- PCOM aneurysms can be one of the easiest or one of the most difficult aneurysms to treat surgically. The PCOM artery is one of the first branches visualized during dissection of the carotid cistern and the dome of the aneurysm is typically directed away from approach trajectory. Wide dissection of the sylvian fissure is typically not necessary for successful clipping of these aneurysms. In fact, retraction of the temporal lobe is often avoided (particularly when the fundus points laterally) until the surgeon partially exposes the neck of the aneurysm. Anterior cliniodectomy is rarely required for clipping of PCOM aneurysms. Park et al, found that only 6 out of 96 patients with PCOM aneurysms required clinoidectomy during surgical treatment.[42] When looking for predictors of possible clinoidectomy, he found three anatomical factors. The distance between the tip of the anterior clinoid process and the proximal neck of the aneurysm (measured using CTA) was significantly smaller in the clinoidectomy group (4.4 ± 0.7 mm vs 7.2 ± 1.4mm). From this data, one can extrapolate that if the distance is greater than 5.8 mm, anterior clinoidectomy is rarely required, and when the distance is less than 4.4 mm, anterior clinoidectomy is frequently required for successful clipping. The other anatomical measurements are somewhat difficult to measure of digital subtraction angiography. The data indicates that the communicating segment of the ICA take a more lateral course in the clinoidectomy group.
- Once the neck of the aneurysm is adequately exposed, the surgeon must pay significant attention to preservation of the PCOM artery, PCOM perforators and the anterior choroidal artery without significant manipulation of the fundus. Leipzig et al, reviewed a large series of aneurysm clipping looking for risk factors of intra-operative rupture.[32] PCOM aneurysms had the second highest rate of intra-operative rupture (second only to ACOM aneurysms) amongst anterior circulation aneurysms (9.3%). Risk factors for intra-operative rupture included an immediate history of subarachnoid hemorrhage as well as lack of temporary clipping. PCOM aneurysms in particular had a significantly higher incidence of intraoperative rupture when no temporary clip was used during clipping of the aneurysm (11.6% vs. 0%). One reason for this finding is that the fundus of the PCOM aneurysm is typically in line with the communicating segment of the ICA allowing a significant portion of the intra-arterial pressure to be applied to the dome of the aneurysm. The communicating segment of the ICA begins just proximal to the origin of the PCOM artery and ends in the ICA terminus. This also explains why ligation of the cervical ICA is protective of rehemorrhage for PCOM aneurysms.[57] As an alternative to temporary clipping, adenosine-induced cardiac arrest may also be used to temporarily reduce the pressure within the aneurysm during application of a clip.[1743]
- This technique is particularly useful for PCOM aneurysm because of the number of vessels that can provide high pressure inflow into the aneurysm. For instance, temporary proximal to an MCA aneurysm will significantly reduce the pressure within the fundus. Similarly, temporary clipping of a dominant A1 will often allow the surgeon to dissect the dome of an ACOM aneurysm without rupture. However, even after a temporary clip is placed on the proximal ICA, the fundus may receive significant inflow retrograde from a large PCOM artery. In addition, a temporary clip on the ICA will often significantly interfere with dissection and clipping of a PCOM aneurysm. Therefore, adenosine arrest provides a temporary reduction of inflow from all these vessels allowing the surgeon to dissect the neck of the aneurysm and apply a clip without rupture of the aneurysm.
- Once the aneurysm is successfully clipped, the surgeon must once again evaluate the integrity of the PCOM artery, perforators and the anterior choroidal artery and make sure that there is no residual flow into the dome of the aneurysm. Because the neck of junctional PCOM aneurysms involves both the ICA and PCOM artery, complete occlusion of the aneurysm may be difficult and may require the use of multiple clips. Intraoperative use of microdopler and indocyanic green angiography are useful adjuncts especially when evaluating the patency of small perforating arteries. Although intra-operative angiography is not effective for evaluating the patency of small perforators, it is often effective in detecting iatrogenic occlusion or stenosis of larger vessels (such as PCOM artery) and residual flow into the dome of the aneurysm. In fact, Alexander et al, found that giant aneurysm and PCOM location were independent predictors of residual aneurysm (detected via intra-op angiography) requiring clip adjustment.[3]
- Although clipping of PCOM aneurysms may occasionally be met with complications, outcomes tend to be good for the majority of the cases. Wirth et al, retrospectively reviewed operative morbidity amongst unruptured aneurysms.[58] He found that PCOM aneurysms had the lowest operative morbidity (5%) compared to aneurysms in other locations (MCA 8%, ICA 12%, ACOM 16%). Although data from this study is somewhat old, and techniques and microscopes have improved surgical outcomes, PCOM aneurysm in general continue to be among the least complicated aneurysms to treat surgically. However, because of the emergence of endovascular therapy and significant technical advancements made with stent/balloon-assisted embolization, aneurysms that come to surgical management will likely be larger and more complicated.
- It is in the experience of the senior author (GWB) that the complexity of aneurysms undergoing surgical clipping has increased with the advent of endovascular treatment as all those with a small or moderate sized necks would be coiled.
Made with Bullet