Abstract

Objective:

A fetal variant posterior cerebral artery (fetal PCA) is an embryological remnant in which the PCA is primarily supplied via the anterior cerebral circulation. Internal carotid artery (ICA) aneurysms originating from the takeoff of fetal PCA vessels deserve special attention before surgical or endovascular obliteration because of a greater potential for ischemic injury. We present the first series of ICA-posterior communicating artery (PComA) aneurysms originating at the takeoff of fetal PCA vessels that were treated by surgical or endovascular intervention.

Methods:

A retrospective chart review was conducted for all patients who underwent surgical and endovascular treatment of an ICA-PComA aneurysm at Los Angeles County-University of Southern California Medical Center during a 15-year period (1991–2006) to identify cases with aneurysms originating from fetal variant PCAs. Data were retrospectively reviewed and analyzed.

Results:

During a 15-year period, 271 patients were treated for 273 ICA-PComA aneurysms. Aneurysms occurring at the origin of fetal PCAs were identified in 30 patients (11%). There were 23 women (77%) and seven men (23%) (sex difference, P = 0.0035). Twenty-four patients underwent surgical clipping, whereas six patients underwent endovascular coiling. The mean aneurysm size was 7 mm. The mean ischemia time with temporary clipping (12 cases) was 4.5 minutes. Intraoperative rupture occurred in four surgical cases (17%). Postoperative angiography demonstrated occlusion of the fetal PCA in one case after clip ligation (3%), with an ensuing occipital infarct yet no clinical symptoms.

Conclusion:

ICA-PComA aneurysms originating from fetal PCA vessels may pose a more substantial risk for infarction and subsequent neurological sequelae with surgical or endovascular obliteration. Fetal variant circulations were identified at the PComA origin in 11% of ICA-PComA aneurysm patients and were more commonly encountered in women. The decision of surgical versus endovascular treatment of fetal PCA aneurysms must be carefully considered, given the greater potential for ischemic injury with parent vessel occlusion.

The posterior communicating artery (PComA) frequently serves as a vital physiological mediator between the anterior and posterior cerebral circulation, facilitating anterograde or retrograde flow as necessary to maintain adequate cerebral perfusion. The PComA plays an integral role in maintaining the completeness of the circle of Willis. A fetal variant posterior cerebral artery (fetal PCA), in which the posterior cerebral arteries (PCA) receive their predominant blood supply from the anterior circulation rather than the posterior circulation, may persist into adulthood. The overall incidence of the fetal-type posterior circulation has been reported to occur in 4 to 29% of patients, whereas bilaterally occurring fetal PCAs have been reported to occur in 1 to 9% of patients (1, 4, 5, 13, 15).

Aneurysms of the internal carotid artery (ICA)-PComA junction comprise approximately 20 to 30% of all cerebral aneurysms and, according to some reports, are the most frequently occurring cerebral aneurysms (1012). ICA-PComA aneurysms, more commonly referred to as “PComA aneurysms,” are typically not aneurysms of the PComA itself but instead are aneurysms of the ICA occurring at the origin of the PComA. A well-recognized complication of surgical or endovascular obliteration of PComA aneurysms is inadvertent injury to the PComA itself, or to related perforating arteries, which may result in ischemic injury to dependent regions. This scenario is especially true in the case of a fetal variant circulation, where inadvertent occlusion of the dominant feeder to these regions can be deleterious, causing potential infarction of the midbrain, thalamus, and occipital region (10). As endovascular treatment of cerebral aneurysms becomes an increasingly used modality for the treatment of intracranial aneurysms, it remains crucial to identify patients with fetal PCA variants, because the risk of obliteration of a fetal PCA may carry more significant clinical consequences.

The aim of this study was to retrospectively analyze the University of Southern California (USC) experience with a series of patients who underwent surgical and endovascular treatment of ICA-PComA aneurysms occurring at the origin of a fetal PCA. We present the first reported series of patients treated for ICA aneurysms occurring at the origin of fetal PCAs.

