The "Transdural" Paradox: The Case of a Paraclinoid Internal Carotid Artery Aneurysm With an Intradural Neck and Extradural Dome.

Paraclinoid internal carotid artery (ICA) aneurysms pose a surgical challenge because of their complex relationship with the distal dural ring (DDR), the boundary between the extradural cavernous sinus and the intradural subarachnoid space. The classification of these aneurysms as strictly intradural or extradural is often complicated by the anatomical variability of the DDR, which can form a dural pouch known as the carotid cave. This anatomical paradox can lead to a "transdural" aneurysm, in which the dome is in the extradural or intradural space, which poses a risk for subarachnoid hemorrhage. The unreliability of preoperative imaging and bony landmarks in definitively classifying these lesions necessitates a flexible and adaptive nomenclature and surgical approach, which is discussed herein. We describe the case of a 37-year-old man with a paraclinoid ICA aneurysm that was found to have an intradural neck and an extradural dome. We performed a combined intradural-extradural operation, which began with meticulous intradural dissection to expose the subarachnoid carotid artery for distal control, followed by an intradural anterior clinoidectomy. This case highlights the critical importance of a surgical strategy that is responsive to intraoperative anatomical findings, especially for paraclinoid aneurysms that defy simple classification.