Surgical anatomy of the juxta-dural ring area

Identification of the Distal Dural Ring Using Three-dimensional Motion-sensitized Driven-equilibrium Prepared T1-weighted Fast Spin Echo Imaging: Application to Paraclinoid Aneurysms

PURPOSE

This study investigated the ability of three-dimentional motion-sensitized driven-equilibrium prepared T1-weighted fast spin echo (3D MSDE-FSE) imaging to identify distal dural rings (DDRs) and paraclinoid aneurysms (ParaC-ANs) and differentiate between intradural and extradural ParaC-ANs and compared it with that of established MR cisternography-based techniques.

METHODS

3D MSDE-FSE images were acquired along with fast imaging employing steady state acquisition (FIESTA), and time-of-flight magnetic resonance angiography (TOF-MRA) on a 3T MRI system in 53 patients with unruptured and untreated ParaC-ANs. Two radiologists applied a 3-point scale to rate the clarity with which the DDR (53 left and 53 right) and ParaC-ANs (total of 55) were depicted in the 3D MSDE-FSE and FIESTA images. The clarity scores, which were determined by averaging the scores of the 2 assessors, on the 3D MSDE-FSE and FIESTA images were compared using the Wilcoxon signed-rank test. Furthermore, the same radiologists classified the ParaC-ANs as intradural, extradural, or transitional on 3D MSDE-FSE images. A third radiologist independently classified the ParaC-ANs as intradural, extradural, or transitional based on the FIESTA and MRA fusion images. The kappa coefficient was used to compare this classification with that based on 3D MSDE-FSE images.

RESULTS

The Wilcoxon signed-rank test revealed no significant difference between 3D MSDE-FSE images and FIESTA images in the scores for the clarity of depiction of the DDRs (P = 0.119). However, the scores for the clarity of the depiction of the ParaC-ANs were significantly greater for the 3D MSDE-FSE images than for the FIESTA images (P < 0.001). The kappa coefficient for comparison of classification based on 3D MSDE-FSE images and FIESTA and MRA fusion images was 0.82.

CONCLUSION

3D MSDE-FSE imaging has the potential to differentiate between intradural and extradural ParaC-ANs by directly recognizing the DDR.

Vessel Wall Imaging Features of Spontaneous Intracranial Carotid Artery Dissection

BACKGROUND AND OBJECTIVES

Intracranial dissection is an important cause of stroke often with nonspecific angiographic features. Vessel wall imaging (VWI) can detect dissections, but intracranial applications remain unvalidated by pathologic specimens. We sought to determine the ability of VWI to identify the rarely reported spontaneous intracranial carotid dissection (sICD) guided by postmortem validation.

METHODS

VWI features of sICD, validated by postmortem specimen analysis in 1 patient, included luminal enhancement within a hypoenhancing outer wall, narrowing the mid to distal ophthalmic (C6) segment, relatively sparing the communicating (C7) segment. VWI examinations were reviewed to identify patients (1) with matching imaging features, (2) no evidence of other vasculopathies (i.e., inflammatory, intracranial atherosclerotic disease [ICAD]), and (3) adequate image quality. These sICD VWI features were compared with those in patients with known ICAD causing similar narrowing of C6 and relative sparing of C7 by a Fisher exact test accounting for multiple samples.

RESULTS

Among 407 VWI examinations, 8 patients were identified with 14 sICDs, all women aged 30-56 years, 6 (75%) bilateral. All patients with sICD had risk factors of dissection (e.g., recently postpartum, fibromuscular dysplasia, and hypertension) and 3 (37.5%) had intracranial dissections elsewhere. Seven (87.5%) were diagnosed as moyamoya syndrome on initial angiography. Enhancing lesions varied from thin flap-like defects (n = 6) to thick tissue along the superolateral wall of the internal carotid artery, within the hypoenhancing outer wall. Compared with 10 intracranial carotid plaques in 8 patients with ICAD, sICD demonstrated stronger (84.6% vs 20.0%, p = 0.003-0.025) and more homogeneous (61.5% vs 0.0%, p = 0.005-0.069) enhancement and less positive remodeling (0.0% vs 60.0%, p = 0.004-0.09). T1 hyperintensity was identified in 5 sICDs in 3 patients but not identified in ICAD. Three patients with serial imaging (8- to 39.8-month maximum intervals) revealed little to no changes in stenosis, wall thickening, or enhancement.

DISCUSSION

sICD is distinguishable on VWI from ICAD by enhancement characteristics, less positive remodeling, and clinical parameters. These VWI features should raise suspicion especially in young women with risk factors of dissection. Temporal stability and a lack of T1 hyperintensity should not discourage diagnosing sICD.

Comprehensive microsurgical anatomy of the middle cranial fossa: Part I-Osseous and meningeal anatomy

The middle cranial fossa is one of the most complex regions in neurosurgery and otolaryngology-in fact, the practice of skull base surgery originated from the need to treat pathologies in this region. Additionally, great neurosurgeons of our present and past are remembered for their unique methods of treating diseases in the middle fossa. The following article reviews the surgical anatomy of the middle fossa. The review is divided into the anatomy of the bones, dura, vasculature, and nerves-in two parts. Emphasis is paid to their neurosurgical significance and applications in skull base surgery. Part I focuses on the bony and dural anatomy.

Contralateral Clipping of Multiple Intracranial Aneurysms

The reported incidence of multiple intracranial aneurysms (MIA) is approximately 7-35% of all intracranial aneurysms. The primary goal in the management of MIAs is to secure the ruptured aneurysm and to treat as many of the remaining lesions as possible without affecting the outcome of the patient. In recent era endovascular treatment is the preferred treatment of multiple bilateral intracranial aneurysms if all aneurysms are amenable to addressed in single stage. But most often all aneurysms were not possible to addressed due to complexity of different aneurysms, technical limitation and infrastructure. In such scenarios options left were two stage sequential craniotomy on either sides and clipping of bilateral aneurysms or unilateral craniotomy and clipping of bilateral MIA. Bilateral two stage surgery or two stage endovascular treatment caries risk of bleeding from one of the untreated aneurysms, morbidity due to two stage and increase the cost of treatment. In properly selected cases of unilateral craniotomy and clipping of bilateral MIA secure the all aneurysm in one stage and decreased morbidity and cost of treatment. When patient selection done meticulously, clipping of MIA including contralateral side aneurysms is feasible and safe.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

Reliability of Bony Landmarks to Predict Intradural Location of Paraclinoid Aneurysms

PURPOSE

When dealing with paraclinoid carotid aneurysms, the distinction between intradural and extradural location is a major component for decision-making as only intradural aneurysms carry a risk of subarachnoid hemorrhage (SAH). The aim of this study was to test the accuracy and reliability of computed tomography (CT) bony landmarks for the distinction between intradural and extradural paraclinoid aneurysms.