Patients and Methods

A retrospective chart review was conducted for all patients who underwent surgical clipping or endovascular coiling of an ICA-PComA aneurysm at USC Medical Center (Los Angeles, CA) during a 15-year period (i.e., 1991–2006). All surgical cases in this series were performed by one attending surgeon (SLG). The study was performed after approval from the USC Institutional Research Board Committee and in compliance with the Health Insurance Portability and Accountability Act of 1996 regulations. Data collection included clinical reports, operative reports, attending neuroradiologist angiography or computed tomographic angiography reports, discharge summaries, and follow-up clinic visits. A fetal variant circulation was defined as one with primary perfusion of the PCA vessels from ICA angiography injections and minimal perfusion of PCA vessels on vertebrobasilar angiography, often with an absent or hypoplastic P1 segment (6, 14, 15). Statistical analysis was conducted with GraphPad Statistical Software (GraphPad Software, Inc., San Diego, CA). Statistical significance was defined as P < 0.05.

Results

Between 1991 and 2006, 271 patients underwent treatment of 273 ICA-PComA aneurysms at the Los Angeles County-USC Medical Center. Surgical clipping was performed in 189 cases (69%), whereas endovascular coiling was performed in 84 cases (31%). In these 273 cases, 30 aneurysms (11%) were noted to originate from the anatomic origin of a fetal PCA and were included in the analysis (Table 1). Surgical clipping was performed in 24 fetal ICA-PComA aneurysms (80%), whereas the remaining six (20%) were treated with endovascular coiling (P = 0.017, χ2 test). Three patients (10%) were noted to have bilateral fetal PCAs, with unilateral ICA-PComA aneurysms. The mean age of the patients was 54 years (range, 18–80 yr). There were seven men (23%) and 23 women (77%) (sex difference, P = 0.0035, χ2 test).

>TABLE 1

Clinical characteristics of 30 patients with internal carotid artery- posterior communicating artery aneurysms occurring at fetal posterior cerebral artery originsa

Treatment Ruptured? Patient no. Age (yr)/sexb Hunt and Hess grade CN III palsy Fisher grade 
Surgical No 37/F Yes N/A 
63/F No N/A 
48/F No N/A 
69/F Yes N/A 
Yes 57/M No 
61/F III Yes 
48/F No 
59/F III Yes 
62/F III No 
10 69/F No 
11 80/F III No 
12 25/F No 
13 45/F IV No 
14 57/M II Yes 
15 51/F III No 
16 40/M II No 
17 50/F IV No 
18 31/F No 
19 72/F No 
20 63/F II No 
21 57/M No 
22 41/F No 
23 69/M III No 
24 18/M No 
Endovascular No 25 62/F No N/A 
Yes 26 41/F II No 
27 73/F No 
28 64/M IV No 
29 38/F IV No 
30 81/F No 
Treatment Ruptured? Patient no. Age (yr)/sexb Hunt and Hess grade CN III palsy Fisher grade 
Surgical No 37/F Yes N/A 
63/F No N/A 
48/F No N/A 
69/F Yes N/A 
Yes 57/M No 
61/F III Yes 
48/F No 
59/F III Yes 
62/F III No 
10 69/F No 
11 80/F III No 
12 25/F No 
13 45/F IV No 
14 57/M II Yes 
15 51/F III No 
16 40/M II No 
17 50/F IV No 
18 31/F No 
19 72/F No 
20 63/F II No 
21 57/M No 
22 41/F No 
23 69/M III No 
24 18/M No 
Endovascular No 25 62/F No N/A 
Yes 26 41/F II No 
27 73/F No 
28 64/M IV No 
29 38/F IV No 
30 81/F No 
a

CN, cranial nerve; N/A, not applicable.

b

Female versus male, statistically significant (P = 0.0035, χ2 test).

The majority of patients (25 of 30, 83%) presented with subarachnoid hemorrhage. Four (17%) of 24 patients who underwent surgical clipping and one (17%) of six patients who underwent endovascular coiling were treated for unruptured aneurysms. Five patients (15%) presented with third cranial nerve palsies; two of these patients had unruptured ICA-PComA aneurysms. Aneurysms were located on the right side in 16 patients (53%) and on the left side in 14 patients (47%). The mean maximal aneurysm diameter was 7 mm (range, 3–20 mm). Five patients (17%) had multiple aneurysms on preoperative angiography. Two of these patients had bilateral ICA-PComA aneurysms. Locations of additional aneurysms in the other three patients were as follows: 1) contralateral cavernous ICA aneurysm, 2) ipsilateral carotid bifurcation and contralateral ophthalmic artery aneurysm, and 3) ipsilateral ICA bifurcation aneurysm.

