Management of anterior inferior cerebellar artery aneurysms: an illustrative case and review of literature

Automated algorithm aided capacity and confidence boost in surgical decision-making training for inferior clivus

Objective

To assess the impact of automated algorithms on the trainees' decision-making capacity and confidence for individualized surgical planning.

Methods

At Chinese PLA General Hospital, trainees were enrolled to undergo decision-making capacity and confidence training through three alternative visual tasks of the inferior clivus model formed from an automated algorithm and given consecutively in three exemplars. The rationale of automated decision-making was used to instruct each trainee.

Results

Following automated decision-making calculation in 50 skull base models, we screened out three optimal plans, infra-tubercle approach (ITA), trans-tubercle approach (TTA), and supra-tubercle approach (STA) for 41 (82.00%), 8 (16.00%), and 1 (2.00%) subject, respectively. From September 1, 2023, through November 17, 2023, 62 trainees (median age [range]: 27 [26-28]; 28 [45.16%] female; 25 [40.32%] neurosurgeons) made a decision among the three plans for the three typical models (ITA, TTA, and STA exemplars). The confidence ratings had fine test-retest reliability (Spearman's rho: 0.979; 95% CI: 0.970 to 0.988) and criterion validity with time spent (Spearman's rho: -0.954; 95%CI: -0.963 to -0.945). Following instruction of automated decision-making, time spent (initial test: 24.02 vs. 7.13 in ITA; 30.24 vs. 7.06 in TTA; 34.21 vs. 12.82 in STA) and total hits (initial test: 30 vs. 16 in ITA; 37 vs. 17 in TTA; 42 vs. 28 in STA) reduced significantly; confidence ratings (initial test: 2 vs. 4 in ITA; 2 vs. 4 in TTA; 1 vs. 3 in STA) increased correspondingly. Statistically significant differences (P < 0.05) were observed for the above comparisons.

Conclusions

The education tool generated by automated decision-making considers surgical freedom and injury risk for the individualized risk-benefit assessment, which may provide explicit information to increase trainees' decision-making capacity and confidence.

Anterior inferior cerebellar artery aneurysm with proximal parent artery stenosis: A case report

Hemodynamic factors are associated with the progression of cerebral aneurysms. We report a 78-year-old woman with an anterior inferior cerebellar artery aneurysm and proximal stenosis of the anterior inferior cerebellar and basilar arteries. The aneurysm exhibited growth on annual follow-up imaging. Aneurysmal rupture occurred 4 years after diagnosis. Coil embolization resulted in aneurysm occlusion with parent artery preservation. Aneurysms adjacent to a more proximal region of severe stenosis in the parent vessel should be considered at high risk for growth or rupture. Such aneurysms require careful monitoring. Particular attention should be paid to posterior circulation aneurysms that occur at anatomically vulnerable sites.

The Anterior Inferior Cerebral Artery Variability in the Context of Neurovascular Compression Syndromes: A Narrative Review

The anterior inferior cerebellar artery (AICA) is situated within the posterior cranial fossa and typically arises from the basilar artery, usually at the pontomedullary junction. AICA is implicated in various clinical conditions, encompassing the development of aneurysms, thrombus formation, and the manifestation of lateral pontine syndrome. Furthermore, owing to its close proximity to cranial nerves within the middle cerebellopontine angle, AICA's pulsatile compression at the root entry/exit zone of cranial nerves may give rise to specific neurovascular compression syndromes (NVCs), including hemifacial spasm (HFS) and geniculate neuralgia concurrent with HFS. In this narrative review, we undertake an examination of the influence of anatomical variations in AICA on the occurrence of NVCs. Significant methodological disparities between cadaveric and radiological studies (CTA, MRA, and DSA) were found, particularly in diagnosing AICA's absence, which was more common in radiological studies (up to 36.1%) compared to cadaver studies (less than 5%). Other observed variations included atypical origins from the vertebral artery and basilar-vertebral junction, as well as the AICA-and-PICA common trunk. Single cases of arterial triplication or fenestration have also been documented. Specifically, in relation to HFS, AICA variants that compress the facial nerve at its root entry/exit zone include parabola-shaped loops, dominant segments proximal to the REZ, and anchor-shaped bifurcations impacting the nerve's cisternal portion.

Flow Diversion for Treatment of Anterior Inferior Cerebellar Artery Aneurysms: Mechanism and Pitfalls from a Novel Management Strategy

BACKGROUND

Anterior inferior cerebellar artery (AICA) aneurysms present a challenge for neurosurgeons and neurointerventionalists alike.

METHODS

Cases of AICA aneurysms managed with endovascular flow diversion at our institute are reviewed with their angiographic outcomes.

RESULTS

Both direct and indirect flow diversion provide complete aneurysm occlusion at follow-up. We propose a stratified method of approaching AICA aneurysms based on location, rupture status, and neck size.

CONCLUSIONS

Careful evaluation of preoperative parameters is paramount in deciding between a surgical or a neuroendovascular approach. Low-profile stents in the future may assist in direct flow diversion of AICA trunk aneurysms. In addition, neurosurgeons need to be well versed in endovascular approaches.

