Intradural versus Extradural Location of Paraclinoid Aneurysms: Preoperative Red Flag Markers

Exact preoperative confirmation of the distal dural ring and intradural location of a paraclinoid internal carotid aneurysm has been an age old dilemma. This study was aimed at identifying anatomical landmarks in cases of paraclinoid aneurysms, which were relatively consistent, and would help in predicting the possibility of an extradural inaccessible location of these aneurysms for surgical clipping.

Ninety surgically managed unruptured paraclinoid aneurysms were retrospectively analyzed with preoperative computerized tomography. Axial relation of the aneurysm neck to the ophthalmic artery (OA), optic strut (OS), and anterior clinoid process (ACP) in terms of vertical distance and the direction of projection were analyzed and tabulated for all 90 cases. Intradural and extradural (inaccessible) aneurysms were compared.

Seven out of the 8 inaccessible necks were medially directed and 1 was ventrally placed (P = 0.053). The OA level when compared to the neck had a positive correlation with inaccessible aneurysms for clipping (P = 0.002) The OS location above the level of the neck had significant correlation with inaccessibility of clipping and extradural location (P < 0.001). The tip of the ACP had no statistical significance with inaccessibility (P = 0.351).

Medially projecting aneurysms with necks below the level of the OS and origin of the OA should be managed with a high index of suspicion and an alternate method of treatment should be sought. The relation of the neck to the ACP does not seem to have significant statistical bearing with decision making.