REFINEMENT OF THE EXTRADURAL ANTERIORCLINOIDECTOMY: SURGICAL ANATOMY OF THEORBITOTEMPORAL PERIOSTEAL FOLD

OBJECTIVE: Extradural removal of the anterior clinoid process is technically chal-lenging because of the limited exposure. In our study of the extradural anterior cli-noidectomy, we describe anatomic details and landmarks to facilitate sectioning ofthe orbitotemporal periosteal fold and elevation of the temporal fossa dura from thesuperior orbital fissure. We assess the morbidity associated with these proceduresas well as compare the indications, advantages, and disadvantages of intra- versusextradural clinoidectomy.METHODS: Of five formalin-fixed cadaveric heads, four were used for cadaveric dis-sections and one was used for histological examination.RESULTS: Sectioning of the orbitotemporal periosteal fold revealed a cleavage planebetween the temporal fossa dura and a thin layer of connective tissue that covers the supe-rior orbital fissure. The lacrimal nerve coursed immediately medial to this surgicallycreated cleavage plane. The superior orbital vein crossed laterally under the cranialnerves, which pass through the superior orbital fissure. This vein is particularly vulner-able as it is composed only of endothelium and a basal membrane.CONCLUSION: Both intra- and extradural techniques for anterior clinoidectomy are impor-tant parts of the neurosurgical armamentarium. Sharp incision of the orbitotemporalperiosteal fold to increase the extradural exposure of the anterior clinoid process shouldbe made at the level of the sphenoid ridge and restricted to the periosteal bridge.Subsequent blunt elevation of the temporal fossa dura should be performed; however,peeling of the temporal fossa dura should be limited to avoid cranial nerve morbidity.

KEY WORDS: Anterior clinoidectomy, Extradural clinoidectomy, Orbitotemporal periosteal fold, Superiororbital fissure, Surgical technique

Neurosurgery 61[ONS Suppl 2]:ONS179–ONS186, 2007 DOI: 10.1227/01.NEU.0000280094.37231.D5

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Sebastien C. Froelich, M.D.Department of Neurosurgery,University of CincinnatiCollege of Medicine,Cincinnati, Ohio, andDepartment of Neurosurgery,University of Strasbourg,Strasbourg, France

Khaled M. Abdel Aziz, M.D.,Ph.D.Department of Neurosurgery,University of CincinnatiCollege of Medicine,Cincinnati, Ohio

Nicholas B. Levine, M.D.Department of Neurosurgery,University of CincinnatiCollege of Medicine,Cincinnati, Ohio

Philip V. Theodosopoulos, M.D.The Neuroscience Institute,Department of Neurosurgery,University of CincinnatiCollege of Medicine, andMayfield Clinic,Cincinnati, Ohio

Harry R. van Loveren, M.D.Department of Neurosurgery,University of South Florida,Tampa, Florida

Jeffrey T. Keller, Ph.D.The Neuroscience Institute,Department of Neurosurgery,University of CincinnatiCollege of Medicine, andMayfield Clinic,Cincinnati, Ohio

Reprint requests:Jeffrey T. Keller, Ph.D.,c/o Editorial Office,Department of Neurosurgery,University of CincinnatiCollege of Medicine,231 Albert Sabin Way, ML 0515,Cincinnati, OH 45267-0515.Email: editor@mayfieldclinic.com

Received, June 14, 2006.

Accepted, May 14, 2007.

Anterior clinoidectomy is a technicallychallenging procedure because of thedeep location of the anterior clinoid

process (ACP) and the presence of eloquentsurrounding structures. An intradural tech-nique is preferred by most neurosurgeonsbecause it provides wide exposure of theACP and direct observation of the internalcarotid artery (ICA) and optic nerve. Un-roofing the optic canal and drilling the ACPextradurally are more difficult tasks thatrequire precise knowledge of the three-dimensional anatomy of the ACP and sur-rounding neurovascular structures.

