THE MICROSURGICAL ANATOMY OF THE SUPERIOR HYPOPHYSEAL ARTERY

INTEREST IN THE anatomy of the proximal segment of the intracranial in ternal carotid artery has been kindled by the recognition that there a re multiple potential sites of aneurysm formation in this region. Thes e various aneurysm locations have characteristic hemodynamic and clini cal features as well as surgical considerations. Recently recognized a s a distinct clinical and anatomical entity are aneurysms that are hem odynamically related to the superior hypophyseal artery. Although aneu rysms arising in proximity to the superior hypophyseal artery are not rare, the anatomy of this vessel arising from the medial or posteromed ial aspect of the proximal internal carotid artery is poorly understoo d. We performed a cadaveric microsurgical anatomical study of 20 inter nal carotid arteries between the ophthalmic and posterior communicatin g arteries to develop a better understanding of the anatomical relatio nships of the superior hypophyseal artery. There were an average of 1. 8 superior hypophyseal arteries arising from each carotid artery with an average diameter of 0.22 mm. The origin of the superior hypophyseal arteries was within 5 mm of the ophthalmic artery origin in 85% of th e specimens. There were two distinct patterns of superior hypophyseal artery anatomy. In 42%, a large, dominant superior hypophyseal artery branched like a candelabra with smaller branches to the pituitary stal k, optic nerve, and chiasm. The average diameter of the larger branche s was 0.3 mm. In the absence of a large dominant branch, two or three medial vessels were found. In one specimen, an incidental aneurysm was discovered at the origin of the superior hypophyseal artery on the me dial aspect of the internal carotid artery at the origin of a large ca ndelabra-like branch. Our study describes the microsurgical anatomy of the superior hypophyseal artery and lends further support that superi or hypophyseal artery aneurysms are separate anatomical and clinical e ntities from other aneurysms of the proximal internal carotid artery.