METHODS

All patients referred to this institution for a single paraclinoid aneurysm were retrospectively identified. The study included only the patients who presented with diffuse SAH, thus proving the intradural location of the aneurysm. The preoperative images were assessed by two physicians in order to locate the aneurysms using the tuberculum sellae (TS) and the optic strut (OS) landmarks.

RESULTS

A total of 15 patients were included in the study. There were 4 cases (27%) of disagreement with the OS bony landmark and no cases of disagreement with the TS landmark. No aneurysm was consensually considered as extradural by both readers with both bony landmarks; however, five aneurysms (33%) were considered to be extradural by at least one of the physicians with at least one of the two bony landmarks.

CONCLUSION

The results of the study showed several disagreements when using the OS landmark. More importantly, several aneurysms were considered as extradural with at least one of these two CT bony landmarks, even though they were all associated with an SAH. More reliable and accurate landmarks are warranted.

The approach angle to the interoptic triangle limits surgical workspace when targeting the contralateral internal carotid artery

BACKGROUND

The interoptic triangle (IOT) offers a key access to the contralateral carotid artery's ophthalmic segment (oICA) and its perforating branches (PB), the ophthalmic artery (OA), and the superior hypophyseal artery (SHA). It has been previously reported that the assessment of IOT's size is relevant when attempting approaches to the contralateral oICA. However, previous studies have overseen that, since the oICA is a paramedian structure and a lateralized contralateral approach trajectory is then required, the real access to the oICA is further limited by the approach angle adopted by the surgeon with respect to the IOT's plane. For this reason, we determined the surgical accessibility to the contralateral oICA and its branches though the IOT by characterizing the morphometry of this triangle relative to the optimal contralateral approach angle.

METHODS

We defined the "relative interoptic triangle" (rIOT) as the two-dimensional projection of the IOT to the surgeon's view, when the microscope has been positioned with a certain angle with respect to the midline to allow the maximal contralateral oICA visualization. We correlated the surface of the rIOT to the visualization of oICA, OA, SHA, and PBs on 8 cadavers and 10 clinical datasets, using for the last a 3D-virtual reality system.

RESULTS

A larger rIOT correlated positively with the exposure of the contralateral oICA (R = 0.967, p < 0.001), OA (R = 0.92, p < 0.001), SHA (R = 0.917, p < 0.001), and the number of perforant vessels of the oICA visible (R = 0.862, p < 0.001). The exposed length of oICA, OA, SHA, and number PB observed increased as rIOT's surface enlarged. The correlation patterns observed by virtual 3D-planning matched the anatomical findings closely.

CONCLUSIONS

The exposure of contralateral oICA, OA, SHA, and PB directly correlates to rIOT's surface. Therefore, preoperative assessment of rIOT's surface is helpful when considering contralateral approaches to the oICA. A virtual 3D planning tool greatly facilitates this assessment.

Precision microcatheter shaping in vertebrobasilar aneurysm coiling

BACKGROUND

Inventing an optimal curve on a microcatheter is required for successful intracranial aneurysm coiling. Shaping microcatheters for vertebrobasilar artery aneurysm coiling is difficult because of the vessel's long, tortuous and mobile anatomy. To overcome this problem, we devised a new method of shaping the microcatheter by using the patient's specific vessel anatomy and the highly shapable microcatheter. We report our preliminary results of treating posterior circulation aneurysms by this method.

METHODS

An unshaped microcatheter (Excelsior XT-17; Stryker Neurovascular, Fremont, CA, USA) was pretreated by exposure to the patient's vessel for five minutes. The microcatheter was placed in the vicinity of the targeted aneurysm and was left in contact with the patient's vessel before extraction. This treatment precisely formed a curve on the microcatheter shaft identical to the patient's vessel anatomy. Following the pretreatment, the tip of the microcatheter was steam shaped according to the long axis of the target aneurysm. Five consecutive vertebrobasilar aneurysms were treated using this shaping method and evaluated for the clinical and anatomical outcomes and microcatheter accuracy and stability.

RESULTS

All of the designed microcatheters matched the vessel and aneurysm anatomy except in one case that required a single modification. All aneurysms were successfully catheterized without the assistance of a microguidewire, and matched the long axis of the aneurysm. All microcatheters retained stability until the end of the procedure.

CONCLUSIONS

A precise microcatheter shaping for a vertebrobasilar artery aneurysm may be achieved by using the patient's actual vessel anatomy and the highly shapable microcatheter.

A literature review concerning contralateral approaches to paraclinoid internal carotid artery aneurysms

Ipsilateral approaches remain the standard technique for clipping paraclinoid aneurysms. Surgeons must however be prepared to deal with bony and neural structures restricting accessibility. The application of a contralateral approach has been proposed claiming that some structures in the region can be better exposed from this side. Yet, only few case series have been published evaluating this approach, and there is a lack of systematic reviews assessing its specific advantages and disadvantages. We performed a structured literature search and identified 19 relevant publications summarizing 138 paraclinoid aneurysms operated via a contralateral approach. Patient's age ranged from 19 to 79 years. Aneurysm size mainly varied between 2 and 10 mm and only three articles reported larger aneurysms. Most aneurysms were located at the origin of the ophthalmic artery, followed by the superior hypophyseal artery and carotid cave. All aneurysm protruded from the medial aspect of the carotid artery. Interestingly, minimal or even no optic nerve mobilization was required during exposure from the contralateral side. Strategies to achieve proximal control of the carotid artery were balloon occlusion and clinoid segment or cervical carotid exposure. Successful aneurysm occlusion was achieved in 135 cases, while 3 ophthalmic aneurysms had to be wrapped only. Complications including visual deterioration, CSF fistula, wound infection, vasospasm, artery dissection, infarction, and anosmia occurred in a low percentage of cases. We conclude that a contralateral approach can be effective and should be considered for clipping carefully selected cases of unruptured aneurysms arising from medial aspects of the above listed vessels.