Evaluating magnetic resonance imaging characteristics and risk factors for hemifacial spasm

PURPOSE

The specific neurovascular compression (NVC) event responsible for the symptomatic manifestation of hemifacial spasm (HFS) remains difficult to assess accurately using magnetic resonance imaging (MRI). We aim to evaluate the MRI characteristics of HFS.

METHOD

We retrospectively included patients with HFS and divided them into a test group (n = 186) and a validation group (n = 28). The presence, severity, and offending vessel type of NVC in each portion, and the orientation of the offending vessel around the facial nerve, were recorded. Conditional logistic regression analyses were performed to evaluate correlations using test group. The validation group was used to verify whether our findings improved diagnostic performance.

RESULTS

Deformity in the proximal cisternal segment was significantly correlated with HFS occurrence (odds ratio [OR]: 256.58, p = .002), whereas contact was not (p = .233). Both contact and deformity in the root detachment point (OR: 19.98 and 37.22, p < .001 and p = .013, respectively) or attached segment (OR: 4.99 and 252.52, p = .001 and p < .001, respectively) were significantly correlated with HFS occurrence. Our findings improved specificity, positive predictive value, and accuracy of diagnosis than conventional diagnostic methods. The vertebral artery predominantly compress the facial nerve in the inferior-anterior position, the anterior inferior cerebellar artery predominantly in the inferior position, the posterior inferior cerebellar artery predominantly in the inferior position, vein predominantly in the posterior-superior position.

CONCLUSIONS

This study further demonstrates that within the susceptible portion of facial nerve, different portions of the nerve respond differently to NVC. Each offending vessel has its own preferred conflict orientation. Our study offers reference for neurosurgeons in diagnosis and treatment.

Ruptured proximal pontine artery aneurysm and association with cerebellopontine angle cistern arterial venous malformation fed by the same artery: A surgical challenge

Background

The coexistence of hyper-inflow aneurysms and cerebellopontine angle cistern (CPAc) arterial venous malformations (AVMs) have been rarely reported and most commonly associated with high risk of bleeding.

Case Descriptions

We present two cases of CPAc AVMs admitted for acute subarachnoid hemorrhage from rupture of a parent right pontine artery aneurysm. Admission history, neurology at presentation, pre/post-operative imaging, approach selection, and results are thoroughly reviewed and presented. The acute origin angle of the vessel from the basilar artery made both malformations unsuitable for endovascular treatment. The surgical strategy was differently tailored in the two patients, respectively, using a Le Fort I/transclival and a Kawase approach. The aneurysm was clipped in the first case, and the AVM was excised in the second one, as required by the anatomical context. Aneurysm exclusion and AVM size reduction were obtained in the first case, while complete AVM removal and later aneurysm disappearance were obtained in the second one. A high-flow cerebrospinal fluid leak in the first case was successfully treated by an endoscopic approach. Both patients experienced a satisfactory neurological outcome in the follow-up.

Conclusion

Pontine artery aneurysms, especially when associated with CPAc AVMs, represent a surgical challenge, due to their rarity and anatomical peculiarity, which typically requires complex operative approaches. Multimodal preoperative imaging, appropriate timing, and accurate target selection, together with versatile strategies, are the keys to a successful treatment.

Treatment and Outcome of Anterior Inferior Cerebellar Artery (AICA) Aneurysms: Helsinki Series of 15 Consecutive Patients

Objective Anterior inferior cerebellar artery (AICA) aneurysms are rare posterior circulation lesions that are challenging to treat. This article presents the treatment and clinical outcome of AICA aneurysms in an unselected cohort of patients.

Methods A retrospective analysis of patient record files, digital subtraction angiography, and computed tomography angiography images of 15 consecutive patients harboring AICA aneurysms treated between 1968 and 2017.

Results Of the 15 AICA aneurysm patients reviewed, 12 (80%) were females. Twenty percent had intracerebral hemorrhage and 40% presented with intraventricular hemorrhage. Eleven out of 15 (73%) patients presented with subarachnoid hemorrhage (SAH); 82% of SAH patients had a good-grade SAH (Hunt and Hess grade 1–3). Eleven patients (73%) were treated surgically, three (20%) were treated conservatively, and one (7%) had coil embolization. In 27% of patients, a subtemporal approach with anterior petrosectomy was performed. A retrosigmoid approach was used in the remaining 73%. In 18% of the patients, a parent vessel occlusion was necessary to occlude the aneurysm. Five out of 11 (47%) of the patients developed postoperative cranial nerve deficits. Twenty-seven percent developed shunt-dependent hydrocephalus. All patients who presented with an unruptured AICA aneurysm had good clinical outcome (modified Rankin scale [mRS] 1–2). In patients with SAH, 82% achieved good clinical outcome and 18% had poor clinical outcome (mRS 3–6) after 1 year.

Conclusion Surgical treatment of AICA aneurysms has a high rate of cranial nerve deficits but most of patients have a good long-term clinical outcome.

Dissecting aneurysm of the anterior inferior cerebellar artery in the internal auditory canal presenting with deafness without hemorrhage: A case report and literature review

Background:

Anterior inferior cerebellar artery (AICA) aneurysms in the internal auditory canal (IAC) are rare. We have reported a case of dissecting AICA aneurysm in the IAC presenting initially with the eighth nerve palsy followed by the seventh nerve palsy without hemorrhage.

