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This study aims to analyze the incidence of variations in the origin of the superior thyroid artery (STA) in Thai people and the vertical distances from the origin sites of the STA to the level of carotid bifurcation (CB).A total of 220 carotids were retrospectively investigated. The 110 carotid arteries and branches were examined in 55 embalmed cadavers. The 110 carotid angiographs based on 2D digital subtraction and 3D rotational angiography examinations from 55 patients were analyzed. The data from both investigations showed the origin of the STA from the external carotid artery (ECA) in 26.8%, including branches of the thyrolingual trunks in 1.4%, whereas its origin at the CB level and the common carotid artery (CCA) was found as high as 73.2% of the samples. Regarding the sides, the origin from the ECA was dominant on the right while that from the CCA predominated on the left. The average vertical distance from external carotid origin site of the STA to the CB level was 4.6±2.9 millimeters.The average vertical distance from common carotid origin site of the STA to the CB level was 6.1±5.5 millimeters. It is noted that the origin sites of the STA arose within a range of 10 millimeters above the CB to 10 millimeters below the CB level in 95.5% of the carotids investigated. The present study revealed a relatively high incidence of the STA arising from the CCA and CB level in Thai. The surgical approaches of the neck at/below the CB level should be performed with great care of these STA origins in order to avoid accidental injuries.
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