Importance of superficial temporal artery protection
In recent years, superficial 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[184.108.40.206.16.17]. However, in moyamoya patients undergoing DSA cerebrovascular angiography, we often find that the superficial 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 superficial 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 superficial temporal artery injury during operation
The superficial temporal artery is easily damaged during the craniotomy. The main reasons for which are as follows: First, insufficient 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 superficial temporal artery. Most of the superficial 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 superficial 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 superficial temporal artery. Secondly, this could be due to the anatomical characteristics of the superficial temporal artery itself. The imaging study of the superficial temporal artery by multi-slice spiral CT revealed that the bifurcation and branches of the superficial 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 superficial 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 superficial 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 superficial 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 superficial temporal artery. The advantage being that it completely avoids the main trunk of the superficial 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 flap 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 flap 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.