True Posterior Communicating Artery Aneurysms: Report of 17 Surgically Treated Patients and Review of the Literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.304098
Source of Support: None, Conflict of Interest: None
Keywords: Clipping, diagnosis, endovascular embolization, true PCoA aneurysm
Shouzhong Guo and Wandong Su are contributed equally to this work.
In 1979, Yoshida et al. for the first time used the term of “true” posterior communicating artery (PCoA) aneurysm and defined it as an aneurysm originating from the PCoA itself. However, true PCoA aneurysms seem to have simply been grouped in more common PCoA aneurysms traditionally and have not been well studied as a single lesion, with only a few case reports and small case series being reported to date. The present study is undertaken to describe our experience with the diagnosis and surgical treatment of 17 patients and review the relevant literature.
Between Jan 2010 and Dec 2015, we treated 17 patients with true PCoA aneurysms. The ratio of male to female was 6:11, and patient age ranged from 38 to 76 years old with a mean age of 59.5. All patients complained of severe headache of acute onset with or without vomiting, one patient suffered progressive deterioration in sensorium, and one patient presented with oculomotor paralysis. The duration of symptoms prior to admission ranged from 6 hours to 10 days. The Hunt-Hess grade for subarachnoid hemorrhage (SAH) upon admission was I-II in 16 patients, IV in the other one patient. There was a medical history of hypertension in 7 patients, coronary artery disease in two patients and colon cancer in one patient.
Preoperatively, all patients underwent computed tomography (CT) scanning as preliminary screening. A true PCoA aneurysm was confirmed by preoperative and intraoperative three dimensional computed tomography angiography (CTA) or digital subtraction angiography (DSA). 4 patients underwent microsurgical clipping. Thirteen patients, including patient with post-embolization aneurysmal recurrence underwent endovascular manipulation. 10 patients were managed with detachable coils, 3 patients were treated with stent-assisted coils, and 2 patients were managed with double-microcatheter technique. Follow-up outcomes were evaluated using the GOS.
All patients presented SAH on CT scanning. CTA or DSA confirmed aneurysms originating from PCoA itself. Left vs. right was 7:10. The maximum diameter of the aneurysms ranged from 2.5mm to 7.5mm (mean, 4.9mm). 12 aneurysms were narrow-neck with a body to neck ratio lager than 1.5, and 5 aneurysms were broad-neck. All the 17 true PCoA aneurysms were distal to the junction of ICA and PCoA, and no aneurysm located at the middle portion of the PCoA and proximal to PCA. sixteen patients had fetal PCA.
4 aneurysms were clipped via Pterional craniotomy, and the postoperative course was smooth [Figure 1]. There were no surgery-related complications or subsequent hemorrhages. Thirteen aneurysms were treated with endovascular embolization [Figure 2] and [Figure 3]. One case experienced intraoperative bleeding due to aneurysm rupture and the bleeding site was successfully occluded immediately with coils. Successful endovascular management was performed in 13 patients. 12 aneurysms got immediate complete occlusion, and one aneurysm got near-complete embolization, while follow-up angiography 3 months later showed no progression of the remnant. There was no recurrence of aneurysms according to follow-up angiograms in all patients. 16 patients recovered well (GOS score 5), and the other one whose preoperative Hunt-Hess grade was IV was moderate disability (GOS score 4) during the following period.
True PCoA aneurysms were previously considered rare. In 1979, Yoshida et al. reported one (0.2%) true PCoA aneurysm in their series of 490 IAs among 419 patients. In another study, Yasargil and Smith reported 6 cases, which constituted about 0.9% of all IAs and 4.6% of all PCoA aneurysms in their series. In a recent biomorphometric study, He et al. reported 10 cases of true PCoA aneurysms among a total of 315 (3.2%) IAs and 77 (13.0%) PCoA aneurysms. Their study represents the largest case series until then. In 2010, a systematic review reported 70 cases of true PCoA aneurysms and showed that true PCoA aneurysms represent about 1.3% of all IAs and 6.8% of all PCoA aneurysms. In the present study, we report 17 true PCoA aneurysms, accounting for 2.5% of all IAs (684 aneurysms) and 7.8% of PCoA aneurysms (219 aneurysms) during the same period. The precise incidence of true PCoA aneurysms remains unavailable. Multicenter and large case series studies are needed.
