Non-moyamoya vessel network formation along steno-occlusive middle cerebral artery

Abstract

Objective: In this study, we sought to examine the prevalence and clinical relevance of deep tiny flow voids (DTFV) in patients with steno-occlusive middle cerebral artery (MCA) disease on high-resolution MRI (HRMRI).

Methods: We retrospectively reviewed the HRMRI and clinical data of 477 patients with MCA steno-occlusive disease. The presence and distribution of DTFV, defined as 3 or more flow voids along the affected MCA on at least 2 consecutive T2-weighted image slices on HRMRI, were observed. The relationships among DTFV, the degree of stenosis (mild <50%, moderate 50%-70%, severe 70%-99%, and occlusion), and infarctions were analyzed. To clarify the difference between DTFV and moyamoya collaterals, we compared the HRMRI findings of the patients with DTFV and 102 patients with moyamoya disease.

Results: The prevalence of DTFV was 1.4% in mild stenosis, 12.8% in moderate stenosis, 40.6% in severe stenosis, and 50.7% in MCA occlusions. Of the 112 patients with DTFV, 57 (50.9%) had all 4 quadrants (superior, inferior, dorsal, and ventral sides) of the MCA involved. DTFV were more common in asymptomatic patients than in symptomatic patients with severe stenosis (49.3% vs 30.9%, p = 0.025) and occlusions (68.0% vs 41.7%, p = 0.033). Obvious flow voids in the basal ganglia region were observed in 58 patients (56.9%) with moyamoya disease but in none of the patients with DTFV (p < 0.001).

Conclusions: DTFV are common in patients with severe steno-occlusive MCA disease, especially in asymptomatic patients. We hypothesize that DTFV originate from new vessel network formation in response to chronic cerebral ischemia.

© 2016 American Academy of Neurology.

Figures

Figure 1. DTFV in patients with a stenotic or occlusive MCA in high-resolution MRI

(A–E) In a patient with a moderate MCA stenosis (arrowhead, B), no DTFV are revealed (empty arrowheads, C–E). (F–J) In a patient with severe MCA stenosis (arrowhead, G), DTFV (short arrows, H and I) along the affected MCA (empty arrowheads, H and I) are seen, as compared with the reference segment (empty arrowhead, J). (K–O) In a patient with right MCA occlusion, DTFV (short arrows, M and N) can be seen around the occluded MCA (empty arrowheads, M and N), as compared with the left MCA for reference (empty arrowhead, O). DTFV = deep tiny flow voids; MCA = middle cerebral artery.

Figure 2. Measurements of luminal area and division of quadrants

(A) Magnetic resonance angiography shows a stenosis at the M1 segment of the right MCA. (B, C) The luminal area of the sites can be measured manually (demonstrated by the magnified images). The plaque (arrow, B) at the maximal lumen narrowing site and the reference site (arrow, C) are shown. (D) Four quadrants (superior, inferior, dorsal, and ventral) are separated to assess the distribution of deep tiny flow voids along the MCA. MCA = middle cerebral artery.

Figure 3. Distribution of multiple flow voids in moyamoya disease

(A–E) In a patient with moyamoya disease, bilateral internal carotid artery occlusions are shown (arrowheads, A). Multiple dispersed flow voids (arrows, B–E) are seen around the circle of Willis, in the right sylvian fissure, and in the basal ganglia regions.