Anterior clinoidectomy using an extradural and intradural 2-step hybrid technique

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  • 1 Department of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona;
  • | 2 Skull Base and Cerebrovascular Laboratory, University of California, San Francisco, California; and
  • | 3 Department of Neurosurgery, First Affiliated Hospital of Chinese PLA General Hospital, Beijing, People’s Republic of China
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Anterior clinoidectomy is a difficult yet essential technique in skull base surgery. Two main techniques (extradural and intradural) with multiple modifications have been proposed to increase efficiency and avoid complications. In this study, the authors sought to develop a hybrid technique based on localization of the optic strut (OS) to combine the advantages and avoid the disadvantages of both techniques.

Ten cadaveric specimens were prepared for surgical simulation. After a standard pterional craniotomy, the anterior clinoid process (ACP) was resected in 2 steps. The segment anterior to the OS was resected extradurally, while the segment posterior to the OS was resected intradurally. The proposed technique was performed in 6 clinical cases to evaluate its safety and efficiency.

Anterior clinoidectomy was successfully performed in all cadaveric specimens and all 6 patients by using the proposed technique. The extradural phase enabled early decompression of the optic nerve while avoiding the adjacent internal carotid artery. The OS was drilled intradurally under direct visualization of the adjacent neurovascular structures. The described landmarks were easily identifiable and applicable in the surgically treated patients. No operative complication was encountered.

A proposed 2-step hybrid technique combines the advantages of the extradural and intradural techniques while avoiding their disadvantages. This technique allows reduced intradural drilling and subarachnoid bone dust deposition. Moreover, the most critical part of the clinoidectomy—that is, drilling of the OS and removal of the body of the ACP—is left for the intradural phase, when critical neurovascular structures can be directly viewed.

ABBREVIATIONS

ACP = anterior clinoid process; ACTH = anterior clinoidectomy using a 2-step hybrid; ICA = internal carotid artery; LSW = lesser sphenoid wing; OC = optic canal; OphA = ophthalmic artery; OS = optic strut; SOF = superior orbital fissure.

Anterior clinoidectomy is a difficult yet essential technique in skull base surgery. Two main techniques (extradural and intradural) with multiple modifications have been proposed to increase efficiency and avoid complications. In this study, the authors sought to develop a hybrid technique based on localization of the optic strut (OS) to combine the advantages and avoid the disadvantages of both techniques.

Ten cadaveric specimens were prepared for surgical simulation. After a standard pterional craniotomy, the anterior clinoid process (ACP) was resected in 2 steps. The segment anterior to the OS was resected extradurally, while the segment posterior to the OS was resected intradurally. The proposed technique was performed in 6 clinical cases to evaluate its safety and efficiency.

Anterior clinoidectomy was successfully performed in all cadaveric specimens and all 6 patients by using the proposed technique. The extradural phase enabled early decompression of the optic nerve while avoiding the adjacent internal carotid artery. The OS was drilled intradurally under direct visualization of the adjacent neurovascular structures. The described landmarks were easily identifiable and applicable in the surgically treated patients. No operative complication was encountered.

A proposed 2-step hybrid technique combines the advantages of the extradural and intradural techniques while avoiding their disadvantages. This technique allows reduced intradural drilling and subarachnoid bone dust deposition. Moreover, the most critical part of the clinoidectomy—that is, drilling of the OS and removal of the body of the ACP—is left for the intradural phase, when critical neurovascular structures can be directly viewed.

ABBREVIATIONS

ACP = anterior clinoid process; ACTH = anterior clinoidectomy using a 2-step hybrid; ICA = internal carotid artery; LSW = lesser sphenoid wing; OC = optic canal; OphA = ophthalmic artery; OS = optic strut; SOF = superior orbital fissure.

In Brief

The authors found a practical intraoperative landmark to localize the optic strut during anterior clinoidectomy and used it as the basis for performing anterior clinoidectomy in two steps: extradural phase and intradural phase. This anatomically based technique can increase the safety of anterior clinoidectomy by providing easily identifiable landmarks and reducing intradural bone drilling, which could put the adjacent neurovauscular structures at risk.

Anterior clinoidectomy may be required to access lesions at the central skull base.9,10,16,25,30,39 However, removal of the anterior clinoid process (ACP) is technically demanding because of its proximity to eloquent structures such as the optic nerve or internal carotid artery (ICA), the variability of adjacent bony anatomy, and the complexity of dural reflections in the region.21,24,26,32 Several authors have described the relevant anatomy and the technical nuances of anterior clinoidectomy.5,17,18,24,38,45 Two main techniques have been defined for anterior clinoidectomy: extradural and intradural.11,28–30 Both techniques are widely used and have proponents based on each procedure’s relative advantages. In addition, many authors have proposed various modifications of these techniques (including different instrument utilizations) to increase safety.3,4,6,13,23,29,30,34–36,40,43,44,46 Despite the several advantages and limitations described for each technique, there is no evidence to support a technical preference. The main disadvantage of the extradural anterior clinoidectomy is the lack of direct visual control of critical adjacent neurovascular anatomy (that is, ICA and optic nerve).12,23,27 On the other hand, the intradural anterior clinoidectomy requires exquisite drilling skills to remove the anterior clinoid near eloquent structures directly exposed (that is, frontal and temporal lobes, ICA, and optic nerve).3,9,16,44

Specifically, drilling of the optic strut (OS) is one of the riskiest maneuvers during an anterior clinoidectomy. The OS is a bony ridge that spans between the optic canal (OC) and the superior orbital fissure (SOF). Superior and medial to the OS is the optic nerve and ophthalmic artery (OphA), while the ICA ascends just posterior and inferior to it (Fig. 1).5,13,32 Understanding the location and orientation of the OS is particularly difficult during extradural clinoidectomy because this bridge of bone lies beyond the ACP.13,22 Likewise, understanding the OS during an intradural clinoidectomy may be challenging because of its variable shape and orientation13,19 and lack of a “see-through” image, which makes for difficult anatomical judgment as drilling progresses toward the body of the sphenoid bone. In addition, an unusual origin and course of the OphA can increase the risk.33 To the best of our knowledge, there is not a reliable landmark to estimate the location of the OS during an anterior clinoidectomy in the literature.

FIG. 1.
FIG. 1.