To increase the extradural exposure of theACP, Dolenc (12, 13) and Dolenc and Roger

(14) proposed division of the periosteal foldbetween the periorbita and the dura of tempo-ral fossa. He emphasized the risk of injuringthe cranial nerves that course through thesuperior orbital fissure (SOF). Recent reportspropose more extensive elevation of the tem-poral fossa dura from the SOF to increase theexposure of the ACP before drilling (4, 28). Inso doing, Cranial Nerves (CNs) III and IV andbranch V1, which course through the SOF, areexposed, and may be at risk of injury.

In our study, we provide anatomic detailsand useful landmarks for safely sectioning theorbitotemporal periosteal fold, elevating thetemporal fossa dura from the SOF, and per-forming anterior clinoidectomy. We assess the

ANATOMYSurgical Anatomy and Technique

morbidity associated with these procedures and compare theindications, advantages, and disadvantages of intra- versusextradural clinoidectomy.

MATERIALS AND METHODS

Five formalin-fixed cadaveric heads were injected with colored sili-cone in accordance with our previously described technique (34). Fourspecimens were used for cadaveric dissections, and one was used forhistological examination of the cavernous-orbital region.

Cadaveric DissectionEach head was fixed in a Mayfield headholder and positioned for a

standard pterional approach. An extradural anterior clinoidectomy wasperformed using an operative microscope (Zeiss Contraves; Zeiss, Inc.,Montpelier, MD). The clinoid space, anterior cavernous sinus, and SOFwere explored for additional anatomic study.

Histological ExaminationThe cavernous-orbital region including the ACP and optic canal was

removed en bloc and placed in 10% neutral-buffered formalin solutionfor 2 weeks. Each specimen was decalcified in Decalcifier I and II(Surgipath Medical Industries, Richmond, IL) for 4 weeks and thendehydrated, processed in a Citadel 2000 processor (Shandon,Pittsburgh, PA), and embedded in paraffin. Coronal sections of 6-μmthickness were obtained using a Reichert-Jung 2055 microtome(Cambridge Instruments, Heidelberg, Germany). Two of 15 sectionswere additionally processed by heating at 65�C for 98 hours, and werestained with hematoxylin-eosin and Masson’s trichrome, respectively.

RESULTS

The clinoid space is the surgically created space obtainedafter the subperiosteal resection of the ACP (8, 19, 22, 35).Precise knowledge of its limits and underlying eloquent struc-tures is mandatory for performance of anterior clinoidectomy.

Clinoid SpaceThe clinoid space is limited superiorly and laterally by the

dura that covers the superior and lateral aspects of the ACP. Itsmedial aspect is formed by the optic nerve sheath (Figs. 1 and2). Just below the optic nerve sheath is the inferior root of thelesser sphenoid wing (optic strut), which extends from the baseof the ACP to the body of the sphenoid bone (Fig. 2B). The sizeand shape of the optic strut varied in our specimens with diam-eter ranging from 3 to 7 mm and section shapes extending fromround to oval. The clinoid segment of the ICA runs along theposterior margin of the optic strut and is covered by a thinperiosteal membrane (Figs. 1A and 2A). The inferior surface ofthe clinoid space is formed by a thin layer of periosteum thatcovers the oculomotor nerve. The trochlear and frontal nervescross over the oculomotor nerve anteriorly (Fig. 1B).

