Presigmoid Transpetrosal Approach for Superficial Temporal Artery to Distal Posterior Cerebral Artery Bypass and Trapping of Aneurysm

Abstract

BACKGROUND AND IMPORTANCE

Aneurysms of the posterior cerebral artery (PCA) are uncommon, estimated at less than 1% of all cerebral aneurysms, and less than half occur distal to the P1/2 junction. Unfortunately, the conventional bypass approach for PCA aneurysms—primarily occipital artery to distal PCA cortical branches—has a history of unsatisfying results.

CLINICAL PRESENTATION

A 42-yr-old female presented with Fisher 3 Hunt-Hess 2 subarachnoid hemorrhage secondary to ruptured distal PCA aneurysm. She was initially evaluated by the endovascular service, but due to recent subarachnoid hemorrhage, endovascular treatment with flow diversion and/or vessel sacrifice was felt to be relatively contraindicated and the patient was referred for surgical evaluation for possible bypass. The patient subsequently underwent surgery for trapping of aneurysm and concomitant superficial artery to distal PCA bypass.

CONCLUSION

A novel approach for the treatment of a ruptured distal PCA aneurysm is described, consisting of posterior transpetrosal exposure and division of the tentorium with superficial temporal artery to P3 bypass.

ABBREVIATIONS

BTO

balloon test occlusion

COPE

Committee on Publication Ethics

CSF

cerebrospinal fluid

IRB

Institutional Review Board

OA

occipital artery

PCA

posterior cerebral artery

SAH

subarachnoid hemorrhage

STA

superficial temporal artery

Distal aneurysms of the posterior cerebral artery (PCA) are rare lesions. Conventional approaches to these aneurysms include open or endovascular vessel sacrifice, with or without revascularization. Occipital artery (OA) to distal PCA bypass is a technically difficult operation with a relatively low rate of success. A new approach to these aneurysms is described consisting of presigmoid transpetrosal exposure and superficial temporal artery (STA) to distal (PCA) bypass.

CLINICAL PRESENTATION

A 42-yr-old right-handed female presented with diffuse subarachnoid hemorrhage (SAH) to an outside hospital; subsequent angiography was performed showing a fusiform dissecting pseudoaneurysm of the PCA. The patient was transferred to our institution on postbleed day 6. The patient complained of headache without lateralizing or focal neurological deficits. She was evaluated by the endovascular service (R.J.); endovascular treatment including flow diversion was felt to be high risk due to the need for dual antiplatelet therapy in the setting of SAH. Preoperative angiography was reviewed, demonstrating a fetal configuration of the PCA with a fusiform aneurysm of the P2 segment; selective external carotid views confirmed the presence of a suitable donor STA (Figure 1). Craniotomy for the trapping of the aneurysm and STA-PCA was recommended.

FIGURE 1.

Preoperative anteroposterior A and lateral B digital subtraction angiography demonstrates a fetal configuration of the PCA with a fusiform aneurysm of the P2 segment; selective external carotid views confirmed the presence of a suitable donor STA for bypass C.

Institutional Review Board (IRB)/ethics committee approval and patient consent statement: This study was performed in accordance with institutional IRB policies and the Committee on Publication Ethics (COPE) standards for reporting of case reports. Consent for publication has been obtained from the patient.

Surgery

The patient was positioned supine and the STA was mapped on the scalp with a Doppler probe to 12 cm above the zygoma. A horseshoe incision was made beginning at the mastoid tip and extending over the STA (Figure 2). The STA was skeletonized, transected, and a temporarily clipped while the craniotomy was performed.

FIGURE 2.

Artist's illustration of the horseshoe incision extending from the mastoid tip behind the ear and extending in continuity to the course of the STA anteriorly.

A rectangle middle fossa craniotomy was performed centered two-thirds posterior to the external auditory canal. A posterior petrosectomy was performed with a combination of cutting and diamond burs exposing the dura of Trautmann's triangle, presigmoid dura, and sinodural angle (see Video). Violation of the otic capsule was avoided by recognition of the operculum of the endolymphatic sac, which serves as a landmark for the posterior semicircular canal (Figure 3). The tentorium was divided after protection of the trochlear nerve (Figure 4). The aneurysm, distal bifurcation of the PCA to the posterior temporal and P3 segments, and the proximal PCA were identified. After temporary clipping, the STA bypass was performed, with an interrupted 10-0 suture on the far end of the bypass and a running 10-0 on the near side (Figure 5). Patency was confirmed with Doppler ultrasound, and fluorescent video-angiography. In addition to the PCA aneurysm, an abnormal vessel (likely a duplicated PCA) was identified, with a saccular aneurysm located at the origin of this vessel and the ICA, which was clipped. The bony defect was filled with collagen onlay graft and fibrin glue and covered with a titanium mesh. A lumbar drain was placed to mitigate the risk of cerebrospinal fluid (CSF) leak.