A: Right oblique view of the sphenoid bone showing the bony anatomy of the paraclinoid area. The anterior clinoid process (ACP) is a medial continuation of the lesser sphenoid wing (LSW). The superior orbital fissure (SOF; area surrounded by dashed line) lies between the LSW and the greater sphenoid wing (GSW). The optic strut (OS; that is, the posterior root of the LSW) is a bony bridge between the optic canal (OC; asterisk) and the SOF. The roof of the OC is the medial continuation of the anterior root of the LSW that blends into the planum sphenoidale medially. B: Cadaveric dissection of the right cavernous sinus and paraclinoid area after complete removal of the ACP. The OS is drilled out (asterisk) to open the small space between the optic nerve (ON) and the ICA. The clinoidal segment of the ICA lies between the proximal dural ring (PDR) and distal dural ring (DDR). The oculomotor nerve runs just below the PDR to exit the cavernous sinus and enter the SOF. III = oculomotor nerve; IV = trochlear nerve; VI = abducens nerve; ant. = anterior; DS = dorsum sellae; FR = foramen rotundum; GG = Gasserian ganglion; PCA = posterior cerebral artery; PCP = posterior clinoid process; seg. = segment; V1 = first division of trigeminal nerve; V2 = second division of trigeminal nerve; V3 = third division of trigeminal nerve. Figure is available in color online only.

In the current report, we present a combined modification of the extradural and intradural clinoidectomy techniques, what we call an “anterior clinoidectomy using a 2-step hybrid” (ACTH) technique. We based our technique on early localization of the OS. We aimed to combine the advantages of the extradural and intradural techniques, while avoiding the disadvantages of both techniques as much as possible. We performed our proposed technique first in cadaveric specimens and later in a series of patients requiring anterior clinoidectomy as part of their surgical intervention, to assess its safety.

Methods

Bony Anatomy of the OS

Fifteen dry skulls were assessed bilaterally to study the anatomy of the SOF, ACP, and OS, as well as to establish key spatial relations with surgical significance. A line was projected from the lateral end point of the SOF to the anteromedial corner of the OC (Fig. 2 line A). Next, a second line (Fig. 2 line B) was drawn parallel to line A, from the posterolateral corner of the OC to intersect with the lesser sphenoid wing (LSW). The relationship between line B and the junction between the OS and the ACP was recorded as intersecting, posterior, or anterior.

FIG. 2.
FIG. 2.

Oblique view of the bony skull base. Line A (red dashed line) is projected laterally, from the anteromedial corner of the orifice of the OC to the lateral end of the SOF. Line B (green dashed line) is parallel to line A. It is projected from the posterolateral corner of the orifice of the OC to intersect laterally with the LSW. Line B corresponds to the OS, which attaches to the ACP from inferior. During the ACTH technique, the trapezoid area between the 2 lines is drilled extradurally, while the remainder of the ACP is drilled intradurally. See Fig. 1 legend for abbreviations. Figure is available in color online only.

Anterior Clinoidectomy Using a 2-Step Hybrid Technique

Ten adult cadaveric specimens were prepared for surgical simulation using our previously published embalming protocol.2 The head was secured to the surgical table with a 3-pin clamp (Mizuho America Inc.), with the neck flexed and the head rotated 45° to the contralateral side. A standard pterional craniotomy was performed, followed by flattening of the sphenoid ridge. The meningo-orbital band was incised to allow better exposure of the LSW (Fig. 3 and Video 1).

VIDEO 1. Clip showing cadaveric surgical simulation of the ACTH technique. Copyright Michael T. Lawton. Published with permission. Click here to view.

FIG. 3.
FIG. 3.

Steps of the ACTH technique performed on the right side of a cadaveric specimen. A: A standard pterional craniotomy with flattening of the sphenoid ridge is completed. B: The meningo-orbital band (containing the meningo-orbital artery) is cut to facilitate retraction of the temporal dura from the sphenoid wings. The lateral end of the meningo-orbital band marks the lateral end of the SOF. C: The frontal dura is elevated from the orbital roof to expose the posterior orifice of the OC. Line A (dashed yellow line) is projected from the anteromedial corner of the OC (red arrow) to the lateral end of the SOF (yellow arrow). Line B (dashed green line) is projected laterally from the posterolateral corner of the OC (green arrow), parallel to line A. D: The bony area between lines A and B is drilled extradurally. This maneuver resects the anterior fragment of the ACP and unroofs the OC. E: The dura is opened, and the paraclinoid region is exposed after a sylvian fissure split. Sharp cuts are placed over the ACP area (dashed white lines) to expose the posterior fragment (that is, the body) of the ACP. F: The most anterior part of this remaining bony fragment corresponds to the OS and is drilled carefully. G: At this point, the ACP is disconnected from all of its attachments to the sphenoid bone and can be resected en bloc. H: Final view after completion of the anterior clinoidectomy. The clinoidal segment of the ICA is exposed between the proximal (dashed green line) and distal (dashed red line) dural rings. a. = artery; n. = nerve. See Fig. 1 legend for additional abbreviations. Figure is available in color online only.

The frontal dura was elevated from the orbital roof to expose the optic foramen. In addition, the temporal dura was elevated from the greater sphenoid wing (GSW) in the middle cranial fossa. Next, the anterior attachments of the ACP to both the OC and the LSW were exposed. Then, the ACP was removed in 2 stages: the extradural and the intradural.

Extradural Stage

The anterior root of the ACP was disconnected using lines A and B. First, the anteromedial corner of the OC was identified, and line A was projected to the lateral-most point of the meningo-orbital band, which corresponded to the lateral end point of the SOF (this was double-checked with a Rhoton dissector). Next, the posterolateral corner of the OC was identified, and line B was projected parallel to line A. The first stage of the ACTH technique was completed by drilling extradurally within the trapezoid area bounded by lines A and B (Fig. 3). This maneuver detached the ACP from both the roof of the OC (that is, anterior root of the ACP) and the LSW. No extradural drilling was performed posterior to line B.

Intradural Stage

Next, the dura was opened, and the sylvian fissure was dissected. A longitudinal incision was placed on the body of the ACP from its tip to reach the region of the drilling at line B. The incision was then tailored into a Y shape to expose the body of the ACP (Fig. 3). Under direct visual control of the adjacent neurovascular structures, the OS and the remainder of the ACP were drilled intradurally. At the end, the ICA, the optic nerve, and the lateral opticocarotid recess were exposed. In addition, the reliability of line B as a landmark for localizing the OS was assessed in the simulated surgical setting.

