Study of Thyro-Lingual Trunk and its Clinical Relevance

Abstract

Every surgery is planned on the anatomical arrangement of the structures. Any variation in the arterial arrangement may lead to haemorrhagic episodes during intraoperative procedures. In this study, variations in the branching pattern of external carotid artery were noted. In two of the cases, thyrolingual trunk was observed. In the first case, thyrolingual trunk was arising from the common carotid artery, 17 mm below carotid bifurcation and in the second one at the carotid bifurcation. The knowledge of anatomical variation is necessary during intra-arterial chemotherapy and to prevent haemorrhagic accidents during intraoperative procedures.

Introduction

Superior thyroid artery is the first anterior branch from external carotid artery arising just below the level of greater cornu of hyoid bone [1]. It sweeps downwards and medially towards the superior pole of thyroid gland. Superior thyroid artery supplies the major portion of thyroid gland. Lingual artery branches off anteromedially from the external carotid artery in the carotid triangle. Depending upon the level of origin of lingual artery, it may run almost straightforward at the level of upper border of greater cornu of hyoid bone or may run upwards above this level and then curves downwards and forwards again, or simply curves downwards and forwards towards the tongue [2]. It is related deep to the hyoglossus muscle which separates it from the hypoglossal nerve. The superior thyroid, lingual and facial arteries may have common origin [3–5].

The study was undertaken to explore the variable branching pattern of carotid arterial system and its clinical implications. Variations in the branches of external carotid artery is a well-known fact. Therefore, the knowledge of variations is important to the surgeon while approaching for ligation of arteries and neck dissections.

Materials and Methods

Neck dissection was performed in 21 formalin-preserved cadavers at the department of anatomy, People’s College Of Medical Sciences And Research Centre, Bhopal, India. Carotid arterial systems were explored by incising the carotid sheath, and variability in branching pattern was noted.

Observations

During routine dissection, common carotid, external carotid and internal carotid arteries were explored to see the possible arterial variations. We observed that the superior thyroid artery was arising in common with the lingual artery, i.e. thyrolingual trunk. Thyrolingual trunks were observed in two out of 21 cadavers. The incidence of TL trunk was found to be 9.5% (2/21). In both the cases, TL trunk was observed unilaterally on right side. Thyrolingual trunks were seen directly arising from common carotid artery and at the carotid bifurcation.

Case 1: Unilateral presence of TL trunk was observed in a 74-year-old male cadaver on right side. Thyrolingual trunk was directly arising from common carotid artery about 17 mm below the carotid bifurcation. Common trunk first runs upwards and medially, dividing into lingual and superior thyroid arteries (Fig. 1). Lingual artery runs obliquely upwards and medially to reach the posterior border of hyoglossus muscle, and superior thyroid artery runs towards the superior pole of thyroid gland.

Fig. 1.

Photograph showing thyrolingual trunk arising from the common carotid artery. CCA Common carotid artery, TL Thyrolingual trunk, STA Superior thyroid artery, CB Carotid bifurcation

Case 2: Thyrolingual trunk was arising anteromedially, at the bifurcation of the common carotid artery on the right side (Fig. 2) in a 67-year-old male cadaver. Lingual artery sharply turns straight upwards, and superior thyroid artery runs obliquely downwards and medially to reach at the superior pole of lobe of thyroid gland.

Fig. 2.

Photograph showing thyrolingual trunk at carotid bifurcation. TL Thyrolingual trunk, STA Superior thyroid artery, CB Carotid bifurcation

In both the cases, the branching patterns of common carotid artery and external carotid artery were normal on the left side.

Discussion

Beyond the rare origin of thyroidea ima artery from common carotid artery, no branches are given off from the common carotid artery, except the terminal branches [2]. In the neck, common carotid artery bifurcates into external carotid artery and internal carotid artery at the level of superior border of thyroid cartilage in the carotid triangle [1]. External carotid artery branches off giving eight branches which supply mainly the scalp, face and neck region. Few branches arise with a common trunk, i.e. linguo-facial trunk or thyrolingual trunk or thyrolinguofacial trunk [1, 5]. The frequency of origin of lingual artery in common with superior thyroid artery is less than with the facial artery [1].

Thyrolingual trunk may arise from external carotid artery or from common carotid artery. The frequency of origin of thyrolingual trunk from external carotid artery has been reported in most cases [6, 7] than from common carotid artery in which it has been reported in less than 0.1% of cases [7]. In the present study two thyrolingual trunks were seen, one originating from the common carotid artery and the other at carotid bifurcation.

Ergür and İçke, [8] in 2004 reported thyrolingual trunk arising from the left common carotid artery, 7.6 mm from the carotid bifurcation. Babu [9] described that the thyrolingual trunk originating from the right common carotid artery, arising 2 cm below the carotid bifurcation in one case during the dissection of 200 cadavers. Lemaire et al. [10] reported a case with the thyrolingual trunk, originating from the common carotid artery on the right side, 30 mm below the carotid bifurcation. In this study, the thyrolingual trunk originates 17 mm below carotid bifurcation in the first case and in the second case originates at the carotid bifurcation.

The knowledge of such arterial variation is useful during intra-arterial chemotherapy for the treatment of tongue cancers, musculomucosal island flap for partial tongue reconstruction, superselective intraarterial chemotherapy for head and neck carcinomas, these variations should be kept in mind [5, 8, 12–14]. Zumre et al. [5] observed thyrolingual trunk in 2.5% and thyrolinguofacial trunk in 2.5% of the cases in human foetuses. Ergür Kİ and İçke Ç, [8] reported the frequency as 3.57%. In the present case, the thyrolingual trunk was observed with a frequency of 9.5% (2/21). Van den Berg et al. [15] observed thyrolingual and thyrolinguofacial trunks in cases of paragangliomas during MR angiography. All possible arterial variations in the neck should be taken into consideration, as these may increase the risk of haemorrhagic accidents during surgery and also be responsible for angiographic misinterpretation [16].

Although infrequently surgeons consider ligation of external carotid artery as a means of controlling haemorrhage, either traumatic or operative. In such situation, surgical dictate for ligating the external carotid artery is to demonstrate a branch and for ligating above the demonstrated branch which is usually the STA. However, the disaster may befall upon the patient, should he have such anomalous TL trunk which originates at the bifurcation of common carotid artery.

Conclusion

Anatomical knowledge is the cornerstone of surgery. Thyrolingual trunk is a rare arterial variation in the neck, increasing the risk of vascular accidents during surgery. Rarity of condition may lead to misinterpretation during MR angiographic study. Knowledge of these variations is also essential during intra-arterial chemotherapy.

We strongly recommend that it is not just sufficient to demonstrate the branch but also demonstrate the carotid bifurcation before the surgeon undertakes the ligation of ECA.