Optic nerve injury-associated blunt cerebrovascular injury: Three case reports

RATIONALE

Blunt cerebrovascular injury (BCVI) is a rare complication that may occur after craniocervical trauma. The current literature is limited to extracranial carotid artery injuries; however, no reports have been published on blunt intracranial carotid injury (BICI), especially those associated with optic nerve injury.

PATIENT CONCERNS

Here we report on 3 BICI cases that demonstrated optic nerve injuries after craniofacial injuries. All 3 patients showed post-trauma vision loss on the injured side.

DIAGNOSES

Optical canal fractures can be found in these patients, and carotid sulcus was compressed by the fragments. Computed tomography angiography (CTA) and digital subtraction angiography (DSA) were performed in all 3 patients.

INTERVENTIONS

Case 1 was given no further treatment, except for symptomatic support and rehabilitation therapy. Case 2 was treated with antiplatelet therapy for 3 days, and then a stent was inserted in the injured internal carotid. Case 3 received antiplatelet therapy and a internal carotid compression test was performed simultaneously for 2 weeks, then the injured internal carotid was completely blocked.

OUTCOMES

Case 1 developed cerebral infarction that resulted in unilateral hemiplegia. Due to timely treatment, the remaining 2 patients had a better prognosis.

LESSONS

CTA should be performed primarily to exclude vascular injury and for CTA-positive patients, a further DSA should be performed to investigate pathological changes and for a definitive diagnosis. At last, the current therapeutic protocols for BCVI are not entirely applicable to intracranial vascular injury, and appropriate protocols for the treatment of BICI should be selected based on the combination of test results and the actual condition of the patient.

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Comparison of the effectiveness of using the optic strut and tuberculum sellae as radiological landmarks in diagnosing paraclinoid aneurysms with CT angiography

OBJECTIVE

The treatment of paraclinoid aneurysms remains challenging. It is important to determine the exact location of the paraclinoid aneurysm when considering treatment options. The authors herein evaluated the effectiveness of using the optic strut (OS) and tuberculum sellae (TS) as radiographic landmarks for distinguishing between intradural and extradural paraclinoid aneurysms on source images from CT angiography (CTA).

METHODS

Between January 2010 and September 2013, a total of 49 surgical patients with the preoperative diagnoses of paraclinoid aneurysm and 1 symptomatic cavernous-clinoid aneurysm were retrospectively identified. With the source images from CTA, the OS and the TS were used as landmarks to predict the location of the paraclinoid aneurysm and its relation to the distal dural ring (DDR). The operative findings were examined to confirm the definitive location of the paraclinoid aneurysm. Statistical analysis was performed to determine the diagnostic effectiveness of the landmarks.

RESULTS

Nineteen patients without preoperative CTA were excluded. The remaining 30 patients comprised the current study. The intraoperative findings confirmed 12 intradural, 12 transitional, and 6 extradural paraclinoid aneurysms, the diagnoses of which were significantly related to the type of aneurysm (p < 0.05) but not factors like sex, age, laterality of aneurysm, or relation of the aneurysm to the ophthalmic artery on digital subtraction angiography. To measure agreement with the correct diagnosis, the OS as a reference point was far superior to the TS (Cohen's kappa coefficients 0.462 and 0.138 for the OS and the TS, respectively). For paraclinoid aneurysms of the medial or posterior type, using the base of the OS as a reference point tended to overestimate intradural paraclinoid aneurysms. The receiver operating characteristic curve indicated that if the aneurysmal neck traverses the axial plane 2 mm above the base of the OS, the aneurysm is most likely to grow across the DDR and present as a transitional aneurysm (sensitivity 0.806; specificity 0.792).

CONCLUSIONS

High-resolution thin-cut CTA is a fast and crucial tool for diagnosing paraclinoid aneurysms. The OS serves as an effective landmark in CTA source images for distinguishing between intradural and extradural paraclinoid aneurysms. The DDR is supposed to be located 2 mm above the base of the OS in axial planes.

Junctional Internal Carotid Artery Aneurysms: The Schrödinger's Cat of Vascular Neurosurgery

Objectives Despite advances in neuroimaging, it is not always definitive whether a paraclinoid aneurysm is intradural or entirely extradural. We illustrate the potential use of surgical exploration in these aneurysms that we refer to as "junctional" aneurysms. Methods Retrospective review of eight patients with unruptured aneurysms who underwent a planned surgical exploration of a junctional aneurysm. Results Of the eight patients, three underwent exploration of the aneurysm during surgery for a different aneurysm. All three of these were found to be extradural. Five patients underwent a craniotomy for the exclusive purpose of clarifying the location of the aneurysm. Two of these cases were found to be intradural and were clipped. Two cases were found to be extradural. In one patient, the initially extradural aneurysm was converted into an intradural aneurysm during removal of the anterior clinoid process, necessitating surgical clipping. One transient third nerve palsy was observed. Discussion Until further progress in neuroimaging allows clinicians to determine unequivocally the exact anatomical location of a paraclinoid aneurysm, we advocate the use of the term junctional aneurysm to reflect the clinical uncertainty inherent in management decisions made regarding these aneurysms. We have illustrated a strategy of surgical exploration in select patients.

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

INTRODUCTION

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.

METHODS

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.

RESULTS

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.

CONCLUSION

Eighty-kilovolt high-resolution CBCT has the potential to provide detailed anatomy for neurosurgical operations when utilizing suitable modes and contrast protocols.

Toward an endovascular internal carotid artery classification system

SUMMARY

Does the world need another ICA classification scheme? We believe so. The purpose of proposed angiography-driven classification is to optimize description of the carotid artery from the endovascular perspective. A review of existing, predominantly surgically-driven classifications is performed, and a new scheme, based on the study of NYU aneurysm angiographic and cross-sectional databases is proposed. Seven segments - cervical, petrous, cavernous, paraophthlamic, posterior communicating, choroidal, and terminus - are named. This nomenclature recognizes intrinsic uncertainty in precise angiographic and cross-sectional localization of aneurysms adjacent to the dural rings, regarding all lesions distal to the cavernous segment as potentially intradural. Rather than subdividing various transitional, ophthalmic, and hypophyseal aneurysm subtypes, as necessitated by their varied surgical approaches and risks, the proposed classification emphasizes their common endovascular treatment features, while recognizing that many complex, trans-segmental, and fusiform aneurysms not readily classifiable into presently available, saccular aneurysm-driven schemes, are being increasingly addressed by endovascular means. We believe this classification may find utility in standardizing nomenclature for outcome tracking, treatment trials and physician communication.

