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

Analysis of the Prechiasmatic Sulcus in Chiari Malformation Type I

OBJECTIVE

To assess morphologic features of the prechiasmatic sulcus (PS) in Chiari malformation type I (CM-I).

METHODS

Computed tomography images were obtained in patients with CM-1 (mean age: 21.26 ± 16.46 years; sex: 25 females and 17 males) and 58 healthy control subjects (mean age: 28.12 ± 22.60 years; sex: 29 females and 29 males). The following parameters were measured to determine the anatomy of the PS: planum length, sulcal length, sulcal angle (SA), and interoptic distance. Considering sulcal length and SA measurements, 4 types of PS were identified: narrow-steep-groove (NSG), narrow-flat-groove (NFG), wide-steep-groove, and wide-flat-groove.

RESULTS

SA was greater in the CM-I group (32.80 ± 18.21°) compared with the control group (23.05 ± 14.53°) (P = 0.004), but the other parameters were similar in both groups. Distribution ranking of PS types was as follows: NFG (31%) > NSG (26.20%) > wide-steep-groove (23.80%) > wide-flat-groove (19%) in the CM-I group; wide-flat-groove (37.90%) > wide-steep-groove (20.70%) = NFG (20.70%) = NSG (20.70%) in the control group. Distribution rate of PS types relative to both groups showed that the classification system was not affected by CM-I (P = 0.226).

CONCLUSIONS

SA value was approximately 25% greater in the CM-I group than in the control group; thus, CM-I patients had more vertical groove. The percentage of narrow-type (NSG + NFG) PS in the CM-I group was higher than in the control group.

Efficacy of 3D evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® for determination of their intradural localization

BACKGROUND

Determination of the intradural unruptured paraclinoid aneurysm localization is difficult, but critical for selection of the optimal treatment strategy.

OBJECTIVE

To assess efficacy of the three-dimensional (3D) evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® (LGP; Elekta AB; Stockholm, Sweden) for determination of their intradural localization.

METHODS

Overall, 125 incidentally diagnosed unruptured paraclinoid aneurysms in 118 patients (mean age, 55 years) underwent 3D evaluation of their localization within LGP using post-contrast thin-slice constructive interference in steady state (CISS) images, which in 41 cases were additionally co-registered and fused with the axial computed tomography angiography (CTA) source images.

RESULTS

According to the evaluation within LGP, paraclinoid aneurysms were considered intradural, transitional, and extradural in 75, 25, and 25 cases respectively. Overall, 51 of 75 aneurysms deemed to be intradural, underwent microsurgical management, and intraoperative visual inspection confirmed their intradural localization in 45 cases, whereas it was transitional in 3, and extradural in 3. If during preoperative 3D evaluation within LGP only post-contrast CISS images were used, prediction of the pure intradural localization of aneurysm was correct in 88 % of cases (95 % CI: 79-97 %), and of the pure or partial (i.e., transitional) intradural localization in 94 % of cases (95 % CI: 88-100 %), whereas it was 100 % if co-registration and fusion of the contrast-enhanced CISS and CTA source images was done.

CONCLUSION

Intradural localization of the unruptured paraclinoid aneurysms may be effectively predicted based on their 3D evaluation within LGP using post-contrast thin-slice CISS and CTA source images, which may help with clinical decision-making.

The Intersection Between the Oculomotor Nerve and the Internal Carotid Artery to Distinguish Extracavernous and Intracavernous Paraclinoid Aneurysms Using Anatomic Dissections-A New 3T Magnetic Resonance Imaging Protocol Confirmed by Three-Dimensionally Printed Biomodels

OBJECTIVE

To evaluate the relationship between the oculomotor nerve (CNIII) and the internal carotid artery (ICA) as a new anatomic-radiologic landmark for distinguishing the exact location of a paraclinoid intracranial aneurysm (IA).

METHODS

Microanatomic dissections were performed in 20 cavernous sinuses to evaluate the ICA paraclinoid region. Based on anatomic observations, a new magnetic resonance (MRI) protocol to classify paraclinoid aneurysms was proposed. MRI of 42 IAs from 34 patients was independently analyzed and classified as intracavernous, extracavernous, or transitional by 2 neuroradiologists. To validate the proposed MRI protocol, each IA was classified by a three-dimensionally (3D) printed biomodel and agreement with the radiologic classifications was evaluated. Of 42 IAs, 23 undergoing microsurgeries were also classified by direct visualization.

RESULTS

We observed that the true cavernous sinus roof is defined by the carotid-oculomotor membrane, which has an intimate relationship with the intersection between the superior limit of the CNIII and the ICA. Based on this intersection, all 42 IAs were radiologically classified and agreement with the 3D printed biomodels was observed in 95% IAs. Concordance tests showed a statistically significant (P < 0.05) agreement between the classifications. All 23 IAs treated had the radiologic and 3D biomodel classification confirmed.

CONCLUSIONS

The intersection between the ICA and the CNIII, which crosses it transversely in its entire diameter, is a reliable anatomic-radiologic landmark to correctly classify paraclinoid aneurysms. Through a new MRI protocol, it is possible to radiologically identify this intersection and to easily distinguish the intracavernous and extracavernous ICA paraclinoid aneurysms.

