Treatment of an infundibular aneurysm by posterior communicating origin disconnection, induced flow reversal and flow diversion after attempted surgical clipping: Case report

Abstract

Infundibular aneurysms are rare lesions that present unique challenges for both surgical and endovascular approaches. We present a case of a 58-year old man with an incidental 7.5 × 3 mm infundibular aneurysm that incorporated the origin of the posterior communicating artery (PCoA). The fusiform aneurysm incorporated the supraclinoid ICA to the terminus. An attempt at surgical clip reconstruction of the aneurysm to preserve the PCoA was not technically possible due to atherosclerosis at the aneurysm neck. The aneurysm was treated with disconnection of the PCoA origin, induced flow reversal and placement of a flow diverter, after confirmation of adequate collateral flow to the PCoA perforators from the posterior circulation. The case illustrates important concepts in the evaluation and management of infundibular aneurysms, including both reconstructive and deconstructive strategies.

Introduction

Infundibular aneurysms are rare but may be differentiated from benign infundibula by size and morphology and may grow to form true aneurysms or cause subarachnoid hemorrhage.^1–5 Treating large infundibular aneurysms presents a therapeutic challenge, as preservation of flow within the branch vessel, usually the posterior communicating artery (PCoA), limits endovascular options. We present a case of a fusiform infundibular aneurysm that was not amenable to surgical clipping, but which was successfully treated with placement of coils to disconnect the PCoA from the anterior circulation, along with flow diversion of the ICA.

Case report

A 58-year old, right-handed truck driver presented after a syncopal episode and was found to have two incidental right sided aneurysms: a saccular middle cerebral artery (MCA) bifurcation aneurysm and a larger fusiform infundibular aneurysm involving the origin of the PCoA. He had no history of prior rupture or associated symptoms. On examination, the patient was neurologically intact. A diagnostic catheter angiogram was performed, which demonstrated a 7.5 × 3 mm right PCoA infundibular aneurysm, which was irregular with a daughter saccule (Figure 1). The PCoA originated from the apex of the dome of the aneurysm. Selective injection of the right vertebral artery demonstrated patency of the right P1 segment and adequate collateral filling of the PCoA from the posterior circulation. The PCoA was not fetal or near-fetal in configuration. Due to the size and morphology of the PCoA aneurysm, treatment was recommended.

Figure 1.

A 58-year old man presented after a syncopal episode and was found to have a 7.5 × 3 mm fusiform, infundibular aneurysmof the right PCoA (DSA lateral (A), high-mag oblique (B), 3D reconstruction (C)). After multidisciplinary discussion, a plan for surgicalintervention to treat the aneurysm with clip reconstruction with a goal of preserving flow within the PCoA was devised. At surgery, theinfundibular aneurysm with PCoA originating from the dome was demonstrated (D). E, fusiform aneurysm involving the distal supraclinoid ICA, with atherosclerosis, prevented clip reconstruction. The patient was brought back two months later for endovascular treatment. From a radial approach, a microcatheter was placed at the apex of the aneurysm and the infundibular aneurysm was embolized with 3 Penumbra PC400 coils (F, G, post-embolization DSA AP and lateral oblique views). The microcatheter was repositioned in the proximalright MCA, and a 4.5 × 20 mm Pipeline Flex flow diverting stent was placed spanning from the proximal right M1 segment to the ophthalmic segment of the right ICA (H, I, unsubtracted DSA images AP and lateral oblique). J, Final post-embolization lateral DSA demonstrates no fillingof the PCoA from the anterior circulation and obliteration of the aneurysm. K, post-operative CTA demonstrates patency of the stent and satisfactory coil placement.

The patient elected for surgical management in order to possibly preserve flow in the PCoA and its perforators. At surgery, the aneurysm was found to be fusiform and incorporate not only the PCoA origin, but also the supraclinoid internal carotid artery (ICA) to the terminus. Severe atherosclerosis of the aneurysm neck meant that aneurysms clips would not close on the aneurysm, and there was a high risk of embolizing parts of diseased, atheromatous material from the aneurysm into the PCoA or ICA. The aneurysm was not able to be treated, but the ipsilateral MCA aneurysm was treated with routine microsurgical clipping, and the patient made an uneventful recovery and was discharged home.

Two months later, the patient was brought to the angiography suite for embolization, after pre- treatment with dual antiplatelet medication (aspirin and clopidogrel) for 7 days. Using a 6 French sheath in the right radial artery, a Navien intermediate catheter which was advanced under fluoroscopic guidance to the petroclival junction. Diagnostic angiography confirmed adequate filling of the right PCoA from the right posterior cerebral artery (PCA). It was clear that treatment with a single or multiple flow diverting stents was unlikely to provide a cure for this fusiform infundibular aneurysm, as the large PCoA originated from the aneurysm dome. Therefore, a treatment plan was devised in which the aneurysm was first coiled, disconnecting the PCoA origin from the anterior circulation but taking care not to place coils within the PCoA itself. Continuous monitoring of SSEPs and MEPs confirmed adequate perfusion of PCoA perforators. After coiling with 3 PC400 coils (Penumbra, Alameda, CA), a 4.5 × 20 mm Pipeline flow diverting stent (Medtronic, Dublin, Ireland) was placed from the proximal M1 segment of the right MCA distal to the aneurysmal dilatation, to the ophthalmic segment of the ICA, spanning the area of fusiform aneurysmal neck. Adequate flow reversal with filling of the PCoA from the posterior circulation was confirmed at the end of the case, although PCoA perforators were not specifically visualized angiographically due to the small caliber of these vessels. The patient was observed in the intensive care unit overnight, made a good recovery and was discharged home on post-procedure day 2, neurologically intact.