Clinical Case Series

To assess the clinical safety and feasibility of the proposed technique, we performed the ACTH technique on a series of 6 patients requiring anterior clinoidectomy as part of the surgical strategy to address their intracranial pathology.

Results

The proposed 2-step hybrid technique for removal of the ACP was safely performed in all specimens by using line B as a landmark to localize the OS. In dry skulls, line B was found to intersect the OS (14 [47%] of 30) or was just anterior to it (16 [53%] of 30). Anterior clinoidectomy was successfully performed in all specimens using the ACTH technique. In all cadaveric specimens, line B reliably predicted the location of the OS and was never found posterior to the OS. Therefore, line B was used to infer the posterior limit of extradural ACP drilling, ensuring that the OS was never violated during this stage. At most, the anterior portion of the OS was drilled extradurally, leaving its posterior part for intradural removal. This strategy allowed safe intradural drilling of the OS as the adjacent neurovascular structures, including the OphA, were protected under direct vision. In addition, early decompression of the optic nerve was achieved during the extradural phase, which enabled easier intradural manipulation of the optic nerve to gain control over the origin and course of the OphA while the OS was drilled. En bloc removal of the body of the ACP was possible by drilling the OS early during the intradural drilling because it was previously detached from its anterior (the roof of the OC) and lateral roots (the LSW) during the extradural phase. As a significant portion of bone drilling was performed extradurally, intradural bone dust collection was minimal. Overall, the efficiency of intradural drilling was increased as the anterior and lateral roots were previously removed.

Clinical Experience

The ACTH technique was performed without complication in all 6 patients. The average age of the patients was 51 years (range 35–79 years). In 5 patients, the pathology was a paraclinoid aneurysm, whereas 1 patient had a basilar artery apex aneurysm (Table 1). In all patients, the relevant landmarks (lines A and B) were easily identified intraoperatively and were efficiently used to guide localization of the OS and direct the drilling. A case illustration is provided in Fig. 4 and Video 2.

VIDEO 2. Operative video demonstrating the ACTH technique in the case of a paraclinoid aneurysm. Copyright Michael T. Lawton. Published with permission. Click here to view.

TABLE 1.

Summary of patients reported in this study, undergoing ACTH technique as part of their surgical treatment strategy for aneurysm clipping

Case No.Age (yrs), SexPathologySurgical ApproachAneurysm Outcome/ Complication(s)
149, FLt ventral wall ICA aneurysm, rt dorsal wall ICA aneurysmLt pterional, lt ACTH*Obliterated/none
235, FRt SHA aneurysmRt pterional, rt ACTHObliterated/none
353, FLt OphA aneurysmLt pterional, ACTHObliterated/none
446, FRt OphA, rt MCA aneurysmRt pterional, ACTHObliterated/none
579, MBA apex aneurysmRt orbitozygomatic, ACTHObliterated/none
641, FRt OphA aneurysmRt pterional, ACTHObliterated/none

BA = basilar artery; MCA = middle cerebral artery; SHA = superior hypophyseal artery.

Bilateral aneurysms clipped through a unilateral approach.

FIG. 4.
FIG. 4.

Case 6. A 41-year-old woman was diagnosed with a progressively enlarging aneurysm (An.; white arrow, A) arising from the lateral aspect of the clinoid segment of the right ICA (red arrow, B). Note the right carotico-clinoid foramen on the right side (yellow arrow, C). The patient declined endovascular coiling and chose to proceed with surgical clipping. Through a right pterional craniotomy, the dura of the middle fossa was peeled away from the cavernous sinus after first cutting the meningo-orbital band. The OC (black arrow, D) was identified extradurally. The extradural portion of the ACP was removed to disarticulate it from its OC and LSW by using the guide of lines A and B (yellow dashed lines, E). The portion of the ACP posterior to line B (black arrow, E) was left for the intradural stage. The dura was then opened, and the sylvian fissure was widely split to separate frontal and temporal lobes. The dissection was taken down to the carotid cistern, where the dura over the clinoid was flapped and entered to connect the intra- and extradural spaces (F). The remaining anterior clinoid bone (G) was removed to expose the aneurysm (asterisk, H). The DDR (white arrow, H) was dissected, and the ophthalmic artery was identified. The aneurysm was clipped (I), sparing the ophthalmic artery. Postoperative CT angiograms (J and K) confirmed successful obliteration of the aneurysm. The patient recovered well and was neurologically intact after surgery. OA = ophthalmic artery. Figure is available in color online only.

Discussion

We report a novel surgical technique—the ACTH technique—to remove the ACP in 2 stages (extradural and intradural) based on reliable landmarks (lines A and B; Fig. 5). The evidence provided in this study validates the use of line B as a robust landmark to infer the position of the OS, regardless of surgical trajectory. Using this line as a landmark ensured that the posterior part of the OS was never drilled extradurally, which left removal of the posterior segment of the ACP (adjacent to the ICA) for the intradural stage and under direct visual control (Figs. 1 and 3). The described technique for ACP removal allows one to perform the relatively easy parts of the procedure (that is, unroofing the OC and detaching the ACP from the LSW) extradurally, while leaving the more difficult and relatively risky parts of the procedure (that is, drilling and removal of the ACP) for the intradural phase, when there is direct visual control over the adjacent neurovascular anatomy.

FIG. 5.
FIG. 5.

Artist’s illustration of the 2-step anterior clinoidectomy. Craniotomy and skin incision (A). Lines A and B (dashed black lines, B; see text for more information) are drawn based on localization of the OC and the lateral end of the SOF. Extradural stage of the technique (C and inset D). The MOB is cut, and the trapezoid area of bone between the 2 lines is drilled out. This stage unroofs the OC. The intradural stage of the technique is completed by placing cuts over the ACP dura (E–G). ACA = anterior cerebral artery; DistR = distal dural ring; MCA = middle cerebral artery; MOB = meningo-orbital band; OA = ophthalmic artery; ProxR = proximal dural ring. See Fig. 1 legend for additional abbreviations. Copyright Michael T. Lawton. Published with permission. Figure is available in color online only.