SOF and Orbitotemporal Periosteal FoldAt the level of the SOF, the outer and inner layers of the lat-

eral wall of the cavernous sinus separate from one another (21).The inner layer, which is composed of the cranial nerve per-ineurium and surrounding connective tissue, extends with the

nerves into the posterior orbit. The outer layer is formed by thetemporal fossa dura (Fig. 2B). Along the lateral margin of theSOF, the periosteal layer of the dura mater is contiguous withthe periosteal layer of the periorbita. This bridge of periosteumat the lateral edge of the SOF appears in the surgical field as aperiosteal fold stretched between the periorbita and temporalfossa dura (Fig. 3A). The width of the periosteal fold variesaccording to the shape of the lateral end of the narrow part ofthe SOF, which ranges from round and large to thin and sharp.The length of the orbitotemporal periosteal fold corresponds tothe distance between the temporal fossa dura and periorbita.This length varies according to the bone thickness of the greatersphenoid wing that laterally closes the lateral narrow part ofthe SOF. A complex network of highly variable small duralveins, and eventually the orbitomeningeal artery, course intothe orbitotemporal fold. In one specimen, the orbitomeningealartery coursed through a distinct bony canal (Hyrtl’s canal)that is located lateral to the superolateral edge of the SOF.

Sectioning the orbitotemporal periosteal fold along the edgesof the SOF reveals a cleavage plane between the temporal fossadura and the inner layer of the lateral wall of the cavernoussinus (Fig. 3B) (7, 21). The lacrimal nerve runs tangentially tothe lateral narrow part of the SOF below the lesser wing of thesphenoid and immediately superior or superolateral to thesuperior orbital vein (SOV). The lacrimal nerve, which washardly dissectible from the SOV and thick surrounding connec-tive tissue, always lies immediately medial to this surgicallycreated cleavage plane (Fig. 2C).The distance between thisplane and the lacrimal nerves at the level of the orbitotemporalperiosteal fold varied from 1.2 to 4 mm.

The SOV exits the muscular cone between the lateral andsuperior rectus. It then laterally crosses under the annulus of

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A B

FIGURE 1. A superior view of the clinoid space. A, dura has been incisedover the superior aspect of the ACP. The ACP and orbital roof have beenremoved. B, the transparent layer of periosteum covering the inferioraspect of the ACP has been incised. CN III is overcrossed anteriorly by CNIV and the frontal branch of CN VI. OTPF, orbitotemporal periosteal fold.Courtesy of Mayfield Clinic, Cincinnati, OH.

Zinn and the CNs that pass through the SOF. At this point, theSOV wall is particularly fragile, because it is composed only ofendothelium and a basal membrane covered by the temporalfossa dura (Fig. 2C). Posteriorly, only a thin layer of connectivetissue, which is essentially composed of perineurium, sepa-rates this surgical plane from CNs III and IV and branch V1

(Fig. 2, A and B).

Extradural Extended Anterior Clinoidectomy: Surgical Technique and Landmarks

After the standard frontotemporal craniotomy is performed,the dura covering the middle and anterior cranial fossa is ele-vated from the greater sphenoid wing and the orbital roof. Thedura is progressively elevated from the sphenoid ridge medi-

ally toward the ACP, and thesphenoid ridge is drilled usinga high-speed diamond drill.

After the superolateral bonyedge of the SOF is opened, theorbitotemporal periosteal foldis visualized and incised usinga No. 15 blade. The incisionshould be made at the level ofthe sphenoid ridge to avoidinjury of the CNs coursingthrough the SOF, especially thelacrimal nerve (Fig. 2B). Thelevel of the incision determinesthe position of the cleavageplane into this multilayer con-

nective tissue dural wall that covers the SOF. The more medialthe incision of the orbitotemporal periosteal fold, the thinnerwill be the remaining dura that covers the CNs passing throughthe SOF. Incision of this fold also reveals the orbitomeningealartery that is divided. Coagulation of this artery should be min-imized because of its close proximity to the lacrimal nerve.

The cleavage plane created between the temporal fossa duraand the connective tissue covering the SOF is then extendedposteriorly to increase the exposure of the lateral and superioraspects of ACP (Fig. 4). Elevation of the dura should stop whenexposure of the ACP is considered sufficient for drilling.Depending on the size of the ACP, in most cases it is unneces-sary to extend the cleavage plane more posteriorly and uncoverCNs III and IV and branch V1 that pass through the SOF.

