Inferolateral trunk: anatomical study, surgical relevance, and technical nuances in lateral transcavernous endoscopic endonasal surgery

OBJECTIVE: During endoscopic endonasal surgery (EES), inferolateral trunk (ILT) sacrifice may be required to efficiently and safely achieve tumor resection within the lateral compartment (LC) of the cavernous sinus (CS). The authors investigated the surgical anatomy and variations of the ILT, aiming to provide practical information to safely expose, coagulate, and transect this artery during EES. METHODS: In this anatomical study, 24 postmortem, lightly embalmed, colored silicone-injected human head specimens were dissected and 41 sides were examined. The origin, course, branching pattern, and relation of the ILT with surrounding structures were investigated. Clinical charts of patients surgically treated for pituitary adenomas (PAs) with LC invasion from July 2018 to April 2023 at the authors' institution were also retrospectively analyzed. Illustrative cases are provided. RESULTS: The ILT was found in 93% (38/41) of sides, mainly arising from the inferolateral aspect (91%, 30/33 sides) of either the middle or posterior third (82%, 27/33 sides) of the horizontal segment of the internal carotid artery. After a short common trunk (mean length 3 mm), the artery divided into 2 (21%, 8/38) or, more frequently, 3 (74%, 28/38) branches, supplying blood to cranial nerves (CNs) III, IV, V1, V2, V3, and VI and the Gasserian ganglion. While the sympathetic plexus was always located anterior to the ILT, CN VI was found anterior to the ILT in 82% (31/38) of sides. The lateral parasellar ligament (LPL) enwrapped the ILT and its branches in 43% (15/35) of sides. In the coronal plane, the ILT origin was found at the level of the sellar floor (0 ± 1 mm) and the LPL (0 ± 2 mm), both of which can serve as surgical landmarks during lateral transcavernous EES. In the case series of 25 EESs for PAs with LC invasion, the ILT was sacrificed in 5 cases (20%) without any permanent postoperative CN deficits. CONCLUSIONS: This study served as a detailed anatomical investigation of the ILT, which is crucial when accessing the LC of the CS. The authors proposed two reliable landmarks to identify the ILT intraoperatively: the sellar floor and the LPL. Furthermore, investigations confirmed that the ILT can be sacrificed without causing permanent CN deficits given the existence of a collateral supply.