Rationale for Designing an Alternative Anterior Clinoidectomy Technique

In 1952, Hauser and Gass introduced the intradural ACP removal technique.14 In 1985, Dolenc proposed the extradural anterior clinoidectomy technique.11 Both techniques are widely accepted, and the selection of one over the other is based on surgeon preference. However, proponents of each technique also emphasize the relative advantages and disadvantages of each technique in relation to the other.3,9,12,15,41,44 The main advantage of the intradural technique is having all adjacent neurovascular structures under visual control while drilling.13,23,41 When clipping aneurysms of the ophthalmic segment of the ICA, the intradural technique allows for protection of the aneurysm dome, which can erode the ACP body.9,13,23,35,41

On the other hand, the intradural anterior clinoidectomy carries several disadvantages. Injury to the neurovascular structures is one of the most feared risks during power drilling of the ACP.3 This risk relates to both the total drilling time and the experience and dexterity of the surgeon. The latter challenge can undoubtedly be overcome by practice. However, even a small slip of the drill can lead to catastrophic situations.3,4,41 Moreover, postoperative headache can occur due to subarachnoid accumulation of bone dust. We believe the only way to overcome these problems is to maximally limit the time in which the drill is used in the intradural space.

The extradural technique has its own advantages and shortcomings. The main advantage is that ACP removal is entirely performed in the extradural space, allowing a layer of dura to protect the adjacent eloquent structures. However, the dura blocks the view of key neurovascular structures near the ACP. Additionally, the extradural clinoidectomy entails peeling the temporal dura propria from the lateral wall of the cavernous sinus along the entire length of the ACP, which can notoriously cause venous bleeding and/or potential damage to the nerves traveling in the sinus.

Advantages of the ACTH Technique

We propose a technique of 2-step hybrid anterior clinoidectomy that combines the advantages of both the extradural and the intradural clinoidectomy and increases overall safety and efficiency (Fig. 6). The proposed technique is based on correct localization of the OS, which divides the anterior clinoidectomy into 2 separate phases—extradural and intradural.

FIG. 6.
FIG. 6.

Diagram showing the relative advantages and disadvantages of the classic extradural and intradural clinoidectomy techniques. The ACTH combines the advantages and avoids the disadvantages of the former techniques. CCF = carotico-clinoid foramen; IOB = interosseous bridge. Figure is available in color online only.

Advantages of the Extradural Phase

In the extradural phase, the ACP is detached from its anterior root as well as its lateral attachment to the LSW. The OS is not removed during the extradural phase; therefore, the adjacent neurovascular structures are under direct visual control while intradural drilling is performed. By using the landmarks provided (that is, lines A and B), this phase can be efficiently performed and does not involve drilling near the OphA or the ICA (Fig. 5). The only structure that requires protection during the extradural phase is the optic nerve, which is already protected by the dura and can be seen directly.

Using the ACTH technique, most of the drilling is performed extradurally, and the total amount of intradural drilling is reduced. This greatly minimizes the risk of damage to adjacent neurovascular structures. Moreover, intradural drilling is reduced and the collection of bone dust in the intradural space is minimized, which may prove beneficial in reducing postoperative headaches.1,42 Furthermore, with the ACTH technique, peeling off the dura propria of the temporal lobe at the lateral wall of the cavernous sinus is minimal, potentially reducing venous bleeding and minimizing cranial nerve injury.

Advantages of the Intradural Phase

The intradural part of the ACTH technique is performed after the dura is opened and the sylvian fissure is split. The sylvian fissure split is an essential part of addressing lesions in the paraclinoid area. Therefore, in most cases, splitting the sylvian fissure is not an additional maneuver. At this point, the location of the OS is easily noticed by palpating the bony step created on the ACP after the extradural drilling. After placing a Y-shaped incision on the dura covering its area, the ACP can be easily drilled out or even removed en bloc after drilling the OS, which is the only remaining attachment of the ACP.

Drilling of the OS is one of the trickiest parts of performing an anterior clinoidectomy. Angled surgical trajectories can lead to the use of skewed drill orientations, which can lead to plunging into the ICA or the optic nerve. In the purely extradural and intradural clinoidectomy techniques, there are no reliable landmarks for estimating the location of the OS. The position of the OS relative to the sphenoid body, as well as its shape and angulation, is subject to variability.20 Despite this variability, line B can reliably help the surgeon avoid drilling the posterior extent of the OS extradurally, which prevents drilling adjacent to the ICA—not directly visible during the extradural phase of the clinoidectomy. Drilling along line B is also beneficial to guide intradural drilling because the location of the OS is already determined by the bony step created on the ACP after the extradural drilling.

With the proposed technique, the OS is drilled during the intradural phase, which has several advantages. Correct localization and intradural drilling of the OS can be critical when there is an unusual origin and/or course of the OphA. The OphA can originate from the clinoidal or cavernous segments of the ICA and pass through the OS or SOF to reach the orbit.33 In such cases, extradural drilling is associated with the risk of injuring the OphA because neither the OS nor the initial course of the OphA can be viewed extradurally. On the other hand, in the purely intradural technique, the possible origin of the OphA may be seen, although it usually requires extensive mobilization of the optic nerve. With the ACTH technique, decompression of the optic nerve is achieved early and safely (that is, extradurally), which helps with localization of the OphA origin in the intradural space. This is especially advantageous in paraclinoid vascular pathologies in which a direct visual of the ICA and OphA is necessary during the second stage of the ACTH technique. Correct localization of the OS also allows the surgeon to practice utmost care while drilling this bony landmark to protect a possible OphA passing through the OS. Conversely, with tumors of the medial sphenoid region, such as clinoid meningiomas, this advantage is less pronounced. This is mainly attributable to the fact that exposure of the OphA may not be necessary and that the extra space already created by the gradual tumor growth helps to complete an extradural clinoidectomy without major difficulties.

The ACTH Technique and Anatomical Variations of the ACP

Anatomical variations of the ACP can add difficulty and complications to a purely extradural clinoidectomy.31 The ACP is a variable structure in terms of its shape and dimensions.7 With longer ACPs, the extradural clinoidectomy becomes more difficult since it is necessary to peel the frontotemporal dura posteriorly, along the entire length of ACP, which can cause damage to underlying brain. The ACTH technique offers the advantage of a staged clinoidectomy. Therefore, regardless of the ACP length, the posterior (possibly elongated) extension of the ACP is left to intradural drilling, which is further facilitated by the sylvian fissure split that provides a better view of the ACP region. Intradural removal of the posterior part of the ACP has been previously advised.37 This is especially critical in cases of certain anatomical variations of the ACP, such as an interosseous bridge between the ACP and posterior clinoid process, which is found in about 5% of ACPs, or a carotico-clinoid foramen (that is, a bony bridge connecting the ACP tip to a middle clinoid process),31 which is seen in more than 14% of ACPs.7,8 Extradural anterior clinoidectomy is extremely dangerous in these cases because pulling the tip of the ACP blindly can carry the risk of transection of the ICA, oculomotor nerve, or optic apparatus.13,29,31 Again, the ACTH technique offers a safe alternative to the purely extradural clinoidectomy in such cases since these variations can be directly seen and addressed during the intradural phase of the ACTH technique (Fig. 4).

