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Origin of thyroid arteries in a Kenyan population
Abstract
Introduction: The thyroid gland receives blood supply predominantly from paired superior and inferior thyroid arteries. The superior thyroid artery originates from external carotid while the inferior thyroid artery is a branch of thyrocervical trunk. Unusual origins of superior thyroid artery include common carotid and cervical part of internal carotid arteries while those for the inferior thyroid artery are subclavian, common carotid or the vertebral arteries. These origins vary between populations. Knowledge of variant anatomy of these arteries is important in surgical procedures within the neck. This study describes variant origin of the thyroid arteries in a Kenyan population.
Materials and Methods: Fifty formalin fixed cadavers from the Department of Human Anatomy, University of Nairobi were available for the study. Skin incisions were made from the chin to the supra-sternal notch, along the clavicle to the acromion and then to the mastoid process. Skin flaps and platysma muscle were refl ected for exposure of the anterior triangle of the neck. The sternocleidomastoid was cut close to its origins on the clavicle and reflected superiorly. The strap muscles were transected and reflected to expose the thyroid gland lying within the visceral fascia. The dissection field was cleaned by blunt and sharp dissection to expose the gland. The two thyroid arteries were identified from either pole of the gland and traced to their respective origins.
Data Analysis: Data was coded, tabulated and analysed using SPSS 16.0 for windows® (SPSS Inc., Chicago, Illinois) for percentages and frequencies of the observed variations in origin and nerve relations. Results were presented in tables and macrographs.
Results: Superior thyroid artery originated from external carotid and common carotid artery in 74.4% and 25.6 % of cases respectively. The right side displayed a higher frequency of origin from the common carotid artery. The inferior thyroid artery arose from thyrocervical trunk in 87.5% and from subclavian artery in 12.5% of cases. There was a higher incidence of the inferior thyroid artery originating from the subclavian on the left than the right side.
Conclusion: Over 25% of superior thyroid arteries and 11 % of inferior thyroid arteries show variant origins. The common carotid and subclavian arteries were the most frequent variant sites of origin for superior and inferior thyroid arteries respectively. Bilateral asymmetry was observed. Neck surgeons should be aware of these variations during ligation and selective embolisation of thyroid arteries to avoid complications during surgery.
Materials and Methods: Fifty formalin fixed cadavers from the Department of Human Anatomy, University of Nairobi were available for the study. Skin incisions were made from the chin to the supra-sternal notch, along the clavicle to the acromion and then to the mastoid process. Skin flaps and platysma muscle were refl ected for exposure of the anterior triangle of the neck. The sternocleidomastoid was cut close to its origins on the clavicle and reflected superiorly. The strap muscles were transected and reflected to expose the thyroid gland lying within the visceral fascia. The dissection field was cleaned by blunt and sharp dissection to expose the gland. The two thyroid arteries were identified from either pole of the gland and traced to their respective origins.
Data Analysis: Data was coded, tabulated and analysed using SPSS 16.0 for windows® (SPSS Inc., Chicago, Illinois) for percentages and frequencies of the observed variations in origin and nerve relations. Results were presented in tables and macrographs.
Results: Superior thyroid artery originated from external carotid and common carotid artery in 74.4% and 25.6 % of cases respectively. The right side displayed a higher frequency of origin from the common carotid artery. The inferior thyroid artery arose from thyrocervical trunk in 87.5% and from subclavian artery in 12.5% of cases. There was a higher incidence of the inferior thyroid artery originating from the subclavian on the left than the right side.
Conclusion: Over 25% of superior thyroid arteries and 11 % of inferior thyroid arteries show variant origins. The common carotid and subclavian arteries were the most frequent variant sites of origin for superior and inferior thyroid arteries respectively. Bilateral asymmetry was observed. Neck surgeons should be aware of these variations during ligation and selective embolisation of thyroid arteries to avoid complications during surgery.
