A novel method of ultrasound-guided zygomaticotemporal nerve block for awake craniotomy
Article information
Dear Editor,
The zygomaticotemporal nerve is a peripheral branch of the maxillary nerve that innervates the skin of the temple region and is responsible for sensory perception [1]. Zygomaticotemporal nerve blocks are commonly used to treat migraines and to relieve pain [2] at the headpin site during awake craniotomy [2,3]. However, the blocking effect is somewhat unstable, with a relatively high failure rate [3]. Moreover, its proximity to the deep temporal artery raises concerns regarding accidental puncture [4]. Thus, we developed an ultrasound-guided zygomaticotemporal nerve block approach, in which a local anesthetic is injected into the deep temporal fascia. Written consent for this case report was obtained from the patients.
A 42-year-old male with a left frontal tumor was scheduled to undergo awake craniotomy. A zygomaticotemporal nerve block was performed before the induction of general anesthesia. The probe was placed parallel to the zygomatic arch, at the level of the zygomatic tubercle (Fig. 1A). A 25 gauge needle (Terumo Corporation, 25 mm regular bevel) was inserted parallel to the lateral part, where the temporal muscle, superficial temporal fascia, and deep temporal fascia were visible, and guided to the deep layer of the deep temporal fascia. A local anesthetic (0.375% ropivacaine, 3 ml) was administered, and spread of the drug in the form of a convex lens was confirmed (Fig. 1B).
(A) Probe position. The linear probe is placed parallel to the upper part of the zygomatic arch at the level of the zygomatic tubercle (ZT), with the needle inserted from the lateral side. (B) Ultrasound image. The needle is inserted from the outside using the parallel technique (yellow line), and a local anesthetic is administered to the deep layer of the deep temporal fascia in the lateral orbital bone. (C) After blocking, the cold test revealed decreased cold sensation in the zygomaticotemporal nerve block area (purple dotted line area). DLDTF: deep layer of the deep temporal fascia, DTFP: deep temporal fat pad, LA: local anesthetic agent, OB: orbital bone, SLDTF: superficial layer of the deep temporal fascia, TPF: temporoparietal fascia, Tm: temporal muscle.
A cold test was performed using an ice pack to confirm that the nerve block had taken effect [5]. The numerical rating scale (NRS) 10 was used to compare both sides of the face innervated by the zygomaticotemporal nerve. The blocked side showed a clear decrease in cold sensation (approximately 4 points on the NRS 10) compared to the unblocked side (Fig. 1C).
After induction of general anesthesia, a headpin was inserted into the same area; however, no increase in blood pressure or heart rate was observed at the time of insertion, and the patient did not complain of pain in the temple area during the awake phase.
Previous studies have described landmark zygomaticotemporal nerve blocks [2,4]. However, the failure rate of the landmark block method is relatively high (16.6%), and inadequate analgesia in the innervated area may be the cause of temporal pain during awake craniotomy [3]. Moreover, the deep temporal artery runs deep into the temporalis muscle, posing the risk of accidental puncture [4].
Ultrasound-guided zygomaticotemporal nerve blocks have been previously reported [2,4]. Mahajan et al. [2] reported a method in which the block is injected in the vicinity of a “honeycomb-like” nerve identified on echocardiography. However, the zygomaticotemporal nerve is thin and has many branches that are difficult to identify using ultrasonography. Thus, we recognized the challenges of using ultrasound guidance to directly observe and block the zygomaticotemporal nerve.
Previous anatomical findings have found that the zygomaticotemporal nerve penetrates the temporalis muscle from the zygomaticotemporal foramen, where it runs in the deep layer of the deep temporal fascia [1], and subsequently travels to the shallow layer, where it branches out into shallow branches. The deep temporal fascia is composed of a superficial and a deep layer. The space between the superficial and muscle layers is occupied by connective and adipose tissues [1,2]. The extramuscular branch of the zygomaticotemporal nerve exits the zygomaticotemporal foramen, travels between the temporalis muscle and the lateral orbital rim without entering the temporalis muscle, and ultimately pierces the temporal fascia [1].
Accordingly, to block the extramuscular branch of the zygomaticotemporal nerve, we propose a compartment block technique in which a local anesthetic is injected into the deep layer of the deep temporal fascia lateral to the orbit. This “intra-fascial method targeting the deep layer of the deep temporal fascia” is conducted as follows: with the patient in the lateral position, a probe is placed parallel to the lateral aspect of the zygomatic tubercle of the lateral orbit and upper part of the zygomatic arch to identify the superficial and deep layers of the deep temporal fascia above the temporalis muscle. Approximately 3–5 ml of local anesthetic is subsequently administered to the deep layer of the deep temporal fascia, lateral to the orbit.
Because the deep temporal artery does not run through this area, and the vasculature can be confirmed via ultrasound pre-scanning, the risk of accidentally puncturing a blood vessel is reduced. Therefore, this block method is a simple and safe procedure that may be more effective than traditional landmark blocks.
In another case, a local anesthetic was administered below the deep layer of the deep temporal fascia, between the deep temporal fat pad and temporalis muscle, relatively lateral to the orbital rim. However, the cold test showed little reduction in cold sensation (NRS 9), and the effect was limited to a relatively small area. Effective blockade of the zygomaticotemporal nerve region was thus not achieved (Supplementary Fig. 1). Therefore, we concluded that administering local anesthetic between the superficial and deep layers of the deep temporal fascia may be more effective.
In conclusion, our case proposes a new approach for an ultrasound-guided zygomaticotemporal nerve block near the deep temporal fascia, which may be more effective than traditional approaches. Further investigations are required to determine the efficacy of this method; in particular, cadaveric studies are needed to determine the extent to which local anesthetics spread during the ultrasound-guided zygomaticotemporal nerve block.
Notes
Funding: None.
Conflicts of Interest: No potential conflict of interest relevant to this article was reported.
Author Contributions: Takehito Sato (Conceptualization; Data curation; Methodology; Project administration; Writing – original draft); Masashi Takakura (Writing – review & editing); Kanako Ozeki (Writing – review & editing); Koichi Akiyama (Supervision; Writing – review & editing)
Supplementary Material
(A) Local anesthetic administered to the deep temporal fat pad (under the deep layer of the deep temporal fascia). The yellow arrowhead indicates the needle tip. (B) Cold sensation test revealing that cold sensation was reduced only in a small area of the dotted line of the dermatome (only the area where the local anesthetic was administered).