- Department of Radiology, Division of Vascular and Interventional Radiology, Duke University Medical Center, Durham North Carolina, USA
- Department of Surgery, Division of Neurological Surgery, Duke University Medical Center, Durham North Carolina, USA
Correspondence Address:
Gavin W. Britz
Department of Surgery, Division of Neurological Surgery, Duke University Medical Center, Durham North Carolina, USA
DOI:10.4103/2152-7806.74147
© 2010 Golshani K This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.How to cite this article: Golshani K, Ferrell A, Zomorodi A, Smith TP, Britz GW. A review of the management of posterior communicating artery aneurysms in the modern era. Surg Neurol Int 22-Dec-2010;1:88
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Abstract
Background:Technical advancements have significantly improved surgical and endovascular treatment of cerebral aneurysms. In this paper, we review the literature with regard to treatment of one of the most common intra-cranial aneurysms encountered by neurosurgeons and interventional radiologists.
Conclusions:Anterior clinoidectomy, temporary clipping, adenosine-induced cardiac arrest, and intraoperative angiography are useful adjuncts during surgical clipping of these aneurysms. Coil embolization is also an effective treatment alternative particularly in the elderly population. However, coiled posterior communicating artery aneurysms have a particularly high risk of recurrence and must be followed closely. Posterior communicating artery aneurysms with an elongated fundus, true posterior communicating artery aneurysms, and aneurysms associated with a fetal posterior communicating artery may have better outcome with surgical clipping in terms of completeness of occlusion and preservation of the posterior communicating artery. However, as endovascular technology improves, endovascular treatment of posterior communicating artery aneurysms may become equivalent or preferable in the near future. One in five patients with a posterior communicating artery aneurysm present with occulomotor nerve palsy with or without subarachnoid hemorrhage. Factors associated with a higher likelihood of recovery include time to treatment, partial third nerve deficit, and presence of subarachnoid hemorrhage. Both surgical and endovascular therapy offer a reasonable chance of recovery. Based on level 2 evidence, clipping appears to offer a higher chance of occulomotor nerve palsy recovery; however, coiling will remain as an option particularly in elderly patients or patients with significant comorbidity.
Keywords: Cerebral aneurysm, clipping, coiling, posterior communicating artery
INTRODUCTION
Posterior communicating artery (PCOM) aneurysms are one of the most common aneurysms encountered by neurosurgeons and neurointerventional radiologists and are the second most common aneurysms overall (25% of all aneurysms) representing 50% of all internal carotid artery (ICA) aneurysms.[
ANATOMY
There are considerable variations in the anatomy of the PCOM complex, which have both surgical and endovascular implications. The size of the PCOM artery ranges from a small artery often not visualized on angiography, to a large artery nearly the size of the posterior cerebral artery (PCA). A fetal PCOM variant is defined as a PCOM artery, which has the same caliber as the P2 segment of the PCA and is associated with an atrophic P1 segment. Because fetal PCOM arteries are the primary supply to the PCA, care must be taken not to compromise flow to this artery during clipping or coiling of PCOM aneurysms. The incidence of the fetal PCOM variant is 4-29% of patients and bilateral fetal PCOM variants occur in 1-9% of patients.[
The direction of the dome also has significant surgical implications. A classification system has been described by Yasargil.[
NATURAL HISTORY
Although patients with a PCOM aneurysm typically present with subarachnoid hemorrhage (SAH), they can also present with SDH or an isolated OMNP. Although the pattern of SAH is often typical involving the basal cisterns, PCOM aneurysms may present with isolated hemorrhage in the temporal lobe, temporal horn of the lateral ventricle or sylvian fissure (mimicking a middle cerebral artery aneurysm). In addition, 1.3-7.9% of aneurysms may present with an SDH, and a PCOM aneurysm responsible for the hemorrhage is 43% of cases (2/3rd of convexity SDH).[
The risk of rupture of cerebral aneurysm was recently evaluated by the ISUIA.[
Jane et al, evaluated the risk of rehemorrhage in ruptured ACOM and PCOM aneurysm, finding a 50% risk of rerupture within the initial six months followed by 3.5%/year thereafter.[
Surgical Clipping of PCOM Aneurysms
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.[
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.[
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.[
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.[
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.