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FIGURE 2. Coronal histological sections of the right cavernous orbitalregion. Sections are at the levels of clinoidal segment C5 of the ICA (A), theoptic strut (B), and the lateral narrow part of the SOF (C). OA, ophthalmicartery; FN, frontal nerve; LN, lacrimal nerve, NcN, nasocilliary nerve; LSW,

lesser sphenoid wing; LRM, lateral rectus muscle; MRM, medial rectus mus-cle; IRM, inferior rectus muscle; GSW, greater sphenoid wing; SRM, supe-rior rectus muscle; SS, sphenoid sinus. Courtesy of Mayfield Clinic,Cincinnati, OH.

FIGURE 3. A frontotemporal approach depicts exposure of the ACP before (A) and after (B) release of the orbitotem-poral periosteal fold (OTPF) lateral to the lacrimal nerve. Courtesy of Mayfield Clinic, Cincinnati, OH.

The superior bony edge of the optic canal is then identified(Fig. 4B), and the dorsal and lateral walls of the optic canal areunroofed using a diamond drill under continuous irrigation(Fig. 4C). The last remnants of cortical bone can be removedwith a microdissector.

Once the optic canal is unroofed, the central cancellousbone of the ACP is removed, and the cortical bone is thinned.Care must be taken when the drilling is directed anterolater-ally to avoid damage of the underlying CN III. The optic strutis drilled anteromedially, inferior to the optic nerve sheath.With additional drilling in the posterior direction, the clinoidsegment of the ICA comes into view (Fig. 4D). After the ACPis freed from the optic strut, the clinoid tip becomes mobile.The clinoid tip is finally dissected from the petroclinoid andinterclinoid ligament and is carefully twisted and pulled outwith a microronguer.

DISCUSSIONAnterior clinoidectomy is a technically challenging proce-

dure that requires a clear understanding of its indications,

potential complications, and the advantages and disadvan-tages of extra- versus intradural clinoidectomy. Recent reportsdescribe sectioning of the orbitotemporal periosteal fold toincrease ACP exposure and thus facilitate extradural anteriorclinoidectomy (4, 28). In our cadaveric study, we restrictedincision of this fold to the periosteal bridge. Made at the levelof the sphenoid ridge, the incision was safely performed lat-eral to the lacrimal nerve. Thereafter, only blunt dissectionwas necessary to create a cleavage plane between the tempo-ral fossa dura and the connective tissue that covers the SOF.We discuss the potential morbidity associated with this surgi-cal step that exposes the contents of the SOF, including CNs IIIand IV and branch V1.

Indication of Anterior Clinoidectomy: Extradural versus Intradural Technique

Anterior clinoidectomy has been described as part of theapproach to ophthalmic and clinoidal segment aneurysms toimprove visualization of the aneurysm neck and ophthalmicartery and to establish proximal control of the ICA (5, 9, 12, 15,

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FIGURE 4. Extradural anterior clinoidectomy technique and section of theorbitotemporal periosteal fold (OTPF) using the right frontotemporalapproach. A, OTPF incision should be made at the level of the sphenoidridge to avoid injury to the CN coursing through the SOF. B, temporal

fossa dura is elevated from the contents of the SOF. C, optic canal is iden-tified and unroofed. D, ACP is freed from the optic strut and the clinoidtip is removed. LSW, lesser sphenoid wing. Courtesy of Mayfield Clinic,Cincinnati, OH.

18, 20, 23, 29–31, 39, 40). Partial anterior clinoidectomy mayalso be necessary for posterior communicating aneurysms toadditionally expose the aneurysm neck and the posterior com-municating artery, which may be obstructed by the ACP (30,40). The intradural technique is usually preferred as an intraop-erative option for exposing the aneurysm neck. Using this tech-nique, before drilling, the surgeon identifies CN II, the ICA,and the aneurysm, which may erode the ACP. The intraduraltechnique is also recommended when a caroticoclinoid fora-men is identified from computed tomographic scan before sur-gery. Anterior clinoidectomy and unroofing of the optic canalwith mobilization of the optic nerve and ICA have also beenused to increase the size of the opticocarotid triangle andcarotid oculomotor window for access to the interpeduncularcistern lesions and basilar bifurcation aneurysms (10, 16, 26, 37,41, 42). Both extra- and intradural techniques have been used,in accordance with the surgeon’s preference.

