Contrast-enhanced MR angiography of intracranial giant aneurysms

Abstract

Background and purpose: Intravoxel phase dispersion and flow saturation often prevent adequate depiction of intracranial giant aneurysms on 3D time-of-flight (3D-TOF) MR angiography (MRA). Additional diagnostic difficulties may arise from T1 contamination artifact of an associated blood clot. Our aim was to assess whether contrast-enhanced MRA could improve the evaluation of giant aneurysms and to compare two different types of contrast-enhanced MRA.

Methods: We studied 11 aneurysms in 10 patients (age range, 31-77 years) with giant aneurysms of the anterior (n = 9) and posterior (n = 2) cerebral circulation by comparing 3D-TOF, first-pass dynamic contrast-enhanced MRA, and steady-state contrast-enhanced 3D-TOF sequences. Additional comparison with digital subtraction angiography (DSA) was performed in eight aneurysms.

Results: In nine of 11 aneurysms, 3D-TOF did not adequately show the lumen and exiting vessels. Contrast-enhanced 3D-TOF and dynamic contrast-enhanced MRA showed the aneurysm sac and exiting vessels in all of these cases. Dynamic contrast-enhanced MRA showed a better intravascular contrast than did contrast-enhanced 3D-TOF, which led to better delineation of the aneurysms. T1 contamination artifact from intra- or extraluminal blood clot was evident on the 3D-TOF images in four cases. The artifact was less marked on the contrast-enhanced 3D-TOF image and was completely eliminated on the dynamic contrast-enhanced MRA image by subtraction of precontrast images. The diagnostic information provided by dynamic contrast-enhanced MRA was comparable to that provided by DSA.

Conclusion: Precontrast 3D-TOF is inadequate for the assessment of giant cerebral aneurysms. Both contrast-enhanced 3D-TOF and dynamic contrast-enhanced MRA reliably show the aneurysm sac and connected vessels. Dynamic MRA provides a superior contrast between flow and background and eliminates T1 contamination artifact. It should therefore be considered as the MRA sequence of choice.

fig 1.

78-year-woman with bilateral cavernous carotid aneurysms. A–D, T2-weighted fast spin-echo (FSE) image (A) (4200/99/2 [TR/TE_eff/excitations]) shows bilateral enlargement of cavernous sinus by giant aneurysms of internal carotid arteries. These are of mixed signal intensity with high signal in areas of turbulent flow. 3D-TOF (B) (40/6.9/1; flip angle, 20°) shows only the entering vessels, but not aneurysm sacs nor exiting vessels, which are seen on contrast-enhanced 3D-TOF (C) (40/6.9/1/45°) and dynamic contrast-enhanced MRA sequences (D) (6.4/1.4/1/30°, slice thickness = 1.5 mm). These also show extension of aneurysmal dilatation into both middle cerebral arteries (MCAs). On the contrast-enhanced 3D-TOF sequence (C), the signal intensity of aneurysm sacs and distal vessels is attenuated compared with that of contrast-enhanced dynamic MRA (D), which provides excellent contrast between vessels and background

fig 2.

77-year-old man with giant basilar artery aneurysm. A–C, On T2-weighted FSE image (A) (5182/99/1), a giant basilar artery aneurysm is mainly of high signal. Patency of its lumen can therefore not be assumed. Targeted MIP projection of the posterior circulation from the 3D-TOF (B) (35/6/1/20°) sequences, acquired with overlapping slabs, shows the entering vessels, only a small part of the aneurysm sac, and no exiting vessels. Aneurysm and exiting vessels are well seen on dynamic contrast-enhanced MRA sequence (C) (5/2/1/25°)

fig 3.

62-year-old woman with giant aneurysm of left cavernous carotid artery (CCA). A–F, early (A) and late (B) frames of DSA run after left CCA injection. Early frame (A) shows entering vessel and high-velocity inflow jet. Full extent of aneurysm sac and exiting vessels are only shown on late frame of DSA run (B) where visualization of distal vessels is faint owing to turbulent flow and contrast dilution in the aneurysm sac. MIP of 3D-TOF (C) (40/6.9/1/20°) and contrast-enhanced 3D-TOF (D) (40/6.9/1/45°). Precontrast 3D-TOF (C) shows only entering vessels and high-velocity inflow jet, similar to early frame of the DSA (A), accounting for different projection angle, whereas contrast-enhanced 3D-TOF (D) also shows aneurysm sac and distal vessels. Axial source images of 3D-TOF (E) and contrast-enhanced 3D-TOF (F) show intraluminal clot. Low signal clot adherent to posterolateral wall of aneurysm is visible on 3D-TOF axial source images (E), but dropout of signal from nonlaminar flow anteriorly does not allow exclusion of additional clot. Interface between patent aneurysm lumen and low signal clot is much clearer on axial source images of contrast-enhanced 3D-TOF (F)

fig 4.

31-year-old man with ruptured giant aneurysm of the right MCA. A–E, T1-weighted SE image (A) (540/11/2) shows hematoma in right temporal lobe and insula with high signal from methemoglobin. It was shown to be due to rupture of fusiform giant aneurysm of right MCA by DSA (B). On 3D-TOF image (C) (40/6.9/1/20°), aneurysm lumen is indistinguishable from surrounding T1 contamination artifact. Contrast-enhanced 3D-TOF (D) (40/6.9/1/45°) faintly delineates aneurysm but remains severely degraded by T1 contamination artifact. Note that exiting vessel and M2 branches of right MCA, not seen by use of 3D-TOF (C), are, however, visualized. The dynamic contrast-enhanced MRA findings (E) (8.7/1.8/1/30°/3 mm), which is of low spatial resolution in this case, correlate well with those of DSA (B), showing only the aneurysm lumen, and not the hematoma