From a pathological perspective of view, a true PCoA aneurysm may develop from an infundibulum or aneurysmal dilation at the origin of the PCoA. In 1984, Bisaria reported aneurysmal dilation of PCoA in 50 of 126 cadavers and claimed that it is true in clinical cases. Some investigators also reported true PCoA aneurysms developed from infundibular dilations., Now, most neurosurgeons agree that hemodynamic stress plays an important role in the development of a true PCoA aneurysm.,,,, It is suggested that the impact of blood flow on ICA-PCoA junction might result in a common conjunctional aneurysm, and wall shear stress of the blood flow disturbance such as turbulence on PCoA approximately 2-3 mm distal to the junction of the ICA could be conducive to a true PCoA aneurysm, especially in case with occlusion of contralateral ICA or fetal PCA. The present study, which includes 16 fetal PCAs, is another strong evidence for this standpoint. In addition, Pritz reported one ruptured true PCoA aneurysm followed by intracavitary radiation therapy for combined cystic craniopharyngioma. It seems that radiation may contribute to this unusual aneurysm formation. However, as the author doubted, the anterior choroidal artery was equally as adherent to the cyst wall as the PCoA but free of aneurysm. Hence the relationship between the development of a true PCoA aneurysm and radiation-induced vascular wall injury is just suggested.
The clinical presentation of most true PCoA aneurysms is ruptured SAH. He et al. found that true PCoA aneurysms were statistically smaller in mean aneurysm volume than ICA-PCoA conjunctional aneurysms but had similar rupture rate. They suggested that true PCoA aneurysms are more prone to rupture than ICA-PCoA conjunctional ones. All patients in our series presented with SAH of a ruptured aneurysm.
As true PCoA aneurysms are more prone to rupture, it is more important to diagnose a true PCo aneurysm. With the help of modern developed imaging techniques such as three-dimensional CTA and DSA, it is possible to confirm a true PCoA aneurysm preoperatively and carefully evaluate the circumferential anatomy of the aneurysm. However, in ten cases, we couldn't make the diagnosis of a true PCoA aneurysm correctly in the preoperative period, and were identified intraoperatively. It is sometimes difficult to classify true PCoA aneurysms from conjunctional ones preoperatively by flat angiogram because of the vessel-complex visualization of the ICA, the PCoA, and the anterior choroidal artery and variation of these vessels.
Referring to the treatment for true PCoA aneurysms, above all, it is recommended to group true PCoA aneurysms from the common ICA-PCoA conjunctional ones. Safe and successful treatment requires good understanding of the location and three-dimensional configurations of the aneurysm neck in either surgical clipping or endovascular manipulation. Kudo et al. reported one case true PCoA aneurysm misdiagnosed preoperatively. In the operation, the aneurysm ruptured and the bleeding was difficult to control. The patient suffered persistent oculomotor paralysis postoperatively because the oculomotor nerve was clipped inadvertently in a bloody field. The author suggested that the radical source of this complication was inability to predict the location of the aneurysm ostium. In this study, there is no postoperative oculomotor paralysis. The patient with preoperative oculomotor paralysis obtained almost complete recovery in the follow-up period.
In the present study, 4 true PCoA aneurysms were clipped via the pterion approach. It is helpful to rotate the head to the contralateral side for about 60 degrees for a better visualization of the neck of the aneurysm. The sphenoid ridge was drilled routinely to maximize the bony exposure while minimizing the retraction of the brain. As same as clipping a conjunctional PCoA aneurysm, a fundamental principle for surgical clipping of a true PCoA aneurysm is to identify and dissect the proximal portion of the ICA firstly. This work would supply sufficient space for temporary blocking the parent supplying artery of the aneurysm when necessary. Because the short length of the PCoA, once a true PCoA aneurysm ruptured during operation, there was no enough space in the operation field for a temporary clip to block the PCoA. Some neurosurgeons suggested that it is necessary sometimes to drill the anterior clinoid process for temporary interruption., Because true PCoA aneurysms commonly originate from approximately 2-3 mm distal to the junction of the ICA, which is typically an intraoperative blind spot, it is necessary to obtain straight view by tilting the operating table, changing the angle of the microscope, and gently retracting the ICA posteromedially. The PCoA is then followed posteriorly to visualize the neck of the aneurysm. Before dissecting the neck of the aneurysm, it is mandatory to identify the ambient neurovascular structures. Oculomotor nerve runs inferior to the PCoA and must be identified certainly. Because PCoA is mostly fetal type and gives rise to many important branches supplying the optic chiasm, oculomotor nerve, mammillary body, tuber cinereum, ventral thalamus, rostral portion of the caudatenucleus, hypothalamus, and internal capsule, it is imperative to keep these vessels patent to avoid ischemic infarction with severe morbidity. So when clipping a true PCoA aneurysm, we suggest that the longitudinal axis of the clip should be parallel to the PCoA as much as possible to keep the parent artery patent and avoid damage of neurovascular structures. This direction is different from that for an ICA-PCoA conjunctional aneurysm, which usually requires the longitudinal axis of the clip be vertical to the PCoA. Some surgeons suggested that subtemporal approach could provide a better visualization of the aneurysm neck for the aneurysm which projects posteriorly or posteromedially or located at distal two thirds of the PCoA., But some disadvantages of this approach such as potential risk of venous infarction due to sacrifice of the temporal veins restrict its application.
