Classification of the extracranial middle meningeal artery: a human dry skull, dissection and 3D CTA study.

Unexpected treatment failures can occur during middle meningeal artery embolization (MMAE) in the treatment of chronic subdural hematoma cases. This study aimed to classify variations in the anatomy of the extracranial MMA (exMMA) to improve MMAE. Five heads from body donors, 300 dry skulls, and 162 head and neck CT angiography (CTA) images were used to evaluate the overall features of the exMMA. Body donors dissection were incorporated to comprehensive exMMA representation. The distal features of the exMMA were determined by evaluating the outer osseous grooves of the foramen spinosum of the skulls. Measurements of the exMMA were performed using CTA. The angles between the maxillary artery and the exMMA were 109.5° ± 32.5° (left) and 117.1° ± 34.3° (right) (p < 0.05). The angle between the exMMA and the skull base was greater on the left side (79.24° ± 4.21°, p = 0.0017). The diameters of the exMMA were 1.45 ± 0.12 mm (left) and 1.44 ± 0.13 mm (right) (p = 0.82). Multiple types of accessorial foramen spinosum provided the paths for the accessorial MMA. In the new classification, five types were identified. Type A was the most common (73.15%) and represented an easily accessible MMAE type. This was followed by type C (25.62%, difficult to accessible), type D (18.83%, very difficult to accessible), type B (1.23%, fairly accessible), and type E (0.17%, inaccessible). Varying levels of interventional difficulty occur within the exMMAs classification. Careful preoperative evaluations should be performed before MMAE to determine the type of exMMA and potential interventional difficulty.