Treatment of posterior circulation non-saccular aneurysms with flow diverters: a single-center experience and review of 56 patients

Abstract

Background and purpose: Non-saccular aneurysms of the posterior fossa are an uncommon pathology with no clear treatment strategy. The use of flow-diverting stents (FDS) has had mixed results. We sought to evaluate our experience of FDS for the treatment of this pathology.

Methods: We retrospectively reviewed our database of prospectively collected information for all patients treated only with flow diversion for an unruptured non-saccular aneurysm of the posterior circulation between February 2009 and April 2016. The aneurysms were classified as dolichoectasia, fusiform or transitional, and imaging characteristics including maximal diameter, disease vessel segment, MRI features (intra-aneurysmal thrombus, T1 hyperintensity in the aneurysmal wall, infarctions in the territory of the posterior circulation, and mass effect) were recorded alongside clinical and follow-up data.

Results: We identified 56 patients (45 men) with 58 aneurysms. The average age of the patients was 63.5 years. Twenty-two patients were symptomatic from the aneurysms at presentation. The majority of the lesions were vertebrobasilar in location (44.8%) with isolated vertebral lesions representing 29.3% of aneurysms. Transitional aneurysms were the most common (48.2%). The mean maximal diameter of the aneurysms was 11 mm. Angiographic exclusion of the aneurysms was seen in 57.4% of aneurysms with follow-up (n=47). During the follow-up period nine patients died.

Conclusions: Treatment of non-saccular aneurysms of the posterior fossa is technically possible. Early treatment, particularly of the fusiform and transitional subtypes, is recognized, as is treatment prior to the development of symptoms. A 'watch and wait' strategy with regular imaging follow-up could be employed for asymptomatic dolichoectasia.

Keywords: Aneurysm; Flow Diverter; Posterior fossa; Stent; Stroke.

Figure 1

Examples of the different subtypes of aneurysm. (A) Dolichoectasia, smooth dilation of the basilar artery. (B, C) Fusiform dilation of the distal basilar artery. This aneurysm shows partial thrombosis on the MRI (not shown). (D, E) A transitional aneurysm of the basilar artery which is grossly dilated with a more focal abnormality that also shows thrombosis on MRI.

Figure 2

A patient with an asymptomatic V4 fusiform aneurysm (A, white arrow). Two telescoped Pipeline embolization devices were placed in situ with stagnation of contrast medium seen in the aneurysm at the end of the procedure (B, white arrow). A follow-up angiogram performed 4 months after the procedure confirmed closure of the aneurysm and patent vertebrobasilar system (C).

Figure 3

A patient with symptoms of mass effect from a vertebrobasilar transitional aneurysm (A) underwent treatment with 16 telescoped Pipeline embolization devices (B). The procedure was noted to be technically difficult but there were no procedural complications. Follow-up angiography performed 16 months after the procedure showed good reconstruction of the vessel with only a small remnant aneurysm (C). There was no evidence of pontine infarction on MRI.

Figrue 4

(A, B) A patient with dolichoectasia of the basilar artery (7 mm) treated with telescoped Pipeline embolization devices showed no progression of the disease on the follow-up angiogram performed at 14 months.

Figure 5

(A, B) A patient with a transitional basilar artery aneurysm 4 months after treatment with three telescoped Pipeline embolization devices showing complete reconstruction of the vessel with no further filling of the aneurysm.

Figure 6

Breakdown of the modified Rankin Scale (mRS) score pre- and post-intervention for patients who did not present with symptoms related to the aneurysm.

Figure 7

Breakdown of the modified Rankin Scale (mRS) score pre- and post-intervention for patients who presented with symptoms related to the aneurysm.

Figure 8

A patient who presented with recurrent posterior fossa strokes was found to have a transitional vertebrobasilar aneurysm (A). He underwent treatment with 18 telescoped Pipeline embolization devices that extended from the P1 segment to the vertebral artery (B). Flow through the Pipeline devices into the aneurysm and distally into the posterior cerebral arteries could be demonstrated at the end of the procedure (C).

Figure 9

The same patient as in figure 8 acutely deteriorated 24 hours after the procedure. An angiogram confirmed patent basilar artery and good flow distally (A). MRI digital-weighted imaging and ADC showed restricted diffusion in the pons (B, C). A T2-weighted MRI scan performed 5 days later showed a pontine infarction (D) and the patient died shortly thereafter. ADC, apparent diffusion coefficient.

Figure 10

A patient who presented with symptoms of mass effect from a partially thrombosed vertebrobasilar transitional aneurysm was initially treated with five telescoped Pipeline embolization devices placed in the left vertebral artery. The patient was due to have coil occlusion of the contralateral vertebral artery but refused further treatment and later died from progressive mass effect.

Figure 11

A patient with a vertebrobasilar transitional aneurysm (A) treated with 14 flow diverting stents (5 Pipeline embolization devices, 9 p64 devices) and coiling of the contralateral vertebral artery. There has been good reconstruction of the vertebral and basilar artery with a decrease in the aneurysmal filling seen on follow-up angiography (B, 22-month angiogram following initial treatment; C, 28-month angiogram). However, despite dense coil packing in the contralateral vertebral artery, a persistent leak into the aneurysm can be seen through the coil ball mass (D) warranting repeat occlusion of the vertebral artery.

Figure 12

A patient was incidentally found to have dilation of the basilar artery on routine MRI (A). At this point the patient refused further investigation. The patient had repeat MRI 26 months later (B) and the aneurysm had significantly increased in size with mass effect and small pontine infarction. Angiography performed at this time revealed a transitional vertebrobasilar aneurysm (C). The patient was treated with a flow-diverting stent and coil occlusion of the contralateral vertebral artery. A follow-up angiogram performed 24 months later shows good reconstruction of the basilar artery but persistent filling in the region of a large anterior inferior cerebellar artery/posterior inferior cerebellar artery (D, white arrow). A repeat angiogram after a further 6 months shows slightly slower but persistent filling (E). An MRI performed at the same time showed no significant increase in the aneurysm size or mass effect but increasing thrombus within the aneurysm (F).