Conclusions

In this study, we propose a technique that uses specific landmarks to localize the OS during the anterior clinoidectomy. Using the proposed landmarks, we developed a 2-step hybrid anterior clinoidectomy technique to increase its safety and efficiency. This technique combines the advantages of the purely extradural and purely intradural clinoidectomy procedures while avoiding their disadvantages. Our preliminary clinical experience with the ACTH technique supports its use in relevant cases. Further clinical studies comparing the proposed technique with the traditional extradural and intradural clinoidectomy techniques will provide deeper insight into the ACTH technique’s relative advantages and disadvantages and may further delineate its role in skull base surgery.

Acknowledgments

We would like to express our sincere gratitude to the body donors and their families, who, through their altruism, made this project possible. We also thank Kenneth X. Probst for the illustration.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Lawton, Tayebi Meybodi. Acquisition of data: Lawton, Tayebi Meybodi, Yousef, Guo, García, Burkhardt. Analysis and interpretation of data: Lawton, Tayebi Meybodi, Yousef, García. Drafting the article: Tayebi Meybodi, Yousef, Tabani. Critically revising the article: Lawton, Tayebi Meybodi, Yousef, Guo, González Sánchez, García, Benet. Reviewed submitted version of manuscript: Lawton, Tayebi Meybodi, Yousef, Guo, González Sánchez, Tabani, García, Benet. Approved the final version of the manuscript on behalf of all authors: Lawton. Statistical analysis: Tayebi Meybodi, Yousef. Administrative/technical/material support: Lawton, Benet. Study supervision: Lawton.

Supplemental Information

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  • 13

    Froelich SC, Aziz KM, Levine NB, Theodosopoulos PV, van Loveren HR, Keller JT: Refinement of the extradural anterior clinoidectomy: surgical anatomy of the orbitotemporal periosteal fold. Neurosurgery 61 (5 Suppl 2):179186, 2007

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Hauser MJ, Gass H: Optic nerve pressure by aneurysm relieved by decompression of optic nerve; report of a case. AMA Arch Opthalmol 48:627631, 1952

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Heros RC: Anterior clinoidectomy. World Neurosurg 77:441442, 2012

  • 16

    Heros RC, Nelson PB, Ojemann RG, Crowell RM, DeBrun G: Large and giant paraclinoid aneurysms: surgical techniques, complications, and results. Neurosurgery 12:153163, 1983

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Inoue T, Rhoton AL Jr, Theele D, Barry ME: Surgical approaches to the cavernous sinus: a microsurgical study. Neurosurgery 26:903932, 1990

  • 18

    Joo W, Funaki T, Yoshioka F, Rhoton AL Jr: Microsurgical anatomy of the carotid cave. Neurosurgery 70 (2 Suppl Operative):300312, 2012

  • 19

    Kapur E, Mehić A: Anatomical variations and morphometric study of the optic strut and the anterior clinoid process. Bosn J Basic Med Sci 12:8893, 2012

  • 20

    Kerr RG, Tobler WD, Leach JL, Theodosopoulos PV, Kocaeli H, Zimmer LA, et al.: Anatomic variation of the optic strut: classification schema, radiologic evaluation, and surgical relevance. J Neurol Surg B Skull Base 73:424429, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Kim JM, Romano A, Sanan A, van Loveren HR, Keller JT: Microsurgical anatomic features and nomenclature of the paraclinoid region. Neurosurgery 46:670682, 2000

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22

    Kim JS, Lee SI, Jeon KD, Choi BS: The pterional approach and extradural anterior clinoidectomy to clip paraclinoid aneurysms. J Cerebrovasc Endovasc Neurosurg 15:260266, 2013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Kulwin C, Tubbs RS, Cohen-Gadol AA: Anterior clinoidectomy: description of an alternative hybrid method and a review of the current techniques with an emphasis on complication avoidance. Surg Neurol Int 2:140, 2011

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24

    Lee HW, Park HS, Yoo KS, Kim KU, Song YJ: Measurement of critical structures around paraclinoidal area: a cadaveric morphometric study. J Korean Neurosurg Soc 54:1418, 2013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Lee JH, Sade B, Park BJ: A surgical technique for the removal of clinoidal meningiomas. Neurosurgery 59 (1 Suppl 1):ONS108ONS114, 2006

    • Search Google Scholar
    • Export Citation
  • 26

    Lehmberg J, Krieg SM, Meyer B: Anterior clinoidectomy. Acta Neurochir (Wien) 156:415419, 2014

  • 27

    Mahmoud M, Nader R, Al-Mefty O: Optic canal involvement in tuberculum sellae meningiomas: influence on approach, recurrence, and visual recovery. Neurosurgery 67 (3 Suppl Operative):ons108ons119, 2010

    • Search Google Scholar
    • Export Citation
  • 28

    Nacar OA, Rodrıguez-Hernandez A, Ulu MO, Rodrıguez-Mena R, Lawton MT: Bilateral ophthalmic segment aneurysm clipping with one craniotomy: operative technique and results. Turk Neurosurg 24:937945, 2014

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29

    Noguchi A, Balasingam V, Shiokawa Y, McMenomey SO, Delashaw JB Jr: Extradural anterior clinoidectomy. Technical note. J Neurosurg 102:945950, 2005

  • 30

    Nutik SL: Removal of the anterior clinoid process for exposure of the proximal intracranial carotid artery. J Neurosurg 69:529534, 1988

  • 31

    Ota N, Tanikawa R, Miyazaki T, Miyata S, Oda J, Noda K, et al.: Surgical microanatomy of the anterior clinoid process for paraclinoid aneurysm surgery and efficient modification of extradural anterior clinoidectomy. World Neurosurg 83:635643, 2015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32

    Rhoton AL Jr: The cavernous sinus, the cavernous venous plexus, and the carotid collar. Neurosurgery 51 (4 Suppl):S375S410, 2002

