Dural Ring Research Articles

The Transpetrosal-Ridge Approach: A Modification of the Combined Transpetrosal Approach

BackgroundPetroclival tumors are formidable challenges for skull base surgeons. Obtaining adequate surgical access is a paramount consideration. Although the combined transpetrosal approach provides a wide surgical corridor, it is technically challenging and, to a degree, morbid. This article describes the transpetrosal-ridge approach, which is a modification of the combined transpetrosal approach with improvements with regards to ease of execution and reduced surgical morbidity.MethodsThe key elements of the transpetrosal-ridge approach are outlined, followed by a detailed description of the steps. The head is placed in the lateral position. After skin incision and muscle elevation, a temporo-suboccipital craniotomy is performed. Middle fossa dura is elevated to the petrous ridge. A limited mastoidectomy is performed with preservation of the semicircular canals. The remaining petrous ridge is then resected and the posterior fossa dura is opened, with the opening extending through the trigeminal dural ring.ResultsSteps of the combined transpetrosal approach that do not contribute to the final surgical corridor are omitted. Extensive mastoid and petrous apex resection is avoided. Posterior fossa dural opening extending through the trigeminal dural ring is a critical step, as it detaches the superior petrosal sinus and sigmoid sinus from the petrous bone. With the retraction of the temporal lobe and the cerebellum and sigmoid sinus, a wide surgical corridor is obtained.ConclusionsThe transpetrosal-ridge approach is a modification of the combined transpetrosal approach with optimization of the operative steps while continuing to provide a wide surgical corridor to the petroclival region.

Distance Between the Falciform Ligament and Distal Dural Ring as a Surgical Landmark for the Treatment of Paraclinoid Aneurysms

It is difficult to completely comprehend the anatomy of the structures surrounding the paraclinoid region before aneurysm and tumor treatment therein. When treating paraclinoid aneurysms, it is important to determine the location of the aneurysm as intradural or extradural. Thus, accurate prediction of the position of the distal dural ring (DDR) is necessary. To this end, we focused on the falciform ligament (FL), which is easily visualized on images based on its anatomic features. We measured the distance between the FL and the DDR in patients undergoing paraclinoid aneurysm operations. Between January 2017 and July 2018, 15 patients who underwent clipping for paraclinoid aneurysm treatment were retrospectively identified. The distance between the FL and the DDR was measured using a microscale at the time of the operation. The patients comprised 14 women and 1 man. The mean aneurysm diameter was 7.29 ± 2.21 mm and the median size was 6.5 mm. Eleven of the aneurysms were on the left and 4 were on the right side. The mean distance between the FL and the DDR was 3.50 ± 0.17 mm and the median distance was 3.50 mm. The distance between the FL and the DDR was almost the same across cases (3.5 mm). The position of the FL can be easily predicted using preoperative three-dimensional computed tomography angiography based on its anatomic features. In this study, the DDR was located 3.5 mm proximal to the FL along the internal carotid artery. This information is useful for predicting the position of the DDR.

Review of the main surgical and angiographic-oriented classifications of the course of the internal carotid artery through a novel interactive 3D model

The course of the internal carotid artery (ICA) and its segment classifications were reviewed by means of a new and freely available 3D interactive model of the artery and the skull base, based on human neuroimages, that can be freely downloaded at the Public Repository of the University of Barcelona (http://diposit.ub.edu/dspace/handle/2445/112442) and runs under Acrobat Reader in Mac and Windows computers and Windows 10 tablets. The 3D-PDF allows zoom, rotation, selective visualization of structures, and a predefined sequence view. Illustrative images of the different classifications were obtained. Fischer (Zentralbl Neurochir 3:300-313, 1938) described five segments in the opposite direction to the blood flow. Gibo-Rothon (J Neurosurg 55:560-574, 1981) follow the blood flow, incorporated the cervical and petrous portions, and divided the subarachnoid course-supraclinoid-in ophthalmic, communicating, and choroidal segments, enhancing transcranial microscopic approaches. Bouthillier (Neurosurgery 38:425-433, 1996) divided the petrous portion describing the lacerum segment (exposed in transfacial procedures and exploration of Meckel's cave) and added the clinoid segment between the proximal and distal dural rings, of interest in cavernous sinus surgery. The Kassam's group (2014), with an endoscopic endonasal perspective, introduces the "paraclival segment," including the "lacerum segment" and part of the intracavernous ICA, and details surgical landmarks to minimize the risk of injury. Other classifications are also analyzed. This review through an interactive 3D tool provides virtual views of the ICA and becomes an innovative perspective to the segment classifications and neuroanatomy of the ICA and surrounding structures.