Case Description:

A 68-year-old woman presented with a sudden onset of vertigo accompanied by deafness and tinnitus on the right side that was preceded by intermittent right retroauricular pain 2 weeks before. Audiogram showed severe sensorineural hearing loss. Computed tomography and magnetic resonance imaging (MRI) indicated absence of prior subarachnoid hemorrhage. Magnetic resonance angiogram (MRA) suggested a tiny aneurysm at the fundus of the IAC accompanied with thinning of the lateral pontine segment of the AICA. Conservative treatment led to moderate improvement of the symptoms. However, the patient developed the right retroauricular pain again, followed by the right facial paralysis 5 months later but still without signs of hemorrhage on MRI. Digital subtraction angiogram showed dissecting aneurysm in the IAC. The patient was managed with oral steroids and direct intervention was avoided due to a risk of ischemia supposed by large area irrigated by the AICA. Follow-up MRA 18 months after the first presentation showed improvement in the narrowing of the AICA proximal to the aneurysm. The patient was functionally independent despite right-sided hearing loss and slight facial paresis.

Conclusion:

This report warns physicians that a dissecting AICA aneurysm without subarachnoid hemorrhage may cause eighth and seventh nerve palsy.

Anterior Inferior Cerebellar Aneurysm Treated by Aneurysm Resection and Intracranial Artery Anastomosis in situ: A Case Report and Literature Review

Background: Anterior inferior cerebellar artery (AICA) aneurysms are relatively rare in clinical practice, accounting for <1% of all intracranial arteries. After the diagnosis and location are confirmed by angiography, magnetic resonance, and other imaging examinations, interventional, or surgical treatment is often used, but some complex aneurysms require reconstructive surgery. Case Description: An 8-year-old male child was admitted to the hospital due to sudden disturbance of consciousness for 2 weeks. The head CT showed hematocele in the ventricular system with subarachnoid hemorrhage in the basilar cistern and annular cistern. On admission, he was conscious, answered correctly, had a soft neck, limb muscle strength was normal, and had no cranial nerves or nervous system abnormalities. A preoperative examination showed the right side of the anterior distal arteries class under the circular wide neck aneurysm, the distal anterior inferior cerebellar artery supplying a wide range of blood to the cerebellum, the ipsilateral posterior inferior cerebellar artery absent, and the aneurysm close to the VII, VIII nerves. The aneurysm was successfully treated by aneurysm resection and intracranial artery anastomosis in situ of a2 AICA-a2 AICA. Conclusions: AICA aneurysms are relatively rare; in this case, a complex wide-necked aneurysm was successfully treated by aneurysm resection and anastomosis in situ of a2 AICA-a2 AICA. This case can provide a reference for the surgical treatment of complex anterior cerebellar aneurysms.

“Plugged” Anterior Inferior Cerebellar Artery Aneurysm Causing Facial Palsy, Hearing Loss, and Subarachnoid Hemorrhage Treated by a Translabyrinthine Approach

Anterior inferior cerebellar artery (AICA) aneurysms are rare, less than 1%-2% of all intracranial aneurysms. Aneurysms of the distal AICA are even less common and can present with hearing loss and facial paralysis because of their relationship with the internal auditory canal (IAC). A 65-year-old male was followed for fluctuating left facial weakness and left-sided hearing loss for over a year. Serial magnetic resonance imaging (MRI) scans showed a mass near the left IAC, thought to be a vestibular schwannoma. Just prior to his next clinic visit, the patient deteriorated suddenly from a subarachnoid hemorrhage. Cerebral angiography revealed a 5.5 mm saccular aneurysm at the distal left AICA, which was clip ligated via a translabyrinthine (TL) approach. The patient had a good functional outcome (modified Rankin Scale [mRS] 1) after 30 days despite persistent left facial weakness. Stable obliteration of the aneurysm was demonstrated by cerebral angiography postoperatively. Distal AICA aneurysms are rare and can have a similar presentation to tumors in the cerebellar pontine angle. Because of the unique anatomy of the distal AICA, open clip ligation via a TL approach is an effective method to secure these aneurysms.

An a3-Anterior Inferior Cerebellar Artery to p3-Posterior Inferior Cerebellar Artery Bypass With Thrombectomy and Trapping of an Anterior Inferior Cerebellar Artery Aneurysm: 3-Dimensional Operative Video

