Seventy Aneurysms of the Posterior Inferior Cerebellar Artery: Anatomical Features and Value of Computed Tomography Angiography in Microneurosurgery

A Contemporary Clinico-Anatomical Guide to Craniovertebral Junction Surgery

Background  Surgical treatment of ventral and ventrolateral lesions of the craniocervical junction are among the most challenging neurosurgical pathologies to treat. Three surgical techniques, the far lateral approach (and its variations), the anterolateral approach, and the endoscopic far medial approach can be used to approach and resect lesions in this area. Objective  The aim of the study is to examine the surgical anatomy of three skull base approaches to the craniocervical junction and review surgical cases to better understand the indications and possible complications for each of these approaches. Methods  Cadaveric dissections with standard microsurgical and endoscopic instruments were performed for each of the three surgical approaches, and key steps and surgically relevant anatomy were documented. Six patients with appropriate pre-, post-, and intraoperative imaging and video documentation are presented and discussed accordingly. Results  Based on our institutional experience, all three approaches can be utilized to safely and effectively approach a wide variety of neoplastic and vascular pathology. Unique anatomical characteristics, lesion morphology and size, and tumor biology should all be considered when determining the optimal approach. Conclusion  Preoperative assessment of surgical corridors with 3D illustrations helps to define the best surgical corridor. 360 degree knowledge of the anatomy of craniovertebral junction allows safe surgical approach and treatment of ventral and ventrolateral located lesions using one of the three approaches.

Microsurgical treatment of posterior inferior cerebellar aneurysms based on angioarchitecture supplemented by high-resolution vessel wall MRI: a case series report

BACKGROUND

Surgical treatment of posterior inferior cerebellar artery (PICA) aneurysms is challenging because many are nonsaccular and atherosclerotic. We report our tailored approach to PICA aneurysms, which is based on angioarchitecture supplemented by high-resolution vessel wall MRI (HR-VW MRI) findings.

METHODS

From March 2010 to September 2020, 27 patients with 29 PICA aneurysms underwent surgical treatment in our institution. Since October 2016, HR-VW MRI has been used for aneurysmal wall assessment. Clinical characteristics, radiological data and surgical outcomes were analysed.

RESULTS

Nineteen proximal PICA aneurysms (vertebral artery (VA), P1, P2 and P3) were treated using the far-lateral approach. Ten distal PICA aneurysms (P4, P5) were treated using the suboccipital midline approach. Direct clipping or clip reconstruction was achieved in 19 aneurysms. Ten were trapped in conjunction with extracranial-intracranial or intracranial-intracranial bypass, including three occipital artery-PICA reimplantations, three PICA-VA reimplantations, two PICA-PICA side-to-side anastomoses, one PICA-PICA reimplantation and one PICA-PICA reanastomosis. All aneurysms were eventually completely obliterated and all bypasses remained patent. At the last follow-up, 26 patients (96.2%) achieved a good outcome (modified Rankin Scale score <3). Eight patients underwent HR-VW MRI. Among these, the six aneurysms with focal wall enhancement required bypass and the two with negative enhancement were successfully clipped.

CONCLUSION

PICA aneurysms have a higher frequency of complex features such as large or giant size and fusiform or dissecting morphology. Favourable outcomes were achieved with individualised microsurgical strategies based on angioarchitecture. HR-VW MRI may be used as a promising technique to predict aneurysmal atherosclerosis.

Microsurgical treatment of posterior inferior cerebellar aneurysms based on angioarchitecture supplemented by high-resolution vessel wall MRI: a case series report

BACKGROUND

Surgical treatment of posterior inferior cerebellar artery (PICA) aneurysms is challenging because many are nonsaccular and atherosclerotic. We report our tailored approach to PICA aneurysms, which is based on angioarchitecture supplemented by high-resolution vessel wall MRI (HR-VW MRI) findings.

METHODS

From March 2010 to September 2020, 27 patients with 29 PICA aneurysms underwent surgical treatment in our institution. Since October 2016, HR-VW MRI has been used for aneurysmal wall assessment. Clinical characteristics, radiological data and surgical outcomes were analysed.

RESULTS

Nineteen proximal PICA aneurysms (vertebral artery (VA), P1, P2 and P3) were treated using the far-lateral approach. Ten distal PICA aneurysms (P4, P5) were treated using the suboccipital midline approach. Direct clipping or clip reconstruction was achieved in 19 aneurysms. Ten were trapped in conjunction with extracranial-intracranial or intracranial-intracranial bypass, including three occipital artery-PICA reimplantations, three PICA-VA reimplantations, two PICA-PICA side-to-side anastomoses, one PICA-PICA reimplantation and one PICA-PICA reanastomosis. All aneurysms were eventually completely obliterated and all bypasses remained patent. At the last follow-up, 26 patients (96.2%) achieved a good outcome (modified Rankin Scale score <3). Eight patients underwent HR-VW MRI. Among these, the six aneurysms with focal wall enhancement required bypass and the two with negative enhancement were successfully clipped.