Coil Embolization of PCOM Aneurysms
Since the data published in international subarachnoid hemorrhage aneurysm trial (ISAT), endovascular treatment of intracranial aneurysms has become more common.[
The major drawback of endovascular embolization is the high recurrence rate. Raymond et al, reported an evidence of recurrence in 33.6% of patients on follow up and major recurrence requiring retreatment in 20.7% of patients.[
Songsaeng et al, recently found five morphological factors in coiled PCOM aneurysms, which were predictive of initial occlusion and long-term stability on follow-up.[
The most important risk factor for rehemorrhage of a coiled aneurysm is an incomplete initial embolization. Johnston et al, demonstrates this correlation in a retrospective review of 1001 patients undergoing either clipping or coiling of a ruptured aneurysm.[
PCOM aneurysms may be particularly difficult to coil in a ruptured setting without the assistance of a stent or balloon. Many of these aneurysm have an elongated fundus such that even though the dome to neck ratio appears favorable (based on the height of the aneurysm), a residual neck is often left unsecured. This is particularly true when the neck partially or totally involves the origin of the PCOM artery. Although stent-assisted embolization is very useful and sidewall aneurysms of the ICA and balloonassisted embolization is effective for embolization of bifurcation aneurysms, it remains extremely difficult to protect the PCOM artery when the neck of the aneurysm involves its origin. Zada et al, evaluated treatment of PCOM aneurysms with a fetal PCA origin.[
Morbidity and Mortality of Coiling vs. Clipping
Unfortunately, with the exception of the ISAT elderly subgroup analysis, there is very little data that stratifies morbidity and mortality base on aneurysm location. The ISUIA probably provides the most accurate data for coiling and clipping of aneurysms.[
In addition to the immediate risks of morbidity and mortality associated with each procedure, one must also weigh the long-term risks including the risk of rebleeding and the risk of morbidity associated with each retreatment session. Mitchell et al, calculated the projected mortality rates for patient’s enrolled in the ISAT trial based on life expectancy and rates of rehemorrhage.[
Because of the lack of bias and inclusion of morbidity associated with retreatment is missing from many of the published studies to date, one cannot take a dogmatic approach when choosing the treatment modality for aneurysms in which clinical equipoise exists (such as PCOM aneurysms). The decision regarding treatment is best made using a multidisciplinary approach. Gerlach et al, recently published a series of patients with unruptured intracranial aneurysms in which such an approach was used regarding treatment.[
Occulomotor Nerve Palsy and PCOM Aneurysms
Occulomotor nerve palsy (OMNP) is a relatively common presenting sign of a PCOM aneurysm. Roughly 20% of PCOM aneurysms have OMNP on presentation and 80% of aneurysms with OMNP were located in the PCOM origin.[
Recovery of OMNP secondary to a PCOM aneurysm was initially observed after surgical clipping of the aneurysm. The main factor associated with recovery of OMNP was the time to treatment. Botterell et al, and Grayson et al, found that presence of OMNP greater than 10 days prior to operative intervention was associated with a reduced likelihood of a full recovery.[
Because there is no correlation between surgical decompression of the third nerve and resolution of OMNP, one can also make an argument that the source of the OMNP is pulsation rather than direct decompression. Consistent with this hypothesis is the fact that coil embolization of PCOM aneurysms can also relieve OMNP without removal of direct mass effect. Birchall et al, described a series of three elderly patients with SAH and partial OMNP due to a PCOM aneurysm who recovered completely after coil embolization.[
Two case series have been published comparing OMNP outcome between surgical and endovascular treatment of PCOM aneurysms. Chen et al, described a series of 13 patients of whom 6 were treated with coil embolization and 7 were treated with surgical clipping.[
SUMMARY
PCOM aneurysms are one of the most frequently encountered aneurysms. Unique anatomical variations in this aneurysm include the size of the PCOM artery and variable involvement of this artery in the neck of the aneurysm. Anterior clinoidectomy, temporary clipping, adenosine induced cardiac arrest, and intraoperative angiography are useful adjuncts during surgical clipping of these aneurysms. Coil embolization is also an effective treatment alternative particularly in the elderly population. However, coiled PCOM aneurysms have a particularly high risk of recurrence and must be followed closely. PCOM aneurysms with an elongated fundus, true PCOM aneurysms, and aneurysms associated with a fetal PCOM artery may have better outcomes with surgical clipping in terms of completeness of occlusion and preservation of the PCOM artery. However, as endovascular technology improves, endovascular treatment of PCOM aneurysms may become equivalent or preferable in the near future.
One in five patients with a PCOM aneurysm present with OMNP with or without SAH. Factors associated with a higher likelihood of recovery include time to treatment, partial third nerve deficit, and presence of SAH. Both surgical and endovascular therapy offer a reasonable chance of recovery. Based on level 2 evidence, clipping appears to offer a higher chance of OMNP recovery; however, coiling will remain as an option particularly in elderly patients or patients with significant comorbidity.
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