Change in the Location of the Optic Strut Relative to the Anterior Clinoid Process Pneumatization

OBJECTIVE

This study aimed to peruse the alteration of the position of the optic strut (OS) according to the anterior clinoid process (ACP) pneumatization.

METHODS

This retrospective study conducted on cone-beam computed tomography images of 400 patients with a mean age of 36.49±15.91 years.

RESULTS

Anterior clinoid process length, width, and angle were measured as 10.56±2.42 mm, 5.46±1.31 mm, and 42.56±14.68 degrees, respectively. The tip of ACP was measured as 6.60±1.50 mm away from the posterior rim of OS. In the 631 sides (78.87%) did not have ACP pneumatization. In the cases with ACP pneumatization, three different configurations were identified as follows: Type 1 in 71 sides (8.87%), Type 2 in 56 sides (7%), and Type 3 in 42 sides (5.23%). Relative to ACP, the location of OS was determined as follows: Type A in 29 sides (3.64%), Type B in 105 sides (13.12%), Type C in 344 sides (43%), Type D in 289 sides (36.12%), and Type E in 33 sides (4.12%). The spread of data related to the attachment site of OS according to the presence or absence of ACP pneumatization showed that the location of OS was affected by ACP pneumatization (P<0.001). In ACPs with pneumatization, the frequency of OS position relative to ACP was found as follows: Type A in none of sides (0%), Type B in 8 sides (7.6%), Type C in 53 sides (15.4%), Type D in 88 sides (30.4%), and Type E in 20 sides (60.6%).

CONCLUSIONS

The main finding of this study was that the location of OS relative to ACP was affected by ACP pneumatization. In ACPs with pneumatization, OS was located more posteriorly compared with ACPs without pneumatization.

Identification of the Distal Dural Ring and Definition of Paraclinoid Aneurysms According to Bony Landmarks on 3-Dimensional Computed Tomography Angiography: A Cadaveric and Radiological Study

BACKGROUND

Determining if paraclinoid aneurysms are intradural or extradural is critical for surgical planning.

OBJECTIVE

To create an easily reproducible diagnostic method based on bony anatomy that precisely locates the distal dural ring (DDR) to determine the position of paraclinoid aneurysms as intradural, transitional, or extradural.

METHODS

Bilateral anatomic dissections of 10 cadaveric heads (20 sides) were performed to evaluate DDR anatomy. We observed a plane that reflects the position of the DDR passes through 4 bony landmarks: 1) The anterior clinoid-internal carotid artery intersection, 2) the optic strut, 3) the optico-carotid elevation, and 4) the base of the posterior clinoid process. This landmark-based plane can thus define the location of the DDR using 3-dimensional computed tomography angiography (CTA). This was confirmed in 27 surgical patients with intradural/transitional aneurysms and 7 patients with extradural aneurysms confirmed with magnetic resonance imaging (MRI). The DDR plane method easily classified aneurysm locations as intradural (above the DDR plane), extradural (below the DDR plane), or transitional (the DDR plane crosses the aneurysm). The aneurysm's location was subsequently confirmed intraoperatively or with MRI.

RESULTS

The DDR plane method determined if paraclinoid aneurysms were intradural, transitional, or extradural in all 34 cases examined. The visibility of the anatomic features that define the DDR plane was also verified in 82% to 89% of CTA images from 100 patients.

CONCLUSION

The DDR plane method provides a useful diagnostic tool to evaluate the position of the DDR and determine the anatomic location of paraclinoid aneurysms.

A Computed Tomography Study of the Prechiasmatic Sulcus Anatomy in Children

PURPOSE

To investigate the characteristics of the prechiasmatic sulcus in children aged between 1-20 years.

METHODS

Patient files of 200 children admitted to the university hospital on 2019 were analyzed, retrospectively. The computed tomography images of patients were used to obtain anatomical knowledge containing prechiasmatic sulcus types and dimensions.

RESULTS

The measurements related to the sulcal length (6.94 ± 1.25 mm) and sulcal angle (31.01 ± 18.13°) showed that the sulcal length did not alter in children between 1 and 20 years, whereas the sulcal angle did not vary from infancy to prepubescent period, but it was decreasing in postpubescent period. In 29 patients, the sulcal length was observed to divide into 2 parts with an evident angle. The interoptic distance and planum length were found as follows: 14.70 ± 2.85 mm and 14.84 ± 4.12 mm, respectively. The order of PS types was observed as type 4 (26.5%, 53 cases) > type 2 (26%, 52 cases) > type 1 (24%, 48 cases) > type 3 (23.5%, 47 cases).

CONCLUSIONS

The sulcal length did not vary in children, whereas the sulcal angle decreased with an irregular pattern. The sulcal angle decreased after prepubescent period, possibly due to the sphenoid sinus pneumatization and spheno-occipital synchondrosis. The sulcal length angle mostly in infants and young children may cause surgical orientation difficult during the resection of tumors using transcranial approaches.

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.

