AIM: To define the existence and precise anatomical boundaries of the medial corridor (MC) within the cavernous sinus (CS), using an endoscopic endonasal transsphenoidal approach, and to correlate these anatomical findings with clinical patterns of CS invasion in patients with pituitary adenomas. MATERIAL and METHODS: An endoscopic endonasal transsphenoidal technique was used to perform anatomical dissections on 10 CSs obtained from 5 adult cadaveric heads. Key neurovascular landmarks were systematically identified, and quantitative measurements of their spatial relationships were recorded. To establish clinical relevance, anatomical observations were correlated with radiological and intraoperative findings from 20 patients with pituitary adenomas demonstrating CS invasion on preoperative imaging. RESULTS: The MC was consistently identified in all cadaveric specimens, confirming its reproducible anatomical presence. The mean distance between the anterior genu of the internal carotid artery (ICA) and the pituitary gland was 5.0 ± 1.5 mm. Clinical correlations revealed that pituitary adenomas preferentially invade the superior compartment of the CS via the MC prior to lateral and posterior extension. The oculomotor nerve (cranial nerve III) was a reliable anatomical landmark defining the lateral boundary of the MC. CONCLUSION: Comprehensive anatomical delineation of the MC is critical for refining endoscopic surgical strategies, maximizing the extent of safe tumor resection, and minimizing neurovascular morbidity. The consistently identified interval of approximately 5 mm between the anterior genu of the ICA and the pituitary gland provides a robust and practical intraoperative reference point for safe navigation through the MC of the CS.