From Where Does the STA Originate, and What is the Relationship Between the STA Origin and the Surrounding Tissue?
Patterns for the origin of the carotid artery branches have been known to be widely varied, although the embryological development of the ECA and the internal carotid artery (ICA) is complex, and the developmental mechanisms are unclear. The STA is generally the first ECA branch. However, the origin of the STA has long been discussed, and the authors often encounter patients with an STA that originates from the CCA. Previous studies have reported that the STA originated from CB in 23% to 70% of patients and from the CCA in 1.5% to 47.5% of patients.[1–6] This varied frequency is caused by the CB definition; many researchers defined the CB from the initial widening level of the vessel to the containing angle between the ICA and ECA, and some defined this area as the ECA or CCA.[1,3] The CB level was reported at the body of the hyoid bone, superior border of the thyroid cartilage, the tip of the greater horn of the hyoid bone, and body of the thyroid cartilage in 40, 39, 15, and 6% of patients, respectively. The higher the CB level, the more likely it was that the STA originated from the CCA within 1 cm proximal to the CB.[4,5]
What are the Variations in the Branching Patterns of the FA, LA, and STA?
Few reports have summarized the branching positions of FA, LA, and STA. Natsis et al used 100 cadaveric carotid arteries to classify these 3 branches and reported each of their frequency; in Type I no common trunks are present and in Type II the common trunk is always observed. The origin of the STA is described as ECA, CB, or CCA after type, and the branches forming a trunk are described using their initial letters, ie, thyrolingual (TL), linguofacial (LF), and thyrolinguofacial (TLF; Figure 4).
What is the Frequency of the Branching Pattern for 3 Anterior Branches in This Case?
In this case, the STA originated from the CCA, and the FA and LA formed the common trunk. The frequency of this branching pattern was 1% according to Natsis et al. Two (6.5%) of the patients had a similar branching pattern in Takemura et al's report, which observed 31 carotid arteries. Ozgur et al observed 40 carotid arteries and found no cases similar to the pattern of this branch (Table 1). In this case, the result is similar to these previous reports, demonstrating that the CB was located at the greater horn of the hyoid bone at a high level, and that the STA originated from the CCA. However, the STA originating from the CCA was 2.6 cm proximal to the CB, which was far more proximal than in previous reports, and the FA and LA forming the common trunks rarely occur simultaneously.
How was the STA Chosen for the Recipient Artery?
The authors considered the LF trunk or STA as an anastomotic artery other than the ECA. With regard to the LF trunk, the pedicle may be compressed by the digastric muscle when returning the head to the front, if the LF trunk was anastomosed to the superficial layer of the digastric muscle retracted to the cranial side. Anastomosis to the LF trunk was considered via the back surface of the digastric muscle, which requires dissection of the LF trunk more distally and takes more time due to the presence of the mandible. With regard to the STA, the authors could not identify the STA originating from the carotid artery, although the ECA was dissected to the CCA as much as possible in the operative field. This occurred because the CCA was dissected for the limited area after the level I–III neck lymph node dissection, and the STA was not predicted to originate from the CCA, which was 2.6 cm proximal to the CB. The authors anastomosed the ECA and radial artery from side to end in the operative field based on the assessment that anastomosis to the ECA could make the flap ischemia time shorter than detection of the STA by dissecting the CCA further. The flap ischemic time may not have changed significantly when anastomosing the STA given the distance from the CB to the point of STA origin preoperatively, because it might originate from the CCA slightly proximal to the operative field.
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