Of the 24 patients treated surgically, 12 (50%) underwent temporary clipping of the ICA before ICA-PComA aneurysm clipping (Table 2). The mean ischemia time was 4.8 minutes. The majority of aneurysms were ligated with 7-mm straight clips. Multiple clips were used in 21% of cases. A fenestrated clip was used in one patient in conjunction with a straight clip. Intraoperative rupture occurred in four patients (17%).

TABLE 2

Clinical and radiographic outcomes of 30 patients undergoing treatment for internal carotid artery-posterior communicating artery aneurysms occurring at fetal posterior cerebral artery originsa

Treatment Ruptured? Patient no. Intraoperative rupture? Vasospasm Complications GOS Fetal PCA on postoperative angiography 
Surgical No No None None Preserved 
No None None Preserved 
No Clinical + radiographic None Preserved 
No None None Preserved 
Yes No None None Preserved 
Yes Clinical + radiographic + stroke IOR, stroke, sepsis, death N/A 
No Clinical + radiographic None Preserved 
No Radiographic None Preserved 
No Clinical + radiographic None Preserved 
10 Yes Clinical + radiographic IOR Preserved 
11 No None None Preserved 
12 No None none Preserved 
13 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
14 No Clinical + radiographic + stroke Left occipital infarct (asymptomatic) Occluded 
15 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
16 Yes Clinical + radiographic + stroke IOR, vasospasm, stroke Preserved 
17 No None None Preserved 
18 Yes Clinical + radiographic IOR Preserved 
19 No Clinical + radiographic None Preserved 
20 No Clinical + radiographic None Preserved 
21 No None None Preserved 
22 No Clinical + radiographic None Preserved 
23 No None None n/a 
24 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
Endovascular No 25 No None None Preserved 
Yes 26 No None None Preserved 
27 No None DVT Preserved 
28 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
29 No Clinical + radiographic None Preserved 
30 No None Remnant neck requiring repeat coiling Preserved 
Treatment Ruptured? Patient no. Intraoperative rupture? Vasospasm Complications GOS Fetal PCA on postoperative angiography 
Surgical No No None None Preserved 
No None None Preserved 
No Clinical + radiographic None Preserved 
No None None Preserved 
Yes No None None Preserved 
Yes Clinical + radiographic + stroke IOR, stroke, sepsis, death N/A 
No Clinical + radiographic None Preserved 
No Radiographic None Preserved 
No Clinical + radiographic None Preserved 
10 Yes Clinical + radiographic IOR Preserved 
11 No None None Preserved 
12 No None none Preserved 
13 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
14 No Clinical + radiographic + stroke Left occipital infarct (asymptomatic) Occluded 
15 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
16 Yes Clinical + radiographic + stroke IOR, vasospasm, stroke Preserved 
17 No None None Preserved 
18 Yes Clinical + radiographic IOR Preserved 
19 No Clinical + radiographic None Preserved 
20 No Clinical + radiographic None Preserved 
21 No None None Preserved 
22 No Clinical + radiographic None Preserved 
23 No None None n/a 
24 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
Endovascular No 25 No None None Preserved 
Yes 26 No None None Preserved 
27 No None DVT Preserved 
28 No Clinical + radiographic + stroke Vasospasm, stroke Preserved 
29 No Clinical + radiographic None Preserved 
30 No None Remnant neck requiring repeat coiling Preserved 
a

GOS, Glasgow Outcome Scale; PCA, posterior cerebral artery; IOR, intraoperative aneurysm rupture; N/A, not applicable; DVT, deep vein thrombosis.

Twenty-eight patients underwent postoperative angiography. Preservation of the fetal PCA vessel was demonstrated in 27 (96%) of 28 patients (Figs. 13). In one patient who underwent surgical clipping (Patient 14), the fetal PCA vessel was sacrificed intraoperatively This patient was noted to have a radiographically documented postoperative occipital stroke, yet the patient did not develop any clinical manifestations as a result of this infarct. All six patients who underwent coil embolization demonstrated patency of the fetal PCA vessel on postoperative angiography.

FIGURE 1

Patient 3. Preoperative right anteroposterior (A) and lateral (B) cerebral angiograms demonstrating a large internal carotid artery (ICA)-posterior communicating artery (PComA) aneurysm. Note the filling of the posterior cerebral artery (PCA) with the ICA injection. C, angiogram of the left vertebral artery demonstrating filling of the left PCA but not the right (fetal-type) PCA.

