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

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.