CONCLUSION

PICA aneurysms have a higher frequency of complex features such as large or giant size and fusiform or dissecting morphology. Favourable outcomes were achieved with individualised microsurgical strategies based on angioarchitecture. HR-VW MRI may be used as a promising technique to predict aneurysmal atherosclerosis.

Institutional Experience of Microsurgical Management in Posterior Circulation Aneurysm

Introduction:

Posterior circulation aneurysm constitutes 15%–20% of all intracerebral aneurysms. With the advancement of endovascular techniques, the microsurgery for posterior circulation aneurysms has been pushed back a little. Even the International Subarachnoid Aneurysmal Trial gave support to the concepts of endovascular procedures, but microsurgical modality should not be discouraged. We present our institutional experience of microsurgical techniques on posterior circulation aneurysms.

Materials and Methods:

We performed a retrospective analysis of 37 patients of posterior circulation aneurysm from 2015 to 2019, referred to Bantane Hospital, Japan. We included all posterior circulation aneurysms such as basilar tip, basilar trunk, and vertebral artery-posterior inferior cerebellar artery (VA-PICA) aneurysms, admitted and treated with clipping or bypass and trapping. We assessed the outcome as measured by modified Rankin Score (mRS), complications, and mortality.

Results:

Out of 37 patients, 10 cases were a basilar tip, one case was the basilar trunk, and 26 cases were VA-PICA aneurysm. Intraoperatively, neuromonitoring, indocyanine green dye, dual-image videoangiography (DIVA), and neuro endoscope were used. Two patients of basilar tip aneurysm developed third cranial nerve paresis and six patients of VA-PICA aneurysm developed lower cranial nerve paresis which resolved spontaneously. All the patients were discharged with mRS of 0 or 1. No mortality was recorded in our study.

Conclusion:

Microsurgical clipping of posterior circulation aneurysm is safe in unruptured aneurysm with a very low risk of mortality and morbidity under experienced hands. All postoperative complications in our study were transient and resolved with time with no residual deficits. Preoperative simulation, intraoperative neuromonitoring, DIVA, and neuro endoscope help achieve complete obliteration of aneurysmal sac and avoid complications.

Treatment of intracranial vertebral artery dissecting aneurysms involving the posterior inferior cerebellar artery origin

Background

Vertebral artery dissecting aneurysm (VADA) involving the origin of the posterior inferior cerebellar artery (PICA) is a complex disease entity in which the dual goals of preventing future rebleeding and maintaining perfusion of the lateral medulla must be considered. We present an illustrative case and review the literature surrounding treatment strategies.

Case Description

We report a patient presenting with extensive subarachnoid hemorrhage due to rupture of an intracranial VADA involving the PICA origin. After consideration of the patient's cerebral vasculature and robustness of collaterals, a flow-diverting stent was placed with angiographic resolution of the lesion and maintenance of antegrade PICA flow. Ultimately, the patient experienced a contralateral intraparenchymal hemorrhage leading to death. Review of the literature identified 124 cases of VADA involving the PICA origin described over the past decade. The methods of surgical and endovascular treatment of these cases were reviewed, with particular focus on the rationale of treatment, outcomes, and complications.

Conclusion

Numerous treatment options for VADA involving PICA have been reported with different risk and benefit profiles. Flow-diverting stents appear to offer the most favorable balance of securing the aneurysm and avoiding medullary infarction, but the risks and optimal anti-thrombotic treatment strategy are incompletely understood. In select cases, in which the surgical risk is low or in which the anatomy is favorable (e.g., nondominant parent vessel or robust collateral circulation in the involved territories), parent artery trapping with or without microsurgical revascularization can be considered.

Posterior Inferior Cerebellar Artery Aneurysm: Have You Ever Been Misdiagnosed?

RATIONALE AND OBJECTIVES

The posterior inferior cerebellar artery aneurysm (PICAA), especially distal PICAA, is easily missed by a doctor, leading to misdiagnosis and treatment delays. The objective of this article is to report the computed tomography angiography (CTA) presentations of 30 cases of PICAA proved by digital subtraction angiography (DSA) or surgical operation, and analyze the causes of misdiagnosis of PICAA by CTA.

MATERIALS AND METHODS

Thirty cases of patients with PICAA that were proved by DSA or surgical operation were included in this study, all of whom underwent CTA before surgical procedure. The relationship between the locations of PICAA and the rates of missed diagnosis by CTA was analyzed. The detection rates of the PICAA by volume rendering (VR) images and original thin axial images of CTA were compared.

RESULTS

Twelve cases (12 of 30, 40%) of aneurysm lied on the proximal end of posterior inferior cerebellar artery (PICA) (border with vertebral artery) and all of them (12 of 12,100%) were clearly displayed on the VR images of CTA and correctly diagnosed by doctors. Eighteen cases (18 of 30, 60%) of aneurysm lied on the distal part of the PICA, whereas only 2 of them (2/18, 11.1%) were displayed on the VR images and correctly diagnosed before surgical procedure. After surgical operation, the respective review of the CTA images demonstrated that all aneurysms (30 of 30, 100%) can be found on the thin axial images after careful observation and are shown on VR images after adjusting the display threshold when the locations of the PICAA through thin axial images were known, including the distal PICAA.