FIGURE 1

Patient 3. Preoperative right anteroposterior (A) and lateral (B) cerebral angiograms demonstrating a large internal carotid artery (ICA)-posterior communicating artery (PComA) aneurysm. Note the filling of the posterior cerebral artery (PCA) with the ICA injection. C, angiogram of the left vertebral artery demonstrating filling of the left PCA but not the right (fetal-type) PCA.

FIGURE 2

Three-dimensional computed tomographic angiography reconstruction image demonstrating a trans-sellar view of the right ICA-PComA aneurysm and fetal PCA.

FIGURE 2

Three-dimensional computed tomographic angiography reconstruction image demonstrating a trans-sellar view of the right ICA-PComA aneurysm and fetal PCA.

FIGURE 3

Postoperative right anteroposterior (A) and lateral (B) angiograms demonstrating complete occlusion of the aneurysm after clip ligation, with preservation of the fetal PCA.

FIGURE 3

Postoperative right anteroposterior (A) and lateral (B) angiograms demonstrating complete occlusion of the aneurysm after clip ligation, with preservation of the fetal PCA.

Small residual neck remnants were noted on postoperative angiography in two patients who were treated surgically (8.3%). One patient (Patient 30) who was treated with endovascular coiling (17%) was noted on follow-up angiography to have a residual aneurysm, which required additional coil embolization 3 months after initial coiling. Fifteen patients (50%) demonstrated radiographic evidence of vasospasm on postoperative angiography. Ten of these patients had clinical manifestations of vasospasm and required hypertensive, hypervolemic, hemodilution therapy. One patient required subsequent angioplasty for refractory vasospasm. None of the patients experienced postoperative visual deficits. Glasgow Outcome Scale (GOS) scores for the 30 patients at the time of discharge were as follows (Table 2): GOS 5 (20 patients, 67%), GOS 4 (five patients, 17%), GOS 3 (three patients, 10%), GOS 2 (one patient, 3%), GOS 1 (one patient, 3%).

Discussion

According to some series, ICA-PComA aneurysms are the most frequently occurring cerebral aneurysms, comprising approximately 30% of all cerebral aneurysms and more than 50% of all ICA aneurysms (2, 1012). ICA-PComA aneurysms originating at the origin of fetal PCA vessels deserve special attention from neurosurgeons, neurologists, and neuroradiolo-gists. Injury or occlusion of the fetal PCA may result in occipital infarcts and subsequent clinical complications, such as homonymous hemianopsia, alexia, aphasia, and hemiachro-matopsia (6). Perforators originating from the PComA may also be compromised secondary to inadvertent clipping of the par-ent PComA vessel, causing midbrain or thalamic injury. Furthermore, a greater relative frequency of ICA-PComA aneurysms has been reported to occur in patients with fetal variant circulation (4).

In the current study, we report the first operative and endovascular series of ICA-PComA aneurysms originating from the origin of a fetal PCA, which comprised 11% of all ICA-PComA aneurysms treated at USC during the past 15 years. The decision to treat these aneurysms with surgical versus endovascular therapy was based primarily on the patient's clinical status and overall configuration of the aneurysm, including a favorable neck-to-dome ratio and parent vessel size. The current study does not prove the relative efficacy of one modality of treatment over the other for aneurysms of this type, given the clear limitations of the retrospective nature of the study and the relatively small number of patients. On the basis of our experience, however, the frequency of fetal ICA-PComA aneurysms treated with endovascular therapy was significantly lower than the overall frequency of ICA-PComA aneurysms treated with coiling. In most cases, coiling was deferred so that the aneurysm could be clipped under direct surgical observation. The risk of coil migration into the lumen of the fetal PCA was felt to be unacceptably high in the majority of the cases. However, no fetal PCA occlusion occurred in the six cases treated with coiling, in part because of the careful pretreatment assessment of the neck-to-dome architecture.