Discussion

True intracranial infundibula have classically been defined by the following criteria: triangular or funnel shape; artery coming directly out of the apex of the dilatation; and size of <3 mm. ⁶ Although thought to be a normal variant and typically benign, subarachnoid hemorrhage is a possible consequence of rupture of intracranial infundibula even without prior enlargement into saccular aneurysms.^1–5 Infundibula may also enlarge significantly over time and evolve into saccular aneurysms. ⁷ When infundibular dilatations are large (>3–5 mm), or incorporate the parent vessel separate from the branch point, they share more in common with fusiform aneurysms than true infundibula. Nevertheless, the presence of the branch vessel originating directly from the apex of the aneurysm presents particular challenges in devising an optimal management strategy.

Reconstructive therapy that seeks to preserve flow in the branch vessel is most conceptually appealing. However, due to the direct involvement of the vessel origin in the pathology, endovascular coiling or endosaccular treatment are unlikely to provide adequate exclusion of the aneurysm without also sacrificing the branch vessel. Flow diversion, on the other hand, may be less likely to provide definitive treatment as demand from the branch vessel is likely to draw continued flow into the aneurysm. There has been one report of an infundibulum that regressed after flow diversion of an adjacent aneurysm. ⁸ However, fusiform aneurysms and those with branch vessels from the aneurysm neck have been associated with lower complete occlusion rates in large series treated with flow diverting stents.^9,10 An alternative approach in this case may have been to employ multiple flow diverters, potentially in staged fashion, that may have provided enough metal coverage to result in a remodeling of the aneurysm over time.

Microsurgical clip reconstruction affords the potential for aneurysm exclusion with preservation of flow in the branch vessel, and should be the first line option for these aneurysms. However, surgical management may be complicated, and technical factors can limit the applicability of surgical techniques in some cases. Fusiform aneurysms that incorporate 360 degrees of the parent and branch vessel may not be amenable to clip reconstruction without stenosing the parent and limiting flow within both vessels. Larger, fusiform infundibular aneurysms are also often associated with atherosclerosis at the neck, which can hinder microsurgical treatment. Fenestrated clips increase clip closing force and may be reinforced with stacked, booster clips, but in extreme cases clipping may not be technically possible. Furthermore, clipping across an area of atherosclerotic plaque from which a branch vessel originates can send emboli distally into the branch or parent vessel.

Deconstructive therapy is generally safe when there is documented, adequate collateral circulation from the Circle of Willis to perfuse perforating branches of the infundibular vessel. Surgically, it is important to place clips both across the aneurysm neck, preventing antegrade flow from the parent vessel, and across the apex of the infundibular aneurysm, in order to prevent retrograde filling of the aneurysm from the collateral circulation. From an endovascular approach, a key consideration is packing the aneurysmal portion without coil extravasation into the small branch vessel. Even a single coil within a PCoA or AChA can cause infarction due to reduction of flow into small perforators. In the current case, attempted deployment of the first coil, which was a standard framing coil, resulted in coil advancing into the PCoA. The coil was removed and a thicker, PC400 coil with increased coil diameter was placed which was able to be positioned entirely within the aneurysm (Figures 1–2). In one angiographic study, the presence of perforators from a communicating segment aneurysm wall was associated with agenesis of the posterior communicating artery; when the PCOM was present, this configuration was very rare. ¹¹ Despite angiographic evidence of collateral circulation, disconnection of a branch vessel during treatment carries a small risk of procedure-related neurologic deficit. Continuous monitoring of SSEPs and MEPs under conditions of burst suppression and general anesthesia is an important intra-procedural precaution. Pausing prior to coil detachment to monitor signals for 5–10 min may be warranted in cases in which the adequacy of collateral circulation is uncertain. For cases in which fusiform changes are seen to extend into the parent vessel, such as the case described in this report, flow diversion in addition to coiling may offer the greatest likelihood of providing a lasting exclusion of the aneurysm with remodeling of the endothelium of the parent vessel.

Figure 2.

Cartoon demonstrating the technique of coil embolization of the infundibular aneurysm with subsequent stent placement. A, lateral oblique view of infundibular aneurysm incorporating PCoA origin. B, cut-away view. C, microguidewire advanced through the infundibular aneurysm into the PCoA. D, microcatheter advanced over the guidewire to the apex of the aneurysm but not into the PCoA proper. E, coils deployed in the aneurysm. F, catheter repositioned and flow diverting stent placed from proximal MCA to supraclinoid ICA. PCA = posterior cerebral artery; BA = basilar artery; PCoA = posterior communicating artery; MCA = middle cerebral artery; ACA = anterior cerebral artery; ICA = internal carotid artery.

Conclusions

Infundibular aneurysms are rare and present a challenge for both surgical and endovascular treatment strategies. Atherosclerosis at the neck of a wide-necked, fusiform aneurysm can make surgical treatment challenging. Endovascular solutions incorporating stent- or flow diversion-assisted coiling with disconnection of the circulations and induced flow reversal may be necessary in order to treat fusiform aneurysms in which the Circle of Willis provides adequate collateral flow from the unaffected circulation.