  • 33

    Rhoton AL Jr: The orbit. Neurosurgery 51 (4 Suppl):S303S334, 2002

  • 34

    Romani R, Elsharkawy A, Laakso A, Kangasniemi M, Hernesniemi J: Complications of anterior clinoidectomy through lateral supraorbital approach. World Neurosurg 77:698703, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Romani R, Elsharkawy A, Laakso A, Kangasniemi M, Hernesniemi J: Tailored anterior clinoidectomy through the lateral supraorbital approach: experience with 82 consecutive patients. World Neurosurg 77:512517, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 36

    Sai Kiran NA, Furtado SV, Hegde AS: How I do it: anterior clinoidectomy and optic canal unroofing for microneurosurgical management of ophthalmic segment aneurysms. Acta Neurochir (Wien) 155:10251029, 2013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Sekhar LN: Comment on Coscarella E, Baskaya MK, Morcos JJ: An alternative extradural exposure to the anterior clinoid process: the superior orbital fissure as a surgical corridor. Neurosurgery 53:166, 2003

    • Search Google Scholar
    • Export Citation
  • 38

    Seoane E, Rhoton AL Jr, de Oliveira E: Microsurgical anatomy of the dural collar (carotid collar) and rings around the clinoid segment of the internal carotid artery. Neurosurgery 42:869886, 1998

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Sundt TM Jr, Piepgras DG: Surgical approach to giant intracranial aneurysms. Operative experience with 80 cases. J Neurosurg 51:731742, 1979

  • 40

    Takahashi JA, Kawarazaki A, Hashimoto N: Intradural en-bloc removal of the anterior clinoid process. Acta Neurochir (Wien) 146:505509, 2004

  • 41

    Tripathi M, Deo RC, Damodaran N, Suri A, Srivastav V, Baby B, et al.: Quantitative analysis of variable extent of anterior clinoidectomy with intradural and extradural approaches: 3-dimensional analysis and cadaver dissection. Neurosurgery 11 (Suppl 2):147161, 2015

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Weber JD, Samy RN, Nahata A, Zuccarello M, Pensak ML, Golub JS: Reduction of bone dust with ultrasonic bone aspiration: implications for retrosigmoid vestibular schwannoma removal. Otolaryngol Head Neck Surg 152:11021107, 2015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 43

    Yang Y, Wang H, Shao Y, Wei Z, Zhu S, Wang J: Extradural anterior clinoidectomy as an alternative approach for optic nerve decompression: anatomic study and clinical experience. Neurosurgery 59 (4 Suppl 2):ONS253ONS262, 2006

    • Search Google Scholar
    • Export Citation
  • 44

    Yonekawa Y, Ogata N, Imhof HG, Olivecrona M, Strommer K, Kwak TE, et al.: Selective extradural anterior clinoidectomy for supra- and parasellar processes. Technical note. J Neurosurg 87:636642, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 45

    Yoon BH, Kim HK, Park MS, Kim SM, Chung SY, Lanzino G: Meningeal layers around anterior clinoid process as a delicate area in extradural anterior clinoidectomy: anatomical and clinical study. J Korean Neurosurg Soc 52:391395, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 46

    Youssef AS, Abdel Aziz KM, Kim EY, Keller JT, Zuccarello M, van Loveren HR: The carotid-oculomotor window in exposure of upper basilar artery aneurysms: a cadaveric morphometric study. Neurosurgery 54:11811189, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • View in gallery

    A: Right oblique view of the sphenoid bone showing the bony anatomy of the paraclinoid area. The anterior clinoid process (ACP) is a medial continuation of the lesser sphenoid wing (LSW). The superior orbital fissure (SOF; area surrounded by dashed line) lies between the LSW and the greater sphenoid wing (GSW). The optic strut (OS; that is, the posterior root of the LSW) is a bony bridge between the optic canal (OC; asterisk) and the SOF. The roof of the OC is the medial continuation of the anterior root of the LSW that blends into the planum sphenoidale medially. B: Cadaveric dissection of the right cavernous sinus and paraclinoid area after complete removal of the ACP. The OS is drilled out (asterisk) to open the small space between the optic nerve (ON) and the ICA. The clinoidal segment of the ICA lies between the proximal dural ring (PDR) and distal dural ring (DDR). The oculomotor nerve runs just below the PDR to exit the cavernous sinus and enter the SOF. III = oculomotor nerve; IV = trochlear nerve; VI = abducens nerve; ant. = anterior; DS = dorsum sellae; FR = foramen rotundum; GG = Gasserian ganglion; PCA = posterior cerebral artery; PCP = posterior clinoid process; seg. = segment; V1 = first division of trigeminal nerve; V2 = second division of trigeminal nerve; V3 = third division of trigeminal nerve. Figure is available in color online only.

  • View in gallery

    Oblique view of the bony skull base. Line A (red dashed line) is projected laterally, from the anteromedial corner of the orifice of the OC to the lateral end of the SOF. Line B (green dashed line) is parallel to line A. It is projected from the posterolateral corner of the orifice of the OC to intersect laterally with the LSW. Line B corresponds to the OS, which attaches to the ACP from inferior. During the ACTH technique, the trapezoid area between the 2 lines is drilled extradurally, while the remainder of the ACP is drilled intradurally. See Fig. 1 legend for abbreviations. Figure is available in color online only.

  • View in gallery

    Steps of the ACTH technique performed on the right side of a cadaveric specimen. A: A standard pterional craniotomy with flattening of the sphenoid ridge is completed. B: The meningo-orbital band (containing the meningo-orbital artery) is cut to facilitate retraction of the temporal dura from the sphenoid wings. The lateral end of the meningo-orbital band marks the lateral end of the SOF. C: The frontal dura is elevated from the orbital roof to expose the posterior orifice of the OC. Line A (dashed yellow line) is projected from the anteromedial corner of the OC (red arrow) to the lateral end of the SOF (yellow arrow). Line B (dashed green line) is projected laterally from the posterolateral corner of the OC (green arrow), parallel to line A. D: The bony area between lines A and B is drilled extradurally. This maneuver resects the anterior fragment of the ACP and unroofs the OC. E: The dura is opened, and the paraclinoid region is exposed after a sylvian fissure split. Sharp cuts are placed over the ACP area (dashed white lines) to expose the posterior fragment (that is, the body) of the ACP. F: The most anterior part of this remaining bony fragment corresponds to the OS and is drilled carefully. G: At this point, the ACP is disconnected from all of its attachments to the sphenoid bone and can be resected en bloc. H: Final view after completion of the anterior clinoidectomy. The clinoidal segment of the ICA is exposed between the proximal (dashed green line) and distal (dashed red line) dural rings. a. = artery; n. = nerve. See Fig. 1 legend for additional abbreviations. Figure is available in color online only.

