ORIGINAL CONTRIBUTION Anatomy of the sphenopalatine artery and its implications for transnasal neurosurgery* Background: The knowledge of sinonasal vasculature is inevitable in transnasal neurosurgery. We performed an anatomical study on the sphenopalatine artery from the perspective of skull base procedures. Methodology: To analyse the anatomical landmarks of the sphenopalatine artery, arterial skull corrosion casts (26 head halves) underwent endoscopic transnasal phantom surgery. Furthermore, we performed microsurgical dissection on formaldehyde-fixa- ted cadavers with arterial perfusion (14 head halves) as well as studied Cone Beam CT-scans of anonymised patients and cadavers (115 head sides). Results: In our cadaveric material, the sphenopalatine foramen is located at the transition of the superior and middle nasal meatus (95.0%) or in the superior nasal meatus (5.0%). It is the main entry point of the branches of the sphenopalatine artery into the nasal cavity. In most cadaveric cases (25.0%), at this level there are 2 branches superiorly and 1 vessel inferiorly to the ethmoid crest. An average of 2.4 vessels leave the sphenopalatine foramen superiorly to the ethmoid crest, 97.8% of them belong to the sphenopalatine artery´s posterior septal branches. An average of 2.1 branches leave the sphenopalatine foramen inferiorly to the ethmoid crest; all of them belong to the posterior lateral nasal branches. There are no cases with a single artery at the plane of the sphenopalatine foramen. We describe a triangular bony structure bordering the sphenopalatine foramen anteriorly which is built up by the palatine and ethmoid bone as well as the maxilla. According to the radiographic studies, this triangular prominence is surrounded superiorly by a posterior ethmoid cell (57.4%), the sphenoid sinus (41.7%) or the orbit (0.9%) with a varying contri- bution of the superior nasal meatus; inferolaterally by the maxillary sinus (98.3%) or the pterygopalatine and infratemporal fossa (1.7%) and inferomedially by the middle nasal meatus. The medial vertex of the bony triangle corresponds to the ethmoid crest of the palatine bone. In transnasal endoscopic surgery, the posterior lateral nasal branches of the sphenopalatine artery appear at the triangle´s inferomedial edge, the posterior septal branches emerge at its superior edge. Conclusions: The triangular bony structure is a landmark to find and differentiate the posterior lateral nasal and posterior septal branches of the sphenopalatine artery and to identify the sphenoid sinus. Key words: transnasal endoscopy, transethmoid-paraseptal approach, skull base surgery, sphenopalatine artery, sinonasal ana- tomy Márton Eördögh 1 , András Grimm 2 , Islam Gawish 1 , Lajos Patonay 2 , Robert Reisch 3 , Hans Rudolf Briner 4,# , Gábor Baksa 2,# 1 Department of Neurosurgery, KRH Klinikum Nordstadt, Hannover, Germany 2 Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary 3 ENDOMIN – Centre for Endoscopic and Minimally Invasive Neurosurgery, Hirslanden Clinic, Zurich, Switzerland 4 Center for Otorhinolaryngology, Head and Neck Surgery, Hirslanden Clinic, Zurich, Switzerland Rhinology 56: 82-88, 2018 https://doi.org/10.4193/Rhino17.181 *Received for publication: August 10, 2017 Accepted: October 14, 2017 # contributed equally 82 Introduction Transnasal neurosurgery embraces approaches to the pituitary gland and the skull base. The paradigm that these procedures begin at the level of the sphenoid sinus is shifting as an enor- mous experience is gathered on the sinonasal physiology and its relation to the quality of life. The knowledge of the sino- nasal vascular anatomy became inevitable both for ENTs and neurosurgeons to perform extended intranasal dissection for