Anatomic Variations of the Fetal PCA Circulation

There are many potential anatomic variations of the posterior circle of Willis, depending in part on the caliber of the PComAs and their relationship to the PCAs. In the “normal” adult circle of Willis, the PComA is smaller than the PCA or is even altogether absent. The other extreme is the fetal-type PCA, in which the P1 segment is absent or hypoplastic and the PComA is significantly larger. Finally, there exists a “partial” state in which the P1 segment is smaller than the PComA, and flow into the distal PCA originates from both the anterior and posterior circulation (15). One angiographic study demonstrated that the PCA receives at least partial contribution of flow from the ICA via the PComA in 57% of cerebral hemispheres (75% of patients) (6). There is also considerable variation among perforating branches originating from the PComA. The PComA supplies an average of eight perforating vessels, which in turn pertuse the midbrain, thalamus, optic chiasm, optic tract, pituitary stalk, internal capsule, and hypothalamus (2, 8, 10, 12). The largest of these branches, the anterior thalamoperforating artery, enters the floor of the third ventricle anterior to the mamillary bodies (2).

Prevalence of the Fetal PCA Variation and Relationship to Cerebral Aneurysms

The authors of many previous studies have attempted to define the prevalence of fetal PCAs. The results of these studies have varied tremendously, depending mainly on the criteria used to define a fetal PCA and the modality used to do so. The “gold standard” remains cerebral angiography, in which fetal PCAs can be identified because the PComA is the major source of filling of the PCA, whereas minimal or no blood fills the PCA from the vertebrobasilar system, secondary to a hypoplastic or altogether absent P1 segment. The overall prevalence of unilateral fetal PCAs has been reported to occur in 4 - 29% of the population, whereas the prevalence of bilateral fetal PCAs has been reported to occur in 1 to 9% of the population (1, 2, 4, 6, 15). The authors of one report used magnetic resonance angiography to study anatomic subtypes of the circle of Willis in a group of patients with known ICA aneurysms; they demonstrated that the most common anatomic subtype (47% of patients with ICA aneurysms) was the fetal variant circulation (4). This phenomenon has been attributed to increased blood flow and secondary shear stress into the larger-caliber fetal PCA vessel (3, 4). The same study also noted that the fetal-type circulation was significantly more common in women (35.7 versus 21.9%, P < 0.01). This finding was corroborated in the present study, with 75% of patients being women. Previous studies have noted that asymmetries between the two PComAs are also associated with a greater incidence of aneurysms (7) and that aneurysms more frequently occur on the side ipsilateral to the larger-diameter PComA (9).

Does the Fetal PCA Anatomy Confer a Protective Benefit against Ischemic Injury?

It remains unclear as to whether a fetal-variant PCA confers a universal protective effect in patients at risk for cerebral ischemia. It is understood that patients with a thrombotic or embolic occlusion of a major cerebral artery may depend on flow (anterograde or retrograde) through the PComA for collateral circulation. For instance, larger-diameter PComAs (>1 mm) have been shown to confer a protective effect in patients with complete occlusion of the ipsilateral ICA, secondary to retrograde flow through the PComA vessel (14). In another study, Jongen et al. (6) reviewed a group of patients with occipital lobe infarcts, as compared with a group of healthy controls, by using magnetic resonance angiography. They demonstrated a significantly lower proportion of fetal PCA variant circulation in the patient group with occipital infarcts. On the other hand, a recent study by van Raamt et al. (15) reported that patients with fetal-type circulations may not develop as robust a lep-tomeningeal collateral circulation because the anterior and posterior circulations are both derived from the ICA. They proposed that patients with fetal PCAs are, therefore, more prone to developing vascular insufficiency because of this underdeveloped collateral circulation. Therefore, it may very well be that an intermediate state allowing bidirectional flow through the PComA as well as the ability to develop adequate collateral flow may confer the greatest protective benefit. In one of our patients (Patient 12), the fetal PCA was obliterated intraopera-tively. However, this patient did not develop any clinical sequelae as a result of this stroke. A plausible explanation is that the stroke was limited, owing to sufficient collateral perfusion.

Operative Strategy

There are certain anatomic features relative to the proximal ICA that add complexity to ICA-PComA aneurysm surgery. The immobility of the carotid artery caused by the tethering effect of the distal dural ring makes visualization of the circumference of the artery difficult. Furthermore, in the anatomic position presented by a typical pterional/transsylvian approach, the origin of the PComA is frequently obscured by the overlying neck or sac of the aneurysm itself (Fig. 4A). Frequently, some deflection of the rostral side of the aneurysm sac in a more caudal direction needs to be accomplished before the PComA origin is appreciated (Fig. 4B).

FIGURE 4

Schematics demonstrating a traditional view of a pterional/ transsylvian approach to a large ICA-PComA aneurysm. A, the origin and body of the PComA are obscured by the aneurysm. B, gentle deflection of the aneurysm with a blunt instrument can be used to identify the PComA and its origin.

