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Anterior Inferior Cerebellar Artery Aneurysm: Saccular Non-ruptured Aneurysm of the Premeatal Segment of the Anterior Inferior Cerebellar Artery, Treated with Flow Diverter Implantation into the Basilar Artery, with Complete Aneurysm Occlusion, Preservation of the Parent Artery, and Good Clinical Outcome

  • Rene Viso
  • Ivan Lylyk
  • Javier Lundquist
  • Pedro LylykEmail author
Living reference work entry
  • 49 Downloads

Abstract

A 43-year-old female patient who presented with hearing loss was found to have a small saccular aneurysm of the left anterior inferior cerebellar artery (AICA) arising at its origin from the basilar artery (BA). The aneurysm was treated with endovascular implantation of a Pipeline Embolization Device (PED) flow diverter into the BA, jailing the origin of the AICA and thus reducing the inflow into the aneurysm sac. The postoperative course was uneventful and the hearing loss remained stable. Angiographic follow-up examinations at 6 and 12 months confirmed complete occlusion of the aneurysm. Implantation of a flow diverter into the BA appears to be a viable option in the treatment of proximal AICA aneurysms, as conventional deconstructive techniques in the treatment of these aneurysms can cause severe neurologic deficit. Flow diversion is also technically more straightforward than stent- or balloon-assisted coil occlusion. The various technical options for the treatment of AICA aneurysms are the main topic of this chapter.

Keywords

Anterior inferior cerebellar artery (AICA) Flow diverter Posterior fossa aneurysm Pipeline Embolization Device (PED) Slipstream effect 

Patient

A 43-year-old female patient presented with hearing loss. The attending otorhinolaryngologist obtained cranial MRI and non-contrast computed tomography (NCCT) which demonstrated a proximal dilatation of the left AICA.

Diagnostic Imaging

The cranial MRI/MRA demonstrated an aneurysm of the proximal left AICA for which a DSA examination was subsequently performed (Fig. 1).
Fig. 1

DSA performed for a suspected aneurysm at the origin of the left AICA. The working projection (a) and DSA in a lateral view (arrow (b)) showed a small saccular aneurysm in the premeatal segment of the left AICA at its origin from the BA. The 3D reconstruction demonstrated the origin of the AICA from the aneurysm neck (arrow (c))

Treatment Strategy

The primary goal of the treatment was to prevent aneurysm growth and rupture, the latter causing subarachnoid hemorrhage (SAH), without compromising the BA, its pontine branches, or the AICA. Surgical access to this area was considered very difficult. Simple coil occlusion of the aneurysm was judged to have high risk for AICA occlusion. Catheterization of the left AICA with the aim of inserting a self-expanding stent or a (low-profile) flow diverter was considered hazardous. The only viable alternative was either conservative management or an indirect impact on the aneurysm by the implantation of a flow diverter into the BA, taking advantage of the so-called slipstream effect (i.e., the hemodynamic effect on an aneurysm as a result of flow diverter stent insertion without covering the aneurysm neck).

Treatment

Procedure, 08.09.2011: endovascular treatment of an incidental aneurysm arising from the proximal left AICA with a Pipeline Embolization Device flow diverter implanted into the BA

Anesthesia: general anesthesia: 10,000 IU unfractionated heparin (Riveparin, Rivero) IV

Premedication: 1× 100 mg ASA (Aspirin, Bayer Vital) PO daily and 1× 75 mg clopidogrel (Troken, Laboratorio Bagó) PO daily, both started 5 days prior to the intervention

Access: right femoral artery, 7F sheath (Terumo); guide catheter: Fargo Plus (Balt Extrusion); microcatheter: Marksman 0.027" (Medtronic); microguidewire: Transend 0.014" (Stryker).