In situ bypasses to the anterior inferior cerebellar artery (AICA) are unusual because, with only one artery in the cerebellopontine angle (CPA), no natural intracranial donors parallel its course. In rare cases, the posterior inferior cerebellar artery (PICA) may have the tortuosity or redundancy to be mobilized to the AICA to serve as a donor. This video demonstrates this p3 PICA-to-a3 AICA in situ side-to-side bypass. A 75-yr-old woman presented with ataxia and hemiparesis from a large thrombotic right AICA aneurysm compressing the brainstem. Strategy consisted of bypass, trapping, and brainstem decompression. Written informed consent for surgery was obtained from the patient. A hockey-stick incision was made to harvest the occipital artery as a backup donor, but its diminutive caliber precluded its use. The bypass was performed through an extended retrosigmoid craniotomy. The aneurysm was trapped completely and thrombectomized to relieve the pontine mass effect. Indocyanine green videoangiography confirmed patency of the bypass, retrograde filling of the AICA to supply pontine perforators, and no residual aneurysmal filling. This unusual in situ bypass is possible when redundancy of the AICA and PICA allow their approximation in the CPA. The anastomosis is performed lateral to the lower cranial nerves in a relatively open and superficial plane. The extended retrosigmoid approach provides adequate exposure for both the bypass and aneurysm trapping. In situ AICA-PICA bypass enables anterograde and retrograde AICA revascularization with side-to-side anastomosis. The occipital artery-to-AICA bypass and the V3 vertebral artery-to-AICA interpositional bypass are alternatives when intracranial anatomy is unfavorable for this in situ bypass.1-6 Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Parent Artery Occlusion against Dissecting Aneurysm Involving the Proximal Anterior Inferior Cerebellar Artery: Case Report and Literature Review

Dissecting aneurysms of the anterior inferior cerebellar artery (AICA) are rare. Few reports suggested that coil embolization and parent artery occlusion (PAO) would be valuable treatment options against dissecting AICA aneurysms. We report a case of PAO against dissecting aneurysm involving the proximal AICA and discuss the therapeutics and literature review of this pathology. A 69-year-old woman was referred to our hospital, and neurological examination revealed a semicoma (Hunt and Hess grade IV). Brain computed tomography (CT) established the diagnosis of Fisher group 3 subarachnoid hemorrhage (SAH), CT angiography revealed an extravasation near the clivus, while digital subtraction angiography showed no signs of dissection. Conservative treatment was administered, and repeated angiography on day 13 showed a pseudoaneurysm and false lumen in the left proximal AICA. The patient was in poor health condition, and endovascular therapy (EVT) of the left AICA was performed to minimize invasion. The PAO was successful with no severe ischemic damage to the brainstem and cerebellum. However, the general condition gradually deteriorated, and the patient expired on day 24. Since open surgery for dissecting AICA aneurysm is technically challenging and revascularization procedure is often required, the rapidly developing EVT is a viable alternative. Although preservation of the proximal AICA is usually necessary, PAO without revascularization procedure was performed to avoid the high risk of regrowth and re-rupture of the dissecting aneurysm with respect to the patient’s poor health condition. Hence, EVT is a viable option when microsurgery is contraindicated for treating dissecting AICA aneurysms.

Anterior Inferior Cerebellar Artery Bypasses: The 7-Bypass Framework Applied to Ischemia and Aneurysms in the Cerebellopontine Angle

BACKGROUND

Aneurysms of the anterior inferior cerebellar artery (AICA) are rare. Primary clip reconstruction of these lesions is a challenge because of the limited surgical exposure and frequent nonsaccular aneurysm morphology. Endovascular treatment options exist, but outcomes are equivalent to those for open surgery. Historically, AICA aneurysms not amenable to clipping or primary coiling have been treated with parent vessel sacrifice.

OBJECTIVE

To determine whether an AICA revascularization strategy would afford for the safe treatment of AICA aneurysms and other posterior circulation pathologies without compromising perfusion of the AICA territories.

METHODS

We describe a series of AICA bypasses to treat 4 AICA aneurysms and 3 vertebral artery/AICA occlusions.

RESULTS

We used 7 types of bypasses to revascularize the AICA territory. Bypass types included extracranial-to-intracranial (EC-IC) bypass without an interpositional graft, EC-IC with an interpositional graft, in situ bypass, reanastomosis, reimplantation, intracranial-to-intracranial bypass with interpositional graft, and combination bypasses. In particular, we performed the following 7 bypasses: OA-a3 AICA, OA-RAG-a3 AICA, p3 PICA-a3 AICA, a2 AICA reanastomosis, V4 VA-a3 AICA, V3 VA-SVG-a3 AICA, and a combined OA-a3 AICA bypass and p3 PICA reanastomosis. AICA revascularization allows for the safe treatment of AICA aneurysms and other posterior circulation pathologies without compromising perfusion of the AICA territories.

CONCLUSION

All 7 AICA bypasses are feasible for application to AICA aneurysms and ischemic disease. Our experience with the 7-bypass framework demonstrates the utility of the framework as a decision-making tool and the breadth of bypass innovation possible in this anatomically challenging region.

A Classification for the Anterior Inferior Cerebellar Artery-Subarcuate Artery Complex Based on the Embryological Development

