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Table of Contents    
ORIGINAL ARTICLE
Year : 2020  |  Volume : 68  |  Issue : 5  |  Page : 1115-1124

Posterior Inferior Cerebellar Artery Aneurysms: Comparison of Results of Surgical and Endovascular Managements at One Single Center


1 Department of Interventional Neuroradiology, Beijing Neurosurgical Institute and Beijing Tiantan Hospital, Capital Medical University; Department of Neurosurgery, Puyang People's Hospital, Henan, China
2 Department of Neurosurgery, Aerospace Center Hospital, Haidian, Beijing, China
3 Department of Neurosurgery, Aerospace Center Hospital, Haidian, Beijing; Department of Neurosurgery, Weifang Hospital of traditional Chinese Medicine, Weifang, China
4 Department of Interventional Neuroradiology, Beijing Neurosurgical Institute and Beijing Tiantan Hospital, Capital Medical University, Henan, China

Date of Web Publication27-Oct-2020

Correspondence Address:
Dr. Youxiang Li
Beijing Neurosurgical Institute, Beijing Tiantan Hospital, Capital Medical University, Nan Si Huan Xi Lu 119, Fengtai District, Beijing - 100 070
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.294555

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 » Abstract 


Aims: The objective of this article is to report our experience with the two treatment approaches in patients with PICA aneurysms and find predictive factors for treatment-related complications.
Materials and Methods: Between January 2011 and December 2015, patients with PICA aneurysm who underwent surgical and endovascular treatment were retrospectively collected and reviewed. Patients' demographic features, treatment-related complications, and long-term angiographic and clinical outcomes (modified Rankin Scale [mRS]) between the two groups were compared. Multivariable logistic analysis was used to find statistically significant predictive factors for treatment-related complications.
Results: A total of 55 PICA aneurysms were identified, 13 were ruptured, and 42 unruptured. Endovascular treatment was performed in 26 patients and surgical clipping in 29 patients. Treatment-related complications occurred in one patient in the embolization group compared with 9 in the microsurgical surgery group (3.8% vs. 31.0%, P = 0.010). Multivariate logistic analysis showed that treatment modality was the only predictor for treatment-related complications. A lower recurrence rate was found in the microsurgical surgery group compared with the embolization group (3.4% vs. 7.7%, P = 0.493). Clinical follow-up showed that endovascular treatment achieved better outcomes (mRS ≤2) compared with surgical treatment (96.2% vs. 89.7%, P = 0.359).
Conclusions: This study of PICA aneurysms demonstrates that results of both treatment modalities are comparable. To obtain the best treatment outcomes, cooperation between interventional neuroradiologist and endovascular neurosurgeons in deciding the optimal treatment is essential.


Keywords: Aneurysm, management, endovascular, surgical, outcome, posterior inferior cerebellar artery
Key Message: To decide the optimal treatment of PICA aneurysms, cooperation between microvascular and endovascular neurosurgeons is essential and necessary.


How to cite this article:
Yin Q, Guo H, Wei J, Liu P, Lv M, Li Y. Posterior Inferior Cerebellar Artery Aneurysms: Comparison of Results of Surgical and Endovascular Managements at One Single Center. Neurol India 2020;68:1115-24

How to cite this URL:
Yin Q, Guo H, Wei J, Liu P, Lv M, Li Y. Posterior Inferior Cerebellar Artery Aneurysms: Comparison of Results of Surgical and Endovascular Managements at One Single Center. Neurol India [serial online] 2020 [cited 2020 Nov 24];68:1115-24. Available from: https://www.neurologyindia.com/text.asp?2020/68/5/1115/294555




Intracranial aneurysms are present in 1–6% of the population. Aneurysms of the posterior circulation account for approximately 10% of intracranial aneurysms. More specifically, posterior inferior cerebellar artery (PICA) aneurysms account for 0.5–3%.[1],[2]

Factors such as the vicinity of important intracranial structures, including the brainstem and cranial nerves, and limited operative working space have made microsurgical clip ligation of these aneurysms technically challenging.[3] In addition, the small caliber of the PICA and the broad neck often associated with these aneurysms create unique challenges in preserving this artery during microsurgical and endovascular treatment.[4],[5],[6],[7],[8]

