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) transfacial, cranial and craniofacial (combined) approaches, and 2) endonasal endoscopic approaches. Malignancies in the ventral cranial base often distort the nasal cavity making it difficult to locate the internal carotid artery (ICA), and an inadvertent damage could lead to serious complications.
Objectives: The objectives of this study are: 1) To describe relevant anatomical landmarks for localizing the ICA, 2) To create a projection system in localizing the ICA, and 3) To validate these landmarks in clinical cases.
Method: Ten formalin-fixed cadaver heads, injected with blue and red silicon, were used. The cadavers were 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). Relevant anatomical landmarks are the vertical lamella of the superior turbinate, palatine bone, vidian canal, eustachian tube were analyzed for localizing the segments of the ICA.
Result: We described three anatomical landmarks: 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 superior landmark are the basal lamella of the middle turbinate and the lacrimal crest, which projects laterally to the lamina papyracea. The lamina papyracea allows for an understanding of the orbit anatomy and reaches to the paraclinoid ICA, through the orbitosellar line which connects the orbit to the sellar region. The middle landmarks: the posterior adhesion of the middle turbinate to the ethmoidal crest; this bony structure allows for identification of the sphenopalatine foramen and the vidian canal is above and medial to the pterygopalatine foramen, and provides a guide to the genu of the ICA. In addition we created a vertical line from the vidian canal to the lateral opticcarotid recess for localizing the paraclinoid carotid. The main anatomical landmarks of the inferior pillar, is the posterior adhesion of the inferior turbinate with the conchal crest and the eustachian tube. The distance from the eustachian tube to the carotid was on average 22 mm. Three clinical cases were shown to exemplify each anatomical landmark.
Conclusion: The correlation of the 3 anatomical landmarks 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.