CONCLUSIONS

Thin axial CT images are most important and reliable for the detection of distal PICAA. Overdependence on three-dimensional VR images of CTA is the main cause of misdiagnosis.

Association between vertebral artery hypoplasia and vertebral artery aneurysms: A case-control study

BACKGROUND

The aim of this retrospective case-control study is to determine the association of vertebral artery hypoplasia (VAH) and other anatomical variants with saccular vertebral artery posterior inferior cerebellar artery (VA-PICA) aneurysms.

METHODS

The prevalence of VAH, vertebral artery (VA) atresia, VA aplasia, and PICA aplasia was analyzed using CT angiography in 64 patients with VA-PICA aneurysms (43 ruptured and 21 unruptured) and compared to 128 age- and sex-matched controls. Logistic regression was performed to identify independent risk factors for aneurysm formation.

RESULTS

Univariate analysis showed patients with VA-PICA aneurysms had significantly higher incidence of VAH (53% vs. 17%; odds ratio [OR] 4.8; 95% confidence interval [CI] 2.4-9.4; p < 0.0001) and VA aplasia (14% vs. 1%; OR 20.8; 95% CI 2.5-168.0; p = 0.004) compared with controls. Multivariate analysis identified VAH (odds ratio, 3.6; 95% CI 1.8-7.3; p < 0.0001) as an independent strong risk factor for VA-PICA aneurysm formation. VA-PICA aneurysms are detected significantly more often in the dominant VA, which is contralateral to VAH. Other anatomical variants are not related to aneurysm formation.

CONCLUSIONS

VAH and VA aplasia are potential risk factors for VA-PICA aneurysms. Altered hemodynamics caused VAH may result in intracranial aneurysm formation. Additional research should clarify the pathophysiological association of VAH, VA aplasia, or vascular occlusion with arteriosclerosis and intracranial aneurysm formation.

Anatomic Features of Paraclinoid Aneurysms: Computed Tomography Angiography Study of 144 Aneurysms in 136 Consecutive Patients

BACKGROUND

Paraclinoid aneurysms are among the most challenging aneurysms to treat. Computed tomography (CT) angiography helps in evaluating the radiological characteristics of these aneurysms next to bony structures.

OBJECTIVE

To present the CT angiography characteristics of paraclinoid aneurysms in order to better understand such pathology.

METHODS

The study examined CT angiography-based anatomical characteristics obtained retrospectively from 136 patients with 144 paraclinoid aneurysms selected from single-defined catchment populations in Finland. We examined the diameters of the parent artery (internal carotid artery), the location of the aneurysm, its dimensions (width, height, neck), and aneurysm wall irregularity.

RESULTS

We analyzed 144 paraclinoid aneurysms in 136 patients admitted to the hospital during 2000-2014. Multivariable analysis reveals that rupture aneurysms have the following radiological features: aneurysm larger than 5 mm in diameter (P = .006), irregular wall (P = .046), superior location, larger aspect ratio (P = .039), and neck wider than parent artery (P < .001).

CONCLUSION

Smaller diameter of the internal carotid artery and superior location, as well as a large and irregular aneurysm wall, are radiological characteristics of ruptured paraclinoid aneurysms, which CT angiography can measure easily.

Variations of Occipital Artery-Posterior Inferior Cerebellar Artery Bypass: Anatomic Consideration

BACKGROUND

Advances in diagnosis of posterior inferior cerebellar artery (PICA) aneurysms have revealed the high frequency of distal and/or dissecting PICA aneurysms. Surgical treatment of such aneurysms often requires revascularization of the PICA including but not limited to its caudal loop.

OBJECTIVE

To examine the microsurgical anatomy involved in occipital artery (OA)-PICA anastomosis at various anatomic segments of the PICA.

METHODS

Twenty-eight PICAs in 15 cadaveric heads were examined with the operating microscope to take morphometric measurements and explore the specific anatomy of bypass procedures.

RESULTS

OA bypass to the p2, p3, p4, or p5 segment was feasible with a recipient vessel of sufficient diameter. The loop wandering near the jugular foramen in the p2 segment provided sufficient length without requiring cauterization of any perforating arteries to the brainstem. Wide dissection of the cerebellomedullary fissure provided sufficient exposure for the examination of some p3 segments and all p4 segments hidden by the tonsil. OA-p5 bypass was placed at the main trunk before the bifurcation in 5 hemispheres and at the larger hemispheric trunk in others.

CONCLUSION

Understanding the possible variations of OA-PICA bypass may enable revascularization of the appropriate portion of the PICA when the parent artery must be occluded. A detailed anatomic understanding of each segment clarifies important technical nuances for the bypass on each segment. Dissection of the cerebellomedullary fissure helps to achieve sufficient exposure for the bypass procedures on most of the segments.