Over the last three decades, several series using both endovascular and open surgical techniques have reported results and complications of treatment for these aneurysms.[9],[10],[11],[12],[13] The best treatment strategy and technique for PICA aneurysm continue to be debated.[14],[15],[16],[17],[18] Surgical or endovascular approaches are aimed at preserving the PICA and permanently occluding the aneurysm. Current endovascular techniques include primary coiling, stent-assisted coiling (SAC), balloon-assisted coiling, occlusion of the parent artery with coils or liquid embolic materials, and flow diversion.[19] Recent studies predominantly focus on endovascular techniques for management of these aneurysms.

Data comparing the two treatment approaches for aneurysms in this specific location were limited. We presented a consecutive series of 55 PICA aneurysms and assessed treatment outcomes based on mode of management and anatomical location and found significant predictive factors for treatment-related complications.


 » Methods Top


Patient population

From January 2011 through December 2015, we treated 55 PICA aneurysms in 55 patients through endovascular or microsurgical approaches at our hospital. As to the 55 PICA aneurysms, 42 were ruptured and 13 were unruptured. Twenty-six patients were treated with an endovascular approach and 29 with surgical approach. Clinical presentation included subarachnoid hemorrhage (SAH) in 42 patients, and in 13 patients, the aneurysm was incidentally discovered or presented with aneurysm-unrelated symptoms. Time from rupture to treatment was 0–3 days in 28 patients, 4–14 days in 13 patient, and ≥14 days in 1 patient.

Variable assessment

Data for ruptured and unruptured aneurysms were recorded from the time of admission until hospital discharge, death, or loss to follow-up. Patient's clinical characteristics included age, gender, comorbidities, presenting symptoms, Hunt and Hess (HH) score at time of admission, neurological status, and choice of management (endovascular vs. microsurgical). For each aneurysm, the treatment type and any procedural complications were determined from the operative reports.

Some authors defined proximal PICA aneurysms as those originating from the medullary PICA tract.[8] By location, aneurysms arising at the vertebral artery–PICA junction (VPJ) and aneurysms arising within the five segments of PICA – anterior medullary (AM), lateral medullary (LM), tonsillomedullary, telovelotonsillar (TVT), and cortical branches – were included in the study group. In this study, proximal PICA aneurysms were defined as aneurysms originating from the PICA–vertebral artery (VA) junction or the anterior and LM segment of the PICA. Aneurysms arising beyond the LM segment were defined as distal PICA aneurysms.[15],[16]

Dependent variables included the complications for the endovascular and microsurgical clipping. By type, aneurysms accepted into the study group included saccular and dissecting aneurysms. Coexistence with cerebellar arteriovenous malformations (AVMs) or aneurysms at other location was also recorded.

The complications of SAH, such as direct effects of the bleed, vasospasm, hydrocephalus, the need for ventriculoperitoneal shunt placement, and other medical complications directly related to endovascular or surgical treatment, were recorded and evaluated. As to the endovascular treatment, thromboembolic complications were defined as angiographic evidence of thrombosis during or at the end of procedure, or new ischemic manifestations on computed tomography (CT) or magnetic resonance imaging (MRI) scans. Hemorrhagic complications were determined by contrast leakage during the procedure or postprocedure CT scans as newly developed hemorrhage on CT or MRI studies within 30 days of the procedure.

As to the microsurgical group, we recorded the postoperative aneurysm rupture, neurologic deficit, cranial nerve palsy, medical complications, and need for shunting.

Management selection

SAH was diagnosed by CT. As to all the patients in our group, assessment of aneurysms was performed with computed tomography angiography (CTA) and digital subtraction angiography (DSA).

All patients and their corresponding aneurysms were at least reviewed by a comprehensive cerebrovascular team, consisting of neurosurgeons and interventional neuroradiologists, and intensive care specialists, before a decision regarding the type of management was determined. Factors that influenced a decision for endovascular management were older age, poor SAH grade, and shape, that is, whether the aneurysm was purely saccular in shape with a good dome-to-neck ratio and relationship to an AVM. Factors more suggestive for microsurgical management included aneurysm morphology with a broad neck, ruptured state, need for cerebellar decompression, better presenting grade, and young age. In every case where multiple aneurysms or associated AVM were present, the source of the bleeding was identified based on pattern and distribution of the bleed on CT and/or the geometry of the aneurysm.

