|Year : 2021 | Volume
| Issue : 4 | Page : 251-254
Cadaveric study on variations in the source and level of origin of superior thyroid artery
BY Shyamala1, B Akhilandeswari2
1 Department of Anatomy, ESIC PGIMSR Bangalore, Bengaluru, Karnataka, India
2 Department of Anatomy, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India, India
|Date of Submission||22-Nov-2019|
|Date of Acceptance||12-Oct-2020|
|Date of Web Publication||21-Dec-2021|
Dr. B Y Shyamala
House No 1670, BDA Houses, Austin town, Bengaluru - 560 047, Karnataka
Source of Support: None, Conflict of Interest: None
Introduction: Superior thyroid artery (STA) is one of the branches of the external carotid artery (ECA) which supplies the upper larynx, neck, and thyroid gland. The anatomic features of this artery and its relation to neighboring bony landmarks are important in surgical approaches. The primary objective is to find the source of origin of STA. Secondary objective is to find the level of origin of STA with reference to the origin of ECA and midpoint of the upper border of the thyroid cartilage. Material and Methods: The present study was carried out on 60 hemi necks obtained from human adult cadavers from Anatomy Department, Bangalore Medical College, Bangalore, Karnataka. The dissection was carried out according to instructions of Cunningham's practical manual. The origin and branching pattern of the STA were noted and measured. Results: The STA arose from the common carotid artery in 5% (3) cases and from the ECA in 95% (57). Among the 95% cases, 46.7% (28) arose at the origin of ECA, and in 1.7% (1) case, STA arose as a common trunk with lingual and facial arteries. The mean distance between the point of origin of STA and the point of origin of ECA is 5.4 ± 5.3 mm. The mean distance between the point of origin of STA and superior border of thyroid cartilage is 40 ± 7.6 mm. Discussion and Conclusion: The origin of STA from carotid bifurcation ranged from 1 to 25 mm. Most studies show equal incidence of origin of STA from ECA and carotid bifurcations.
Keywords: Cadaveric study superior thyroid artery, thyrolinguofacial trunk, variant origin
|How to cite this article:|
Shyamala B Y, Akhilandeswari B. Cadaveric study on variations in the source and level of origin of superior thyroid artery. J Anat Soc India 2021;70:251-4
|How to cite this URL:|
Shyamala B Y, Akhilandeswari B. Cadaveric study on variations in the source and level of origin of superior thyroid artery. J Anat Soc India [serial online] 2021 [cited 2022 Jan 21];70:251-4. Available from: https://www.jasi.org.in/text.asp?2021/70/4/251/333191
| Introduction|| |
Superior thyroid artery (STA) usually arises from the front of external carotid artery (ECA). The STA is the dominant arterial supply of the thyroid gland, upper larynx, and the neck region.,
Every surgery was planned based on the anatomical arrangement of the structures. The knowledge of variations in the source of origin of the STA is important for surgical procedures such as cricothyroidotomy, radical neck dissection, and catheterization. Any variation in the arterial arrangement may lead to hemorrhagic complications during the intraoperative period. Various studies in recent years have found a lot of variations in the source of origin of STA.,,
The distance of the point of origin of STA from the thyroid cartilage also helps the surgeons to locate the vessel during surgery. Knowledge of variations in the origin of STA will be helpful to minimize the risk of complications.
| Materials and Methods|| |
The present study was carried out on 60 hemi necks obtained from human adult cadavers from the Department of Anatomy, Bangalore Medical College and Research Institute, Bangalore, Karnataka. The study was done over a period of 3 years. The bodies which are given to the students for dissection (10 bodies per year) and also the preserved specimens were used for the study. Adult cadavers of both sexes were used in the study. The specimens in which the carotid artery was damaged while doing embalming were excluded. Cadavers with very short neck and any gross abnormality were excluded.
Careful dissection was done in the anterior triangle of neck. The carotid sheath is cut to expose carotid bifurcation and the course of ECA. Origin of STA and its branches were traced by fine dissection. The distances were measured using rulers.
The data of STA origin, the distance between the origin of STA and the bifurcation of common carotid artery (CCA) and the distance between the origin of STA and midpoint of superior border of the thyroid cartilage, were noted and tabulated.
The following classification by Vazquez et al. was used to record data regarding origin of STA. The schematic representation is shown in [Figure 1].
|Figure 1: Schematic representation of Vazquez classification in the right carotid artery|
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- Type one-origin from the carotid bifurcation
- Type two-origin from CCA
- Type three-origin from ECA
- Type four a – thyrolingual trunks
- Type four b – thyrolinguofacial trunks.
| Results|| |
Source of origin of STA
The present study comprised of 60 STAs, out of which 33 were right and 27 were left. The result of the study is shown in [Table 1], [Figure 2] and [Figure 3]. In a few cases, the origin of STA from CCA is bilateral. In cases where origin of STA from CCA is unilateral, the STA from the other side took origin from ECA very close (≤5 mm) to CCA bifurcation. We also found that variations on the left side are more common.
|Table 1: The source and type of origin of superior thyroid artery in the present study|
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|Figure 2: The right superior thyroid artery taking origin from external carotid artery|
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|Figure 3: Left superior thyroid artery arising from thyrolinguofacial trunk|
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In our study, 41 specimens were from males and 19 from females. Variations among males and females are shown in [Table 2]. The origin of STA from carotid bifurcation is more common in females.
|Table 2: The difference in origin of superior thyroid artery in males and females|
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The level of origin of superior thyroid artery
The minimum distance between the point of origin of STA and the point of origin of ECA is one mm with a maximum of 25 mm. The mean of the distance is 5.4 mm with standard deviation (SD) of 5.3 mm.