Anterior clinoidectomy has been described as part of theextradural cranial base approach to cavernous sinus lesions(12, 20, 35, 38). In such cases, the extradural technique is pre-ferred, because the neurovascular structures remain protected.However, indications for intracavernous surgery have beentempered during the last decade in response to advances inradiosurgery, which allow for durable control of meningiomaswith low morbidity rates and endovascular techniques that canbe used to treat intracavernous vascular lesions.

Finally, for patients with meningiomas that have a duralbase over the ACP, anterior clinoidectomy is indicated toremove hyperostotic bone that may give rise to recurrence (1,6, 32, 33). The extradural technique is advocated because itallows for early control of the dural base and feeding vesselsbefore tumor resection. For patients with large sphenocav-ernous or clinoidal meningiomas, the extradural techniquealso allows for early identification of the ICA and the opticnerve proximal to the tumor.

ComplicationsPerforming anterior clinoidectomy remains a challenging

task with potential complications owing to its deep locationbetween the ICA and CNs II and III. Injuries to CN II and IIIcan be caused by unexpected motion of the drill or by heat, inthe case of insufficient irrigation (24). Even without intraduralmanipulation of CN III, Nutik (29) reported that oculomotorparesis and/or palsy occurred postoperatively in 3 of 30patients. Nutik also conveyed that the superior division of theCN III, which lies close to the ACP, was more likely to beinjured. Yonekawa et al. (41) reported that decreased visualacuity and/or inferior visual field defects occurred in 3 of 40patients who underwent unroofing of the optic canal; similarly,Nutik (29) reports this complication occurred in 1 of 30patients. According to our study, CN IV and the frontal branchof CN V, which lies below the base of ACP, may also be at riskduring clinoidectomy.

Although reported rarely, the C5 segment of the ICA or aparaclinoidal aneurysm, especially when associated with bonyerosion of the ACP, can be injured during clinoidectomy (25,

27). According to Seoane et al. (36), the presence of an oph-thalmic artery coursing through the optic strut should not beoverlooked when the optic strut is being drilled. Lower mor-bidity rates have been recently reported in association with theuse of an ultrasonic bone curette. This tool does not spin, andit therefore offers better stability; additionally, it incorporates acooling irrigation system (3, 17).

Finally, opening of the sphenoid sinus or the ethmoid aircells during anterior clinoidectomy can lead to postoperativecerebrospinal fluid leak, meningitis, or pneumoencephalos.When the optic canal is unroofed, drilling medially to it shouldbe avoided because of the risk of entering the sphenoid sinus orethmoid air cells (2, 11). Pneumatization of the ACP can occuroccasionally through the optic strut and less often through thesuperior wall of the optic canal (2, 11). When an air cell isencountered, great care should be taken to keep the mucosaintact and to close the opening with muscle, bone wax, and/orfibrin glue.

Sectioning of the Orbitotemporal Periosteal FoldOne drawback of the extradural anterior clinoidectomy tech-

nique is the limited extent of elevation of the frontotemporaldura over the ACP. The trajectory of CN II and the exact posi-tion of the ICA may be difficult to ascertain before drilling, andthe space available for this procedure is particularly limited.The tip of the ACP, which firmly anchors to the inter- andpetroclinoid ligaments, is usually dissected blindly. Bleedingfrom the diploic veins and/or from the venous plexus sur-rounding the C5 segment of the ICA can also make the laststeps of the anterior clinoidectomy difficult.

