Ultrasound-guided Maxillary Nerve Block: An Anatomical Cadaveric Study. Determination of Dispersion in Ultrasound-guided Suprazygomatic Maxillary Nerve Block in Cadavers.

The second division of the trigeminal nerve, the maxillary nerve (MN), exits the cranial region of the face via the foramen rotundum. From there, it travels laterally and forward through the pterygopalatine fossa, passes through the infra-orbital foramen at the bottom of the pterygomaxillary fossa, and ends up on the floor of the orbit. The MN is a purely sensory nerve that delivers innervation to the lower eyelid, upper lip, cheek, upper dental arch, maxillary sinus, hard and soft palate, posterior nasal cavity, and nasal ala. Effective anesthesia of the maxillary area can be achieved by surgeon's submucosal infiltration, witch appears to change the operative environment, or by inserting a needle in the pterygopalatine fossa (PPF). Although anesthetic infiltration around the mouth cavity or surgical site is simpler to execute than a selective nerve block, it might not be practical in some circumstances, such as when the surgical site is infected or inflamed. Therefore, the maxillary nerve block is preferred over local anesthetic infiltration when the surgical field covers the second third of the face and beyond the oral cavity, for example in maxillary osteotomy. The MN block can also be used for procedures of neurodestruction using neurolytic agents, for permitting anatomic differential neural blockade, and for the diagnostic evaluation of facial pain to determine whether pain is sympathetic or somatic in origin. However, the MN block can result in a number of problems, including as temporal blindness, hematoma formation, diplopia, temporary ophthalmoplegia and ptosis, penetration of the orbit, and brainstem anesthesia. Two approaches for maxillary nerve block in the pterigopalatina fossa have been described: infrazygomatic and suprazygomatic. Several risks associated with the infrazygomatic route of the maxillary block have been described, including the possibility of maxillary artery puncture and orbital or skull penetration. The suprazygomatic approach to maxillary nerve block has been shown to be safer for treating people with trigeminal neuralgia and for the anesthetic management of surgeries of the mid face. The amount of anesthetic injected into the pterygopalatine fossa for MN block is linked to certain issues, whereas other complications are related to the specific anatomical approach used. The typical volume of the PPF in adults has been reported from investigations in dry skulls as close to one ml. However, when executing this block clinically, two to five milliliters are usually injected. As a result, the excess amount of local anesthetic may move intracranially or into the orbit through the infratemporal fossa. Meanwhile, the location of this remaining volume has not been formally investigated.

Due to its many benefits, including safety profile, convenience of use, and low radiation exposure, the use of ultrasound guiding for regional anesthetic and pain mitigation has grown in popularity. Key anatomical features can be identified with its assistance, and by seeing the needle tip as it advances, it facilitates ideal needle insertion. The use of ultrasound pictures has been linked to a variety of superficial to deep nerve blocks in relation to head and neck blocks. Thus, the use of ultrasound for maxillary nerve block for clinical purpose is now mandatory. Although a safe and reliable suprazygomatic MN block technique has been validated providing satisfactory analgesia for midface surgery and chronic maxillofacial pain syndromes, where the remaining local anesthesia diffuses after filling the pterygopalatine fossa in maxillary nerve block has not been formally investigated.

Some authors suggest that with the injection of sufficient volume into the PPF during the maxillary nerve block, some remaining volume could diffuse to the pterygomandibular space, suggesting a communication between the two. And these data could justify the reported high analgesic power of the maxillary nerve block in maxillofacial surgery, which in addition to blocking the branches of the maxillary nerve itself located in the PPF, could also block branches of the mandibular nerve located in the pterygomandibular space. Therefore, randomized controlled trials are needed to determine in greater detail the dispersion of the injected volume outside the PPF when the maxillary nerve block is performed.

The goal of this anatomical study is to identify the extent of local anesthesia spreaded that might influence anesthetic coverage and blockrelated complications.