Visualization and Classification of Deeply Seated Collateral Networks in Moyamoya Angiopathy with 7T MRI

Abstract

Background and purpose: Collateral networks in Moyamoya angiopathy have a complex angioarchitecture difficult to comprehend on conventional examinations. This study aimed to evaluate morphologic patterns and the delineation of deeply seated collateral networks using ultra-high-field MRA in comparison with conventional DSA.

Materials and methods: Fifteen white patients with Moyamoya angiopathy were investigated in this prospective trial. Sequences acquired at 7T were TOF-MRA with 0.22 × 0.22 × 0.41 mm³ resolution and MPRAGE with 0.7 × 0.7 × 0.7 mm³ resolution. Four raters evaluated the presence of deeply seated collateral networks and image quality in a consensus reading of DSA, TOF-MRA, and MPRAGE using a 5-point scale in axial source images and maximum intensity projections. Delineation of deeply seated collateral networks by different imaging modalities was compared by means of the McNemar test, whereas image quality was compared using the Wilcoxon signed-rank test.

Results: The relevant deeply seated collateral networks were classified into 2 categories and 6 pathways. A total of 100 collateral networks were detected on DSA; 106, on TOF-MRA; and 73, on MPRAGE. Delineation of deeply seated collateral networks was comparable between TOF-MRA and DSA (P = .25); however, both were better than MPRAGE (P < .001).

Conclusions: This study demonstrates excellent delineation of 6 distinct deeply seated collateral network pathways in Moyamoya angiopathy in white adults using 7T TOF-MRA, comparable to DSA.

Fig 1.

Schematic illustrations of deeply seated collateral networks are shown in coronal (A) and sagittal (B) MR imaging views. Six pathways of collateral vessels according to perfusing territories can be divided into collateral networks to cortical vessels (remote, type a and b) and to major trunk vessels (local, types c–f). Anastomoses between striate arteries or choroidal arteries and cortical arteries directly or via medullary arteries (a); septal transcallosal anastomoses between choroidal arteries with pericallosal arteries (b); anastomoses between choroidal arteries or the posterior communicating artery and thalamostriate arteries (c); intrastriatal anastomosis among striatal arteries (d); intrathalamic anastomosis among thalamic arteries (e); and focal Moyamoya vessels in the basal cistern (f).

Fig 2.

Case 1. Selective right internal carotid angiography (anteroposterior, A; lateral view, B) shows anastomotic connections to cortical arteries from the anterior choroidal artery (black arrowheads, type b) as well as from thalamostriate arteries (white arrows, type a). Collateral networks are excellently visualized in MIP from TOF-MRA with slab thickness of 20 mm (white arrows and black arrowheads) (C). Transcallosal connections to cortical arteries (white arrowheads) not detected by DSA are poorly visualized on MPRAGE (D).

Fig 3.

Case 8. Selective right internal carotid angiography (anteroposterior, A; right 45°oblique view, B) shows anastomosis between the posterior communicating artery and the thalamostriate arteries (arrows, type c). MIP from TOF-MRA (C) demonstrates this anastomosis clearly as well as connection with the anterior choroidal artery (asterisk). The latter anastomosis could neither be detected in DSA nor visualized by MIP from MPRAGE (D).

Fig 4.

Case 5. Selective right internal carotid angiography (right 45° oblique, A; left 45° oblique view, B) shows intrastriatal anastomoses among thalamostriate arteries running through the periventricular space (arrows, type d). MIP from TOF-MRA (C) excellently demonstrates these networks as well as focal connections among Moyamoya vessels in the basal cistern (asterisk, type f). MIP from MPRAGE (D) moderately depicts the network; however, basal Moyamoya vessels are poorly visualized.

Fig 5.

Case 6. Selective left vertebral angiography (anteroposterior, A; lateral view, B) shows no marked anastomosis. The MIP from TOF-MRA (C) demonstrates excellent visualization of inner thalamic anastomosis among posterior thalamostriate arteries (white arrows, type e), whereas the visualization is only moderate on MIP from MPRAGE (D).

Fig 6.

Case 10. Selective right vertebral angiography (anteroposterior, A; lateral view, B) shows a tiny, barely visible anastomosis (black arrows) between the posterior thalamostriate artery and a medullary-cortical artery. MIP from TOF-MRA (C) and MIP from MPRAGE (D) do not delineate the anastomosis. The white arrow (C) indicates the supposed anatomic location of the anastomosis.