Prevalence of Incidental Clinoid Segment Saccular Aneurysms

Clinoid segment aneurysms are cerebral vascular lesions recently described in the neurosurgical literature. They arise from the clinoid segment of the internal carotid artery, which is the segment limited rostrally by the dural carotid ring and caudally, by the carotid-oculomotor membrane. Even although clinoid segment aneurysms represent a common incidental finding in magnetic resonance studies, its prevalence has not been yet reported. To determine the prevalence of incidental clinoid segment saccular aneurysms diagnosed by magnetic resonance imaging as well as their anatomic architecture and their association with smoking, arterial hypertension, age, and sex of patients. A total of 500 patients were prospectively studied with magnetic resonance imaging time-of-flight sequence and angioresonance with contrast material, to search for incidental saccular intracranial aneurysms. The site of primary interest was the clinoid segment, but the presence of aneurysms in any other location was determined for comparison. The relation among the presence of clinoid segment aneurysms, demographic factors, and secondary diagnosis of arterial hypertension, smoking, and other vascular/neoplastic cerebral lesions was analyzed. We found a global prevalence of incidental aneurysms of 7% (95% confidence interval, 5-9), with a prevalence of clinoid segment aneurysms of 3% (95% confidence interval, 2-4). Univariate logistic regression analysis showed a statistically significant relationship among incidental aneurysms, systemic arterial hypertension (P= 0.000), and smoking (P= 0.004). In the studied population, incidental clinoid segment aneurysms constitute the variety with highest prevalence.

Anatomia Microcirúrgica do Segmento Clinóide da Artéria Carótida Interna e do Cavo Carotídeo

Embora a região clinóide seja comumente abordada pelos neurocirurgiões em várias afecções, sua anatomia e extremamente complexa e variável. O segmento clinóide da artéria carótida interna (ACI) se encontra na transição entre o seio cavernoso e o espaço subaracnóide, limitado pelos dois anéis durais. O segmento posteromedial do anel dural distal não tem contato com nenhuma estrutura óssea, esta peculiaridade anatômica facilita a formação do cavo carotídeo. Os anéis proximal e distal tornam-se relevantes por serem os limitesanatômicos. O entendimento do segmento clinóide é importante para o correto diagnóstico e abordagem dos aneurismas desta região. Controle proximal, clinoidectomia anterior, opções de clips fenestrados e auxílio do endoscópio são detalhes técnicos de grande utilidade no manejo dos aneurismas do cavo carotídeo.

A Novel and Freely Available Interactive 3d Model of the Internal Carotid Artery.

We describe a new and freely available 3D interactive model of the intracranial internal carotid artery (ICA) and the skull base that also allows to display and compare its main segment classifications. High-resolution 3D human angiography (isometric voxel's size 0.36mm) and Computed Tomography angiography images were exported to Virtual Reality Modeling Language (VRML) format for processing in a 3D software platform and embedding in a 3D Portable Document Format (PDF) document that can be freely downloaded at http://diposit.ub.edu/dspace/handle/2445/112442 and runs under Acrobat Reader on Mac and Windows computers and Windows 10 tablets. The 3D-PDF allows for visualisation and interaction through JavaScript-based functions (including zoom, rotation, selective visualization and transparentation of structures or a predefined sequence view of the main segment classifications if desired). The ICA and its main branches and loops, the Gasserian ganglion, the petrolingual ligament and the proximal and distal dural rings within the skull base environment (anterior and posterior clinoid processes, silla turcica, ethmoid and sphenoid bones, orbital fossae) may be visualized from different perspectives. This interactive 3D-PDF provides virtual views of the ICA and becomes an innovative tool to improve the understanding of the neuroanatomy of the ICA and surrounding structures.