  • View in gallery

    Case 6. A 41-year-old woman was diagnosed with a progressively enlarging aneurysm (An.; white arrow, A) arising from the lateral aspect of the clinoid segment of the right ICA (red arrow, B). Note the right carotico-clinoid foramen on the right side (yellow arrow, C). The patient declined endovascular coiling and chose to proceed with surgical clipping. Through a right pterional craniotomy, the dura of the middle fossa was peeled away from the cavernous sinus after first cutting the meningo-orbital band. The OC (black arrow, D) was identified extradurally. The extradural portion of the ACP was removed to disarticulate it from its OC and LSW by using the guide of lines A and B (yellow dashed lines, E). The portion of the ACP posterior to line B (black arrow, E) was left for the intradural stage. The dura was then opened, and the sylvian fissure was widely split to separate frontal and temporal lobes. The dissection was taken down to the carotid cistern, where the dura over the clinoid was flapped and entered to connect the intra- and extradural spaces (F). The remaining anterior clinoid bone (G) was removed to expose the aneurysm (asterisk, H). The DDR (white arrow, H) was dissected, and the ophthalmic artery was identified. The aneurysm was clipped (I), sparing the ophthalmic artery. Postoperative CT angiograms (J and K) confirmed successful obliteration of the aneurysm. The patient recovered well and was neurologically intact after surgery. OA = ophthalmic artery. Figure is available in color online only.

  • View in gallery

    Artist’s illustration of the 2-step anterior clinoidectomy. Craniotomy and skin incision (A). Lines A and B (dashed black lines, B; see text for more information) are drawn based on localization of the OC and the lateral end of the SOF. Extradural stage of the technique (C and inset D). The MOB is cut, and the trapezoid area of bone between the 2 lines is drilled out. This stage unroofs the OC. The intradural stage of the technique is completed by placing cuts over the ACP dura (E–G). ACA = anterior cerebral artery; DistR = distal dural ring; MCA = middle cerebral artery; MOB = meningo-orbital band; OA = ophthalmic artery; ProxR = proximal dural ring. See Fig. 1 legend for additional abbreviations. Copyright Michael T. Lawton. Published with permission. Figure is available in color online only.

  • View in gallery

    Diagram showing the relative advantages and disadvantages of the classic extradural and intradural clinoidectomy techniques. The ACTH combines the advantages and avoids the disadvantages of the former techniques. CCF = carotico-clinoid foramen; IOB = interosseous bridge. Figure is available in color online only.

  • 1

    Barnett SL, Whittemore B, Thomas J, Samson D: Intradural clinoidectomy and postoperative headache in patients undergoing aneurysm surgery. Neurosurgery 67:906910, 2010

    • Crossref
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  • 2

    Benet A, Rincon-Torroella J, Lawton MT, González Sánchez JJ: Novel embalming solution for neurosurgical simulation in cadavers. J Neurosurg 120:12291237, 2014

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  • 3

    Chang DJ: The “no-drill” technique of anterior clinoidectomy: a cranial base approach to the paraclinoid and parasellar region. Neurosurgery 64 (3 Suppl):ons96ons106, 2009

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  • 4

    Chang HS, Joko M, Song JS, Ito K, Inoue T, Nakagawa H: Ultrasonic bone curettage for optic canal unroofing and anterior clinoidectomy. Technical note. J Neurosurg 104:621624, 2006

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    Collignon F, Link M: Paraclinoid and cavernous sinus regions: measurement of critical structures relevant for surgical procedure. Clin Anat 18:39, 2005

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    Coscarella E, Başkaya MK, Morcos JJ: An alternative extradural exposure to the anterior clinoid process: the superior orbital fissure as a surgical corridor. Neurosurgery 53:162167, 2003

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    • PubMed
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    • Export Citation
  • 7

    da Costa M, Santos B, Paz D, Rodrigues T, Abdala N, Centeno R, et al.: Anatomical variations of the anterior clinoid process: a study of 597 skull base computerized tomography scans. Oper Neurosurg 12:289297, 2016

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  • 8

    Dagtekin A, Avci E, Uzmansel D, Kurtoglu Z, Kara E, Uluc K, et al.: Microsurgical anatomy and variations of the anterior clinoid process. Turk Neurosurg 24:484493, 2014

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  • 9

    Day AL: Aneurysms of the ophthalmic segment. A clinical and anatomical analysis. J Neurosurg 72:677691, 1990

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    Day JD, Giannotta SL, Fukushima T: Extradural temporopolar approach to lesions of the upper basilar artery and infrachiasmatic region. J Neurosurg 81:230235, 1994

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    Dolenc VV: A combined epi- and subdural direct approach to carotid-ophthalmic artery aneurysms. J Neurosurg 62:667672, 1985

  • 12

    Fahlbusch R, Schott W: Pterional surgery of meningiomas of the tuberculum sellae and planum sphenoidale: surgical results with special consideration of ophthalmological and endocrinological outcomes. J Neurosurg 96:235243, 2002

    • Crossref
    • PubMed
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    • Export Citation
  • 13

    Froelich SC, Aziz KM, Levine NB, Theodosopoulos PV, van Loveren HR, Keller JT: Refinement of the extradural anterior clinoidectomy: surgical anatomy of the orbitotemporal periosteal fold. Neurosurgery 61 (5 Suppl 2):179186, 2007

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Hauser MJ, Gass H: Optic nerve pressure by aneurysm relieved by decompression of optic nerve; report of a case. AMA Arch Opthalmol 48:627631, 1952

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Heros RC: Anterior clinoidectomy. World Neurosurg 77:441442, 2012

  • 16

    Heros RC, Nelson PB, Ojemann RG, Crowell RM, DeBrun G: Large and giant paraclinoid aneurysms: surgical techniques, complications, and results. Neurosurgery 12:153163, 1983

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Inoue T, Rhoton AL Jr, Theele D, Barry ME: Surgical approaches to the cavernous sinus: a microsurgical study. Neurosurgery 26:903932, 1990

  • 18

    Joo W, Funaki T, Yoshioka F, Rhoton AL Jr: Microsurgical anatomy of the carotid cave. Neurosurgery 70 (2 Suppl Operative):300312, 2012

