Anatomy of the bony canal containing the middle meningeal artery for a vessel-sparing craniotomy in moyamoya disease

OBJECTIVE: The middle meningeal artery (MMA) often traverses a bony canal, rendering it vulnerable during craniotomy. In moyamoya disease (MMD), it serves as a collateral pathway for cerebral perfusion, making vessel preservation essential during bypass surgery. This study examined the anatomy of MMA bony canals in dry skulls and compared findings in patients with MMD and atherosclerotic cerebrovascular disease (ACVD). METHODS: A total of 175 adult and pediatric dry skulls and cranial CT scans of MMD (n = 100) and ACVD (n = 100) patients were analyzed retrospectively. The relationship of bony canals to the convergence of the coronal, sphenofrontal, and sphenoparietal sutures, serving as an anatomical landmark, was assessed. RESULTS: Bony canals containing the frontal MMA branch were present in 91.2% of adult skulls (≥ 18 years). Before fontanelle closure (< 2 years), the incidence was 1.8%, increasing to 47.7% in skulls ≥ 2 years (p < 0.0001). The mean canal length was 12.0 ± 5.9 mm in adult skulls, 10.1 ± 4.5 mm in skulls ≥ 2 years, and 7.5 ± 3.5 mm in skulls < 2 years (p = 0.212). In adult skulls, the mean distances of the canal entry and exit points posterior to the landmark were 11.6 ± 4.8 mm and 13.8 ± 6.4 mm, respectively. Parietal branch canals were rare (≤ 12.9%) and typically located below the squamous suture. Clinically, MMD patients were younger than ACVD patients (41.6 ± 12.2 vs 55.0 ± 11.6 years, p < 0.0001) and had a similar prevalence of frontal branch canals (80.0% vs 84.0%, p = 0.36). Bony canals were longer (15.9 ± 9.7 mm vs 13.3 ± 6.2 mm, p = 0.02) and wider (1.6 ± 0.4 mm vs 1.3 ± 0.5 mm, p < 0.0001) in MMD patients. CONCLUSIONS: After fontanelle closure, the likelihood of the MMA traversing a bony canal located within one thumb's width posterior to the pterion increases with age. Comprehensive knowledge of MMA anatomy is crucial for its preservation during bypass surgery.