Objective  To hierarchize the anterior inferior cerebellar artery (AICA)-subarcuate artery (SAA) complex's variations in the surgical field. Background  The AICA's "subarcuate loop" (SL) presents multiple variations, closely related to the SAA. AICA-SAA complex's variations may represent major issues in cerebellopontine angle (CPA) surgery. As the spectrum of configurations is originated during the development, a systematized classification was proposed based on the interaction between the petrosal bone and the AICA in the embryonic period. Methods  The variations were defined as follow: Grade 0: free, purely cisternal AICA, unidentifiable or absent SAA; Grade 1: purely cisternal AICA, loose SL, SAA > 3 mm; Grade 2: AICA near the subarcuate fossa, pronounced SL, SAA <3 mm; Grade 3: "duralized" AICA, unidentifiable SAA, or included in the petromastoid canal (PMC); and Grade 4: intraosseous AICA, unidentifiable SAA, or included in the PMC. The classification was applied to a series of patients assessed by magnetic resonance constructive interference in steady state sequence. Surgical examples were also provided. Results  Eighty-four patients were evaluated, including 161 CPA. The proportions found in the gradation remained within the range of previous publications (Grade 0: 42.2%; Grade 1: 11.2%; Grade 2: 35.4%; Grade 3: 10.6%; and Grade 4: 0.6%). Moreover, the degrees of the classification were related to the complexity of the anatomical relationships and, therefore, to the difficulty of the maneuvers required to overcome them. Conclusion  The proposed AICA-SAA complex classification allowed to distinguish and objectify pre- and intraoperatively the spectrum of variations, to thoroughly plan the required actions and instrumentation.

Which Patients with Aneurysms Involving the a1-a2 Segment of the Anterior Inferior Cerebellar Artery Would Benefit from Parent Artery Occlusion?

Anterior inferior cerebellar artery (AICA) trunk aneurysms are rare entities. Given the eloquence of the AICA in supplying the cerebellum and brainstem, in theory, sacrifice or occlusion of the a1-a2 segment in lesions involving the AICA may lead to various complications. However, some patients might experience no complication or favorable recovery. The subgroup of patients who would benefit from parent artery occlusion (PAO) among those with aneurysms involving the a1-a2 segment of the AICA remains to be explored. In this report, we present 2 cases of AICA dissecting aneurysms at the a1-a2 segment that were successfully occluded via coiling without postprocedural complications. A comprehensive literature review was also performed on patients with AICA aneurysms with occlusion at the a1-a2 segment. Sixteen patients were identified, and all of the cases had satisfactory outcomes. Of these patients, 11 of 16 (68.75%) had no neurologic deficits, and 5 of 16 (31.25%) had acceptable neurologic deficits. The prognosis was associated with collateral circulation of the AICA, and collateral circulation was discussed. In case of an a1-a2 aneurysm that is hard to occlude without sacrificing the parent artery, careful hemodynamic and morphologic evaluation for collateral flow is warranted. If collateral flow is demonstrated or the aneurysm is flow-related with cerebellar arteriovenous malformation, PAO of the a1-a2 segment can be an acceptable option.

Multiple aneurysms on the subarcuate artery arising from the anterior inferior cerebellar artery in a patient with a Borden type I transverse-sigmoid dural arteriovenous fistula manifesting as subarachnoid hemorrhage: A case report

BACKGROUND

Peripheral anterior inferior cerebellar artery (AICA) aneurysms are rare and commonly associated with vascular malformations, such as cerebellar arteriovenous malformations (AVMs). We present a case wherein multiple AICA feeding aneurysms on the subarcuate artery as a feeding artery of a Borden type I transverse-sigmoid dural arteriovenous fistula (dAVF) manifested as subarachnoid hemorrhage.

CASE DESCRIPTION

A 67-year-old woman presented with acute severe headache. Brain computed tomography (CT) demonstrated subarachnoid hemorrhage mainly in the posterior fossa. A transverse-sigmoid dAVF was detected on magnetic resonance angiography (MRA) and three-dimensional-CT angiography (3D-CTA), with no cortical venous reflex. The patient underwent conventional angiography, which showed multiple aneurysms on a small branch of the AICA, feeding a transverse-sigmoid dAVF (Borden type I). The AICA aneurysms seemed flow dependent and ruptured owing to high-flow arteriovenous shunts through the dAVF. Based on the source images of the MRA, the small artery arising from the AICA was considered the subarcuate artery, and it was confirmed on 3D-CTA after the artery was successfully embolized with Onyx without any complications. Multiple aneurysms on the subarcuate artery are extremely rare, and the artery has not been identified as a feeding artery of the transverse-sigmoid dAVF.

CONCLUSION

A rare case of multiple ruptured aneurysms on the subarcuate artery was reported in a patient with a Borden type I dAVF at the transverse-sigmoid sinuses manifesting as subarachnoid hemorrhage. Onyx embolization of the parent artery occlusion was feasible and useful in treating this type of feeding artery aneurysm of the AICA with a dAVF.

Endoscopic Endonasal Transclival Approach versus Dual Transorbital Port Technique for Clip Application to the Posterior Circulation: A Cadaveric Anatomical and Cerebral Circulation Simulation Study

Purpose  Simulation training offers a useful opportunity to appreciate vascular anatomy and develop the technical expertise required to clip intracranial aneurysms of the posterior circulation. Materials and Methods  In cadavers, a comparison was made between the endoscopic transclival approach (ETA) alone and a combined multiportal approach using the ETA and a transorbital precaruncular approach (TOPA) to evaluate degrees of freedom, angles of visualization, and ergonomics of aneurysm clip application to the posterior circulation depending on basilar apex position relative to the posterior clinoids. Results  ETA alone provided improved access to the posterior circulation when the basilar apex was high riding compared with the posterior clinoids. ETA + TOPA provided a significantly improved functional working area for instruments and visualization of the posterior circulation for a midlevel basilar apex. A single-shaft clip applier provided improved visualization and space for instruments. Proximal and distal vascular control and feasibility of aneurysmal clipping were demonstrated. Conclusions  TOPA is a medial orbital approach to the central skull base; a transorbital neuroendoscopic surgery approach. This anatomical simulation provides surgical teams an alternative to the ETA approach alone to address posterior circulation aneurysms, and a means to preoperatively prepare for intraoperative anatomical and surgical instrumentation challenges.