Implant: Pipeline Embolization Device 4.5/16 mm (Medtronic)

Course of treatment: The V3 segment of the right vertebral artery was catheterized with a 6F Fargo Plus guide catheter. A Marksman microcatheter with a 0.014" microwire was navigated to the distal third of the BA. A PED 4.5/16 mm was then deployed, covering the origin of the left AICA and the aneurysm neck. The PED was deliberately oversized in order to achieve lesser coverage of the pontine branches originating from the BA. Significant intra-aneurysmal flow modification was seen after the deployment of the PED, with instantaneous contrast medium stagnation in the aneurysm sac (Fig. 2).
Fig. 2

Endovascular treatment of a left AICA aneurysm. Pre-treatment planning based on 3D reconstructed images of a rotational DSA (a), leading to a working projection (b). Flow diverter placement in the BA, jailing the AICA (c). DSA in posterior-anterior projection after the deployment of the flow diverter (early arterial phase (d), parenchymal phase (e)) showing the contrast stagnation inside the aneurysm sac. VasoCT confirming the adequate apposition of the PED to the vessel wall (f)

Duration: 1st–12th DSA run: 40 min; fluoroscopy time: 26 min.

Complications: none

Postmedication: 1× 100 mg ASA PO daily for life and 1× 75 mg clopidogrel PO daily for 6 months

Clinical Outcome

The procedure was well-tolerated, and the patient was discharged home 2 days later without any new neurological deficit. There was no progression of the hearing loss, which remained stable at the 3-year follow-up.

Follow-Up Examinations

Follow-up MRI/MRA at 6 and 12 months showed complete occlusion of the aneurysm with no evidence of ischemic lesions on FLAIR MRI. DSA at 6 months and at 12 months confirmed complete occlusion of the aneurysm with no in-stent stenosis. The aneurysm sac had involuted, while the AICA remained patent (Fig. 3).
Fig. 3

Follow-up examinations after the treatment of a left AICA aneurysm with flow diverter implantation into the BA. DSA follow-up at 6 months (a–d) showed complete aneurysm occlusion (a). A DSA run in the previous working projection confirmed the patency of the left AICA (red circle) (b)). VasoCT ruled out any in-stent stenosis (c) and 3D DSA also demonstrated the patency of the left AICA (d). Follow-up MRA/MRI at 6 months also confirmed the patency of both AICAs in the TOF MRA sequences (e), and no ischemic lesions were found in the FLAIR sequences (f). The 12-month follow-up DSA (g, h) and MRA (i) results were essentially unchanged, showing the occlusion of the aneurysm and the continued patency of the left AICA

Discussion

The AICA arises most frequently from the proximal third of the basilar artery and is anatomically related to the pons, the lateral recess, the foramen of Luschka, the cerebellopontine fissure, the middle cerebellar peduncle, and the petrosal surface of the cerebellum and can be considered as four segments (Rhoton 2007). The anterior pontine segment is adjacent to the abducens nerve and runs from the origin from the BA to the level of the inferior olive. The lateral pontine segment begins at the anterolateral margin of the pons and runs through the cerebellopontine angle. Branches to the facial and vestibulocochlear nerves arise from this segment. The lateral pontine segment is subdivided into the premeatal, meatal, and postmeatal segments and is followed by the flocculopeduncular segment, related to the flocculus, the middle cerebellar peduncle, and the cerebellopontine fissure. The most distal part of the AICA, the cortical segment, supplies the petrosal surface. The premeatal segment starts at the origin from the BA and ends at the meatal loop. The postmeatal segment arises from the distal part of the meatal loop (Lv et al. 2016) (Fig. 4.), and various subdivisions have been proposed. Bambakidis et al. (2009) proposed a division based on the location of the aneurysm and the internal auditory meatus; however, while these classifications have surgical implications, they are not relevant for neurointerventional purposes (Bambakidis et al. 2009; Lv et al. 2016).
Fig. 4

Anatomical segments of the AICA

Approximately 15% of all intracranial aneurysms occur in the posterior circulation; however, aneurysms of the AICA represent only 0.1–0.5% of all intracranial aneurysms (Mizushima et al. 1999). Locksley (1966) reports that only 2 AICA aneurysms out of 6368 aneurysms were studied. AICA aneurysms have a female preponderance. SAH is the clinical manifestation of AICA aneurysms in more than 70% of cases; however, neuropathies of the Vth, VIth, VIIth, and VIIIth cranial nerve may also occur. Saccular aneurysms are more frequent (>60%) than fusiform vessel dilatations (Lv et al. 2016). The most frequent aneurysm location reported by Lv et al. (2016) was the meatal segment (44%), followed by the premeatal segment (34%), with only 21% of the aneurysms located in the postmeatal segment.