Several authors have recently described the incision of theorbitotemporal periosteal fold at the level of the lateral edge ofthe SOF as a key step to increase the exposure of the ACP, thusfacilitating the extradural clinoidectomy (4, 28). Dolenc (12, 13)and Dolenc and Roger (14) first described this technical nuanceas part of the surgical approach to cavernous sinus lesions.With division of the orbitotemporal periosteal fold, the duramater can be further elevated from the superior and lateralaspects of the ACP. Cranial nerve III (below the inferolateralaspect of the ACP) and the intracranial entrance of the opticcanal are easily identified, thereby allowing for enhancedappreciation of the trajectory to CNs II and III before onebegins to drill. The clinoid tip can be removed under directvision rather than being dissected and removed blindly. Dolenc(12, 13) and Dolenc and Roger (14) emphasized that theorbitotemporal periosteal fold should be cut using curved scis-sors with the tips pointing posteriorly, and that its incisionshould not exceed 4 mm because of the risk of injury to thelacrimal branch of CN VI.

Using our technique, incision of this fold is restricted to theperiosteal bridge. When made at the level of the sphenoidridge, the incision can be safely performed lateral to thelacrimal nerve. Thereafter, only blunt dissection is necessaryto create a cleavage plane between the temporal fossa duraand the connective tissue that covers the SOF. In our cadavericspecimens, the lacrimal nerve coursed tangentially to the lat-

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eral part of the SOF, just medial to this surgically createdcleavage plane.

To reduce the risk of injury to the SOF contents, Coscarellaet al. (4) proposed that incision of the periosteal fold medial tothe foramen rotundum should be the first step in elevating thetemporal fossa dura covering the lateral aspect of the SOF.After they visualized the nerves passing through the SOF,Coscarella et al. divided the orbitotemporal periosteal fold.Noguchi et al. (28) also advocated peeling both the temporalfossa dura from the SOF and the anterior aspect of the cav-ernous sinus to increase the exposure of the ACP. In this sce-nario, elevation of the temporal fossa began at the lateral edgeof the SOF (as we also described). Neither of these groupsreported any morbidity associated with the elevation of thetemporal fossa dura from the SOF.

In our opinion, exposure of the SOF contents is unnecessarywhen an extradural anterior clinoidectomy is performed,unless peeling and removal of the outer layer of the cavernoussinus is planned for other purposes. We found that oneshould be careful when elevating the temporal fossa durafrom the SOF and the cavernous sinus, because it is some-times associated with postoperative transient diplopia andfacial numbness. Several factors may account for such mor-bidity, including traction of CNs III and IV and branch V1

when peeling the temporal fossa dura; ischemia caused bydisruption of the blood supply to these nerves; sectioning ofthe more superficial fascicules of CN VI during elevation ofthe temporal fossa dura from the SOF; and finally, the supe-rior orbital vein that drains into the anterior cavernous sinusis particularly vulnerable when the dura is peeled from theSOF. Use of coagulation to control the bleeding from this veincan also result in CN damage.

Therefore, when performing an extradural anterior clinoidec-tomy, the surgeon should stop the elevation of the dura whenadequate exposure of the ACP is achieved. Depending on theshape and volume of the ACP, visualization of CNs III and IVand branch V1 is unnecessary in most cases.

CONCLUSIONS

Anterior clinoidectomies, whether performed extra- orintradurally, are difficult procedures with limited indications,and each has its particular advantages and disadvantages.These techniques should be part of a surgeon’s armamentar-ium, especially for treating cranial base tumor and vascularlesions. When one is performing an extradural clinoidectomy,division of the orbitotemporal periosteal fold is a useful step toincrease exposure of the ACP. The sphenoid ridge at the levelof the superolateral edge of the SOF is a useful landmark forincision of this fold. The incision should be made at the level ofthe sphenoid ridge and parallel to the direction of the sphenoidridge, thereby entering a safe cleavage plane between the tem-poral fossa dura and the SOF contents. However, elevation ofthe temporal fossa dura over CNs III and IV and branch V1 thatpass through the SOF should be minimized because of poten-tial morbidity to these nerves.