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This study aimed to investigate the application of 3-dimensional computed tomography angiography (3D-CTA) for defining cavernous sinus aneurysms and intradural aneurysms involving the internal carotid artery around the anterior clinoid process.Results from 42 patients with an aneurysm of the internal carotid artery around the anterior clinoid process who underwent 3D-CTA were reviewed and compared with those of observed clinical operations.Among the 42 patients, there was a total of 45 aneurysms of the internal carotid artery around the anterior clinoid process. After surgery, 33 of the 45 aneurysms were confirmed as intradural aneurysms, and the other 12 were confirmed as aneurysms in the cavernous sinus. 3D-CTA imaging of the medial sagittal plane showed that 31 out of 31 (100%) intradural aneurysms of the internal carotid artery were above the virtual line between the inferior border of the anterior clinoid process and the tuberculum sellae, and 12 out of 14 (86%) cavernous sinus aneurysms were below the virtual line (P < 0.0001).The virtual line between the inferior border of the anterior clinoid process and the tuberculum sellae on 3D-CTA indicates the proximal dural ring of the internal carotid artery. This line helps differentiate cavernous sinus aneurysms from intradural aneurysms involving the internal carotid artery around the anterior clinoid process.

Application of 3-Dimensional Computerized Tomography Angiography for Defining Cavernous Sinus Aneurysms and Intradural Aneurysms Involving the Internal Carotid Artery Around the Anterior Clinoid Process.

This study aimed to investigate the application of 3-dimensional computed tomography angiography (3D-CTA) for defining cavernous sinus aneurysms and intradural aneurysms involving the internal carotid artery around the anterior clinoid process. Results from 42 patients with an aneurysm of the internal carotid artery around the anterior clinoid process who underwent 3D-CTA were reviewed and compared with those of observed clinical operations. Among the 42 patients, there was a total of 45 aneurysms of the internal carotid artery around the anterior clinoid process. After surgery, 33 of the 45 aneurysms were confirmed as intradural aneurysms, and the other 12 were confirmed as aneurysms in the cavernous sinus. 3D-CTA imaging of the medial sagittal plane showed that 31 out of 31 (100%) intradural aneurysms of the internal carotid artery were above the virtual line between the inferior border of the anterior clinoid process and the tuberculum sellae, and 12 out of 14 (86%) cavernous sinus aneurysms were below the virtual line (P < 0.0001). The virtual line between the inferior border of the anterior clinoid process and the tuberculum sellae on 3D-CTA indicates the proximal dural ring of the internal carotid artery. This line helps differentiate cavernous sinus aneurysms from intradural aneurysms involving the internal carotid artery around the anterior clinoid process.

Histology of the distal dural ring.

The distal dural ring (DDR) is a conserved intracranial anatomic structure marking the boundary point at which the internal carotid artery (ICA) exits the cavernous sinus (CS) and enters the subarachnoid space. Although the CS has been well described in a range of anatomic studies, to our knowledge no prior study has analyzed the histologic relationship between the ICA and DDR. Correspondingly, our objective was to assess the relationship of the DDR to the ICA and determine whether the DDR can be dissected from the ICA and thus divided, or can only be circumferentially trimmed around the artery. The authors examined ten fresh-frozen, adult cadaveric specimens. A standard frontotemporal craniotomy, orbito-optic osteotomy, and extradural anterior clinoidectomy was performed bilaterally. The cavernous ICA, DDR, and supraclinoid ICA were harvested as an en bloc specimen. Specimens formalin-fixed and paraffin-embedded prior to routine histochemical staining with hematoxylin and eosin and Masson trichrome. In all specimens, marked microscopic investment of the DDR throughout the ICA adventitia was noted. Dural collagen fibers extensively permeated the arterial layers superficial to the muscularis propria, with no evidence of a clear separation between the DDR and arterial adventitia. Histologic analysis suggests that the ICA and DDR are highly interrelated, continuous structures, and therefore attempted intraoperative dissection between these structures may carry an elevated risk of injury to the ICA. We correspondingly recommend careful circumferential trimming of the DDR in lieu of direct dissection in cases requiring mobilization of the clinoidal ICA. Clin. Anat. 30:742-746, 2017. © 2017Wiley Periodicals, Inc.

Adventitial Adversity: Histopathology of the Distal Dural Ring

Introduction: The distal dural ring (DDR) is a well-studied anatomic structure of significant neurosurgical relevance, defined as the point of entry of the internal carotid artery (ICA) into the subarachnoid space. The relationships between the DDR and the surrounding structures have been the subject of some controversy, including debate over whether the ICA can safely be separated from the DDR. These relationships have been subject to multiple gross anatomic investigations, but the only preceding histologic study did not specifically evaluate the relationship between the ICA and the DDR.