In the vast majority of published cases of treated AICA aneurysms, a good clinical outcome (mRS 0–2) was achieved (Lv et al. 2016).

The endovascular treatment of AICA aneurysms depends on the clinical presentation (i.e., ruptured or unruptured), the aneurysm morphology (e.g., saccular, dissecting, fusiform), and the anatomical location of the aneurysm along the AICA. The majority of aneurysms arising from the premeatal segment of the AICA are located adjacent to the BA, enabling endovascular navigation and microcatheterization of the aneurysm. The surgical treatment of this type of aneurysm is restricted due to the anatomical location of the proximal segment of the AICA and the lack of a straightforward surgical approach to the narrow prepontine cistern. Several published series have demonstrated good results from the endovascular treatment of AICA aneurysms. Suh et al. (2011) reported successful endovascular treatment in 7 out of 9 (78%) AICA aneurysms. The treatment of proximal AICA aneurysms with coil occlusion is often feasible, especially for ruptured saccular aneurysms. However, complete obliteration of the aneurysm without assist techniques like balloon- or stent-assisted coil occlusion can be difficult to achieve. Since this type of intervention may be challenging and hazardous, simple coil occlusion should be considered as the first-line treatment for this type of aneurysm (Lv et al. 2016) (Fig. 5).
Fig. 5

Endovascular coil occlusion of a ruptured left AICA aneurysm. A 48-year-old patient presented with a spontaneous SAH, graded as Hunt Hess III and Fisher 4. DSA in posterior-anterior projection (a) and 3D DSA (b) showed a proximal premeatal AICA aneurysm. Endovascular treatment was performed and complete aneurysm occlusion was achieved with coiling (c), with preservation of the AICA

The distal aneurysms of the AICA, both meatal and postmeatal, can be wide-necked or fusiform. Techniques for the management of distal AICA aneurysms include microsurgical wrapping, proximal occlusion, trapping, clipping, and coil occlusion. However, far distal coil occlusion may be difficult, and sometimes a parent vessel occlusion (PVO) is the only therapeutic option (Fig. 6) (Sarkar and Link 2004). The confined anatomic space and the adjacent nerve complex may make microsurgical clipping impossible, and during surgery for parent vessel occlusion, the risks of VIIth and VIIIth cranial nerve injury remain a concern. Anastomoses between PICA and AICA must also be considered, especially in the case of proximal PVO when retrograde filling of the aneurysm via PICA-AICA collaterals is possible. For distal aneurysms of an AICA-PICA variant with a large supply territory, a surgical anastomosis can be created between the occipital artery and the distal AICA-PICA (Kanamori et al. 2016). For distal AICA aneurysms with a small dependent supply territory, endovascular PVO is less invasive than surgical clipping or trapping (Lv et al. 2008). In cases of PVO, whether achieved by microsurgical or endovascular means, there is a risk of retrograde thrombosis of the AICA and subsequent brainstem ischemia (Zager et al. 2002); thus heparinization for at least 1 week after the PVO should be considered. An occlusion of the AICA may lead to ataxia, nystagmus, dysarthria, trigeminal sensory impairment, lateral gaze palsy, facial palsy, and hearing loss (Kikkawa et al. 2018), although some authors have reported no such deficits after AICA occlusion (Zager et al. 2002). The factors affecting these outcomes include the collateral circulation, the anatomical location of the occlusion, and the anatomical location of the labyrinthine artery (Kanamori et al. 2016).
Fig. 6