Several researchers preferred surgical clipping as the complex anatomy of these lesions with successive sharp branch angles within a short distance may preclude safe endovascular access., However, endovascular techniques have got noticeable progress in recent years, enabling to treat complex aneurysms. There were reports about true PCoA treated via endovascular methods.,, As it is micro invasive, feasible, safe and effective, endovascular intervention is the preference of most patients with intracranial aneurysms. In our series, 13 aneurysms were successfully embolized via endovascular methods and the patients got satisfactory recovery. A microcatheter should be navigated into the PCoA firstly and then into the aneurysm sac, which requires an acute approach angle. Sometimes, successful cannulation of the aneurysm with a sole microcatheter is challenging. In our experience, a microcatheter tip with two turns in three-dimension over 3-4mm distance is helpful in many cases. Although the microcatheter sometimes is placed properly, the acuity of the approach angle is too sharp to make a stable position, thereby increasing the risk of coil escaping into the parent artery or intraoperative rupture. Double-microcatheter technique was applied in 2 cases to resolve this problem. This modality is effective because two micro catheters can get stable position through being supported by each other and two coils simultaneous being twisted into an entity. Theoretically, it is also feasible to navigate the microcatheter into the aneurysm via contralateral ICA-anterior communicating artery-ipsilateral ICA-PCoA or vertebral artery-basilar artery-ipsilateral PCA-PCoA. However, P1 segment is hypoplastic in most cases with this lesion and a stent cannot be delivered safely. In practice, the approach through posterior circulation is seldom adopted. It is suggested that wide-neck aneurysms which is not suitable for microsurgical clipping should be treated by stent-assisted coiling. 3 aneurysms in this series were managed by coil and stent. The implantation of a stent can prevent coil escaping from the aneurysm sac to the parent PCoA and get compact embolization of the aneurysm.
The follow-up angiograms showed no evidence of aneurysms with intact PCoAs. In a microanatomical study published in 2010, Gabrovsky et al. found premamillary artery originates from the anterior third of PCoA in 41.7% of the fetal PCoA group. So, the stent may cover the origin of the premamillary artery and results in its occlusion. In a report by Kocak B et al. about dissecting aneurysms of the PCoA, one patient experienced a non-hemorrhagic thalamic infarction due to perforating artery occlusion after endovascular treatment, but the patient's neurological status recovered before normal within 6 weeks after infarction. The extent of ischemic infarctions depends on the degree of the balance of these arteries in same supplying territory. Although it is difficult to judge whether the premamillary artery is patent or not because of its invisibility on angiogram, the postoperative course hints the patency of the premamillary artery. It is supposed that the mesh of the stent could keep the flow in the premamillary artery. In the present study, one post-embolization relapsing patient experienced intraoperative bleeding due to aneurysm rupture. Hemostasis was achieved by coiling rapidly. He got favorable clinical outcomes (GCS 5) in follow-up period.
Diagnosis of a true PCoA aneurysm is difficult sometimes because of the vessel-complex visualization. Successful treatment of this lesion requires a good apprehension of the location and three-dimensional configurations of the aneurysm, which is somewhat different in detail from a common ICA-PCoA conjunctional aneurysm.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]