A CROSS-SECTIONAL STUDY OF SUPERIOR THYROID ARTERY IN HUMAN CADAVERS

Address for Correspondence: Dr. Komala N, Associate Professor, Department of Anatomy, Ramaiah Medical College, Bangalore – 560054, Karnataka, India. Contact No.: Mobile: 9480259177, E-Mail: komas2001@yahoo.com Introduction: The superior thyroid artery is one of the ventral branches arising from external carotid artery in the neck region but it may also arise from common carotid artery or at bifurcation of common carotid artery. It forms a major source of vascular supply to the thyroid gland along with inferior thyroid artery. The relation of the nerve to the artery and apex of lateral lobe of thyroid gland is extremely variable. Inadvertent ligation of external laryngeal nerve along with superior thyroid artery during thyroidectomy results in paralysis of cricothyroid muscle and produces dysphonia. Aims: To identify the variations in the site of origin, the level of origin, number and the length of the superior thyroid artery Materials and Methods: The present study is a cross-sectional study and was carried out in 80 embalmed specimens in Department of Anatomy at Ramaiah Medical College. The superior thyroid artery supplying the thyroid gland was meticulously dissected and digitally photographed. The parameters studied were site of origin, level of origin, number and the length of the artery from the origin to the entry of gland. The measurements were taken three times to avoid intraobserver variation and their mean value has been considered. Data so collected has been entered in a master chart in Microsoft® Excel and has been analyzed using the SPSS version 17.0. Results: In the present study, superior thyroid artery was single, arising predominantly from external carotid artery at the level of upper border of thyroid cartilage and main trunk measured 4.38±1.42 cm. Conclusion: Knowledge of the anatomical variations of superior thyroid artery with respect to its origin, level of origin and its relation to external laryngeal is important before attempting any interventional or surgical procedure in the neck region.


INTRODUCTION
vascular supply to the thyroid gland along with inferior thyroid artery.Thyroid gland is the largest endocrine gland and is responsible for the maintenance of basal metabolic rate of the body [1,2].The high vascularity of thyroid gland is equivalent to that of kidney and suprarenal gland and is 5 ml/gm/min under conditions of extreme stimulation [3].The superior thyroid artery courses towards the apex of lateral lobe of thyroid gland and is accompanied by the external branch of superior laryngeal nerve to which it is closely related.The relation of the nerve to the artery and apex of lateral lobe of thyroid gland is extremely variable.Inadvertent ligation of external laryngeal nerve along with superior thyroid artery during thyroidectomy results in paralysis of cricothyroid muscle and produces dysphonia [3].The superior thyroid artery divides into anterior and posterior divisions close to the apex.The anterior branches of both superior thyroid arteries anastomoses along the upper border of isthmus thereby establishing a collateral circulation route between the two external carotid arteries in cases of unilateral blockage of common carotid artery [4].
An indepth knowledge of the arterial variations is crucial to get bloodless fields for surgical procedures in the head and neck region like in radical neck dissection, thyroidectomy, carotid endarterectomy, catheterization, aneurysm reconstruction, interventional radiology, selective embolisation of thyroid, head and neck tumours [5].The superior thyroid artery is frequently used as a recipient vessel for microvascular free tissue transfer in head and neck surgery [6].The superior thyroid artery perforator flap exhibits reliable vascular anatomy and so is ideal in the reconstruction of a wide range of head and neck defects [7].AIM: To identify the variations in the number, length, site of origin and the level of origin of superior thyroid artery.
on variations in origin of superior thyroid artery' it was found that percentage of superior thyroid artery arising from ECA was 68%.Considering a relative precision of 15% and alpha error of 5%, sample size was estimated to be 80.The superior thyroid artery supplying the thyroid gland was meticulously dissected and digitally photographed.The measurements were taken three times to avoid intraobserver variation and their mean value has been considered.