Endovascular PVO as treatment of a distal (postmeatal), dissecting ruptured AICA aneurysm in a 56-year-old female patient with spontaneous SAH, graded as Fisher 4. DSA in the working projection showing the ruptured dissecting aneurysm (red circle (a)). Endovascular treatment with PVO with coils (b). Follow-up DSA showing the complete occlusion of the distal AICA (c). The patient did sustain clinically apparent cranial nerve deficit

Consideration should be given to the technical aspects of selective coil occlusion of distal AICA aneurysms with preservation of the parent artery (Fig. 7), and an approach via the contralateral VA can be geometrically advantageous. The microcatheter should be advanced into the distal portion of the AICA beyond the aneurysm origin and slowly pulled back into the vicinity of the aneurysm neck, allowing a controlled navigation of the microcatheter into the aneurysm sac (Koizumi et al. 2015). A combination of an acute AICA origin from the BA, a small diameter AICA, and a far distal aneurysm location can result in failure of endovascular treatment (Suh et al. 2011).
Fig. 7

Selective coil occlusion of a ruptured aneurysm of the meatal segment of the right AICA. A 63-year-old female patient with spontaneous SAH, graded Fisher 4. DSA showed a lobulated ruptured and presumably dissecting meatal AICA aneurysm (a, b). Endovascular treatment with coil occlusion of the aneurysm and preservation of the parent vessel was possible (c)

Assist techniques such as stent-assisted coil occlusion cannot always be utilized in AICA aneurysms. Ruptured AICA aneurysms are frequently associated with intraventricular hemorrhage, necessitating extraventricular drain placement, which carries an increased risk of intracerebral hemorrhage if dual antiplatelet medication is used (Koizumi et al. 2015). The risk of stent thrombosis is increased due to the small diameter of the AICA (Suh et al. 2011). The implantation of a flow diverter into an AICA has been a concern given the usual small diameter and the proximal perforating branches. New low-profile flow diverters (e.g., FRED Jr. (MicroVention) and p48 (phenox)) have been designed for vessels between 2 and 3 mm, but currently we are not aware of the use of such flow diverters in the AICA. There are, however, reports concerning the successful use of flow diverters for PICA aneurysms (Bhogal et al. 2018; Srinivasan et al. 2018). In proximal AICA aneurysms, the placement of the flow diverter is comparable to those placed at the BA-PICA junction (type 1a Srinivasan classification), given the absence of a suitable proximal landing zone in the AICA. The flow diverter must therefore be placed into the BA, jailing the AICA origin (Srinivasan et al. 2018) (Fig. 8).
Fig. 8

Endovascular treatment of a premeatal AICA aneurysm in a 71-year-old female patient with multiple unruptured intracranial aneurysms. DSA in the working projection showing a basilar bifurcation aneurysm treated with Y-stent assisted coil occlusion (a, b) and a right BA-AICA junction aneurysm. Y-stent-assisted coil occlusion of the basilar bifurcation aneurysm was performed, and a LVIS Jr. (MicroVention) was placed into the BA, covering the AICA aneurysm (b) with contrast stagnation in the parenchymal DSA phase (c). VasoCT showing the placement of the LVIS Jr. stent with adequate opening (d). Occlusion of the AICA aneurysm was confirmed by follow-up DSA 1 year later (e, f)

In conclusion, simple coil occlusion and flow diverter implantation into the BA are viable options for the treatment of proximal AICA aneurysms adjacent to the BA. For distal AICA aneurysms, selective coil occlusion can be performed if the anatomy is favorable (i.e., sufficient diameter and straight course of the parent vessel). PVO is the remaining endovascular option and can be achieved by coil insertion, particularly in the treatment of postmeatal aneurysms.

Cross-References

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Rene Viso
    • 1
  • Ivan Lylyk
    • 1
  • Javier Lundquist
    • 1
  • Pedro Lylyk
    • 1
    Email author
  1. 1.Interventional NeuroradiologyClínica La Sagrada Familia, ENERIBuenos AiresArgentina

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