patient (like many) was obese and hypertensive. His aorta was ectatic and tortuous, and angiography, using multiple catheters of different shapes, had to be split into two sessions because of the high contrast medium dose. Sometimes when I do angios for this condition, I get lucky and see the fistula quickly: other times I may spend hours doing all the necessary pedicles, as in this patient. At the end I was unable to see the fistula, and I thought MRA was unlikely to help, but I didn’t want to do another angio!. The MRA shows the fistula at D10. I went back to the angios from this pedicle, and in retrospect they were not quite normal, possibly demonstrating an abnormal vein, but this finding was equivocal at best. I have no doubt that for my next patient with dural avf, I will do MRA first. It is accepted that spinal angiography in this condition carries a small but definite risk of causing spinal cord infarction, and so neurologists are always reluctant to ask for the test. The patient is planned for surgery rather than embolisation, due to the tortuosity of the vessels. We will get a follow up MR 4-6 weeks after that.”

Normal spinal cord blood supply

The spinal cord has three major arteries that run the length of the cord, the anterior spinal artery that lies in the anterior median fissure, and two posterior spinal arteries that run near the dorsal root entry zones.

What kind of pathology is it?

Lesion belonging to the group of acquired arteriovenous fistulae, similar to those encountered in the head (see dural arteriovenous fistula). They could be considered as a sub type of AVM..
They mainly affect men after the fifth decade. A slowly progressive spinal cord syndrome, sometimes with a relapsing-remitting course, is usually found, with paraparesis, bowel and bladder dysfunction and impotence. Sensory levels are unusual and sometimes a picture suggesting a radiculopathy is also found. Neurologically the diagnosis is not easy but such a syndrome in an adult male should prompt neuroradiological investigation. Nowadays MR is the modality of choice. It usually shows an abnormal signal with T2 hyperintensity within the spinal cord over a few levels, most frequently at the conus and epiconus level but also in the dorsal or more rarely in the cervical region. Gadolinium injection usually produces enhancement sometimes with a patchy appearance without clearly defined margins within the abnormal signal area. The signal abnormality is due to venous engorgement and perivascular oedema in dilated intramedullary venous capillaries, subjected to an abnormally high pressure. Sometimes, but not always, dilated tortuous vessels are seen, usually in the dorsal aspect of the cord. The cord may be focally slightly expanded.
However, once the MR abnormality is found, a spinal angiogram should be performed. All the intercostal and lumbar arteries must be selectively injected until the fistula is found. The fistula is usually an almost direct communication, sometimes with a tiny capillary network, between a radicular artery and a draining vein that is filled retrogradely and appears dilated, often over many segments. The fistula itself lies within the dura, at the level of the neural foramen. Sometimes the fistula may be very high, at the level of the foramen magnum, fed by branches of the vertebral artery or external carotid artery.
Treatment of the dural fistula may be surgical, with ligation and coagulation of the connection with the draining vein at the level of the dura, or embolization with injection of glue to achieve the same result. Particles may also be used but the treatment may be only temporary. Following effective treatment patients usually improve significantly and return to normal unless the diagnosis has been delayed for many months or years.

The Encyclopaedia of Medical Imaging Volume VI:1

Spinal angiography, AP projection, injection of a right dorsal intercostal artery. Arrowheads indicate the fistula at the level of the dura of the neural foramen. Arrows indicate the enlarged spinal veins

Patient's preparation:

As usual for a CE-MRA
The CTL phase array coil is used.
The arms of the patient are placed above the head to reduce wrap-around artifact in the right-left direction.

MR examination

Examination has been performed with the Signa Infinity 1.5T EchoSpeed+ EXCITE

A large FOV T2 weighted FSE scan is acquired first to localize the level of the spinal malformation. High resolution T2 and T1 weighted sequences are than performed with the use of small FOV. The CE-MRA is performed; T1 weighted sequences (sagittal and axial), after contrast media injection, are finally acquired at the end of the examination.

Large FOV T2 FSE	High Res. T2 FSE	High Res. T1 FSE + Gadolinium
Images courtesy of Dr S. Halpin, University of Wales

Protocols

Large FOV T2 FSE

High Res. T2 FSE

CE-MRA

High Res. T1 FSE + Gadolinium

CE-MRA

The angiography sequence is fluoro-triggered. When contrast media fills the descending aorta, the 3D sequence is triggered. No delay between detection and triggering is needed, as the sequence is a free breathing acquisition.
The angiography sequence must be multi-phase. It gives 2 advantages:

• The increase of the triggering window

• The obtaining of arterial and venous phase

The wash-in / wash-out of the fistula is extremely fast. The use of the elliptic centric encoding with a short acquisition time helps to obtain a pure arterial phase followed by a venous phase. The injection of contrast media is a slow infusion at a rate of 2 ml/sec followed by the infusion of saline flush.
The use of the turbo mode (turbo 2) reduces the min TR and therefore decreases acquisition time. It helps as well to improve the compromise spatial resolution / acquisition time. The major drawback of this option is the increase in the wrap around artifact within the slice encoding direction. This artifact is affecting the first and last slices of the 3D slab and must be estimated when slices are prescribed.
Finally, in plane and through plane resolution must be high enough to visualize the feeding artery of the lesion that is the goal of the examination.

CE-MRA : arterial phase

Images courtesy of Dr S. Halpin, University of Wales
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CE-MRA : venous phase

Note the complete wash-out of the fistula and the enhancement of the spinal veins.

Images courtesy of Dr S. Halpin, University of Wales
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Conclusion:

MR angiographic technique is capable of localizing non-invasively a spinal dural AVF with its small feeding artery and draining veins. Then, the clinician can take the decision of the appropriateness of embolization. MR angiography can as well substitute DSA in the post-treatment evaluation of spinal vascular malformations.

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