Disposal of Occipital Condyle in Far Lateral Approach for Ventrolateral Foramen Magnum Meningiomas

To investigate the necessity of drilling the occipital condyle in a tailored far lateral approach for resection of ventrolateral foramen magnum meningiomas (FMMs). Clinical data of 15 patients with ventrolateral FMMs who underwent surgery during a 6-year period were reviewed retrospectively. A retrocondylar approach was performed in 8 cases (6 above the vertebral artery [VA] and 2 below the VA) in which the dural attachment was surgically accessible with no restriction of the initial part of the V4 segment of the VA, and a partial transcondylar approach was performed in 7 cases on both sides of the VA where the dural attachment associated with the VA auxiliary space was reached by superolateral displacement of the VA by drilling of the condyle. Exposure of the V3 segment of the VA was performed in all patients, but no circumcision of the dural ring along with transposition of the VA was needed. Simpson grade II resection was achieved in all patients. Postoperative complications were encountered in 20% of patients, predominantly associated with cranial nerve impairment. No tumor recurrence was demonstrated during follow-up lasting 7-68 months (mean 29.2 months). The surgical approach for ventrolateral FMMs varies depending on the location of dural attachment with reference to VA dural entry. Bone removal is warranted in FMMs arising from both sides of the VA to allow superolateral displacement of the VA to some extent, improving surgical accessibility to the hidden VA auxiliary space and achieving a more radical tumor resection. It should be a reasonable alternative to the conventional aggressive VA transposition in cases of ventrolateral FMMs.

Risk Factors for Visual Impairments in Patients with Unruptured Intradural Paraclinoid Aneurysms Treated by Neck Clipping without Bypass Surgery

Although paraclinoid aneurysms are now frequently referred for endovascular treatment, the durability of obliteration is still to be determined. Therefore, direct surgery for paraclinoid aneurysms still remains indispensable. The present study aimed to evaluate the risk factors for the visual impairments in patients with unruptured intradural paraclinoid aneurysms. The data of 133 patients with 136 aneurysms treated by neck clipping without bypass surgery was evaluated. Visual impairments included decreased visual acuity and visual field defect. The aneurysm was classified into superior projecting aneurysm, ventral projecting aneurysm, and carotid cave aneurysm. Plug-in method was defined as filling interspace, which was formed between the internal carotid artery and the sutured dura in case of detachment of the dural ring. Postoperative new visual impairments were observed in 30 aneurysms (22%). During the follow-up period (median, 600 days), postoperative new visual impairments continued in 23 aneurysms (17%). Multivariate analysis showed that carotid cave location and plug-in method were related to new visual impairments at 30 days (odds ratio [OR], 2.6; 95% confidence interval [CI] 1.1-6.1; P= 0.031 and OR, 4.1; 95% CI 1.4-12; P= 0.008) and at 6 months (OR, 4.1; 95% CI 1.5-11; P= 0.005 and OR, 3.3; 95% CI 1.1-11; P= 0.045). The present study showed that carotid cave location and plug-in method during dural closures were related to postoperative continued visual impairments. Neurosurgeons should carefully consider the surgical indication for unruptured carotid cave aneurysms and avoid plug-in methods.

Microsurgical clipping of a superior hypophyseal artery aneurysm: part 2: distal dural ring dissection and clipping: 3-dimensional operative video.

Microsurgical clipping of a superior hypophyseal artery aneurysm: part 2: distal dural ring dissection and clipping: 3-dimensional operative video.

Prevention of Visual Function in the Operation of Paraclinoid Aneurysms

Objective: Paraclinoid aneurysms are aneurysms of the internal carotid artery (ICA) around the anterior clinoid process (ACP), including carotid cave and IC-ophthalmic aneurysms. To treat those aneurysms by direct clipping, it would need the removal of ACP and opening of the external dural ring, which might harm the optic nerves and their function. Then, the endovascular surgery is sometimes recommended especially in the case with carotid cave aneurysm. However, the recent paper reported that the complication and recurrence rates of endovascular surgery are relatively high. This direct surgery is useful, but difficult for the young and middle surgeon because those aneurysms are rare and dangerous lesion. We reviewed our recent cases and assessed the pitfall for prevention of visual function. Method: A total of eight cases with paraclinoid aneurysms treated in our hospital since December 2012 are assessed. Result: One case was treated by endovascular and seven were treated by direct surgery. Five cases were completely clipped with the removal of ACP, however, one of five showed visual impairment after surgery. In this case with right carotid cave aneurysm, ICG-VA during the surgery had shown disappearance of aneurysm and patency of ICA and perforators, however, her right vision gradually worsened 2days after surgery. Right ophthalmic artery was patent on her MRI/MRA and 3D-CTA, and her right optic disc was normal. Operative video was assessed, and showed that her right optic was contracted to ICA during the dissection of aneurysm and ophthalmic artery because of incomplete cutting of falcifalm fold, suggesting that this physiological compression to the optic nerve might cause the visual function. Conclusion: For prevention of visual function in the surgery of paraclinoid aneurysms, the complete opening of dural ring, the removal of optic strut, and the appropriate cutting of falcifalm fold are important as well as the removal of ACP. We emphasize that those techniques are essential as well as the removal of ACP to mobilize the optic nerve and perform the safe surgery.

