Ultrasound-Guided Mandibular Nerve Block in the Infratemporal Fossa for Awake Craniotomy: A Cadaveric Feasibility...

Awake craniotomies are an essential neurosurgical technique, allowing surgical intervention in adjacent areas while preserving eloquent brain areas such as Brodmann areas 1-4, Broca's area, and Wernicke's area. Central to the success of awake craniotomy is the provision of safe and effective analgesia throughout the procedure. The traditional scalp block for an awake craniotomy involves anatomical landmark localization of six nerves: supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, and greater and lesser occipital nerves. Employing adjunctive techniques via trigeminal nerve branch blocks can maximize nerve-impulse blockade in areas of interest during this procedure. To study a novel and potentially viable technique of local anesthesia administration to the mandibular branch of the trigeminal nerve (V3), we studied four adult cadaveric specimens preserved in 70% alcohol. Two out of four cadaveric specimens underwent bilateral infratemporal fossa (ITF) dissection to confirm the innervation of the temporal muscle and visualize the regional anatomy. The remaining two cadaveric specimens underwent dye injection (5 mL of methylene blue) within the target areas of the ITF. Injections were guided by a linear ultrasound probe, placed parallel to the zygomatic arch. Two fossae were injected in the interfascial plane of the superior and inferior heads of the lateral pterygoid muscle, while the other two fossae received injections between the periosteum of the infratemporal fossa and the fascia of the lateral pterygoid muscles. The correct injection site was confirmed by direct dye visualization after dissection of the infratemporal fossa. Our cadaveric study demonstrates a potential local distribution of anesthesia when the ultrasound-guided injection is placed below the zygoma, deep in the plane between the periosteum of the infratemporal fossa and the fascia of the lateral pterygoid muscles. Dissection of the ITF following dye injection demonstrated dye distribution at the level of the entrance of V3 at the foramen ovale. The use of ultrasound guidance allows for the administration of methylene blue dye within the ITF, reaching deep territories, including the V3 entrance. This novel technique offers a promising approach to improve scalp block for awake craniotomies by enabling anesthesia of V3 using ultrasound guidance. However, additional clinical studies are required to evaluate the efficacy and safety of this approach.