Retropharyngeal course of the superior thyroid artery - a novel finding.

Purpose: The anatomical variables of the superior thyroid artery (STA) are well-studied. It typically leaves the external carotid artery (ECA) and descends on the inferior pharyngeal constrictor muscle to reach the thyroid lobe. We serendipitously found a novel possibility: the bilateral retropharyngeal course of the STA, which we report here.

Method: The case was found while studying the archived angioCT file of a 56-year-old male.

Results: The right carotid bifurcation (CB) was in the coronal plane at 3.3 mm inferior to the greater horn of the hyoid bone (GHHB). The initial segment of the ECA was medial to the GHHB. The origin of the right STA was at 2.7 cm medial to the GHHB greater hyoid horn from the anterior side of the ECA. The left CB was at 2.5 mm posterior to the left hyoid tubercle. It was oriented sagittally oblique, with the left ECA antero-medially to the left ICA. The left STA arose from the medial side of the ECA at 5.6 mm postero-superior to the hyoid tubercle. Each STA descended medially to the GHHB and, further, the superior horn of the thyroid cartilage on that side. At the root of the superior horn of the thyroid cartilage, each STA turned laterally between the common carotid artery and the posterior margin of the lamina of the thyroid cartilage and continued to the thyroid lobe on that side. Thus, both STAs coursed posteriorly to the pyriform recess of the hypopharynx on that side.

Conclusion: Finding bilateral STAs is extraordinary but possible. Such extremely rare variants can be accurately identified during preoperative angioCT scans.