Quantitative study of the opticocarotid and carotid-oculomotor windows for the interpeduncular fossa, before and after internal carotid artery mobilization and posterior communicating division.

The management of basilar apex (BX) aneurysms remains problematic. We quantified the surgical exposure of the BX through the opticocarotid window (OCW) and the carotid-oculomotor window (COW), before and after mobilization of the internal carotid artery and division of the posterior communicating artery (PCoA). Eleven silicone-injected cadaveric heads were dissected bilaterally. The surgical dissection was divided into 4 major steps: (1) supraorbital modified orbitozygomatic craniotomy, (2) mobilization of the internal carotid artery after drilling out the anterior clinoid process intradurally and cutting the distal dural ring, (3) drilling out the posterior clinoid process and dorsum sellae, and (4) dividing the PCoA from the posterior third portion of the vessel. A frameless navigation system was used to quantify the surgical exposure area of the BX through the OCW and COW. The total surgical area increased significantly from steps 1 to 4 (P < .001) in both OCW and COW groups. Overall, there was a larger total surgical area obtained in the COW compared with the OCW (P = .010). ICA mobilization increased the surgical area for temporary (P < .001) and permanent (P < .003) clip application in both windows. The division of PCoA significantly increased the overall surgical area for permanent clip application (P < .003). Compared with the OCW, the COW had a significantly increased change in the area for permanent clip application in the low-lying group (P = .03). When approaching the BX via the pterion route, the appropriate surgical step and window should be selected according to characteristics of the PCoA and height of the BX.

Quantitative analysis of variable extent of anterior clinoidectomy with intradural and extradural approaches: 3-dimensional analysis and cadaver dissection.

Drilling of the anterior clinoid process (ACP) is an integral component of surgical approaches for central and paracentral skull base lesions. The technique to drill ACP has evolved from pure intradural to extradural and combined techniques. To describe the computerized morphometric evaluation of exposure of optic nerve and internal carotid artery with proposed tailored intradural (IDAC) and complete extradural (EDAC) anterior clinoidectomy. We describe a morphometric subdivision of ACP into 4 quadrangles and 1 triangle on the basis of fixed bony landmarks. Computerized volumetric analysis with 3-dimensional laser scanning of dry-drilled bones for respective tailored IDAC and EDAC was performed. Both approaches were compared for the area and length of the optic nerve and internal carotid artery. Five cadaver heads were dissected on alternate sides with intradural and extradural techniques to evaluate exposure, surgical freedom, and angulation of approach. Complete anterior clinoidectomy provides a 2.5-times larger area and 2.7-times larger volume of ACP. Complete clinoidectomy deroofed the optic nerve to an equal extent as by proposed the partial tailored clinoidectomy approach. Tailored IDAC exposes only the distal dural ring, whereas complete EDAC exposes both the proximal and distal dural rings with complete exposure of the carotid cave. Quantitative comparative evaluation provides details of exposure and surgical ease with both techniques. We promote hybrid/EDAC technique for vascular pathologies because of better anatomic orientation. Extradural clinoidectomy is the preferred technique for midline cranial neoplasia. An awareness of different variations of clinoidectomy can prevent dependency on any particular approach and facilitate flexibility.

Localization and Treatment of Unruptured Paraclinoid Aneurysms: A Proton Density MRI-based Study.

