Application of Improved Incision in the Protection of Supercial Temporal Artery.

Objective: To explain the clinical importance of protecting the supercial temporal artery and introduce a method of protecting the supercial temporal artery. Methods: This study retrospectively analyzed the clinical data of 75 emergency patients undergoing frontotemporal craniotomy. The data was divided into traditional incision group and improved incision group according to the different surgical incision methods. Results: There were 38 cases in the traditional incision group, 13 of which had supercial temporal artery injury. Only 8 cases (21%) underwent the anatomical separation of supercial temporal artery during the operation. Whereas there were 37 cases in the improved incision group, with none showing supercial temporal artery injury. Conclusion: No strong consciousness of protecting the supercial temporal artery was shown in the clinical emergency surgery. The improved incision is a simple and easy way to protect the supercial temporal artery.


Introduction
The super cial temporal artery originates from the external carotid artery in the neck of the mandible. It passes through the parotid gland and going up and down to the subcutaneous and branching from the root of the zygomatic arch. It mainly includes the frontal and the parietal branch( Figure 1). It is commonly used to treat the artery that supplies blood in moyamoya disease and as a vascular pedicle to provide repair of fascial ap [1.2.6.8.12.14]. However, clinically no strong awareness has been shown to the protect the super cial temporal artery, and it can be easily injured and occluded in the emergency craniotomy. The relevant reports on protecting it are few [15]. This study we used an improved incision to replace the traditional incision to protect the super cial temporal artery, as summarized below.

Methods
Inclusion criteria: (1) emergency patients undergoing craniotomy; (2) rst operation. Exclusion criteria: (1) those with contusion, laceration, bleeding, and infection on the skin area to be operated; (2)  Image examination: All the patients underwent head CT examination before the operation. Head CTA examinations were performed on the patients with spontaneous cerebral hemorrhage without a history of hypertension. Among them, one patient was diagnosed with moyamoya disease by preoperative examination, three were diagnosed by CTA examination after operation, and four cases (12.5%) were con rmed by DSA examination.

Results
There were 38 cases with traditional incision, including 13 cases with super cial temporal artery injury.
Only 8 of these cases (21%) underwent intraoperative anatomical separation of the main trunk of the super cial temporal artery. Whereas there were 37 cases with improved incision and none had injury. As the improved incision completely avoided the proximal end of the trunk and branch of the super cial temporal artery, there was no need to dissect the super cial temporal artery during the operation. Also, there was no injury of the super cial temporal artery when the cutaneous muscle ap was separated.
This shows the obvious advantages in the protection of the super cial temporal artery. The patients in this group were followed up for 6 months. There was no super cial temporal artery occlusion and related complications in the improved incision group, while 13 cases had super cial temporal artery occlusion in the traditional incision group.

Discussion
Importance of super cial temporal artery protection In recent years, super cial temporal artery-middle cerebral artery anastomosis has been used in the treatment of moyamoya disease. This improves the blood supply in ischemic patients and reduces the rebleeding rate in hemorrhagic patients [3.5.9.11.16.17]. However, in moyamoya patients undergoing DSA cerebrovascular angiography, we often nd that the super cial temporal artery on one side is not visible.
A common reason for which is iatrogenic injury occurring during an earlier craniotomy, performed to clear the hematoma in bleeding. When the bypass criteria are met, the opportunity is lost due to the donor blood vessel. In this group of cases, up to 40% of them suffer from super cial temporal artery injury, and the proportion will be even higher because there are still operations not described in the record. Delayed hemorrhage, and temporalis swelling, and atrophy often happens clinically [4.7], however, they are overshadowed due to more serious clinical manifestations after head injury or cerebral hemorrhage. Therefore, they are not taken seriously.

Causes of super cial temporal artery injury during operation
The super cial temporal artery is easily damaged during the craniotomy. The main reasons for which are as follows: First, insu cient attention given by the surgeon. During the operation, the protection of deep brain tissue is mostly advocated, followed by the dura mater, and skull, thereby less attention is given to the scalp. In emergency surgery, to optimize rescue time, there are few people who dissect deliberately considering the protection of super cial temporal artery. Most of the super cial temporal artery is injured and occluded, and there are no obvious clinical consequences after the surgery, showing limited awareness of the surgeon to protect it. In this group, the rate of the cases, wherein the surgeons actively protected the super cial temporal artery was only 21%. In hospitals that cannot perform bypass surgery, there is a lack of understanding, and the rate may be even lower, indicating the lower awareness in protecting super cial temporal artery. Secondly, this could be due to the anatomical characteristics of the super cial temporal artery itself. The imaging study of the super cial temporal artery by multi-slice spiral CT revealed that the bifurcation and branches of the super cial temporal artery are complex and changeable in the upper and lower zygomatic arches (Figure 3) [10.13]. It is therefore not as constant as traditionally considered . Its backbone is mostly located on the zygomatic arch, and the distance between its position and the tragus varies from person to person. It is not reliable to protect the super cial temporal artery by empirically cutting the scalp 1 cm before the tragus. In an operation, the shape is often marked out on the body surface by touching the pulse. In some patients, the pulsation is not obvious. At such times, ultrasound and navigation can be used to assist positioning for protecting the super cial temporal artery. However, in emergency surgery or in primary hospitals, it has not been popularized yet.

Advantages and disadvantages of improved incision
To better protect the super cial temporal artery, there is no need to deliberately dissect and separate the blood vessel. According to the experience, we suggest of using an improved incision that starts behind the ear (Figure 4). In this study, those who used the improved incision were able to expose the key foramen, the root of the zygomatic arch and other important skull marks during the operation, and successfully complete the operation to achieve the purpose of decompression. Also, they ensured the integrity of the main trunk and main branches of the super cial temporal artery. The advantage being that it completely avoids the main trunk of the super cial temporal artery and the branches of the facial nerve during the incision of the scalp and also the incision of the root of the temporal muscle. This reduces the intraoperative bleeding and complications related to postoperative temporal muscle injury. It also fully exposes the temporal lobe and the posterior part of the middle skull base. Part of the incision is located behind the ear, which is preferable, than the traditional incisions in the appearance. However, its disadvantage is that it may erroneously enter the external auditory canal when the cutaneous muscle ap is separated, and the exposure of the front part of the middle cranial fossa is slightly limited. To overcome these shortcomings, we marked supramastoid crest when separating the cutaneous muscle ap to prevent it from erroneously entering the external auditory canal. On the exposure of the front part of the middle skull base, with the help of an assistant, the temporal muscle was peeled upwards. The surgeon removed the squamous part of the temporal bone and the base of the skull was fully decompressed.

Conclusion
The super cial temporal artery plays an important role in some of the patients, and the awareness of protecting it should be enhanced during the operation. The improved incision was a simple and easy way to protect the super cial temporal artery. At least the super cial temporal artery should be treated differently when using the traditional incision for craniotomy. Suspected patients with moyamoya disease should be well protected before surgery, and even if separation and cut-off are inevitable, this needs to be fully explained.

Declarations
Funding (This study was supported by the Young and Middle-aged subjects of Wannan medical college (WK2019F18)).
Con icts of interest (The authors have no nancial or other con icts of interest in relation to this research and its publication).
Availability of data and material (The data of this study are true and transparent)