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COMMENTS

Froelich et al. nicely describe relevant technical aspects of anterior cli-noidectomy. The review of technical issues and indication is thor-

ough, and the references were carefully selected. We do agree with theauthors that the opening of the orbitotemporal dural fold is a key partof the procedure. This can be complemented with a “mini peeling” ofthe anterior part of the lateral wall of the cavernous sinus, as recentlydescribed, to improve exposure and help the surgeon with respect tospatial orientation; this is especially the case for less-experienced neu-rosurgeons. This procedure, which was first reported by Dolenc andhas been subsequently reviewed by many authors, opens a major chap-ter of modern neurosurgery. The resection of the clinoid allows thesurgeon to safely enter the cavernous sinus. As the authors clearlypoint out, resection of meningiomas or secreting adenomas with inva-sion to the cavernous sinus is now less frequent as a result of the refine-ment of radiosurgery. Nevertheless, there are still some lesions withaggressive evolution despite the use of radiosurgery (such as chordomasand some aggressive prolactinomas that are refractory to dopaminergic

agonists), and in these selected cases, the neurosurgeon must offer asafe resection of the lesion. The advantages of clinoid resection aremultiple and include unroofing of the anteromedial triangle of the cav-ernous sinus; liberation of the optic nerve after removal of the opticcanal roof, opening of the falciform ligament and the optic nervesheath; and liberation of the carotid artery (after complete release of thedistal dural ring allows safe mobilization of the carotid artery) with lessrisk of laceration or thrombosis. In the case of large pituitary adenomaswith severe elongation of the optic pathway, we remove the anterior cli-noid invariably to improve visual outcome and achieve a radical resec-tion of the lesion, especially the portion medial to the ipsilateral carotidartery and beneath the optic nerve, which are usually blind spots dur-ing the conventional pterional transsylvian approach.

This is a nice description of anterior clinoidectomy that clearly dis-cusses most of the major surgical concepts to consider when dealingwith lesions of the paraclinoid region.

David Rojas-Zalazar Jorge MuraEvandro P. de OliveiraSão Paulo, Brazil

In this article, the authors have studied the “orbitotemporal periostealfold” and the extent to which it may be safely sectioned in perform-

ing extradural anterior clinoidectomy. The findings are quite useful.However, in performing clinoidectomy for intracranial aneurysms thatare located close to the clinoid process (e.g., clinoidal aneurysms, pos-terior paraclinoid aneurysms, giant paraclinoid aneurysms), I prefer touse an intradural technique. In such a situation, the orbitotemporalperiosteal fold and the dura mater over the clinoid may be maintainedas a layer and retracted medially with sutures, while the aneurysm isconcurrently under view intradurally. The clinoidectomy is still per-formed extradurally. A temporary occlusion of the cervical internalcarotid artery may sometimes be necessary while manipulating thebone pieces near the aneurysm.

Laligam N. SekharSeattle, Washington

Froelich et al. describe the anatomy and histology of the orbitotempo-ral periosteal fold and a technique for an extradural anterior cli-

noidectomy. The technique involves incising the orbitotemporalperiosteal fold at the level of the sphenoid ridge and using carefulblunt dissection to expose the anterior clinoid process. The contributionof Professor Dolenc to this field has been profound.

At our institution, we most frequently use an anterior clinoidectomy forophthalmic aneurysms. Recognizing that an extradural approach is reason-able, we prefer an intradural approach for several reasons. First, the degreeof anterior clinoidectomy required is best known at the time of aneurysmexposure, which enables us to avoid extra drilling and save time.Furthermore, aneurysm adhesions are best visualized from an intraduralapproach. For this application, we have found the ultrasonic claw dissec-tor (Synergetics, St. Charles, MN) to be a safe alternative to the air drill.

