Surgical anatomy of the inferior hypophyseal artery and its relevance for endoscopic endonasal skull base surgery

OBJECTIVE: The inferior hypophyseal arteries (IHAs) are intimately related to pituitary and cavernous sinus (CS) lesions. There is still no anatomical study specifically analyzing the IHAs. The aim of this study was to investigate the surgical anatomy and variations of the IHA, and to translate this knowledge into surgical practice. METHODS: Twenty anatomical specimens with vascular injection were used for endoscopic and transcranial dissection. The origin, arrangement patterns of the meningeal hypophyseal trunk (MHT), segmentation, trajectory, branching pattern in each segment, and dominance of the IHAs were investigated. RESULTS: The IHA was identified in all 40 sides (100%). The IHA originated from the MHT in 37 sides (92.5%) and directly from the cavernous internal carotid artery in 3 sides (7.5%). According to the relationship of the IHA with the MHT, dorsal meningeal artery (DMA), and tentorial artery (TA), the authors classified five patterns of IHA origin: type A (common trunk) was found in 16 sides (40%), type B (IHA-DMA branch trunk) was found in 8 sides (20%), type C (IHA-DMA stem trunk) was found in 7 sides (17.5%), type D (IHA-TA trunk) was found in 6 sides (15%), and type E (independent type) was found in 3 sides (7.5%). All IHAs could be divided into proximal (cavernous) and distal (glandular) segments. Four branching patterns of the proximal segment were observed: 0 branches (12.5%), 1 branch (42.5%), 2 branches (40%), and 3 branches (5%). Three patterns of the distal IHA were noticed: 1) single (25%), 2) bifurcation (65%), and 3) trifurcation (10%). The IHAs entered the posterior third of the medial wall of the CS in 75%, intermediate third in 17.5%, and anterior third in 7.5%. The proximal IHA ran in close relation with the lower third of the posterior clinoid process (PCP) in 80%, middle third in 15%, and upper third in 5%. CONCLUSIONS: The IHA can be divided into proximal and distal segments. Its proximal segment is most often found crossing the CS at the level of the lower third of the PCP and entering the posterior third of the medial wall of the CS. A detailed understanding of the surgical anatomy of the IHA and its variability will help surgeons dealing with challenging lesions within the CS and when performing transcavernous approaches, interdural posterior clinoidectomies, and pituitary gland transpositions.