  • 19

    Kapur E, Mehić A: Anatomical variations and morphometric study of the optic strut and the anterior clinoid process. Bosn J Basic Med Sci 12:8893, 2012

  • 20

    Kerr RG, Tobler WD, Leach JL, Theodosopoulos PV, Kocaeli H, Zimmer LA, et al.: Anatomic variation of the optic strut: classification schema, radiologic evaluation, and surgical relevance. J Neurol Surg B Skull Base 73:424429, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Kim JM, Romano A, Sanan A, van Loveren HR, Keller JT: Microsurgical anatomic features and nomenclature of the paraclinoid region. Neurosurgery 46:670682, 2000

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22

    Kim JS, Lee SI, Jeon KD, Choi BS: The pterional approach and extradural anterior clinoidectomy to clip paraclinoid aneurysms. J Cerebrovasc Endovasc Neurosurg 15:260266, 2013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Kulwin C, Tubbs RS, Cohen-Gadol AA: Anterior clinoidectomy: description of an alternative hybrid method and a review of the current techniques with an emphasis on complication avoidance. Surg Neurol Int 2:140, 2011

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24

    Lee HW, Park HS, Yoo KS, Kim KU, Song YJ: Measurement of critical structures around paraclinoidal area: a cadaveric morphometric study. J Korean Neurosurg Soc 54:1418, 2013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Lee JH, Sade B, Park BJ: A surgical technique for the removal of clinoidal meningiomas. Neurosurgery 59 (1 Suppl 1):ONS108ONS114, 2006

    • Search Google Scholar
    • Export Citation
  • 26

    Lehmberg J, Krieg SM, Meyer B: Anterior clinoidectomy. Acta Neurochir (Wien) 156:415419, 2014

  • 27

    Mahmoud M, Nader R, Al-Mefty O: Optic canal involvement in tuberculum sellae meningiomas: influence on approach, recurrence, and visual recovery. Neurosurgery 67 (3 Suppl Operative):ons108ons119, 2010

    • Search Google Scholar
    • Export Citation
  • 28

    Nacar OA, Rodrıguez-Hernandez A, Ulu MO, Rodrıguez-Mena R, Lawton MT: Bilateral ophthalmic segment aneurysm clipping with one craniotomy: operative technique and results. Turk Neurosurg 24:937945, 2014

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29

    Noguchi A, Balasingam V, Shiokawa Y, McMenomey SO, Delashaw JB Jr: Extradural anterior clinoidectomy. Technical note. J Neurosurg 102:945950, 2005

  • 30

    Nutik SL: Removal of the anterior clinoid process for exposure of the proximal intracranial carotid artery. J Neurosurg 69:529534, 1988

  • 31

    Ota N, Tanikawa R, Miyazaki T, Miyata S, Oda J, Noda K, et al.: Surgical microanatomy of the anterior clinoid process for paraclinoid aneurysm surgery and efficient modification of extradural anterior clinoidectomy. World Neurosurg 83:635643, 2015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32

    Rhoton AL Jr: The cavernous sinus, the cavernous venous plexus, and the carotid collar. Neurosurgery 51 (4 Suppl):S375S410, 2002

  • 33

    Rhoton AL Jr: The orbit. Neurosurgery 51 (4 Suppl):S303S334, 2002

  • 34

    Romani R, Elsharkawy A, Laakso A, Kangasniemi M, Hernesniemi J: Complications of anterior clinoidectomy through lateral supraorbital approach. World Neurosurg 77:698703, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Romani R, Elsharkawy A, Laakso A, Kangasniemi M, Hernesniemi J: Tailored anterior clinoidectomy through the lateral supraorbital approach: experience with 82 consecutive patients. World Neurosurg 77:512517, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 36

    Sai Kiran NA, Furtado SV, Hegde AS: How I do it: anterior clinoidectomy and optic canal unroofing for microneurosurgical management of ophthalmic segment aneurysms. Acta Neurochir (Wien) 155:10251029, 2013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Sekhar LN: Comment on Coscarella E, Baskaya MK, Morcos JJ: An alternative extradural exposure to the anterior clinoid process: the superior orbital fissure as a surgical corridor. Neurosurgery 53:166, 2003

    • Search Google Scholar
    • Export Citation
  • 38

    Seoane E, Rhoton AL Jr, de Oliveira E: Microsurgical anatomy of the dural collar (carotid collar) and rings around the clinoid segment of the internal carotid artery. Neurosurgery 42:869886, 1998

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Sundt TM Jr, Piepgras DG: Surgical approach to giant intracranial aneurysms. Operative experience with 80 cases. J Neurosurg 51:731742, 1979

  • 40

    Takahashi JA, Kawarazaki A, Hashimoto N: Intradural en-bloc removal of the anterior clinoid process. Acta Neurochir (Wien) 146:505509, 2004

  • 41

    Tripathi M, Deo RC, Damodaran N, Suri A, Srivastav V, Baby B, et al.: Quantitative analysis of variable extent of anterior clinoidectomy with intradural and extradural approaches: 3-dimensional analysis and cadaver dissection. Neurosurgery 11 (Suppl 2):147161, 2015

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Weber JD, Samy RN, Nahata A, Zuccarello M, Pensak ML, Golub JS: Reduction of bone dust with ultrasonic bone aspiration: implications for retrosigmoid vestibular schwannoma removal. Otolaryngol Head Neck Surg 152:11021107, 2015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 43

    Yang Y, Wang H, Shao Y, Wei Z, Zhu S, Wang J: Extradural anterior clinoidectomy as an alternative approach for optic nerve decompression: anatomic study and clinical experience. Neurosurgery 59 (4 Suppl 2):ONS253ONS262, 2006

    • Search Google Scholar
    • Export Citation
  • 44

    Yonekawa Y, Ogata N, Imhof HG, Olivecrona M, Strommer K, Kwak TE, et al.: Selective extradural anterior clinoidectomy for supra- and parasellar processes. Technical note. J Neurosurg 87:636642, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 45

    Yoon BH, Kim HK, Park MS, Kim SM, Chung SY, Lanzino G: Meningeal layers around anterior clinoid process as a delicate area in extradural anterior clinoidectomy: anatomical and clinical study. J Korean Neurosurg Soc 52:391395, 2012

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 46

    Youssef AS, Abdel Aziz KM, Kim EY, Keller JT, Zuccarello M, van Loveren HR: The carotid-oculomotor window in exposure of upper basilar artery aneurysms: a cadaveric morphometric study. Neurosurgery 54:11811189, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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