ObjectiveThe purpose of this study was to evaluate the usefulness of proton density magnetic resonance (PD MR) imaging for localization of paraclinoid internal carotid artery aneurysms.Materials and MethodsFrom April 2014 to April 2015, 76 unruptured paraclinoid aneurysms in 66 patients were evaluated using PD MR and angiography (CT/MR angiography or digital subtraction angiography). The locations (extradural, transdural, intradural) in relation to the distal dural ring (DDR) and projection (superior, inferior/posterior, medial, lateral) of the aneurysms were assessed and compared.ResultsThe most common location of paraclinoid aneurysms was extradural (n = 48, 63.2%), followed by intradural (n = 18, 23.7%), and transdural (n = 10, 13.2%). In the medial projection group (n = 49, 64.5%), 31 were extradural (63.3%), 5 were transdural (10.2%), and 13 were intradural (26.5%). In the inferior/posterior projection group (n = 19, 25.0%), there were 14 extradural (73.7%), 4 transdural (21.0%), and 1 intradural (5.3%). In the superior (n = 4, 5.3%)/lateral (n = 4, 5.3%) projection groups, there were 0/3 extradural (0/75.0%), 1/0 transdural (25.0/0%), and 3/1 intradural (75.0/25.0%).ConclusionPD MR showed sufficient contrast difference to distinguish paraclinoid aneurysms from surrounding dural structures.

Potential of 80-kV high-resolution cone-beam CT imaging combined with an optimized protocol for neurological surgery.

With the development of computed tomography (CT) and magnetic resonance imaging (MRI), the use of conventional X-ray angiography including digital subtraction angiography (DSA) for diagnosis has decreased, as it is an invasive technique with a risk of neurological complications. However, X-ray angiography imaging technologies have progressed markedly, along with the development of endovascular treatments. A newly developed angiography technique using cone-beam CT (CBCT) technology provides higher spatial resolution than conventional CT. Herein, we describe the potential of this technology for neurosurgical operations with reference to clinical cases. Two hundred twenty-five patients who received 80-kV high-resolution CBCT from July 2011 to June 2014 for preoperative examinations were included in this study. For pathognomonical cases, images were taken with suitable reconstruction modes and contrast protocols. Cases were compared with intraoperative findings or images from other modalities. We observed the following pathognomonical types: (1) imaging of the distal dural ring (DDR) and the surrounding structure for paraclinoid aneurysms, (2) imaging of thin blood vessels, and (3) imaging of both brain tumors and their surrounding anatomy. Our devised 80-kV high-resolution CBCT imaging system provided clear visualization of detailed anatomy when compared with other modalities in almost all cases. Only two cases provided poor visualization due to movement artifact. Eighty-kilovolt high-resolution CBCT has the potential to provide detailed anatomy for neurosurgical operations when utilizing suitable modes and contrast protocols.

Different ophthalmic artery origins: Embryology and clinical significance

This retrospective study gives a summary of ophthalmic artery (OA) variations to serve as guidelines for surgical interventionists and trainees. Pubmed and Medline searches were conducted. The OA usually arises intradurally (superomedial, anteromedial, or rarely superolateral) from the internal carotid artery (ICA). Rare extradural origin (primitive dorsal OA) (PDOA) remnant and extremely rare interdural origin (primitive ventral OA) (PVOA) remnant are of significance when sectioning the dural ring. Rarely, a persistent PDOA with ICA origin, or a PDOA remnant with inferolateral trunk origin, enters the orbit via the superior orbital fissure (SOF) for sole or partial orbital supply. Extremely rare, the PDOA and PVOA persist and form double OAs that arise from the ICA and run via the SOF and optic foramen. Occasionally, the OA arises from the middle meningeal artery (MMA), when both the PDOA and VDOA regress and enter the orbit via the SOF. Sole orbital supply via the external carotid artery (ECA), i.e. meningo-ophthalmic artery and/or MMA branches, or dual OAs (ECA and ICA origins) may occur. Other rare OA origins include anterior or posterior communicating artery; anterior or middle cerebral artery; basilar artery; posterior inferior cerebellar artery; and the carotid bifurcation. Primitive arteries (persistent or remnant), and/or abnormal anastomoses play pivotal roles in manifestations of OA variations. Of clinical importance are orbital collateral routes and dangerous extracranial-intracranial anastomoses. Awareness of OA origins and collateral routes is imperative for transarterial embolizations or infusion chemotherapy in the ECA territory to prevent visual complications.

Bilobulated paraclinoid aneurysm mimics double aneurysms: A comparison of endovascular coiling and surgical clipping treatments

This report presents two cases of subarachnoid hemorrhage caused by rupture of paraclinoid aneurysms. Both aneurysms presented a bilobulated appearance upon image study. Both cases were treated successfully, the first with surgical clipping and the second with endovascular coiling. The special bilobulated feature of paraclinoid aneurysm in this particular anatomic location suggests its close relationship with the carotid dural ring. This relationship caused varying degrees of difficulty in both coiling and clipping the aneurysm. We compared the limitations and advantages of both treatments, and suggest that surgical clipping may be the treatment of choice in this region.