In saccular PICA aneurysms with a favorable geometry (i.e., narrow neck and dome to neck ratio >1.5), selective embolization of the aneurysm was performed with preservation of the parent vessel. In proximal wide-necked aneurysms, which are incorporating the origin of the branch, coiling was performed using stent assistance. Aneurysms distal to the TVT segment with acute angles or tortuosities of the PICA precluding microcatheter access to the aneurysm are typically referred for parent artery occlusion. For patients who underwent parent vessel occlusion (PVO), postoperative magnetic resonance imaging and CT were evaluated for ischemia in the PICA territory, and informed consent was obtained from the patient and their family members prior to the endovascular or microsurgical treatment.



Endovascular procedures

Endovascular treatment of the aneurysms was performed on a single plane or a biplane angiography unit. For endovascular management, all aneurysms were treated through the ipsilateral or bilateral vertebral arteries. The guide catheter was positioned depending on the angle of origin of the PICA for an ipsilateral or contralateral catheterization. If the PICA originated from an acute angle from the VA, the microcatheter catheterization was performed through the contralateral VA.

As to the vertebral/PICA aneurysms, if the aneurysm harbored a wide neck, a stent was placed in the vertebral artery or the ipsilateral PICA. The enterprise stent (Codman Neurovascular, Miami Lakes, FL, USA), solitaire stent (Solitaire AB neurovascular remodeling device, eV3, Inc., Irvine, CA, USA), and the low-profile visualized intraluminal support (Lvis or Lvis Jr; MicroVention-Terumo, Tustin, CA) stent were used. The SAC procedure was “jailing” technique, a coiling microcatheter was introduced into the aneurysm sac, and the first coil was inserted without detachment, after which a stent was deployed and coils were introduced subsequently.



According to the size and shape of the aneurysm, appropriate coils were selected. We inserted the coils within the aneurysm as densely as possible to achieve the angiographic complete occlusion, or until another coil could no longer be inserted. After the procedure, three-dimensional angiography was obtained to assess the result. Procedure-related complications and adverse events were recorded. After embolization, the patient was monitored for 24 h at the intensive care unit. Postprocedure CT scans were obtained in all patients within 24 h.

Pharmacology management

As to all the patients treated endovascularly, interprocedure heparinization was achieved by adding 3000 IU of heparin to 500 mL of 0.9% (wt/vol) sodium chloride infusion solution and then administered through the guiding catheter during the procedure. As to the patients treated with SAC, a loading dose of 300 mg aspirin and 225 mg clopidogrel were given at least four hours before the procedure.[20] After the procedure, patients were maintained on daily clopidogrel (75 mg) and aspirin (100 mg) for six weeks, followed by aspirin alone (100 mg daily) for another six months. During the procedure, thromboembolism complications were handled with 0.5 mg loading dose of glycoprotein IIb/IIIa antagonist (tirofiban) injected intra-arterially. As to the patients treated with pure coiling, no antiplatelet drugs were given prior to or after the procedure.

Surgical clipping

Microsurgical management was conducted with middle, far lateral, or retrosigmoid suboccipital approach, and all attempts were made to reconstruct the parent vessel lumen upon clip application, most often using an angled fenestrated clip. In case of coexisting with cerebellar AVM, both the aneurysm and AVM nidus were completely removed. If the diseased segment of the PICA needed to be excluded from circulation, indocyanine green angiography and DSA were performed to subjectively assess for collateral circulation. No revascularization procedures were performed in this cohort.

Clinical and angiographic follow-up

All patients were advised to be clinically evaluated 6, 12, and 24 months after treatment. Discharge and long-term clinical outcomes were assessed by the same practitioner (H. Guo). Angiographic follow-up was also recommended, including 6, 12, and 24-month DSA and magnetic resonance angiography yearly thereafter.