Microsurgical anatomy of the carotid cave

BACKGROUND

The carotid cave was first described more than 20 years ago, but its relationships to the dural rings defining the clinoid segment of the internal carotid artery (ICA), the carotid collar, and the adjacent osseous structures need further definition.

OBJECTIVE

To further define the microanatomy of the carotid cave and its relationships to the adjacent structures.

METHODS

: The cave and its relationships were examined in cadaveric specimens using 3 to 40× magnification.

RESULTS

The cave is an intradural pouch, found in 19 of 20 paraclinoid areas, that extends below the level of the distal dural ring between the wall of the ICA and the dural collar surrounding the ICA. The distal dural ring is tightly adherent to the anterior and lateral walls of the ICA adjacent the anterior clinoid process and optic strut but not on the medial and posterior sides of the artery facing the upper part of the carotid sulcus where the carotid cave is located. The superior hypophyseal artery frequently arises in the cave. The depth and circumferential length of the cave averaged 2.4 mm (range, 1.5-5 mm) and 9.9 mm (range, 4.5-12 mm), respectively. Aneurysms arising at the level of the cave, although appearing on radiological studies to extend below the level of the upper edge of the anterior clinoid, may extend into and may be a source of subarachnoid space.

CONCLUSION

The surgical treatment of aneurysms arising in the cave requires an accurate understanding of the relationships of the cave to the ICA, dural rings, and carotid collar.

3D MR cisternography to identify distal dural rings: comparison of 3D-CISS and 3D-SPACE sequences

PURPOSE

The distal dural ring (DDR) is an anatomical landmark used to distinguish intra- and extradural aneurysms. We investigated identification of the DDR using 2 three-dimensional (3D) magnetic resonance (MR) cisternography sequences--3D constructive interference in steady state (CISS) and 3D sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE)--at 3.0 tesla.

METHODS

Ten healthy adult volunteers underwent imaging with 3D-CISS, 3D-SPACE, and time-of-flight (TOF) MR angiography (TOF-MRA) sequences at 3.0T. We analyzed DDR identification and internal carotid artery (ICA) signal intensity and classified the shape of the carotid cave.

RESULTS

We identified the DDR using both 3D-SPACE and 3D-CISS, with no significant difference between the sequences. Visualization of the outline of the ICA in the cavernous sinus (CS) was significantly clearer with 3D-SPACE than 3D-CISS. In the CS and petrous portions, signal intensity was lower with 3D-SPACE, and the flow void was poor with 3D-CISS in some subjects.

CONCLUSION

We identified the DDR with both 3D-SPACE and 3D-CISS, but the superior contrast of the ICA in the CS using 3D-SPACE suggests the superiority of this sequence for evaluating the DDR.

The new proposed magnetic resonance areas of the cavernous sinus and their relation to the neurosurgical triangles

MRI appears to be the best contemporary method with which to evaluate cavernous sinus anatomy. Based on anatomic landmarks that are easily detectable in the standard MRI examination, the cavernous sinus is divided into six areas. Each of the newly defined areas corresponds to the previously described neuroanatomic triangles. Evaluation of the newly defined areas in a plane perpendicular to these triangles on a MRI scan permits expansion of these two-dimensional areas into three-dimensional spaces; thus, the neurosurgical approach can be observed and their anatomic and pathologic content examined. Radiologic and surgical evaluation of the cavernous sinus is presented.

Heavily t2-weighted magnetic resonance landmarks of the cavernous sinus and paracavernous region

The purpose of this study was to evaluate the magnetic resonance anatomy of the cavernous sinus. Heavily T2-weighted submillimetric sequence in sagittal, coronal, and axial planes was performed in 16 healthy patients. The sequence provides high contrast between fluid and other structures of the cavernous sinus. High signal intensity of the venous spaces of the cavernous sinus provides a kind of a background for internal carotid artery, cranial nerves, and meninges, as well as bony and fibrous structures. The study was performed with the help of an anatomic atlas. Different magnetic resonance (MR) landmarks of the cavernous and parasellar region were introduced and demonstrated. MR images, superior to computer tomography, allow a detailed assessment of the cavernous sinus anatomy. Delineation by magnetic resonance of tiny anatomical structures may help the neurosurgeon trace the exact outline of a tumor and help to plan an adequate strategy if complete resection is attempted.

[Paraclinoid region: descriptive anatomy and radiological correlations with MR imaging]

OBJECTIVE

The paraclinoid region has a complex anatomy. The purpose of this study was to depict in details its anatomical landmarks and their radiological translations with magnetic resonance imaging (MRI).

MATERIAL AND METHOD

Ten anatomical specimens (20 paraclinoid regions) were prepared, then dissected and further analyzed with MRI in order to describe their important radio-anatomical structures (dural folds, osseous surfaces, arteries and nerves) along with their course and measurements, and the reference points of the carotid distal dural ring. The paraclinoid MR protocol consisted in a T2 high-resolution sequence with thin and contiguous slices acquired in a coronal (diaphragmatic) and sagittal oblique (carotid) plane. Reproducibility in living subjects was evaluated on 15 patients (30 paraclinoid regions). Statistical comparison was made between laboratory and MR measurements obtained on cadavers.

RESULTS

A detailed description of paraclinoid anatomy and structures was provided. Its landmarks were satisfactorily identified with the dedicated MR protocol. Reproducibility in living subjects was obtained. No statistical difference was found between laboratory and MR measurements.

CONCLUSION

This study provides a precise description of paraclinoid anatomical structures and their radiological correlations. This paraclinoid MR protocol allows locating paraclinoid lesions in comparison with the cavernous sinus roof, which is of paramount importance for the management of paraclinoid carotid artery aneurysms.

Distinction between Intradural and Extradural Aneurysms Involving the Paraclinoid Internal Carotid Artery with T2-Weighted Three-Dimensional Fast Spin-Echo Magnetic Resonance Imaging

OBJECTIVE

The precise intra- vs. extradural localization of aneurysms involving the paraclinoid internal carotid artery is critical for the evaluation of patients being considered for aneurysm surgery. The purpose of this study was to investigate the clinical usefulness of T2-weighted three-dimensional (3-D) fast spin-echo (FSE) magnetic resonance (MR) imaging in the evaluation of unruptured paraclinoid aneurysms.