Anterior inferior cerebellar artery aneurysms: Segments and results of surgical and endovascular managements

BACKGROUND

Anterior inferior cerebellar artery (AICA) aneurysms are rare and published clinical experience with these aneurysms is limited.

OBJECTIVE

The objective of this article is to report angiographic characteristics and results associated with premeatal, meatal and postmeatal segments, surgical and endovascular therapies.

METHODS

A literature review was performed through PubMed using "anterior inferior cerebellar artery aneurysm" through January 2016. Clinical data, angiograms, management techniques, and patient outcomes were reviewed for 47 collected cases in 30 previous reports.

RESULTS

Of these aneurysms, 21 (44.7%) were associated with meatal segment, 10 (21.3%) were postmeatal and 16 (34.0%) were premeatal. Patients with meatal aneurysms are more likely to present with subarachnoid hemorrhage and hearing loss and facial palsy (77.8%). Patient outcomes of meatal aneurysms presented with more neuropathies (51.7%) and cerebellar symptoms (14.3%) (p = 0.049). Four cases of meatal aneurysm with preoperative cranial nerve deficits (two VII and two VIII) showed improvement after surgery. Endovascular treatment achieved outcomes similar to surgical treatment (p = 0.327).

CONCLUSIONS

AICA aneurysms have a predilection for meatal segment. Patients with meatal aneurysms are more likely to present with subarachnoid hemorrhage and hearing loss and facial palsy. Patient outcomes of meatal aneurysms presented with more neuropathies and cerebellar symptoms. Endovascular treatment achieved outcomes similar to surgical treatment.

Assessment of the Endoscopic Endonasal Transclival Approach for Surgical Clipping of Anterior Pontine Anterior-Inferior Cerebellar Artery Aneurysms

OBJECTIVE

Aneurysms of the anterior pontine segment of the anterior-inferior cerebellar artery (AICA) are uncommon. Their treatment is challenging because critical neurovascular structures are adjacent to it and the available surgical corridors are narrow and deep. Although endoscopic endonasal approaches are accepted for treating midline skull base lesions, their role in the treatment vascular lesions remains undefined. The present study is aimed to assess the anatomic feasibility of the endoscopic endonasal transclival (EET) approach for treating anterior pontine AICA aneurysms and compare it with the subtemporal anterior transpetrosal (SAT) approach.

METHODS

Twelve cadaveric specimens were prepared for surgical simulation. The AICAs were exposed using both EET and SAT approaches. Surgical window area and the length of the exposed artery were measured. The distance from the origin of the artery to the clip applied for proximal control was measured. The number of AICA perforators exposed and the anatomic features of each AICA were recorded.

RESULTS

The EET approach provided a wider surgical window area compared with the SAT (P < 0.001). More AICA perforators were visualized using the EET approach (P < 0.05). To obtain proximal control of the AICA, an aneurysm clip could be applied closer to the origin of AICA using EET (0.2 ± 0.42 mm) compared with SAT (6.26 ± 3.4 mm) (P < 0.001).

CONCLUSION

Clipping anterior pontine AICA aneurysms using the EET approach is feasible. Compared with SAT, the EET approach provides advantages in surgical window area, ensuring proximal control before aneurysm dissection, visualization of perforating branches, and better proximal control.

Microvascular anatomy of the cerebellar parafloccular perforating space

OBJECT

The cerebellopontine angle is a common site for tumor growth and vascular pathologies requiring surgical manipulations that jeopardize cranial nerve integrity and cerebellar and brainstem perfusion. To date, a detailed study of vessels perforating the cisternal surface of the middle cerebellar peduncle—namely, the paraflocculus or parafloccular perforating space—has yet to be published. In this report, the perforating vessels of the anterior inferior cerebellar artery (AICA) in the parafloccular space, or on the cisternal surface of the middle cerebellar peduncle, are described to elucidate their relevance pertaining to microsurgery and the different pathologies that occur at the cerebellopontine angle.

METHODS

Fourteen cadaveric cerebellopontine cisterns (CPCs) were studied. Anatomical dissections and analysis of the perforating arteries of the AICA and posterior inferior cerebellar artery at the parafloccular space were recorded using direct visualization by surgical microscope, optical histology, and scanning electron microscope. A comprehensive review of the English-language and Spanish-language literature was also performed, and findings related to anatomy, histology, physiology, neurology, neuroradiology, microsurgery, and endovascular surgery pertaining to the cerebellar flocculus or parafloccular spaces are summarized.

RESULTS

A total of 298 perforating arteries were found in the dissected specimens, with a minimum of 15 to a maximum of 26 vessels per parafloccular perforating space. The average outer diameter of the cisternal portion of the perforating arteries was 0.11 ± 0.042 mm (mean ± SD) and the average length was 2.84 ± 1.2 mm. Detailed schematics and the surgical anatomy of the perforating vessels at the CPC and their clinical relevance are reported.