FIGURE 4

Schematics demonstrating a traditional view of a pterional/ transsylvian approach to a large ICA-PComA aneurysm. A, the origin and body of the PComA are obscured by the aneurysm. B, gentle deflection of the aneurysm with a blunt instrument can be used to identify the PComA and its origin.

The shape of the clip that is selected to occlude the aneurysm is an important aspect of ICA-PComA aneurysm obliteration. In larger aneurysms, especially those in which coil emboliza-tion is not feasible, the neck of the aneurysm involves a large portion of the circumference of the carotid artery. There arises a natural tendency to select a curved clip that, in obliterating the aneurysm neck, would more closely parallel the curvature of the carotid vessel. Because the origin of the PComA is almost invariably part of the neck of the aneurysm, a curved clip will usually narrow the outflow to the PComA. Thus, it is important to allow a portion of the neck of the aneurysm to fill so that the PComA, especially a fetal variant, remains patent.

The path of the PComA is generally from lateral and posterior on the carotid artery to a more medial trajectory into the posterior fossa arachnoid cistern. A straight clip placed along the wall of the ICA will generally not occlude the PComA in its cisternal segment. However, because the carotid artery is quite immobile in this region, frequently the clip is placed “blindly” relative to the depth and position of the cisternal segment of the PComA. The immobility of the carotid artery makes its medial deflection so as to open the space between the carotid and the edge of the tentorium difficult. Furthermore, this maneuver may very well rupture the aneurysm as the dome is mobilized. We find it more desirable to place a straight clip, and then, once the dome is collapsed, explore the path of the PComA and choroidal arteries, adjusting the trajectory of the microscope or using an endoscope as necessary to see “behind” the carotid vessel.

It is important to identify the presence or absence of a fetal PCA variant on preoperative imaging studies. Although it is our goal to preserve PComA perfusion in all surgical ICA-PComA aneurysm cases, the likelihood of a substantial neurological deficit is heightened by the occlusion of a fetal PCA variant. Fetal variant PCAs are usually larger in diameter, originate more laterally, and course superolaterally to the oculomotor nerve rather than superomedially (10, 11). Furthermore, in the event of prolonged temporary clip occlusion, a wider distribution of cerebral ischemia would be expected to occur. In the event of premature intraoperative aneurysm rupture, temporary occlusion of the PComA or fetal PCA may be necessary as a separate adjunct to gain control for the purpose of accurate aneurysm clip placement.

Many intraoperative modalities exist for confirming patency of the PComA after clip placement. Techniques such as visualization using a mirror or endoscope have been reported (8). Microvascular Doppler probes with 1- to 2-mm tips can also be useful in checking for patency of this vessel. Postoperative angiography remains the gold standard for postoperative confirmation of flow through the fetal PCAs.

Conclusions

ICA-PComA aneurysms originating from the takeoff of fetal variant PCA vessels deserve special attention before surgical or endovascular obliteration. According to our review, fetal variant vessels were observed in 11% of all ICA-PComA aneurysms treated at our institution during the past 15 years, and they were significantly more common in women. These aneurysms carry a greater risk profile in regard to injury to the fetal PCA vessel and dependent perforator and occipital lobe perfusion. The decision of surgical versus endovascular treatment of these aneurysms must be carefully considered, given the greater potential for ischemic injury with parent vessel occlusion.

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Comments

In this retrospective review, Zada et al. report on the 15-year experience of the senior author in treating posterior communicating artery (PComA) aneurysms. They specifically investigated treatment of fetal variant PComA aneurysms. They demonstrated a female predominance of this condition (75%), and 83% of their 24 patients presented with subarachnoid hemorrhages. The series supports surgical treatment for these lesions with 21 of 22 patient treated surgically with postoperative angiograms demonstrating patency of the posterior cerebral artery (PCA) and only 8.3% demonstrating a residual neck remnant. The clip strategy generally deployed involved the use of a straight blade placed along the wall of the internal carotid artery not to occlude the PComA.

PComA aneurysms are common, and when fetal variant circulation is present, it is important to first recognize this and plan the surgical approach accordingly. In an era of endovascular treatment for intracra-nial aneurysms, this report provides a benchmark for endovascular treatments if so chosen. Zada et al. demonstrated the feasibility of surgical treatment with a more than 91% complete occlusion rate and with good outcomes (88% with Glasgow Outcome Scale scores of 4 or 5) in a series in which 83% of patients presented with subarachnoid hemorrhage.