METHODS

Twenty-eight patients with unruptured cerebral aneurysms in their paraclinoid regions were prospectively evaluated using a T2-weighted 3-D FSE MR imaging technique with oblique coronal sections. The MR images were assessed for the location of the cerebral aneurysm in relation to the dural ring and other surrounding anatomic compartments, and were also compared with the surgical or angiographic findings.

RESULTS

All 28 aneurysms were identified by T2-weighted 3D FSE MR imaging, which showed the precise anatomic relationships in regards to the subarachnoid space and the surrounding anatomic structures. Consequently, 13 aneurysms were determined to be intradural and the other 15 were deemed extradural as they were confined to the cavernous sinus. Of the 13 aneurysms with intradural locations, three superior hypophyseal artery aneurysms were found to be situated intradurally upon operation.

CONCLUSION

High-resolution T2-weighted 3-D FSE MR imaging is capable of confirming whether a cerebral aneurysm at the paraclinoid region is intradural or extradural, because of the MR imaging's high spatial resolution. The images may help in identifying patients with intradural aneurysms who require treatment, and they also can provide valuable information in the treatment plan for paraclinoid aneurysms.

Application of contrast-enhanced constructive interference in steady state magnetic resonance imaging to Leksell GammaPlan for localizing c2-c3 aneurysms: technical note

OBJECTIVE

We used gadolinium (Gd)-enhanced constructive interference in steady state (CISS) magnetic resonance imaging with the Leksell GammaPlan (LGP; Elekta AB, Stockholm, Sweden) system for accurate preoperative evaluation of the anatomic localization of intradural and/or extradural C2-C3 aneurysms.

METHODS

Anatomic localization of 8 unruptured aneurysms of the C2-C3 segment was evaluated using Gd-enhanced CISS imaging with LGP. Four patients diagnosed with intradural aneurysms, 1 with a combined intraextradural aneurysm, and 1 with an intracavernous aneurysm underwent operation. The aneurysmal localizations diagnosed preoperatively by Gd-enhanced CISS imaging with LGP were compared with intraoperative findings.

RESULTS

By use of Gd-enhanced CISS imaging with LGP, 3-dimensional visualization of the internal carotid artery, aneurysms at the C2-C3 segment, optic nerve, oculomotor nerve, cavernous sinus, and anterior clinoid process was possible in 8 patients. The localization of intradural or combined intra-extradural aneurysms was diagnosed on the basis of the oculomotor nerve and the cavernous sinus depicted in 3-dimensional images. The oculomotor nerve and the cavernous sinus serve as landmarks for the proximal ring on images of the carotico-oculomotor membrane. Intradural or intra-extradural localization of C2-C3 aneurysms with this novel technique was in complete agreement with intraoperative findings in 6 surgical cases.

CONCLUSION

This study demonstrated the utility of Gd-enhanced CISS imaging used with LGP for accurate preoperative localization of intradural and/or extradural aneurysms at the C2-C3 segments.

Identification of the distal dural ring with use of fusion images with 3D-MR cisternography and MR angiography: application to paraclinoid aneurysms

BACKGROUND AND PURPOSE

The distal dural ring (DDR) represents the anatomic border between the extradural and intradural internal carotid arteries (ICAs). The purpose of this study was to examine whether 3D-MR cisternography and MR angiography (MRA) fusion images can identify the boundary between the CSF and the cavernous sinus, which might represent the DDR.

MATERIALS AND METHODS

Thirty-six consecutive patients with 39 ICA aneurysms were examined with use of MR fusion images with 3D-cisternography and MRA on a 1.5T unit. Two neuroradiologists evaluated the configuration of the carotid cave and the location of the aneurysms on fusion images and classified them as intradural, transdural, and extradural aneurysms.

RESULTS

The borderline between the CSF and the cavernous sinus was visualized on fusion images in all patients. The carotid cave configuration in 72 ICAs was classified as having no dent (n = 31), a shallow dent (n = 27), and a deep dent (n = 14). The MR fusion images led to the classification of 39 ICA aneurysms as 21 intradural, 6 transdural, and 12 extradural. The interobserver agreement of MR fusion images was excellent (kappa = 0.80).

CONCLUSIONS

Fusion images with 3D-cisternography and MRA yielded clear visualization of the boundary between the suprasellar cistern and cavernous sinus indicating the DDR. This imaging technique may provide additional information in consideration of a treatment option for paraclinoid aneurysms.

Intrasellar rupture of a paraclinoid aneurysm with subarachnoid hemorrhage: usefulness of MR imaging in diagnosis

Characterization of paraclinoid aneurysms may be difficult because of the complexity of anatomic structures involved, and differentiation between intradural and extradural lesions is crucial. We report a case of a patient with a unique presentation of a paraclinoid aneurysm with intrasellar hemorrhage in which the presence of intrasellar blood and the relationship of the paraclinoid aneurysmal neck and sac to the dural rings were elegantly demonstrated on MR imaging and were critical in choosing the target lesion for treatment.

Differentiation between paraclinoid and cavernous sinus aneurysms with contrast-enhanced 3D constructive interference in steady- state MR imaging

BACKGROUND AND PURPOSE

Differentiation between paraclinoid and cavernous sinus aneurysms of the internal carotid artery (ICA) is critical when considering treatment options. The purpose of this study was to determine whether contrast-enhanced (CE) 3D constructive interference in steady state (CISS) MR imaging is useful to differentiate between paraclinoid and cavernous sinus aneurysms.

MATERIALS AND METHODS

This study included 11 aneurysms in 10 consecutive female patients, ranging from 52 to 66 years of age. All aneurysms were adjacent to the anterior clinoid process. After conventional and CE 3D-CISS imaging on a 1.5T MR imaging unit, all patients underwent surgery, and the relationship between the aneurysms and the dura was confirmed. Two neuroradiologists evaluated the location of the aneurysms on CE 3D-CISS images and classified them as intradural, partially intradural, and extradural aneurysms. Operative findings were used as a reference standard. To understand the imaging characteristics, we assessed the boundary and signal intensity of the cavernous sinus, CSF, and carotid artery on the side contralateral to the lesion.

