Anatomical Variables of the Superior Thyroid Artery on Computed Tomography Angiograms

Abstract

Background and Objectives: The superior thyroid artery (STA) typically has its origin inferiorly to the greater hyoid horn (GHHB) either from the external carotid artery (ECA) or from the carotid bifurcation (CB) or the common carotid artery (CCA). We aimed to determine the topographic variants of the STA related to the GHHB and the artery of origin and to check their bilateral symmetry. Materials and Methods: Determinations were performed in a sample of 85 archived angio CT adult cases, comprising 53 men and 32 women. The origins of the STAs from the CCA/CB/ECA were classified as types A-C. We defined the vertical topographies of the STA as follows in relation to the GHHB: type 1 (infrahyoid), type 2 (hyoid), and type 3 (suprahyoid). Subtypes of the STA course were added: "a", lateral to the GHHB; "b", medial; and "c", posterior to it. Unilateral combinations of types and bilateral associations of these were established. Results: In 170 carotid axes, we detected STA type A in 8.82%, type B in 28.82%, and type C in 60% of cases. It was absent in 2.35% of the cases. The infrahyoid type 1 of STA was found in 47.06% of cases. The hyoid type 2 was found in 20.59% (2a), 0.59% (2b), and 4.71% (2c). The suprahyoid type 3 was found in 21.18% (3a), 0% (3b), and 3.53% (3c). Thirteen unilateral combinations of types were found. The most prevalent ones were C1 (27.71%), C3a (17.47%), and B1 (15.66%). We established thirty-seven bilateral associations of unilateral combinations of types. The cases with asymmetrical bilateral associations of unilateral combinations of types prevailed. A lowered hyoid bone overlapping the thyroid cartilage was found in one of these cases. The prevailing associations were C1-C1 (bilateral infrahyoid origin of the STA from the ECA, 13/85, 15.29%), C3a-C3a (suprahyoid origins of the STAs from the ECAs and lateral courses over the GHHB, 9/85, 10.58%) and C1-B1 (infrahyoid origins from the ECA and CB, 8/85, 9.41%). Conclusions: The vertical topography of the STA is highly variable and hardly predictable but can be examined in imaging studies. The GHHB may be of use to identify and manage the artery. The STA is rarely absent.

Keywords: anatomical variation; carotid artery; hyoid bone; thyroid artery; thyroid gland.

Figure A1

Right superior thyroid artery with suprahyoid origin and course over lingual artery and greater hyoid horn (C3a combination). Male case. (A) Three-dimensional volume rendering, right side, lateral view. (B) Coronal section through right greater hyoid horn, anterior view. (C) Axial section through right superior thyroid and lingual arteries, inferior view. 1. Common carotid artery; 2. greater hyoid horn; 3. external carotid artery; 4. internal carotid artery; 5. facial artery; 6. lingual artery; 7. superior thyroid artery; 8. submandibular gland; 9. hyoglossus muscle; 10. internal jugular vein.

Figure A2

Superior thyroid arteries with suprahyoid origin from external carotid arteries and course over greater hyoid horn (bilateral association type XXXIII—C3a-C3a). Male case. Three-dimensional volume renderings. (A) Right side, antero-medial view. (B) Left side, medial view. 1. Right common carotid artery; 2. right internal jugular vein; 3. right superior thyroid artery; 4. right external carotid artery; 5. right internal carotid artery; 6. linguofacial trunk; 7. right lingual artery; 8. greater hyoid horn; 9. left superior thyroid artery; 10. left external carotid artery; 11. left internal carotid artery; 12. left internal jugular vein.

Figure 1

(A) Superior thyroid artery originating from carotid bifurcation. Three-dimensional volume rendering. Left side. Female case. Infero-lateral view. 1. Common carotid artery; 2. superior thyroid artery; 3. carotid bifurcation; 4. external carotid artery; 5. greater hyoid horn; 6. lingual artery. (B) Superior thyroid artery originating from common carotid artery. Three-dimensional volume rendering. Left side. Female case. Antero-lateral view. 1. Common carotid artery; 2. greater hyoid horn; 3. internal carotid artery; 4. external carotid artery; 5. lingual artery; 6. superior thyroid artery. (C) Left superior thyroid artery originating from external carotid artery lateral to greater hyoid horn (unilateral combination C2a). Male case. Lateral view. 1. Greater horn of hyoid bone; 2. common carotid artery; 3. external carotid artery; 4. superior thyroid artery; 5. lingual artery; 6. facial artery; 7. occipital artery; 8. internal carotid artery; 9. ascending pharyngeal artery; 10. internal jugular vein. (D) Right superior thyroid artery with suprahyoid and subgonial origin from external carotid artery (1.81 cm long suprahyoid segment, unilateral C3a combination). Male case. Three-dimensional volume rendering. Right infero-lateral view. 1. Internal jugular vein; 2. superior thyroid artery; 3. right common carotid artery; 4. external carotid artery; 5. linguofacial trunk; 6. facial artery; 7. lingual artery; 8. greater hyoid horn. (E) Right superior thyroid artery with suprahyoid origin from internal wall of external carotid artery but with lateral course on greater hyoid horn (unilateral combination C3a). Male case. Three-dimensional volume rendering. Antero-medial view. 1. Common carotid artery; 2. superior thyroid artery; 3. carotid bifurcation; 4. lingual artery; 5. internal carotid artery; 6. external carotid artery; 7. facial artery; 8. greater hyoid horn; 9. thyroid cartilage.