Postoperative or postprocedure angiographic occlusion rate, technical success, follow-up images, and complications were independently evaluated by two interventional neuroradiologists (M. Lv, Y. Li). Evaluation of outcome status was according to the modified Rankin Scale (mRS) as follows: 0, no symptoms at all; 1, no significant disability; 2, slight disability; 3, moderate disability; 4, moderately severe disability; 5, severe disability; and 6, dead.

Statistical analysis

Aneurysm locations and treatment modalities were analyzed to determine the risk factors associated with complications using the Chi-square test. Statistical analysis was performed using SPSS software (version 22.0; SPSS, Chicago, IL, USA). Univariate statistical analysis was performed by using the χ2 or Fisher exact test to assess associations between clinical, angiographic, and procedural variables and treatment outcomes. Variables with P values <0.10 in univariate analysis were chosen for multivariate models using logistic regression analysis. Statistical significance was defined as P < 0.05 in all analyses, and P values and 95% confidences intervals (CIs) for odds ratio were corrected by Bonferroni's method because of multiple testing.


 » Results Top


Baseline characteristics

Patient and aneurysm baseline characteristics are summarized in [Table 1]. As to the 55 PICA aneurysms, 42 (76.4%) were ruptured and 13 (23.6%) were unruptured. As to the 13 unruptured aneurysms, all were found incidentally or presented with aneurysm-unrelated symptoms. Clinical grading according to the HH scale on admission in 42 patients with ruptured PICA aneurysms was as follows: HH I in 11 (26.2%) patients, II in 24 (57.1%) patients, HH III in 6 (14.3%) patients, and HH IV–V in 1 (2.4%) patient.
Table 1: Patient and aneurysm baseline characteristics of the two groups


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There were 33 women (60%) and 22 men (40%), with a mean age of 48.0 ± 14.6 years (range, 6–70 years). Dissecting aneurysm was found in five aneurysms (9.1%) and saccular aneurysm in 50 (90.9%). The mean aneurysm size was 7.2 ± 6.3 mm (range, 1–35 mm). As to the location, 23 (41.8%) were associated with the vertebral segment (VPJ), 22 (40.0%) were proximal segment, and 10 (18.2%) were the distal segment.

Additionally, associated intracranial vascular lesions were identified in six (10.9%) patients. Three patients had associated aneurysms at other locations with one at the middle cerebral artery and two at the internal carotid artery. Three patients had additional AVMs at the cerebellar lobe.

Of the 42 ruptured aneurysms, 23 (54.8%) were treated by endovascular treatment and 19 (45.2%) by microsurgical clipping. Of the 13 unruptured aneurysms, 3 (23.1%) were treated by endovascular treatment and 10 (76.9%) were treated by microsurgical clipping. Overall, 26 patients underwent endovascular procedures and 29 patients underwent surgical clipping. As to the five dissecting aneurysms, two were treated with SAC (one with enterprise and one with Lvis) and three were treated with surgical clipping. One dissecting aneurysm in the surgical group was treated with aneurysm excision with end-to-end anastomosis of the parent vessel. The other two patients were treated with aneurysm excision with preservation of the parent vessel.

Comparison of the basic characteristics between the two groups

As shown in [Table 1], there was no statistically significant difference in the patient age, sex, presence of hypertension history, aneurysm type, aneurysm location, and associated with other anomalies. However, there was significantly higher rate of ruptured aneurysms in the endovascular group (23/26 vs. 19/29; P = 0.046). Additionally, the aneurysm size was significantly larger in the microsurgical group (9.2 ± 7.5 vs. 5.0 ± 3.8; P = 0.013). Although the rate of association with other anomalies was higher in the endovascular group (5/26) than in the microsurgical group (1/29), this difference was not statistically significant (P = 0.061).