CONCLUSIONS

The parafloccular space is a key entry point for many perforating vessels toward the middle cerebellar peduncle and lateral brainstem, and it must be respected and protected during surgical approaches to the cerebellopontine angle.

Using the Endoscopic Endonasal Transclival Approach to Access Aneurysms Arising from AICA, PICA, and Vertebral Artery: An Anatomical Study

Objective To explore the use of the endoscopic endonasal transclival approach (EEA) for clipping anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA), and vertebral artery (VA) aneurysms. Design Anatomical study. Participants Fifteen adult cadavers. Main Outcome Measures Length of artery exposed and distance from the nasal ala to the arteries. Results The length of the right and left VA exposed were 1.7 ± 0.6 cm and 1.6 ± 0.6 cm, respectively. The distance to the right VA was 11.1 ± 0.9 cm and to the left was 11.1 ± 0.8 cm. Right and left AICA were exposed for an average length of 1.1 ± 0.3 cm and 0.8 ± 0.3 cm, respectively. The distance to the right AICA was 10.3 ± 0.8 cm and to the left was 10.3 ± 0.8 cm. The right PICA was exposed for a length of 0.5 ± 0.2 cm at a distance of 10.9 ± 0.5 cm. The left PICA was exposed for a length of 0.5 ± 0.2 cm at a distance of 11.1 ± 0.9 cm. Conclusion The EEA can provide direct access to AICA, PICA, and VA, making it a potential alternative to the traditional approaches for the clipping of aneurysms arising from those arteries.

Ruptured Total Intrameatal Anterior Inferior Cerebellar Artery Aneurysm

Among the distal anterior inferior cerebellar artery (AICA) aneurysms, a unique aneurysm at the meatal loop inside the internal auditory meatus is extremely rare. The authors report a case of surgically treated total intrameatal AICA aneurysm. A 62-year-old female patient presenting with sudden bursting headache and neck pain was transferred to our department. Computed tomography and digital subtraction angiography showed subarachnoid hemorrhage at the basal, prepontine cistern and an aneurysm of the distal anterior inferior cerebellar artery inside the internal auditory meatus. Surgery was performed by retrosigmoid craniotomy with unroofing of the internal auditory meatus. The aneurysm was identified between the seventh and eighth cranial nerve in the meatus and was removed from the canal and clipped with a small straight Sugita clip. After operation the patient experienced transient facial paresis and tinnitus but improved during follow up.

A case of angiographically occult, distal small anterior inferior cerebellar artery aneurysm

Background:

A small aneurysm at an unusual location, such as a distal anterior inferior cerebellar artery (AICA) aneurysm, may conceal as a computed tomography angiography (CTA) and digital subtraction angiography (DSA)-occult aneurysm.

Case Description:

We herein present the case of a patient suffering from a subarachnoid hemorrhage (SAH) with two aneurysms in which the AICA aneurysm was negative by CTA and DSA. CTA demonstrated a right anterior choroidal artery aneurysm, which was revealed to be an unruptured aneurysm after surgical exploration. A small distal AICA aneurysm was detected by 3D rotational angiography (3DRA). The patient fully recovered except for left-side hearing loss four months after the second operation.

Conclusion:

We recommend a meticulous diagnosis by 3DRA in patients with SAH in which the distribution is not coincident with a typical aneurysmal location.

Endovascular treatment of AICA flow dependent aneurysms. A report of three cases and review of the literature

Peripheral anterior inferior cerebellar artery (AICA) aneurysms are rare, accounting for less than 1% of all cerebral aneurysms. To our knowledge 34 flow-related cases including the present study have been reported in the literature. Three patients harbouring four flow dependent aneurysms were referred to our institution. Two patients presented with subarachnoid hemorrhage, one presented with cerebellar manifestations. They were all treated by endovascular embolization of the aneurysm as well as the parent artery using liquid embolic material. Two cases were embolized using NBCA, Onyx was used in the third case. No bleeding or rebleeding were encountered during the follow-up period which ranged from five to nine months. One patient developed facial palsy, cerebellar symptoms and sensorineural hearing loss. The remaining two cases did not develop any post treatment neurological complications. Endovascular management of flow-dependent AICA aneurysms by parent artery occlusion is feasible and efficient in terms of rebleeding prevention. Post embolization neurological complications are unpredictable. This depends upon the adequacy of collaterals from other cerebellar arteries.

Petrosal approaches to posterior circulation aneurysms

Complex posterior circulation aneurysms are formidable lesions with an abysmal natural history. Their management continues to present a challenge to both endovascular and open microsurgical approaches. Affording an expansive, combined supra- and infratentorial exposure, the petrosal approaches are well suited for these challenging lesions when located along the basilar trunk or at a low-lying basilar apex. This report evaluates the evolution and application of petrosal approaches to these lesions. Excluding transsigmoid, infratentorial, or labyrinth-sacrificing approaches, the authors found 23 reports with 61 posterior circulation aneurysms treated via a petrosal approach. Although early morbidity was not negligible, rates of aneurysm occlusion (95% overall) and long-term outcome were quite laudable in light of the challenge posed by these lesions. Moreover, with accumulating experience with petrosal approaches, rates of complications are likely to wane, as neurosurgeons capitalize on the expansive exposure afforded by these indispensable approaches.