Andrew Little Robert F. Spetzler Phoenix, Arizona

Froelich et al. present resection of the anterior clinoid process (ACP),which is systematically and anatomically very correctly described. It

is true that for a long time, many neurosurgeons dealing with thepathologies in this region were reluctant to use the extradural approachand to perform clinoidectomy because there was too little space. This

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is why many of them preferred to perform partial clinoidectomy fromthe intradural side. With all due respect to these neurosurgeons, theintradural clinoidectomy, in particular for vascular lesions, should beavoided because it is too dangerous. We now have at hand a descrip-tion of the extended extradural approach with which the ACP is nicelyvisualized from the inferolateral side, so that the initial steps of drillingthe ACP start on the opposite side from the possible aneurysm and theusual position of the optic nerve and the internal carotid artery. Thisapproach has been repeatedly described and published (1–3, 5). If thisfact is not convincing, then the latest publication (4) does summarizemore than 2000 patients with pathologies at the central cranial base forwhom the anterior clinoidectomy was routinely performed. In all ofthis clinical work, not a single patient suffered any morbidity as aresult of ACP resection. The experience collected through experimen-tal, neuroanatomical, and in particular, clinical work, gives us sufficientexperience to objectively defend the extradural ACP resection asopposed to the intradural one.

Each individual patient requires detailed discussion and relevantconsideration of the underlying anatomical circumstances. Most impor-tant of these are pneumatization of the ACP, and/or pneumatization ofthe walls of the optic canal, as well as erosion of the ACP as a result ofpathologies (trigeminal schwannomas, aneurysms, parasellar heman-giomas) in contrast with hypertrophy of the ACP caused by ACPmeningiomas (in particular, en plaque meningiomas). There is nodoubt that in aneurysm pathology, the origin of the aneurysm as wellas the circumference of the ICA, from which the pathology originates,are important factors. Clinoidectomy should be performed from theopposite side to where the pathology is located, and this is only possi-ble when the ACP is sufficiently exposed by cutting the duplicature ofthe dura and connecting the temporal lobe and the periosteum of theorbital cavity, thereby providing safe passage to the neural and vascu-lar structures from the parasellar to the orbital space.

One can agree that ACP resection offers an important additionalcorridor to reach different pathologies in the central cranial base inaddition to the parasellar space and around the ACP. This is an impor-tant reason why all of the approaches to the pathologies at the dorsumsellae as well as in the retrosellar and clival regions and/or the regionof the oculomotor trigone and even more posteriorly require ACPresection. Personally, I’m convinced that without practical knowledgeof performing this procedure, every neurosurgeon will have problemsdealing with the pathologies in the central cranial base regions.

Again, personally, I wouldn’t describe the ACP resection as verydangerous. I would rather describe it as a difficult procedure thatrequires a lot of training via microanatomical dissections in the labora-tory to achieve the mandatory skill required to dare to perform it. Weshould not put fear into the bones of young neurosurgeons; we have toconvince them that they must acquire skill in the laboratory to acceptthe truth that everything is experience-dependent.

I would like to add that, despite the long list of references, the mostimportant (the Pioneer’s) is still missing.

Vinko V. Dolenc Ljubljana, Slovenia

1. Dolenc VV: Anatomy and Surgery of the Cavernous Sinus. Wien, Springer-Verlag,1989.

2. Dolenc VV: Frontotemporal epidural approach to trigeminal neurinomas. ActaNeurochir (Wien) 130: 55–65, 1994.

3. Dolenc VV: Intracavernous carotid artery aneurysms. in: Spetzler RF, Carter LP(eds): Neurovascular Surgery. New York: McGraw-Hill, 1995, pp 659–673.

4. Dolenc VV: Transcranial epidural approach to pituitary tumors extendingbeyond the sella. Neurosurgery 41: 542–552, 1997.

5. Dolenc VV, Rogers L: Microsurgical Anatomy and Surgery of the Central SkullBase. Wien, Springer-Verlag, 2003.

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