RESULTS

Operative findings disclosed that 5 aneurysms were intradural and 6 were extradural. All except 2 were accurately assessed with CE 3D-CISS imaging. One intradural aneurysm adjacent to a large cavernous aneurysm and 1 cavernous giant aneurysm were assessed as partially intradural. On CE 3D-CISS images, the boundary between the CSF, cavernous sinus, and carotid artery was identified by high signal-intensity contrast in all cases.

CONCLUSION

CE 3D-CISS MR imaging is useful for the differentiation between paraclinoid and cavernous sinus aneurysms.

Usefulness of MR imaging for the assessment of nonophthalmic paraclinoid aneurysms

BACKGROUND AND PURPOSE

The neuroradiologic location of asymptomatic paraclinoid aneurysms is decisive for patient management. In a preliminary study, we designed a paraclinoid MR protocol (PMP) including high-resolution T2-weighted images in 2 orthogonal planes to define the inferior limit of the distal dural ring plane that represents the borderline between the intradural and extradural internal carotid artery. In this clinical study, we compared this protocol with digital subtraction angiography (DSA) for the location of paraclinoid aneurysms.

MATERIALS AND METHODS

During a 3-year period, we performed PMP and conventional angiograms in 14 consecutive patients with 17 asymptomatic paraclinoid aneurysms. Ophthalmic (superior) aneurysms were excluded. Two independent observers reviewed MR imaging data, and a third experienced neuroradiologist analyzed the conventional angiograms. MR imaging and conventional angiograms were independently analyzed, and interpretations obtained with each technique were compared.

RESULTS

PMP allowed correct visualization of the aneurysms in all patients. No significant differences (P >.05) were found between the DSA and PMP for the measurement of the aneurysmal neck or sac. Interobserver agreement was good. MR imaging was discordant with conventional angiography regarding the position around the cavernous sinus of the aneurysmal neck and sac in 5 cases. PMP images were helpful for treatment decisions in 4 cases.

CONCLUSION

PMP is an interesting tool that might be used in association with conventional angiography for the assessment of paraclinoid aneurysms.

Differentiation between intradural and extradural locations of juxta-dural ring aneurysms by using contrast-enhanced 3-dimensional time-of-flight magnetic resonance angiography

BACKGROUND

Juxta-dural ring aneurysms of the ICA have different clinical outcomes and risks for SAH, which are dependent on their position in the intradural or extradural space. The aim of this study was to reveal the precise location of such aneurysms by using CE-MRA.

METHODS

Contrast-enhanced MRA studies were performed in 21 patients with 24 juxta-dural ring aneurysms. The locations were evaluated by source images of CE-MRA and MPR images. We evaluated the accuracy of preoperative MRI findings by comparing imaging results with intraoperative findings in 7 cases.

RESULTS

The CS was clearly enhanced in the CE-MRA technique, which allowed the precise identification of these aneurysms as intradural or extradural. Intracavernous aneurysms were diagnosed when the greater hyperintensity of the aneurysm was located within the less hyperintense region of the contrast-enhanced CS. Nine of the cases were diagnosed as intradural aneurysms, and 15 aneurysms were noted as extradural based on the findings of CE-MRA. Surgery was performed in 7 cases, which included 4 intradural and 3 extradural aneurysms, and the preoperative MRI findings corresponded with the intraoperative findings in all cases.

CONCLUSION

Contrast-enhanced MRA and MPR are very useful techniques for determining the location of juxta-dural ring aneurysms.

Optic Strut as a Radiographic Landmark in Evaluating Neck Location of a Paraclinoid Aneurysm

OBJECTIVE:

The optic strut (OS) is a candidate landmark in computed tomographic (CT) angiographic scans for the discrimination of intradural and extradural/intracavernous aneurysms involving the paraclinoid segment of the internal carotid artery. The goal of this study is to examine and confirm the qualifications of the OS as a landmark in CT angiographic scans for the preoperative evaluation of aneurysms in this region.

METHODS:

Seventeen consecutive patients with 18 unruptured paraclinoid aneurysms who underwent preoperative CT angiography scans and direct surgery between 1998 and 2005 were evaluated retrospectively. We focused on the relationships of the necks of aneurysms to the OS in CT angiographic scans and that of the necks to proximal dural rings during intraoperative examinations.

RESULTS:

Direct surgery revealed that 14 aneurysms, the necks of which were distal to the OS on CT angiographic scans, arose distal to the proximal dural rings. All aneurysms were clipped, except one exhibiting calcification of the neck. Three aneurysms, for which the neck was proximal to the OS on CT angiographic scans, revealed only a portion or nothing of their domes instead of their necks through the proximal dural rings after dissection of the distal dural rings. Dome coating with fibrin glue and a piece of muscle tissue or mere exploration was performed. Another aneurysm, of which the neck straddled the OS on CT angiographic scans, was found to arise across the proximal dural ring. Clipping of the neck was performed after dissection of the proximal dural ring. Of the source images of CT angiographic scans, the axial images were the most useful in evaluating the relationship of the neck of an aneurysm to the OS.

CONCLUSION:

On CT angiographic scans, the OS is a precise identification of the proximal dural ring that forms the superior border of the cavernous sinus. The aneurysms whose necks arise obviously distal to the OS on CT angiographic scans are able to be clipped without dissection of the proximal dural ring.

Radiographic imaging of the distal dural ring for determining the intradural or extradural location of aneurysms

The effectiveness of several anatomical and radiological landmarks proposed to determine whether an aneurysm is located intradurally or extradurally is still debated. In anatomical and radiological studies, we examined the relationships of the distal dural ring (DDR) to the internal carotid artery (ICA) and surrounding bony structures to aid in the localization of aneurysms near the DDR. Anatomical relationships were examined by performing dissections on 10 specimens (5 formalin-fixed cadaveric heads). After the position of the DDR, optic nerve, and tuberculum sellae were marked with surgical steel wire, radiographs were taken in multiple projections. The only bony landmark consistently visible on radiographs was the planum sphenoidale. The superior border of the DDR is located at or below the level of the tuberculum sellae, which laterally becomes the superomedial aspect of the optic strut; thus, the optic strut marks the dorsal limit of the DDR. On 50 dry skulls, we measured the vertical distance between the planum sphenoidale and medial aspect of the optic strut (5.0 +/- 0.4 mm), the interoptic strut distance (14.4 +/- 1.4 mm), and the linear distance between the most posterior aspect of the planum sphenoidale (limbus sphenoidale) and the tuberculum sellae (6.0 +/- 0.5 mm). Using these measurements and the planum sphenoidale, tuberculum sellae, and optic strut as reference landmarks, we determined the location of the aneurysm relative to the DDR on angiographic images. In this way, we were able to identify whether lesions were intra- or extradural.

