Clinical and embryological relevance of a unique thyroidea ima artery variation providing collateral circulation to the mediastinum.

The thyroidea ima artery (TIA) is a highly variable arterial deviation of the blood supply to the thyroid gland with critical implications for surgical neck procedures such as tracheostomy. Though relatively common in the population at large (~3-10%), most TIA variations are related to the initiation of the artery and whether it emerges from the common sites of the brachiocephalic trunk, aortic arch, right common carotid artery, or another more unique vessel as opposed to its dispersion pattern. Generally, TIA variants supply the thyroid gland, often co-occurring with absent inferior or superior thyroid arteries. Here, we report on a unique case of a four-pronged variation of the TIA discovered during an anatomy lab of first year medical students. This variant initiates from the brachiocephalic trunk (diameter 5.3mm, recorded averages 3-5mm) and has three branches terminating in the thyroid and a fourth branch traveling into the thorax and providing accessory circulation in the mediastinum. Specifically, small arterial branches off of the inferior TIA branch supply the pericardium and surrounding fat deep to the sternum, with anastomoses to the left pericardiophrenic artery. Following the large size of the TIA itself, the thyroid gland of this individual is also markedly increased in size (A-P diameter 21mm, lateral width 58mm, S-I diameter 45mm) Potential embryological underpinnings of this variation include overactive HIF-1α vascular remodeling. The size and spread of this TIA variation provide further support for imaging as a requirement before surgical neck procedures to prevent catastrophic bleeding in the event of a TIA variant.