FIGURE 3.

Axial computed tomography showing the extent of posterior petrosal drill-out and relative position of posterior semicircular canal (arrow).

FIGURE 4.

Artist's illustration of the initial dural opening and division of the tentorium; the fusiform aneurysm and trochlear nerve are visible at the medial edge of the tentorium.

FIGURE 5.

Artist's illustration of an overview of aneurysm trapping and distal STA-PCA bypass.

Postoperative Course

The patient was extubated after obtaining a postoperative angiogram (Figure 6). She was noted to have a new third nerve paresis but was otherwise neurologically intact. She was started on aspirin 325 mg daily. Lumbar drainage was discontinued on postoperative day 4, and she was discharged on postoperative day 6. On 3-mo follow-up, the patient was neurologically intact with resolution of her third nerve palsy and with intact visual fields, and she remains neurologically intact with no evidence of stroke at 12-mo follow-up.

FIGURE 6.

Postoperative lateral A selective external carotid digital subtraction angiography shows the filling of distal PCA territory by the STA, and lateral common carotid angiogram B confirms the absence of residual aneurysm.

DISCUSSION

Aneurysms of the PCA are uncommon, estimated at less than 1% of all cerebral aneurysms, and less than half occur distal to the P1/2 junction.¹ The treatment of these lesions remains controversial and requires multidisciplinary management.^2-4 Endovascular vessel sacrifice, with or without OA to distal PCA bypass, has been the mainstay approach to these aneurysms described in the literature,^2,4-7 although other approaches, including flow diversion,⁸ aneurysmorhaphy and clipping,⁹ and in Situ SCA-PCA bypass,¹⁰ have been described.

Hallacq et al⁷ reported a series of 10 P2 segment aneurysms all treated with endovascular PCA occlusion without ischemic complications, which they attributed to the rich collateral supply to the distal PCA. However, a significant visual field deficit may occur in up to 17% of cases,¹¹ and the risk of disabling or life-threatening complications, though rare, is not negligible.⁵ Hence, revascularization following vessel sacrifice ought to be considered when possible. Conventional bypass approaches for PCA aneurysms—primarily OA to distal PCA cortical branches—have a history of unsatisfying results. Chang et al¹² reported a 53% failure rate in 14 patients undergoing OA-PCA bypass for PCA aneurysms, the largest series in the literature. Bypass was associated with a high risk of complication and worse outcomes compared to patients not undergoing bypass, leading the authors to recommend against routine revascularization of these aneurysms prior to vessel sacrifice. Because of the risk of complications, Chang et al¹² advocate for balloon test occlusion (BTO) to determine whether bypass is indicated. However, the predictive value of BTO for PCA aneurysms is not established, and postoperative stroke has been reported even in the presence of a successful distal occipital to cortical PCA branch.¹³

Cadaveric studies have examined the feasibility of the presigmoid and subtemporal corridors for distal PCA bypasses,^14,15 and the retrolabyrinthine approach has previously been described in 3 patients for STA to SCA bypass.¹⁶

Kawashima et al¹⁷ have recently described STA to distal PCA (P3) bypass in 3 patients using a standard subtemporal approach. We believe that the presigmoid transpetrosal approach utilized in the present case has several advantages over a subtemporal approach, including a shallower approach to the ambient cistern making the anastomosis less difficult, reduced risk of kinking of the STA by the tentorium, and no need for the resection of fusiform gyrus in order to expose the aneurysm. These benefits come at the cost of postauricular exposure and transpetrosal drill-out.

CONCLUSION

Our approach decreases the technical hurdle of performing STA-PCA bypass; however, the exposure requires familiarity with skull-base anatomy and may incur an increased risk of approach-related complications such as CSF leak, hearing loss, and facial nerve injury. Familiarity with skull base approaches such as the presigmoid transpetrosal approach described here is valuable for vascular neurosurgeons.

Funding

This study did not receive any funding or financial support.

Disclosures

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.