Initial and follow-up DSA

The initial and follow-up results were summarized in [Table 2].
Table 2: The initial and follow-up angiographic and clinical results of the two groups


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In the endovascular group, pure coiling was performed in 12 patients and SAC in 9 patients (Solitaire AB 2, Enterprise 3, Lvis Jr 3, Lvis 1 [Figure 1]). PVO was performed in five patients with distal PICA aneurysm including two patients with cerebral AVMs. The initial DSA after the procedure showed RS1 in 20 aneurysms (83.5%), RS2 in 5 aneurysms (16.5%), and RS3 in 1 aneurysm.
Figure 1: (a) Computed tomography scan showed subarachnoid hemorrhage in the posterior cranial fossa. (b) 3D angiography of left vertebral artery (VA) showed a wide-necked PICA aneurysm (white arrow). (c) The roadmap view illustrated the positioning of stent microcatheter across the aneurysm neck (white arrow). (d) Under the roadmap, the aneurysm was coiled with the assistance of Lvis 3.5 × 15 mm. (e) Post-procedural left VA angiography manifested the complete occlusion of the aneurysm and the good preservation of the parent vessel. (f) Postembolization unsubtracted angiography showed the clustered coils and the outline of the stent

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In the microsurgical group, middle suboccipital approach was performed in 12 patients [Figure 2], far lateral approach with linear scalp incision in 7 patients, and suboccipital retrosigmoid approach in 10 patients. The subsequent CTA (n = 9) and DSA (n = 20) after the surgery showed complete excision in 25 patients and partial excision in three patients.
Figure 2: (a) Computed tomography scan showed subarachnoid hemorrhage in the posterior cranial fossa. (b) Lateral control angiography of the left VA demonstrated a PICA aneurysm. (c) 3D angiography of left vertebral artery (VA) showed that the aneurysm was located at a small branch of PICA (white arrow). (d) Under the middle suboccipital approach, the aneurysm was completely excised. The postoperative control angiography of the left VA showed the complete excision of the aneurysm sac

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Conventional angiographic follow-up that extended longer than 12 months was available in 24 of 26 patients (92.3%) in the endovascular group during 23.4 ± 11.7 months (range from 12 to 56 months), including 22 with complete occlusion and 2 with near complete occlusion. There was no in-stent stenosis (>50% stenosis) on follow-up angiography. Four remnants were stable, and in one patient, the originally diagnosed remnant was not visible on the DSA at one year.

Conventional angiographic follow-up that extended longer than 12 months was available in 23 of 29 patients (85.2%) in the microsurgical group during 23.4 ± 11.7 months (range from 12 to 56 months), including 21 with complete excision and 2 with near complete excision.

The aneurysm recurrence and retreatment rates were 7.7% (2/25) and 3.4% (1/29), respectively. In the endovascular group, recurrences were found in two VPJ aneurysms 13 months [Figure 3] and [Figure 4] and 7 months after initial treatment by SAC (Enterprise 1, Lvis Jr 1). The two patients were retreated with coiling and suffered no recurrence during the follow-up period. In the surgical clipping group, one patient with AM segment aneurysm suffered recurrence and retreated with pure coiling. No recurrences were seen after PVO.
Figure 3: (a) Computed tomography scan showed subarachnoid hemorrhage in the posterior cranial fossa. (b and c) 3D view and the working position contrast injection of left vertebral artery (VA) showed that the aneurysm was located at the vertebral artery-PICA junction. (d) The roadmap view illustrated the positioning of three microcatheters within the aneurysm sac (white arrow). (e) Since the contralateral VA was aplastic, antegrade stenting through the ipsilateral VA was done. (f) The distal part of the Lvis Jr 2.5 × 17 mm was completely deployed toward the distant part of the V A. (g) The unsubtracted image showed the clustered coils and outline of the stent. (h) Postprocedural left VA angiography manifested the complete occlusion of the aneurysm and the good preservation of the parent vessel

Click here to view
Figure 4: (a) The 13-month follow-up angiography of the patient in Figure 3 showed the recurrence of the aneurysm neck. (b) The unsubtracted image showed the loose packing of the coils within the aneurysm sac. The aneurysm was retreated with pure coiling. (c) Postprocedural left VA angiography manifested the complete occlusion of the aneurysm and the good preservation of the parent vessel. (d) The un-subtracted image showed the dense packing of aneurysm sac

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Procedure-related complications

Treatment-related complications were demonstrated in [Table 3], which included one patient in the endovascular group and nine patients in the microsurgical group.
Table 3: The basic information of the 10 patients with treatment-related complications


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In the endovascular group, one VPJ aneurysm suffered coil perforation during the procedure of coiling and resulted in devastating intracranial hemorrhage and died. No patients required PEG placement.