Localisation en IRM des anévrismes carotidiens paraclinoïdiens

AIM

The distal dural ring plane (DDRP) separates the intracavernous from the supracavernous paraclinoid internal carotid artery. The purpose of this MRI protocol is to evaluate the position of this plane for the characterization of paraclinoid aneurysms.

METHOD

The protocol uses a T2 weighted sequence in two orthogonal planes (diaphragmatic and carotid planes) and two correlation lines in each plane. These lines pass through anatomo-radiological reference points correlated with the medio-lateral and antero-posterior margins of the DDRP. We use the intersection angle of these lines as the inferior radiological limit of the DDRP curve.

RESULTS

An aneurysm located above this angle is supracavernous; an aneurysm located below this angle is intracavernous; an aneurysm crossing this angle is transitional.

CONCLUSION

In difficult cases, this MRI protocol could help better characterize the exact localization of paraclinoid aneurysms on both sides of the cavernous sinus roof.

MRI location of the distal dural ring plane: anatomoradiological study and application to paraclinoid carotid artery aneurysms

The distal dural ring plane (DDRP) separates the intradural from the extradural paraclinoid internal carotid artery. The purpose of this study was to evaluate its position with MR imaging. The protocol used a T2-weighted sequence in two orthogonal planes: diaphragmatic (DIA-P) and carotid (CAR-P). The DDRP passes through four anatomoradiological reference points (RefP). We developed on a cadaveric model a correlation method supported by correlation lines and angles (CA) projecting the RefP toward the DDRP. RefP were correlated to the DDRP in 65-84% of cases in the DIA-P and 60-76% of cases in the CAR-P. CA were identified and correlated to the DDRP, respectively, in 87% and 60% of cases in the DIA-P, and 60% and 51% of cases in the CAR-P (failure often related to a lack of visibility of just one RefP). A higher tissular contrast in living subjects allowed the identification of CA in 90% and 80% of cases, respectively, in the DIA-P and the CAR-P. We propose that CA, when identified, should be considered as an approximation of the inferior radiological limit of the DDRP curve. In difficult angiographical cases, this MRI protocol could help to locate paraclinoid aneurysms on both sides of the cavernous sinus roof.

Paraclinoid and cavernous sinus regions: Measurement of critical structures relevant for surgical procedure

Determination of the safest distance the falciform ligament can be incised from its origin to the orbital apex. Measurement of the distance between the oculomotor foramen and the IV nerve in the lateral wall of the cavernous sinus. Evaluation of the optic strut as an accurate landmark between the intradural (subarachnoid) and extradural segment of the internal carotid artery (ICA). Ten fixed human cadaver heads were examined for a total of 20 sides. A frontotemporal craniotomy, an orbito-optic osteotomy, and extradural anterior clinoidectomy were carried out followed by opening the falciform ligament, circumferentially releasing the distal dural ring and dissection of the lateral wall of the cavernous sinus under the operating microscope. We measured: 1) the distance between the entry of the III nerve and the point where the IV nerve crosses over it into the cavernous sinus; 2) the distance the falciform ligament can be incised along the optic nerve laterally until the IV nerve is encountered at the orbital apex; 3) the distance between the optic strut and the lateral part of the distal dural ring; and 4) the distance between the optic strut and the ophthalmic artery. All measurements were made in millimeters, using small calipers. The distance between the optic strut and the lateral part of the distal dural ring ranges from 3-7.5 mm (mean=5.47 mm). In all our specimens, the ophthalmic artery was found distally from the optic strut in the intradural space at a distance ranging from 0.5-7 mm (mean=3.35 mm). The distance between the entry of the third nerve and the IV nerve into the cavernous sinus ranged from 7-15 mm (mean=10.9 mm). The distance between the origin of the falciform ligament and the IV nerve at the level of the orbital apex ranged from 9-15 mm (mean=10.75 mm). The falciform ligament and the optic sheath should not be opened longer than 9 mm along the lateral optic nerve or injury to the IV nerve can occur. Starting at the oculomotor foramen, the opening of the cavernous sinus should be limited to 7 mm to avoid injuring the IV nerve. Finally, the optic strut can be a reliable bony landmark that separates the subarachnoid space and extradural compartments along the anterior and medial ICA.

Distinction between Paraclinoid and Cavernous Sinus Aneurysms with Computed Tomographic Angiography

OBJECTIVE

To examine the reliability of using the optic strut as a landmark in computed tomographic (CT) angiography, to differentiate between intradural and extradural (cavernous sinus) aneurysms involving the paraclinoid segment of the internal carotid artery (ICA).

METHODS

Microanatomic dissections were performed with five cadaveric heads (10 sides), to establish the relationships of the optic strut to the cavernous sinus and the ICA. Results from these anatomic studies were compared with intraoperative and CT angiographic findings for four patients with nine intracranial aneurysms involving the paraclinoid segment of the ICA.

RESULTS

The inferior boundary of the optic strut accurately localized the point at which the ICA pierced the oculomotor membrane (proximal dural ring) and exited the cavernous sinus. The optic strut and its relationship to the ICA could be well observed on CT angiograms. During surgery, six of six aneurysms that arose distal to the optic strut were identified intradurally and were successfully clipped. Conversely, all aneurysms that arose proximal to the optic strut were observed to lie within the cavernous sinus. An aneurysm at the optic strut was within the clinoid segment or interdural, between the proximal and distal rings.

CONCLUSION

The optic strut, as identified with CT angiography, provided a reliable anatomic landmark for accurate discrimination between intradural and extradural (cavernous sinus) aneurysms.

Radiometric analysis of paraclinoid carotid artery aneurysms

OBJECT

Classification of paraclinoid carotid artery (CA) aneurysms based on their associated branching arteries has been confusing because superior hypophyseal arteries (SHAs) are too fine to appear opacified on cerebral angiograms. The authors performed a retrospective radiometric analysis of surgically treated paraclinoid aneurysms to elucidate their angiographic and anatomical characteristics.

