The Endonasal Endoscopic Perspective of Paraclinoid Aneurysms a Cadaveric Anatomical Analysis

Background: Aneurysms on the paraclinoid segment of the internal carotid artery (ICA) are a rare but challenging to fully assess and treat. Due to the complicated anatomy of the area, several classification systems and terminologies have been proposed focusing on different aspects of the disorder. During endoscopic endonasal dissection of anatomical specimens, several incidental paraclinoid aneurysms were discovered. The anatomical findings of the aneurysms and a literature review on the topic are presented herein.

Materials and Methods: Four anatomical specimens with incidental aneurysms at the paraclinoid segment were used for endoscopic endonasal dissection. All specimens’ vasculature was injected with colored latex. A literature review on the topic was performed.

Results: Aneurysm 1: the aneurysm was tightly wrapped by the carotid collar membrane and contained between the proximal (PDR) and distal dural ring (DDR), with the dome projected medially. There was no perforator in the vicinity of the aneurysm and no apparent connection to subarachnoid space was found as the DDR adhered tightly to the wall of ICA. Aneurysm 2: the aneurysm arose at the origin of the secondary superior hypophyseal artery (SHA), and was located in a pouch-like carotid cave with a medially-oriented dome and subarachnoid access. Aneurysm 3: a inferoposteriorly pointing aneurysm that was associated with a primary SHA and was covered with carotid collar, within a slit-type carotid cave, with potential dissection into the intradural space. Aneurysm 4: the aneurysm had no association with ICA perforator, dome projected inferoposteriorly, with no carotid cave and no intradual access.

Discussion: With the complex and highly variant anatomy of the paraclinoid segment of the ICA, associated perforators, the clinoid space, and carotid cave, the classification systems of paraclinoid aneurysm available on current literature seem insufficient in guiding assessment and management of these medially directed aneurysms. Angiographic classifications cannot predict the aneurysm’s relationship to dural structures (and therefore risk of hemorrhage) and small perforators. Several authors highlighted the use of MRI for determining the intradural/extradural nature of the aneurysm and the risk of intracranial extension and bleeding of paraclinoid aneurysm by assessing its spatial relationship to DDR and diaphragm sellae. However, the presence of SHA and the slit-type carotid cave makes the distinction not definitive, as demonstrated by cases of aneurysms 2 and 3 in our series. Most of paraclinoid aneurysms have medially or inferiorly projecting domes which offer a favorable angle for clipping through EEA. Several successful clippings of paraclinoid aneurysms through an endoscopic endonasal approach (EEA) have been recently reported in the literature. It is critical for surgeons to understand the risk of subarachnoid hemorrhage indication for surgery, and the dural structures that may tightly adhere to the aneurysm to impact safety and necessity of the surgery ([Fig. 1]).

Fig. 1 (A) Aneurysm 1. (B) Aneurysm 2. (C) Aneurysm 3. (D) Aneurysm 4. Green dash line, approximation of proximal dural ring; yellow dash line, approximation of distal dural ring.