Application of ultrasound guidance in the oral and maxillofacial nerve block

Intraoral approach

In the intraoral approach, both the ultrasound probe and the injection needle are placed in the mouth. Hannan et al. (1999) compared intraoral ultrasound-guided IANB to conventional techniques. When comparing the degree of anesthesia of the dental pulp in one side of the mandible, it was found that although the needle tip can be accurately placed around the nerve using ultrasound guidance, no significant difference was found in the success rate between the two techniques. The author also pointed out that the indicator of a successful block used in the study was “pulpal anesthesia”, which is different from the commonly used “lip and tongue numbness”. Also, in this study, the inferior alveolar nerve could not be located using ultrasound, so the position of the inferior alveolar artery was used to locate the nerve (Hannan et al., 1999). Chanpong et al. (2013) were able to identify the inferior alveolar nerve using a new type of hockey stick-shaped ultrasound probe placed at the patient’s pterygomandibular ligament. The average scanning time required to locate the left inferior alveolar nerve was only 19.6 s and the scanning time required to locate the right inferior alveolar nerve was 30.5 s. The subjects stated that the probe did not cause any significant discomfort. In addition, the author successfully performed IANB on cadavers using this method by injecting a dye in order to simulate the diffusion of anesthesia drugs around the nerve when performing this procedure (Chanpong et al., 2013).

In summary, there are several criteria to evaluate the success of traditional IANB, and accurately placing the needle around the nerve is not the only factor that affects anesthesia. Future studies addressing the safety of this method are needed as there are only a few studies (including basic research and clinical research) on the intraoral approach to ultrasound-guided inferior alveolar nerve blocks. It is too early to conclude that the introduction of ultrasound has any effect on the success rate of IANB in the intraoral approach. More studies are needed to explore whether ultrasound can guide this operation.

Extraoral approach

In the extraoral approach of ultrasound-guided inferior alveolar nerve (or mandibular nerve) blocks, the ultrasound probe and the puncture point are located outside of the mouth. The most common purpose behind the extraoral approach is to inject the anesthetic drugs into the pterygomandibular space. The relative positions of the ultrasound probe and the needle tip, and the correct recognition of the anatomical structures from the ultrasound images are important for this procedure. Kumita et al. reported a type of extraoral approach to performing an ultrasound-guided maxillary and inferior alveolar nerve block to induce analgesia after orthognathic surgery. In this method, the ultrasound probe was placed caudad to the zygomatic arch to observe the maxillary artery in the pterygomandibular space. The selected injection site was just around the maxillary artery to help the anesthetic drug infiltrate the inferior alveolar nerve. This study also used the position of the maxillary artery to locate the nerve in the ultrasound images (Kumita, Murouchi & Arakawa, 2017). Using the same method, Kojima et al. (2020) performed ultrasound-guided extraoral approach IANB in patients having drug-related osteonecrosis and undergoing mandibular resection under general anesthesia. The after-surgery analgesic effect was better in the experimental group compared to the control group of patients who did not receive IANB, and the total amount of opioids used in the experimental group was significantly less than the amount used by patients in the control group (Kojima et al., 2020). The above studies showed that ultrasound-guided injection of local anesthetics into the pterygomandibular space can achieve satisfactory results in inferior alveolar nerve (and mandibular nerve) blocks. As an alternative to injecting the anesthetic drugs into the pterygomandibular space, Kampitak, Tansatit & Shibata (2018b) performed a new ultrasound-guided selective mandibular nerve block in cadavers, called the lateral pterygoid plate approach, where the drugs were injected into the base of the skull. During the surgery, the cadaver’s mouth was wide open, the posterior and superior edges of the lateral pterygoid plate were identified using ultrasound, and the adjacent mandibular nerve and its branches were successfully stained by injecting a dye, indicating that a successful nerve block can be performed in the same way (Kampitak, Tansatit & Shibata, 2018b). Tsuchiya et al. (2019) also used a similar approach, in which the lateral pterygoid plate was used as a landmark. In ten cases of parotidectomy, low-molecular weight dextran and local anesthetics were used to block the mandibular nerve under ultrasound guidance, successfully reducing the involuntary movement of the muscles due to surgical stimulation during operation, thus reducing the need for general anesthesia (Tsuchiya et al., 2019).

In summary, there are relatively more studies on the extraoral approach of ultrasound-guided alveolar nerve (or mandibular nerve) blocks compared to intraoral approach. In some variations of the extraoral approach of the mandibular nerve or IANB, patients do not need to open their mouths. Since there are some patients who require a mandibular nerve or IANB that cannot open their mouths due to trauma or pain, the extraoral approach of the alveolar nerve (or mandibular nerve) block is sometimes necessary. However, in the extraoral approach, because the needle goes deeper and the adjacent structures are more complex, the ultrasound can better guide the needle. Jain et al. performed closed-mouth high-position mandibular nerve blocks known as the Vazirani-Akinosi method (Prabhu Nakkeeran et al., 2019) and extraoral ultrasound-guided mandibular nerve blocks in patients with pain and trismus due to fracture or acute pain, before administering general anesthesia. To check for differences between these two block methods, the visual analogue scale (VAS) pain scores and the degree of relief from trismus before and after the block for each patient was compared. The results suggest that ultrasound can help accurately locate nerves and blood vessels anterior to the condyle and assist with injecting anesthetics into the correct location. The ultrasound-guided group of patients required fewer anesthetic drugs, had fewer adverse reactions, and showed better anesthetic effects and higher success rates of block (Jain et al., 2016). The comparison of the different extraoral approaches of IANB is shown in Table 1 and Fig. 4.