METHODS

A retrospective analysis was made of 85 intradural paraclinoid aneurysms in which the presence or absence of branching arteries had been determined at the time of surgical clipping. The lesions were classified as supraclinoid, clinoid, and infraclinoid aneurysms based on their relation to the anterior clinoid process on lateral angiograms of the CA. The direction of the aneurysms were measured according to angles formed between the medial portion of the horizontal line crossing the aneurysm sac and the center of the aneurysm neck on anteroposterior angiograms. Branching arteries were associated with 68 aneurysms, of which 28 were ophthalmic artery (OphA) lesions (32.9%) and 40 were SHA ones (47.1%); associated branching arteries were absent in 17 aneurysms (20%). Twenty-five aneurysms (29.4%) were located at the supraclinoidal level, 46 (54.1%) at the clinoidal, and 14 (16.5%) at the infraclinoidal. The majority of aneurysms identified at the supraclinoidal level were OphA lesions (44%) or those unassociated with branching arteries (48%), with mean directions of 57 degrees or 67 degrees, respectively. At the clinoidal level, the mean directions of aneurysms were 76 degrees in six lesions unassociated with branching arteries (13%), 43 degrees in 16 OphA lesions (35%), and -11 degrees in 24 SHA ones (52%). All aneurysms at the infraclinoidal level arose at the origin of the SHAs, with a mean direction of -29 degrees, and most of these were embedded in the carotid cave.

CONCLUSIONS

Aneurysms arising from the SHA can be distinguished from those not located at an arterial division by cerebral angiography, because SHA lesions are usually located at the medial or inferomedial wall of the internal carotid artery at the clinoidal or infraclinoidal level. Their distribution correlates well with the reported distribution of SHA origins. The carotid cave aneurysm is a kind of SHA lesion that originates at the most proximal intradural CA.

Identification of the carotid artery dural ring by using three-dimensional computerized tomography angiography. Technical note

The carotid artery (CA) dural ring is an important structure in aneurysm surgery of the paraclinoid region. The authors used three-dimensional computerized tomography (3D-CT) angiography to study the CA dural ring. Three-dimensional computerized tomography angiography was performed in patients with cerebral aneurysms and other cerebrovascular diseases. The paraclinoid segment of the internal carotid artery (ICA) was examined by the shaded surface reconstruction method on targeted 3D-CT angiography. The concavity was recognized in the paraclinoid segment of the ICA. The relationship between the concavity and the dural ring was investigated with anatomical studies and surgical findings. In anatomical studies, the concavity in the paraclinoid segment of the ICA on 3D-CT angiography coincided with the level of attachment of the dural ring. Using 3D-CT angiography, it is possible to identify the location of the dural ring in patients being considered for aneurysm surgery.

Skull base techniques for multiple aneurysms in the internal carotid juxta-dural ring region

The aneurysm located in the internal carotid juxta-dural ring region is difficult to surgically obliterate. At surgery, careful drilling of the anterior clinoid process is mandatory, especially when a laterally projecting aneurysm protrudes to or inside the anterior clinoid process.In this paper, treatment procedures using the skull base techniques with intravascular coil embolisation are described by showing a case.

Parameters for contralateral approach to ophthalmic segment aneurysms of the internal carotid artery

OBJECTIVE

This study was undertaken to define more accurately the feasibility and indications of the contralateral pterional approach to ophthalmic segment aneurysms of the internal carotid artery (ICA).

METHODS

Between 1995 and 1999, 46 patients with ophthalmic segment aneurysms of the ICA were surgically treated in our institution. Eleven of the 46 aneurysms were operated using the contralateral pterional approach. All aneurysms were successfully clipped without complications; three patients required bone resection around the aneurysm neck. We studied the 11 patients who were treated with the contralateral approach by defining six parameters to assess the feasibility of the approach and to predict the necessity for bone resection: 1) Parameter A, the distance between the anterior aspect of the optic chiasm and the limbus sphenoidale; 2) Parameter B, the distance between the bilateral optic nerves at the entrance to the optic canal; 3) Parameter C, the interrelation of the optic nerve and the ICA, expressed as a/b in which a is the length from the midline to the optic nerve and b is the length from the midline to the ICA; 4) Parameter D, the size of the aneurysm neck; 5) Parameter E, the direction of the aneurysm from the ICA wall on the anteroposterior angiogram; and 6) Parameter F, the distance from the medial side of the estimated distal dural ring to the proximal aneurysm neck on the lateral angiogram.

RESULTS

Parameters A to F were 8.8 mm (range, 5.4-11.1 mm), 14.5 mm (range, 10.4-22.2 mm), 0.9 mm (range, 0.6-1.3 mm), and 3.0 mm (range, 2.3-4.7 mm), 5 to 160 degrees, and 1.3 mm (range, 0.3-2.4 mm), respectively. All patients had excellent operative outcomes without visual dysfunction. Three patients required drilling of the bone around the optic canal on the craniotomy side; bone drilling was not required when Parameter E was between 30 and 160 degrees and Parameter F was more than 1 mm.

CONCLUSION

Parameters A to D are important for assessing the feasibility of the contralateral approach to ICA-ophthalmic segment aneurysms, and Parameters E and F are most useful for calculating the difficulty of this approach.

Contralateral approach to junctional C2-C3 and proximal C4 aneurysms of the internal carotid artery: microsurgical anatomic study

OBJECTIVE

To evaluate a contralateral approach to aneurysms located in the internal carotid artery cave and proximal C4 segments.

METHODS

In six adult cadaveric head sides, proposed aneurysms in the carotid cave or proximal C4 segments were approached via contralateral craniotomies. We summarize the approach in the following steps: 1) frontotemporal orbital craniotomy, 2) drilling of the lateral sphenoid wing and opening of the dura along the frontotemporal base, 3) drilling of the planum sphenoidale and the tuberculum sellae more extensively toward the aneurysm side and opening of the sphenoid sinus, 4) drilling of the medial part of the anterior clinoid process on the side of the aneurysm and removal of the superior, medial, and inferior walls of the optic canal, 5) opening of the optic sleeve, and 6) opening of the space between the medial wall of the internal carotid artery C2-C3 segments and the lateral edge of the pituitary gland.

RESULTS

The contralateral approach to expose the opposite internal carotid artery cave and proximal C4 segments provided excellent views of the region, without mobilization or retraction of either the optic nerve or the carotid artery.

CONCLUSION

We recommend that this approach be used only for selected aneurysms, which are small and directed medially, anteriorly, or inferiorly, in the defined locations.