Fetal Anatomy of the Optic Strut and Prechiasmatic Sulcus with a Clinical Perspective

OBJECTIVE

The main objective of the study was to show the morphologic features of optic strut (OS) and prechiasmatic sulcus (PS) in the fetal skull base with a surgical anatomical perspective.

METHODS

Twenty-three fetal cadavers (9 female, 14 male) with an average age of 21.70 ± 3.12 (range: 16-28) weeks of gestation in the inventory of the Anatomy Department were included in the study. Measurements were made with a digital image analysis software and goniometer.

RESULTS

The sulcal length, interoptic distance, planum length, and sulcal angle were detected as follows: 3.91 ± 0.74 mm, 6.88 ± 1.04 mm, 6.55 ± 1.51 mm, and 24.52 ± 9.51°, respectively. Considering the location of the posteromedial margin of OS according to PS, OS was identified as the sulcal in 56.5% (13 cases), postsulcal in 30.4% (7 cases), and asymmetric in 13% (3 cases). According to the sulcal length and angle, PS was identified as type 1 in 26.1% (6 cases), type 2 in 21.7% (5 cases), type 3 in 30.4% (7 cases), and type 4 in 21.7% (5 cases).

CONCLUSIONS

Our findings suggest that the sulcal length and angle reach adult size in utero. Taking into account the fetal and the gathered adult measurements, the high percentage of steep angle compared to flat angle show that after birth, PS become more flat, probably depending on the variations of the sphenoid sinus pneumatization. Thus, more studies conducted on the alterations in PS and OS types relative to the pneumatization are needed in terms of patient positioning, selection of appropriate surgical approach, and intraoperative decision-making.

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

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.

Prechiasmatic sulcus and optic strut: an anatomic study in dry skulls

BACKGROUND

Although safe surgical access to the cavernous sinus is related to understanding the anatomical and ethnic variants of the prechiasmatic sulcus and the optic strut, there remains a paucity of studies of the morphology and the bony relationships in the region. The present study provides a systematic morphological and morphometric analysis of the sulcal region and the optic strut anatomy and their relations in a Greek population.

METHODS

The interoptic distance, length of planum sphenoidale, sulcal length and sulcal angle was determined in 96 Greek adult dry skulls. The prechiasmatic sulci and optic struts were morphologically classified and association of sulcal region measures according to type of prechiasmatic sulcus and optic strut were examined.

RESULTS

Mean interoptic distance was 1.69 ± 0.25 cm; sulcal length, 0.72 ± 0.18 cm; length of planum sphenoidale, 1.86 ± 0.32 cm; sulcal angle, 24.05 ± 17.17°. The sulcal angle was significantly smaller in female skulls compared to males (14.82 ± 12.43 vs 28.29 ± 15.24; p < 0.05). Type I (narrow, steep) prechiasmatic sulci were the most commonly observed (35.8%), followed by Type IV (wide, flat) (32.1%), Type II (narrow, flat) (18.5%) and, finally, Type III (wide, steep) sulci (13.6%). The optic strut was presulcal in 8.3% of specimens, sulcal in 31%, postsulcal in 41.7% and asymmetric in 19%.

CONCLUSIONS

The present study augments the current knowledge of the morphology of key anatomical landmarks, prechiasmatic sulcus and the optic strut, for cavernous sinus surgery and indicates population and gender differences. We report significant anatomical variations in the prechiasmatic sulcus, optic strut and surrounding structures. In addition to providing a better understanding of the anatomical landmarks, necessary for the safe navigation in transcranial and endoscopic procedures, the present results also suggest that surgeons must consider population differences in determining the anatomical landmarks and navigation points in the sellar region.

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.

Anatomic variation of the optic strut: classification schema, radiologic evaluation, and surgical relevance

Objective Anatomic variability of the optic strut in location, orientation, and dimensions is relevant in approaching ophthalmic artery aneurysms and tumors of the anterior cavernous sinus, medial sphenoid wing, and optic canal. Methods In 84 dry human skulls, imaging studies were performed (64-slice computed tomography [CT] scanner, axial view, aligned with the zygomatic arch). Optic strut location related to the prechiasmatic sulcus was classified as presulcal, sulcal, postsulcal, and asymmetric. Morphometric analysis was performed. Results The optic strut was presulcal in 11.9% specimens (posteromedial margin bilaterally anterior to limbus sphenoidale), sulcal in 44% (posteromedial part adjacent to the sulcus's anterior two thirds bilaterally), postsulcal in 29.8% (posteromedial margin posterior to the sulcus's anterior two thirds), and asymmetric (left/right) in 14.3%. Optic strut length, width, and thickness measured 6.54 ± 1.69 mm, 4.23 ± 0.69 mm, and 3.01 ± 0.79 mm, respectively. Optic canal diameter was 5.14 ± 0.47 mm anteriorly and 4.79 ± 0.64 mm posteriorly. Angulation was flat (>45 degrees) in 13% or acute (<45 degrees) in 87% specimens. Conclusions Anatomical variations in the optic strut are significant in planning for anterior clinoidectomy and optic-canal decompression. Our optic strut classification considers these variations relative to the prechiasmatic sulcus on preoperative imaging.

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.

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.