Daniel Surdell

H. Hunt Batjer

Chicago, Illinois

Zada et al. report on 30 patients over a 15-year period who had aneurysms located at the origin of the fetal PCA. Their experience indicated very good results whether these aneurysms were treated with an endovascular or a surgical approach. Either approach is very different from that for a standard PComA aneurysm, as everyone realizes. Often endovascular approaches are not possible or complete occlusion is not possible with a stent because of potential risk to the origin of the fetal PCA. At our institution, unless the aneurysm really has a discrete neck, we prefer to treat it with a surgical approach, as our experience with the endovascular approach has been incomplete occlusion even with a stent-assisted or balloon-assisted technique.

In these aneurysms in particular, intraoperative angiography is invaluable to be certain that the fetal PCA is open and that the aneurysm is totally occluded. Because this is different from the standard PComA aneurysm, visualization of the posterior wall is critical. As a wise sage once said, “One of the falsehoods in aneurysm surgery is that this is ‘just a PCom.’”

Robert H. Rosenwasser

Philadelphia, Pennsylvania

Zada et al. have provided an excellent retrospective analysis of the senior author's experience at the University of Southern California in treating patients with fetal PCA aneurysms over a 15-year period. Anatomic variations of fetal PCA circulations, prevalence, and ischemic implications are reviewed, as are outcome data and operative strategies. They emphasize the greater importance of maintaining patency of the fetal PComAs in these patients, as these aneurysms are truly different lesions from internal carotid artery aneurysms arising at the origin of a normal PComA. In our own multidisciplinary practice, we have found that these lesions are more likely to undergo surgical management because of the importance of preserving the PComA, as is the case at University of Southern California. We argue that intraoperative rather than postoperative angiography is the “gold standard” for confirmation of flow through the fetal PCAs, as well as for confirmation during the operation that the aneurysm has been completely obliterated. This is an excellent study.

Alexander Mason

Daniel L. Barrow

Atlanta, Georgia

Aneurysms at the origin of a fetal PCA are very common in any aneurysm practice. In this series from the University of Southern California, a large group of patients with these types of aneurysms are reviewed. Both surgical clipping and endovascular coiling were used to obliterate the aneurysms in this series. Surgical clipping was much more frequently performed, given the imperative to protect the integrity of the parent PCA vessel.

The example case in Figures 1 and 2 of the article nicely illustrates the anatomic issues that are frequently encountered with all carotid artery/PComA aneurysms. The origin of the PComA or fetal PCA is usually intimate with the neck of the aneurysm. This finding may limit the efficacy of coil embolization, as complete packing of the aneurysm may be prevented when preservation of the branch vessel is desired. Although preservation of the origin of a fetal PCA is critically important for a good outcome, preservation of the carotid origin of normal PComAs is also a good practice. Occlusion of the carotid origin of the PComA is often tolerated without sequelae, but this assumption is not universal. Critical perforators come off the PComA. The exact position of these perforators and the dual supply of the PComA from the carotid artery and the PCA are not always reliably defined with angiography. Therefore, the goal of treatment of PComA aneurysms, with or without a fetal PCA, should be preservation of the carotid origin of the parent vessel.

Robert A. Solomon

New York, New York

Learning neurovascular anatomy and its aberrations is a lifelong necessity for practicing neurovascular surgeons. One can study illustrative textbooks, articles (14) and images, watch operative videos and live microneurosurgery, and perform surgery by himself or herself. In planning a surgical procedure starting with the position of the patient's head, the incision, and the bony window, one should pay attention to any anatomic variations as they may cause confusion and problems if detected during surgery. Zada et al. describe nicely the rare occurrence of an internal carotid artery aneurysm at the origin of a fetal variant of the PComA that occurred up to 11% in their series, which is not infrequent. Careless occlusion of the aneurysm neck may cause parent artery occlusion, too, often with subsequent neurological deficits. Confirmation of patency may sometimes necessitate intraoper-ative angiography in addition to endoscopic visualization or Doppler as suggested by the authors.

Reza Dashti

Istanbul, Turkey

Mika Niemelä

Juha A. Hernesniemi

Helsinki, Finland