Value and limitations of contrast-enhanced MR angiography in spinal arteriovenous malformations and dural arteriovenous fistulas

Abstract

Background and purpose: The purpose of this work was to study the validity of MR angiography (MRA) for identification of spinal arteriovenous (AV) abnormalities.

Materials and methods: Thirty-four consecutive patients with suspicion of spinal vascular abnormalities underwent digital subtraction angiography (DSA) after MRA. The level and side of the suspected spinal dural arteriovenous fistula (SDAVF) and the feeding arteries in spinal arteriovenous malformations (SAVMs) were determined from the MRA and compared with DSA.

Results: DSA revealed SDAVF in 20 abnormalities of which 19 were spinal and 1 was tentorial with spinal drainage, as well as SAVM in 11 patients. In 3 patients, MRA and DSA were both normal. For detection of spinal arteriovenous abnormalities, neither false-positive nor false-negative MRA results were obtained. The MRA-derived level of the feeding artery in SDAVF agreed with DSA in 14 of 19 cases. In 5 cases, a mismatch of 1 vertebral level (not side) was noted for the feeding artery. For the tentorial AVF, only the spinal drainage was depicted; the feeding artery was outside the MRA field of view. In intradural SAVM, the main feeding artery was identified by MRA in 10 of 11 patients. MRA could differentiate between glomerular and fistulous SAVM in 4 of 6 cases and between sacral SDAVF and filum terminale SAVM in 2 of 5 cases.

Conclusions: MRA reliably detects or excludes various types of spinal AV abnormalities and localizes the (predominant) arterial feeder of most spinal AV shunts. Although classification of the subtype of SAVMs remains difficult, with MRA it greatly helps to focus subsequent DSA.

Fig 1.

SDAVF in a 61-year-old patient. Comparison of visualization capabilities of MRA and DSA. A, Sagittal T2-weighted image showing signal intensity voids raising the suspicion of a vascular spinal cord abnormality (small white arrows). B, Sagittal MIPs of the MRA examination showing the overview and localization of the dilated vein (small black arrows). C, In the coronal target MRA MIP the feeding segmental artery of the SDAVF was depicted to derive from the eighth thoracic level (T8) on the left side. Localization of the shunt is at dural level (gray arrow). DSA (D) provides more spatial resolution and more insight in the dynamic drainage of the dilated vein compared with MRA (E).

Fig 2.

SDAVF in a 69-year-old male patient visualized by MRA and DSA. Demonstration of a normal spinal cord supplying artery and arterialized veins of a SDAVF supplied from the same segmental artery. A, The sagittal T2-weighted image reveals a signal intensity increase of the thoracolumbar cord and some flow voids at the dorsal aspect of the spinal cord raising the suspicion of a vascular spinal cord abnormality (small white arrows). B, Sagittal MIP of the MRA examination showing the overview and localization of the dilated veins (small black arrows). C, The coronal target MRA MIP demonstrates the feeding segmental artery of the SDAVF at the first lumbar level (L1; gray arrow). D, The localization of this origin is confirmed by DSA. In addition to the fistula with dilated veins (small black arrows), DSA shows an anterior spinal cord supplying artery (white arrow) originating from the same segmental vessel. E, On the targeted MPR image of the MRA examination, the anterior radiculomedullary artery could be visualized retrospectively (white arrow) and localized at the first lumbar level (L1). Please note that the normal spinal cord supplying artery, which is not involved in the AV-shunt, is very thin on both the DSA and MRA image. F, This anterior spinal artery (white arrow) is also demonstrated on the oblique sagittal target MRA MIP and can be separated from the abnormal veins of the SDAVF lying posteriorly (small black arrows). The corresponding DSA projections of the early (G) and late phase (H) for comparison.

Fig 3.

Sacral SDAVF in a 64-year-old male patient visualized by MRA and DSA. Advantage of MRA in demonstrating vascular abnormality in a large FOV. A, Sagittal T2-weighted image showing extensive spinal cord edema and only some enlarged vessels raising the suspicion of a vascular spinal cord abnormality (small white arrows). B, Sagittal MIP of the MRA examination showing the overview and localization of an early filled and dilated vein (small black arrows). C, In the enlarged view, the dilated vein of the filum terminale is more clearly depicted (black arrows). The coronal target MRA MIP shows the arterialized filum vein (D, small black arrows) in the same projection in which DSA (E) could confirm the localization of the very small shunt at the first sacral level (gray arrow).

Fig 4.

SDAVF in a 61-year-old male patient visualized by MRA and DSA. Misinterpretation of the segmental level of origin on MRA. A, Sagittal T2-weighted image showing spinal cord edema (small white arrows). B, Sagittal MIP of the MRA examination showing the overview and localization of the dilated vein (small black arrows). C, In the coronal target MRA MIP the feeding segmental artery of the SDAVF was falsely localized by just 1 level at the seventh thoracic level (T7; black arrow). D, DSA shows that the feeding segmental artery (gray arrow) originates from the sixth thoracic level (T6). E, Selective injection of segmental artery T7 (black arrow) shows no supply to the SDAVF. Retrospectively, the correct level (gray arrow) could be identified on the target MRA MIP (C).

Fig 5.

Perimedullary SAVM in a 43-year-old woman visualized by MRA and DSA. Problem of separating arteries from veins by MRA and of superimpositions in nonselective angiograms. A, Sagittal T2-weighted image showing increased signal intensity of the thoracolumbar cord and enlarged perimedullary and infraconal vessels raising the suspicion of a vascular spinal cord abnormality (small white arrows). B, Sagittal MIP of the MRA examination showing the overview and localization of the dilated vessels (small black arrows). C, In the coronal target MRA MIP a mixture of enhanced tortuous arteries and veins is observed. D, On the selective DSA, the AP projection of the early phase shows filling of the largest SAVM-feeding radiculomedullary artery (white arrow), which is derived from the first lumbar level (L1). E, In the late phase the draining veins can clearly be distinguished from the artery (E) which was not possible with MRA (C). F, Because of the overprojection and the MPR postprocessing, the origin of the large anterior radiculomedullary artery was first falsely localized at the twelfth thoracic level (T12) on the MRA image (black arrow). G, Retrospectively, the correct level could be localized at L1 (black arrow). H, The T12 level gives rise to an additional posterior feeder of the SAVM, only localized by selective DSA (gray arrow).

Fig 6.

SAVM of the filum terminale in a 61-year-old male patient visualized by MRA and DSA. Problem of differentiation between this rare type of SAVM and SDAVFs because of difficult shunt localization and vessel identification in the present MRA. A, Sagittal T2-weighted image showing enlarged infraconal vessels raising the suspicion of a vascular spinal cord abnormality (small white arrows); no signal intensity abnormality of the spinal cord is visible. B, Sagittal MIP of the MRA examination showing the overview and localization of the dilated vessels (small black arrows). C, The blood vessel demonstrated on the coronal target MRA MIP could retrospectively be identified to be an enlarged anterior radiculomedullary (white arrow) and anterior spinal artery with origin from the eleventh thoracic level. DSA for comparison (D). E-G, The continuation of this anterior spinal artery to the filum terminale (white arrowheads) is the feeding artery for this type of AVM situated at the level of L4 in this individual case (gray arrow). Differentiation of the feeding artery, which is running downward (white arrowheads), and the arterialized vein (black arrowheads), which is running upward, is only possible with a good time resolution of the selective angiogram as shown on the DSA images in early (F) and late phases (G).