Figure 2

(A) Superior thyroid artery with infrahyoid origin from external carotid artery (unilateral C1 combination) and perilaryngeal tortuous course. Male case. Three-dimensional volume rendering. Right side. Lateral view. 1. Common carotid artery; 2. superior thyroid artery; 3. external carotid artery; 4. internal carotid artery; 5. internal jugular vein; 6. lingual artery; 7. body of hyoid; 8. thyroid cartilage. (B) Superior thyroid artery with origin at level of hyoid tubercle and initial course internal to greater hyoid horn (type C2b). Oblique sagittal section. Female case. 1. Common carotid artery; 2. superior thyroid artery; 3. external carotid artery; 4. facial artery; 5. lingual artery; 6. greater hyoid horn. (C) Bilateral association type XXXIII (C3a-C3a). Female case. Three-dimensional volume rendering; left anterior oblique view. 1. Right internal jugular vein; 2. right common carotid artery; 3. right superior thyroid artery; 4. right greater hyoid horn; 5. right external carotid artery; 6. right internal carotid artery; 7. left internal jugular vein; 8. left greater hyoid horn; 9. left superior thyroid artery; 10. left internal carotid artery; 11. left external carotid artery.

Figure 3

(A) Superior thyroid arteries originating from external carotid arteries at asymmetric hyoid levels: immediately infrahyoid (type 1) on right side and hyoid (type 2c) on left side. Bilateral association C1-C2c (type XIX), female case. Three-dimensional volume rendering. Right antero-infero-lateral view. 1. Right common carotid artery; 2. right superior thyroid artery; 3. right internal jugular vein; 4. right hyoid tubercle; 5. right internal carotid artery; 6. right external carotid artery; 7. right linguofacial trunk; 8. right lingual artery; 9. left common carotid artery; 10. left superior thyroid artery; 11. left greater hyoid horn; 12. left internal jugular vein; 13. left lingual artery; 14. left facial artery; 15. left external carotid artery; 16. left internal carotid artery. (B) Superior thyroid arteries with suprahyoid origin from external carotid arteries (types C3a on right side and C3c on left side, asymmetric association XXXIV). Overlapped hyoid bone and thyroid cartilage. Male case. AngioCT, three-dimensional volume rendering. Right anterolateral view. 1. Thyroid cartilage; 2. body of hyoid bone; 3. right common carotid artery; 4. right superior thyroid artery; 5. right external carotid artery; 6. right facial artery; 7. right greater horn of the hyoid; 8. left common carotid artery; 9. left greater horn of the hyoid; 10. left superior thyroid artery; 11. left external carotid artery; 12. left facial artery.

Figure 4

Bilateral absence of superior thyroid artery (type V association). Three-dimensional volume renderings. Right side, antero-lateral view (A) and antero-medial view (B). Left side, antero-inferior-lateral view (C) and infero-medial view (D). 1. Body of hyoid bone; 2. thyroid cartilage; 3. common carotid artery; 4. subclavian artery; 5. brachiocephalic trunk; 6. aortic arch; 7. vertebral artery; 8. inferior thyroid artery; 9. external carotid artery; 10. internal carotid artery; 11. facial artery; 12. lingual artery; 13. thyroid lobe.

Figure 5

Superior thyroid arteries with suprahyoid origin from external carotid arteries (bilateral C3c type, bilateral symmetrical association type XXXVII). Bilateral linguofacial trunk. Three-dimensional volume renderings. (A) Right side, antero-lateral view. (B) Left side, antero-lateral view. 1. Right common carotid artery; 2. right hyoid tubercle; 3. right superior thyroid artery; 4. right internal carotid artery; 5. right external carotid artery; 6. right internal jugular vein; 7. right linguofacial trunk; 8. facial artery; 9. lingual artery; 10. left common carotid artery; 11. left hyoid tubercle; 12. left superior thyroid artery; 13. left external carotid artery; 14. left internal carotid artery; 15. left internal jugular vein; 16. left linguofacial trunk; 17. left facial artery; 18. left lingual artery.