Supra-zygomatic approach

Sola et al. (2012) and Chiono et al. (2014) performed bilateral maxillary nerve blocks using ultrasound guidance and the supra-zygomatic approach for pain management in infants who underwent cleft palate repair surgery. In ultrasound images, anatomical structures in the pterygopalatine fossa and needle tip positions could be clearly distinguished in real-time images. The anesthetic drug was injected into the pterygopalatine fossa using ultrasound guidance, and the surgeons could control the spread of the anesthetic over time. The arterial pulsation could also be monitored to help avoid the risk of vascular puncture. Although the maxillary nerve could not be directly identified using ultrasound images, the success rate and safety of the maxillary nerve block in this study were both improved. After the surgery, all patients with a maxillary nerve block had better pain management and used fewer analgesic drugs (Chiono et al., 2014; Sola et al., 2012). Another study performed maxillary nerve blocks during maxillary osteotomy operations in adult patients using supra-zygomatic approach and determined that this method was safer as it avoids the risk of penetrating the orbital contents through the infraorbital fissure (Bouzinac et al., 2014). Echaniz et al. used this method to conduct a study on cadavers to identify the anesthetic drug dose required for a maxillary nerve block. The results showed that only 1 mL of liquid was needed to cover the nerve surface (Echaniz et al., 2019). In the study by Kumita, Murouchi & Arakawa (2017) a maxillary nerve block was performed right after a mandibular nerve block, and the pterygoid fossa could be observed by adjusting the position of the probe. In this study, the insertion point was located at the angle formed by the superior edge of the zygomatic arch and the posterior orbital rim, and the injection site was at the lateral pterygoid plate. The authors pointed out that using ultrasound-guided maxillary and inferior alveolar nerve blocks at the same time significantly improved the effectiveness of perioperative analgesia during gnathoplasty (Kumita, Murouchi & Arakawa, 2017).

Infra-zygomatic approach

The supra-zygomatic approach mentioned above is considered a safer approach by many scholars, but normally it can only be performed using out-of-plane techniques, which are difficult. Moreover, due to the occlusion of the zygomatic arch, there is a period when the needle is seemingly invisible in the ultrasound and the surgeons have to rely on their experience (Anugerah, Nguyen & Nader, 2020). So, there are infra-zygomatic approach which can solve these problems.

(Kampitak, Tansatit & Shibata, 2018a) introduced a kind of ultrasound-guided maxillary nerve block using the infra-zygomatic approach in cadavers, using ultrasound images of the posterior edge of the maxilla and the lateral pterygoid plate as landmarks. In this study, while the mouth of the cadaver was wide open, the injection needle could approach the pterygopalatine fossa through the front edge of the lateral pterygoid plate. This method successfully simulated the block of the maxillary nerve, pterygopalatine ganglion, greater and lesser palatine nerves, and middle and posterior superior alveolar nerves by injecting a dye in place of an analgesic to see how the analgesic would spread in the nerves (Kampitak, Tansatit & Shibata, 2018a). The authors claimed that after administering general anesthesia, the degree of opening of the mouth could be increased (Kampitak & Shibata, 2019). In the infra-zygomatic approach, there are two ways for the needle to enter: the anterior and posterior approaches. Alfaro-de la Torre et al. (2019) compared these two approaches and found that the anterior approach, in which the needle goes front-to-back, can effectively avoid damage to important structures like the facial nerve, parotid gland, and maxillary artery. However, the anterior approach is more difficult to perform. In addition to the two approaches described above, (Takahashi & Suzuki, 2017) reported a novel infra-zygomatic approach, in which the needle passes from in front of the coronoid process. In this paper, this review refer to this method as “the coronoid approach”. The main advantages of this novel method are that the path of the needle is far away from the main blood vessels, and the needle would not advance to the pterygopalatine fossa but instead to the infratemporal crest, which is safer. The mandibular nerve can also be blocked at the same time by tilting the ultrasound probe slightly posteriorly and advancing the needle vertically. Patient discomfort could also be reduced since this method can be performed while the patient’s mouth is closed (Takahashi & Suzuki, 2017; Takahashi & Suzuki, 2018). Chang et al. (2017) and Ying & Du (2017) introduced another version of the infra-zygomatic approach where the needle goes between the coracoid process and the maxilla and easily passes through the fissura pterygomaxillaris to reach the pterygopalatine fossa, effectively avoiding the bone structures.

There are several studies on ultrasound-guided maxillary nerve blocks, but there is still no consensus on which method is better. The comparison of the different approaches to ultrasound-guided maxillary nerve blocking is shown in Table 2 and Fig. 5.