MATERIALS AND METHODS
The present study is a cross-sectional study and was carried out in forty embalmed cadavers in Department of Anatomy at Ramaiah Medical College.Based on the previous studies conducted by Dr Pushpalatha [8] et al titled ' Study In the present study of 80 superior thyroid arteries with 40 right and 40 left arteries, it was observed that in 43(53.75%) it was arising from external carotid artery, in 12(15%) from bifurca-tion of common carotid artery and in 25(31.265%)from common carotid artery.On both right and left side, the first common site of origin is from external carotid artery, second common site is from common carotid artery and third common site is from the bifurcation of common carotid artery.The superior thyroid artery was arising at the level of upper border of thyroid cartilage in 13(16.25 %); below the level in 8(10 %) and above the level in 59(73.75%).On both right and left sides it was predominantly arising above the level followed by at the level and below the level of upper border of thyroid cartilage.In 79 specimens, the superior thyroid artery was single and only one specimen on the right side had double superior thyroid artery arising from external carotid artery as single trunk bifurcating at its origin.
The overall mean length of the superior thyroid artery was found to be 4.38±1.42cm with right being 4.48±1.53cm and left being 4.28±1.30cm.In the present study, superior thyroid artery origin from external carotid artery was observed in 53.75% which is similar to that reported in various studies [3,[8][9][10][11]12,[20][21][22][23][24][25] in the range of 30% to 100%.This is most common origin of superior thyroid artery.The superior thyroid artery origin from common carotid artery in the present study is 31.25% and similar in other studies [15,16,18,20,21] in a range of 1.51% to 52.3%.This is the second common position in present study.The superior thyroid artery origin from bifurcation of common carotid in the present study is 15% and similar in other studies [8,13,15,19,21] in a range of 1.5% to 49%.This is the third common position in present study.The superior thyroid artery origin was predominantly above the level of upper border of thyroid cartilage in present study (73.75%) and in various studies [8,22,23,25] who have reported in a range of 18.42% to 88.09% except in one study (18.42%)where it was least common level of origin.The second common level of origin in the present study is at the level of upper border of thyroid cartilage (16.25%) and in other studies [8,22,23,25] was found in a range of 11.90% to 36%.The third common level of superior thyroid artery origin was below the level of upper border of thyroid cartilage in present and two other studies [8,22] and in one study [17] it was the most common level.In two other studies [23,25] superior thyroid artery origin below the level of upper border of thyroid cartilage was absent.The overall mean length of the superior thyroid artery was found to be 4.38±1.42cm with right Veena Vidya Shankar, Komala N, Shailaja Shetty.A CROSS-SECTIONAL STUDY OF SUPERIOR THYROID ARTERY IN HUMAN CADAVERS.being 4.48±1.53cm and left being 4.28±1.30cm which is higher than that have been reported in two other studies [3,17].CONCLUSION

DISCUSSION
In the present study, superior thyroid artery was single, arising predominantly from external carotid artery at the level of upper border of thyroid cartilage and main trunk measured 4.38±1.42cm.Knowledge of the anatomical variations of superior thyroid artery with respect to its origin, level of origin and its relation to external laryngeal is important before attempting any interventional or surgical procedure in the neck region.

3 .
Data so collected has been entered in a master chart in Microsoft® Excel and has been analyzed using the SPSS version 17.0.Parameters studied: 1. Site of origin of superior thyroid arteryfrom external carotid artery, from bifurcation of common carotid artery or from common carotid artery 2. The level of origin of superior thyroid artery in relation to the upper border of thyroid cartilage -at the level or below the level or above the level of upper border of thyroid cartilage.Number of superior thyroid artery whether it is single or double.4. The length of main trunk of superior thyroid artery in centimeters was measured from its origin to the apex of lateral lobe of the thyroid gland.5.Statistical Methods: Descriptive statistics such as mean and standard deviation has been computed for different parameters.P value <0.05 has been considered as statistically significant.Data analysis was carried out using SPSS version 18.0.chicagoSPSS Inc.

Table 1 :
Site of origin of superior thyroid artery in cadavers.

Table 2 :
Level of origin of superior thyroid artery.At the level Below the level Above the level Total 80(100%) 13(16.25 %) 8(10 %) 59(73.75%)Level of origin in relation to upper border of thyroid cartilage Side n= 80

Table 3 :
Number of superior thyroid artery.

Table 4 :
Length of main trunk of superior thyroid artery.

Table 5 :
Comparison of origin of superior thyroid artery in percentages invarious studies.

Table 6 :
Comparison of level of origin of superior thyroid artery in percentages in various studies.

Table 7 :
Comparison of Mean Length of main trunk of superior thyroid artery on both sides in various studies.