Introduction: Malignancies of the ventral cranial base can often extend into the sinuses, paranasal sinuses, orbit and extracranial fossa. As such, surgical management can be more difficult and often requires enhanced technical ability. Traditionally, two routes are employed to reach these tumors: (1) open or dorsal approaches, which consists of transfacial, cranial and craniofacial (combined) corridors, and (2) ventral or endoscopic approaches. Malignancies in the ventral cranial base often distort the normal anatomy; this is of critical importance, especially when locating the internal carotid artery (ICA), where inadvertent damage could lead to serious complications.
Objectives: The objectives of this study are (1) To describe three anatomical pillars in localizing the ICA, (2) to create a projection system in localizing the ICA, and (3) to expound on these three pillars in clinical cases.
Method: Six formalin-fixed cadaver heads, injected with blue and red silicon, were used. The cadavers were also CT-scanned and images were co-registered to allow for real-time navigation of the osseous structures. The anatomical dissections were performed by endoscopic vision (0o lens).
Result: We described three anatomical pillars: (1) superior—projects to the paraclinoid internal carotid artery (ICA), (2) middle—projects to the genu of the ICA, and (3) inferior—projects to the parapharyngeal ICA. The main anatomical landmarks of the superior pillar, from outside to inside, are the superior and anterior buttress of the middle turbinate and the lacrimal crest, which combined, forms the lateral plane; the uncinate process, bulla ethmoidalis and the ethmoidal cells correspond to the middle plane; and the lamina papyracea corresponds to the medial plane. In the middle part of the lamina papyracea, the orbitosellar line (OSL) was created, which connects the orbit to the sellar region, and projects to the paraclinoid ICA. The main anatomical landmarks of the middle pillar are the middle turbinate more specifically its posterior adhesion to the ethmoidal crest; this bony structure allows for identification of the sphenopalatine foramen and the pterygopalatine artery. The vidian canal is above and medial to the pterygopalatine foramen, and provides a guide to the genu of the ICA. The main anatomical landmarks of the Inferior pillar, from outside to inside and lateral to medial, are the inferior turbinate to its adhesion with the conchal crest and the eustachian tube (ET). The distance from the ET to the carotid was on average 22 mm. Three clinical cases were shown to exemplify each pillar.
Conclusion: The projection system of the three pillars allowed for reliable localization of the ICA, with a more confident ability to control the ICA intraoperatively, especially in the event that anatomy is distorted by surrounding tumor.