Clinical presentation and treatment of distal anterior inferior cerebellar artery aneurysms

Aneurysms located at the distal portion of the anterior inferior cerebellar artery (AICA) are rare, and their clinical features are not fully understood. We report the clinical features and management of nine distal AICA aneurysms in nine patients treated during the past decade at Kagoshima University Hospital and affiliated hospitals. Our series includes seven women and two men. Of their nine aneurysms, eight were ruptured and one was unruptured; six were saccular and three were dissecting aneurysms. The most prevalent location was the meatal loop (n = 5) followed by the postmeatal (n = 3) and premeatal segment (n = 1) of the AICA, suggesting hemodynamic stress as an etiology of these distal AICA aneurysms. Of the nine patients, five presented with angiographic features suggestive of increased hemodynamic stress to the AICA and the common trunk of the posterior inferior cerebellar artery, with vertebral artery stenosis, marked laterality, and a primitive hypoglossal artery. We addressed eight aneurysms (eight patients) surgically; one aneurysm in one patient disappeared in the course of 3 months without surgical treatment. Of the eight surgically treated aneurysms, seven were ruptured and one was unruptured, five were clipped via lateral suboccipital craniotomy, two were trapped via lateral suboccipital craniotomy, and one was embolized. Good outcomes were obtained in six of the eight patients who underwent operation (75 %). We consider increased hemodynamic stress attributable to anatomic variations in the AICA and related posterior circulation to be the predominant contributor to the development of distal AICA aneurysms. Direct clipping and trapping yielded favorable outcomes in our series.

Endovascular management of distal anterior inferior cerebellar artery aneurysms: Report of two cases and review of the literature

BACKGROUND

Aneurysms of the anterior inferior cerebellar artery (AICA), especially those located in the distal portion of the AICA, are rare. There are few reported cases treated with surgery or endovascular embolization.

CASE DESCRIPTION

We report two cases of fusiform distal AICA aneurysms presenting with subarachnoid hemorrhage. Parent artery occlusion with coils and n-butyl cyanoacrilate (n-BCA) resulted in complete aneurysm occlusion and prevented rebleeding. Both patients presented postprocedure neurological deficits, but have made a good recovery at 4 and 10 months, respectively.

CONCLUSION

Occlusion of the parent artery for the treatment of ruptured fusiform distal AICA aneurysms is effective but has significant neurological risks.

Management of anterior inferior cerebellar artery aneurysms: endovascular treatment and clinical outcome

BACKGROUND AND PURPOSE

AICA aneurysms are rare and a challenge to treat surgically. We present our experience of the angiographic results and the clinical outcomes for 9 AICA aneurysms treated by EVT.

MATERIALS AND METHODS

Between 1997 and 2009, EVT was attempted for 9 AICA aneurysms. Six patients presented with SAH, and 3 aneurysms were found incidentally. The location of the aneurysms was the proximal AICA in 7 and the distal AICA in 2. Five aneurysms originated from an AICA-PICA variant. Clinical outcomes and procedural complications were evaluated, and angiography was performed 6, 12, and 24 months after embolization to confirm recanalization of the coiled aneurysm.

RESULTS

EVT was technically successful in 7 patients (78%). Surgical trapping was performed in 1 patient after failure of EVT, and another aneurysm occluded spontaneously, along with the parent artery during EVT. In 7 patients, the AICAs had good patency on postoperative angiography. Stent-assisted coiling was performed in 3 patients. Follow-up angiographies were performed in 7 patients and showed no evidence of recanalization or progressive occlusion with further thrombosis except in 1 patient. There was no evidence of aneurysm rupture during the follow-up period, and 8 patients were able to perform all usual activities (mRS score, 0-1).

CONCLUSIONS

EVT may provide a feasible and safe option as an alternative, though a microsurgical option is initially considered for the management of AICA aneurysms. Further follow-up and more experience are also necessary.

Intrameatal thrombosed anterior inferior cerebellar artery aneurysm mimicking a vestibular schwannoma

Aneurysms of the anterior inferior cerebellar artery (AICA) are a rare entity. Purely intrameatal aneurysms are even rarer. The authors report an intrameatal thrombosed AICA aneurysm mimicking a vestibular schwannoma that was treated by resection and end-to-end anastomosis. This 22-year-old man presented with acute hearing loss, vertigo, and moderate facial palsy. Magnetic resonance imaging showed an atypical intrameatal lesion with dilation of the internal auditory canal. Microsurgical inspection via a retrosigmoid approach and drilling of the posterior wall of the internal auditory canal revealed a thrombosed AICA aneurysm. The aneurysm was excised, and an end-to-end suture was performed to restore AICA continuity. Intraoperative indocyanine green videoangiography as well as postoperative digital substraction angiography showed a good revascularization. Intrameatal AICA aneurysms may present with symptoms similar to vestibular schwannomas. End-to-end reanastomosis after aneurysm resection is a treatment option when clipping is impossible.