In the microsurgical group, nine patients suffered lower cranial neuropathies, as shown in [Table 3]. In three cases, PEG feeding insertion was required and all were localized on the proximal segment of PICA. Tracheotomy was required in two cases.

Multivariate analysis of complications

As shown in [Table 4], the clinical and angiographic characteristics between the patients with complications and those without complications were compared. [Table 3] demonstrates the multivariate logistic regression analyses for predictors of complications.
Table 4: The clinical and angiographic characteristics between the patients with complications and those without complications


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Univariable logistic analysis showed that the location of the aneurysm (proximal), HH grade, treatment approach, and aneurysm status were significantly associated with the presence of complications (P < 0.1).

Multivariate logistic regression analysis [Table 5] showed that treatment approach (OR, 11.519; 95% CI, 1.280–13.632) was the only significantly independent predictor for complications (P = 0.029). Patients with microsurgical approach were more likely to result in complications.
Table 5: Multivariate logistic regression analysis results


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Clinical outcomes

In the endovascular group, one patient died of intraprocedural hemorrhage. The remaining 25 patients recovered with no neurological deficits and discharged. As to the remaining 25 patients, the last clinical follow-up with a mean of 29.1 ± 16.2 months (range from 7 to 53 months) showed that mRS 0 was observed in 24 patients and mRS 1 in one patient. The rate of good neurologic outcome at last known follow-up (average 11 months) was 96.2% (25/26).

In the microsurgical group, one patient died during hospital admission due to previous severe clinical status (HH grade IV SAH). In addition, one patient (HH grade 2) survived of vegetative state due to severe vasospasm. The clinical follow-up at discharge showed mRS 0 in 16 patients, mRS 1 in 2 patients, mRS 2 in 4 patients, mRS 3 in 4 patients, mRS 4 in 1 patient, mRS 5 in 1 patient, and mRS 6 in 1 patient. The last clinical follow-up with a mean of 29.1 ± 16.2 months (range from 7 to 53 months) for the remaining 28 patients showed mRS 0 in 17 patients, mRS 1 in 2 patients, mRS 2 in 8 patients, and mRS 5 in 1 patient. The rate of good neurologic outcome (mRS 0–2) at discharge was 79.3% (23/29). The rate of good neurologic outcome at last known follow-up (average 11 months) was 89.7% (26/29).

There was statistically significant difference in the rate of good neurologic outcome at discharge (P = 0.035); however, the difference at the last follow-up was not statistically significant (P = 0.359).

Among the seven patients who presented with lower cranial nerve palsy after treatment, follow-up information was available in all the patients. Complete recovery was observed in five patients within 1 year. In the remaining two patients, one had persistent dysphagia, and the other patient's ataxia symptom worsened.


 » Discussion Top


The PICA aneurysms usually present with the most complex, tortuous, and variable course and area of supply among the cerebellar arteries. Previous data showed that they might be dissecting, fusiform, or saccular in morphology and the majority arise at the VA–PICA junction, the AM and LM segment, also known as the proximal segment. As shown in our case series, 45 (81.8%) were located at the vertebral segment or proximal segment, and 10 (18.2%) were located at the distal segment.

Recent studies have published different treatment options of PICA aneurysms in a series of patients treated at specific institutions and a variety of microsurgical and endovascular techniques have been utilized to manage these aneurysms based on local experience and treatment policy. However, studies that compare the two treatment modalities for aneurysms in this location are limited. In our analysis, with regard to the 55 patients in our study, patients with microsurgical approach were more likely to result in complications (endovascular group, 1 vs. microsurgical group, 9). Additionally, multivariate logistic regression analysis showed that treatment approach (OR, 10.772; 95% CI, 1.852–22.659) were the only significantly independent predictor for complications. In 2015, Bohnstedt retrospectively assessed the treatment outcomes for 102 PICA aneurysms based on mode of management and anatomical location. The author found that 12 of 65 (18.5%) patients developed new cranial nerve palsies after surgical intervention compared with 5 of 37 (13.5%) (P = 0.415) who developed new cranial nerve palsies after endovascular intervention. Additionally, surgery was related to higher rates of cranial nerve palsies, especially in patients harboring proximal PICA aneurysms. The author concluded that PICA aneurysms are challenging and require a multimodality treatment paradigm.[18]

