PURPOSE: To investigate postsurgical indirect cortical neoangiogenesis in patients with moyamoya disease (MMD) using silent magnetic resonance angiography (MRA). METHODS: We studied 44 patients with MMD (63 hemispheres) who were previously revascularized with combined bypass surgery (23 and 40 hemispheres in pediatric and adult patients, respectively). They underwent follow-up for postoperative bypass patency using time-of-flight (TOF)-MRA and silent MRA between January 2022 and December 2023. The mean duration from surgery to MRA was 8.5 years (range, 1.2-22.3 years). Two observers independently rated the revascularization as follows: 0 (near-complete signal loss or no signal)
1, poor (slightly visible donor arteries)
2, good (acceptable revascularization around the brain surface)
and 3, excellent (good quality of revascularization with perfusion from the cortical surface into the middle cerebral artery). RESULTS: Silent MRA visualized indirect bypass significantly better than TOF-MRA (2.6 ± 0.7 and 1.4 ± 0.8) (P <
0.01). In silent MRA, the mean score of indirect bypass was significantly higher than that of direct bypass (2.6 ± 0.7 and 1.7 ± 1.0
P <
0.01) and indicated good indirect bypass development in both children and adults (91.3% and 85.0%
score ≥ 2). Children exhibited a higher rate of excellent indirect bypass patency than adults (73.9% and 55.0%
score 3). Poor bypass development in indirect bypass (8 hemispheres, mean age: 35.5 ± 17.5 years, mean follow-up period: 11.3 years) was significantly observed in male patients (P <
0.01). CONCLUSION: Silent MRA enables better precision in postsurgical visualization of indirect cortical neoangiogenesis during long-term follow-up and reveals indirect bypass development even in adult patients.