The minimum distance between the point of origin of STA and the superior border of thyroid cartilage is 30 mm, maximum distance is 70 mm, so the mean distance is 45.9 mm with a SD of 7.6 mm.
We also noted in two of the cases, the superior laryngeal artery arose directly from the ECA rather than from STA [Figure 4].
|Figure 4: The right superior thyroid artery arising from carotid bifurcation and SLA taking origin from external carotid artery|
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| Discussion|| |
Origin of superior thyroid artery
The following variations of STA were mentioned in Bergmann's anatomy atlases. An unusually large STA may replace the contralateral vessel or the inferior thyroid artery on the same side. It arose from the CCA in 18% of cases, at the point of division of the CCA in 36%, or from the ECA in 36% of cases. The origin of STA from ECA and at CCA bifurcation shows an equal percentage which is same as our study. Hollinshed quoted Daseler and Anson who found the STA originating from the carotid at or below the CCA bifurcation in 45% of 180 sides.
Above are the variations noted in standard website and textbook, many studies done on various populations show variable results. In a study on 40 ECAs from human fetuses, it was determined that the STA originated from the carotid bifurcation in 70% (15 male–13 female) and the CCA in 5% (two female). The thyrolingual trunk was determined at a ratio of 2.5% (one female) on the left side. The thyrolinguofacial trunk was determined at a ratio of 2.5% (one male) on the right side (Zumre et al.) In a study on 95 cadavers, four cases show that the STA was arising from CCA, and in one of the cases, STA was absent (Anu et al.)
In another study done in Saudi Arabia by Al-Rafiah et al. on 60 cadavers, the STA originated in 46 cases (76.7%) from the ECA at the level of the bifurcation. In two (3.3%) cases, it originated from the ECA above the level of the bifurcation. In one (1.7%) case, it arose from a thyrolinguofacial trunk. In a study by Sanjeev et al., the STA was found to arise from the ECA in 64.86% (24/37) of the cases, and in 35.14% (13/37) of the cases, it was found to arise from the CCA. The STA arose most frequently as a separate branch from the ECA and in only one case, the thyrolingual trunk (2.7%) was noted.
Another study done in the United Kingdom by Vazquez et al. classified the source of origin into four types. The most frequent were type I, 49% from the carotid bifurcation (102/207), 26.6% originated from CCA (55/207), only 23% took origin from ECA (49/207). The results vary from standard anatomy textbooks. Kapre et al. did a study on the variations in the branching pattern of ECA in 21 cadavers. They found thyrolingual trunk in 9.5% (2/21) cases.
In another study on 46 cadavers from Kenyan population, they classified their results based on Vazquez types. STA origin is 2.2%, 10.9%, 80.4%, and 6.5% from type one, two, three, and four, respectively.
In a cadaveric study by Gupta and Agarwal on 60 hemi necks, one case of thyrolinguofacial trunk was found on the left side (3.3%).
Case reports from other studies also show variations in the origin of STA.,,
[Table 3] shows the comparison of the present study with earlier studies.
|Table 3: Comparison in the source of origin of superior thyroid artery found in the present study with earlier studies|
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Level of origin of superior thyroid artery
A study by Lucev et al. on 40 STA found the distance of origin from the bifurcation ranged from 2 to 10.5 mm when it arose from the ECA. The distance of origin from the CCA to the bifurcation also ranged from 2 to 10.7 mm.
In another study done by Ozgur et al., the distance from the origin of the STA to the carotid bifurcation was 3.29 ± 4.27 mm, the distance from the origin of the STA to that of the lingual artery and facial artery was 10.45 ± 5.16 mm and 18.20 ± 8.81 mm, respectively. No differences were observed in the right–left side comparison of the data about the STA at a significance level of P ≥ 0.01.
In another study done in Saudi Arabia by Al-Rafiah et al., the distance of the origin from the bifurcation was from 0.9 to 1.1 cm. In 11 (18.3%) cases, it originated from the CCA. The distance of the origin from the bifurcation was from point four to one.
A study by Sung-Yoon Won measured that the distance of origin of the STA from the ECA was 0.9 ± 0.4 mm below the hyoid bone. The STA was 4.4 ± 0.5 mm distal to the midline at the level of the laryngeal prominence of the thyroid cartilage and 3.1 ± 0.6 mm distal to the midline at the level of the inferior border of the thyroid cartilage. Sanjeev et al. also found that the STA origin was 5 to 16 mm above the carotid bifurcation.
In our study, the origin of STA from carotid bifurcation ranged from 1 to 25 mm which shows not many variations from other studies. We also measured the distance between laryngeal prominence in the midline to STA origin, which ranged between 45.9 ± 7.5 mm which is comparable to the study above.
| Conclusion|| |
Standard textbook descriptions of origin of STA from ECA should be reconsidered, as most of the studies shows near equal incidence of origin of STA from ECA and carotid bifurcations. Even variations between male and female and sides also should be kept in mind. Variations like origin from CCA as a common trunk with other anterior branches of ECA should be kept in mind while doing surgeries in neck region to minimize risk of bleeding. However, large scale study is needed for better reliability of most common variations.
Financial support and sponsorship
This study was financially supported by the Bangalore Medical College and Research Institute, Anatomy Department.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]