A recent systematic review and meta-analysis of 796 posterior inferior cerebellar aneurysms receiving either surgical or endovascular treatment demonstrated that in general, both treatment modalities are technically feasible with high rates of technical success of over 95% and safe with good long-term neurological outcomes of approximately 80%. However, complications are not negligible with procedure-related morbidity of approximately 1/10 of treated patients in both groups.[17] In 2017, Sejkorová et al. retrospectively reviewed 81 PICA aneurysms treated at 3 large tertiary referral centers (43 underwent endovascular and 38 surgical treatment). Among patients treated endovascularly, procedure-related complications occurred in four cases (11.8%). Six patients (19.4%) suffered from complications directly associated with surgery.[16]

Microsurgical clipping

Previous study showed that microsurgical approaches for clip ligation of PICA aneurysms could vary from a minimal midline suboccipital craniotomy to a far lateral craniotomy with partial resection of the first cervical vertebrae, depending on size and location of the aneurysm. As to the 29 patients treated with microsurgery in our study, middle suboccipital approach was performed in 12 patients, far lateral approach with linear scalp incision in 7 patients, and suboccipital retrosigmoid approach in 10 patients. Some investigators have suggested that direct microsurgery has several advantages, such as immediate decompression by removal of blood clot reduction of the need for shunting, and identification of the bleeding sources in cases with multiple lesions and decreasing the risk of rehemorrhage. Since the presence of perforating vessels is more common in the proximal location, surgical treatment of this location was related to higher rates of intracranial nerves palsies when compared with those treated endovascularly with a high incidence of lower cranial nerve deficits ranging from 20% to 66%.[7],[9],[15],[16],[17],[18] The proximal PICA is in close proximity to cranial nerves IX, X, XI, and XII, which places these cranial nerves at risk during microdissection. The vicinity of brainstem and cranial nerves as well as the limited operative working space make clip ligation of PICA aneurysms challenging.

Endovascular treatment

Recently, PICA aneurysms are increasingly being treated with endovascular techniques, which avoid the manipulation of important posterior fossa structures. The incidence of endovascularly treated PICA aneurysms has been reported to be between 0% and 18.8%.[15],[16],[17],[18] Endovascular treatment options include simple coiling, balloon or SAC, vessel sacrifice, and, more recently, flow-diverter stent placement.[10],[11],[12],[13],[15],[16],[17],[18],[19] Our study showed that pure coiling was performed in 12 patients, and SAC in 9 patients (Solitaire AB 2, Enterprise 3, Lvis Jr 3, Lvis 1). In our opinion, selective endovascular obliteration of the aneurysm with preservation of the parent artery is the ideal treatment for saccular PICA aneurysms. Selective embolization of saccular aneurysms with a favorable geometry (narrow neck) can be safely and effectively performed with coils. For wide-necked aneurysms or when the PICA originates from the aneurysm sac, SAC technique can be used. For SAC of PICA aneurysms, either the ipsilateral or contralateral VA approach may be used, depending on the angle of PICA origin.[10] Antegrade stenting via the ipsilateral VA is preferred when the origin of the PICA from the VA forms an obtuse angle, whereas retrograde stenting via the contralateral VA is used in cases with an acute angle between the VA and PICA. If that is not feasible, placement of the balloon into the ipsilateral VA is an alternative. Another potential future treatment option may be a flow-diverting stent, such as the ev3 Pipeline Embolization Device. However, remaining challenges include preservation of small parent vessel diameter and the need for antiplatelet agents in patients with SAH.

Previous data showed that occlusion of the whole PICA might cause LM syndrome (Wallenberg syndrome) with such symptoms as dysarthria, lack of corneal reflex, ataxia or loss of temperature, and pain sensation in the contralateral side of the body.[21] In our study, 10 distal PICA aneurysms were treated with PVO (endovascular group 5; surgical group 5), and only 1 patient in the microsurgical group suffered choking in drinking water and recovered within 6 months. Although no cases in our series received revascularization, for distal segment PICA aneurysms, revascularization should be considered if direct endovascular coiling or surgical clipping is not an option, especially the aneurysm is located on one of the first three segments of PICA. In 2015, Juszkat presented their 10 years of experience in endovascular treatment of ruptured saccular PICA aneurysms, and only in two cases out of 38 (5.3%), they had to deliberately occlude the PICA to exclude the ruptured aneurysm from circulation because the aneurysm was impossible to reach with the microcatheter. In both cases, aneurysms were located on distal segments of the artery (telovelotonsilary and tonsilomedullary).[11] Trivelato et al.[22] compared selective coiling and PAO in isolated PICA dissecting aneurysms and performed literature data analysis of 83 such cases. They concluded that although there is no statistical difference between coiling and PAO in the ratio of complications, there is a significantly higher risk of PICA infarction when PAO is performed. Therefore, although there is an occlusion of the distal PICA, only the subsequent cerebellar territory is affected. The effect of a superficial cortical infarction produced by a distal PICA occlusion usually is not clinically relevant.

Clinical outcome and recurrence

Among the seven patients who presented with lower cranial nerve palsy after treatment, follow-up information was available in all the patients. Complete recovery was observed in five patients within one year. Bohnstedt found that 40.9% of patients with ruptured aneurysms and 41.1% of patients with unruptured aneurysms undergoing surgical treatment experienced a new postoperative deficit.[18] Despite statistically significant differences in complications between endovascularly and microsurgically treated patients, these same differences were not observed in final patient outcomes. This represents the resolution of surgically associated complications such as transient lower cranial nerve palsies or the possibility that a higher percentage of patients with poorer outcomes were lost to follow-up. Some recently published surgical series demonstrated higher rates of good neurological outcomes ranging from 80% to 89%.[15],[16],[17],[18] Our findings are superior to those in these prior reports, with the rates of good neurological outcomes of 96.2% of patients in the endovascular group and 89.7% of patients in the surgical group. In addition, in our subgroup analysis by type of treatment, we found that surgical treatment also had higher overall complete occlusion rates and significantly lower rates of aneurysm recurrence.

The aneurysm recurrence rates in our study were 7.7% (2/25) and 3.4% (1/29), respectively. Bohnstedt found a 5.4% (2 of 37) recurrence rate among endovascularly treated aneurysms requiring retreatment.[18] In Petr's systematic review, patients undergoing surgical treatment had significantly lower rates of aneurysm recurrence (1.1%, 95% CI, 0.3–2.3%) when compared to those undergoing endovascular treatment (8.1%, 95% CI, 5.2–11.7%) (P < 0.0001).[17] Sejkorová found that recurrences occurred in 0% of surgical and in 16.3% of endovascularly treated patients, requiring treatment with a rehemorrhage rate of 3.2% and 0% after endovascular and microsurgical treatment of ruptured aneurysms, respectively.[16]

In general, our results showed that both endovascular and surgical treatment were reasonable options for PICA aneurysms. Hence, the optimal therapy of PICA aneurysms should be performed on a selective, case-by-case basis in order to maximize patient benefits and limit the risk of periprocedural complications. Recently, modern management of PICA aneurysms should aim to make out the best treatment based on aneurysm and patient features.[9],[15] We agree that to aprioristically prefer one technique over another is incorrect. The so-called tailored treatment is crucial in vascular surgery as in other different fields of neurosurgery. To obtain the best treatment outcomes, cooperation between microvascular neurosurgeons and endovascular neurosurgeons in deciding the optimal treatment is essential.


 » Limitations Top


First, this study is subject to biases. It was not large enough for meaningful subgroup analysis. Second, longer clinical and angiographic follow-up is needed to provide more accurate assessments of recurrence and rehemorrhage rates after endovascular and microsurgical treatment. Lastly, in recent two years, hybrid operation room has been established in our hospital; several PICA aneurysms treated with multimodal treatment were not included in our study.


 » Conclusions Top


This study of PICA aneurysms demonstrates that results of both treatment modalities are comparable. To obtain the best treatment outcomes, cooperation between microvascular and endovascular neurosurgeons in deciding the optimal treatment is essential.

Financial support and sponsorship

This work was supported by Beijing Municipal Administration of Hospitals Incubating Program (PX2020039) and the National Natural Science Foundation of China, grant number (81901197).

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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