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1.  Measurement of Critical Structures around Paraclinoidal Area : A Cadaveric Morphometric Study 
Although removal of the anterior clinoid process (ACP) is essential surgical technique, studies about quantitative measurements of the space broadening by the anterior clinoidectomy are rare. The purposes of this study are to investigate the dimension of the ACP, to quantify the improved exposure of the parasellar space after extradural anterior clinoidectomy and to measure the correlation of each structure around the paraclinoidal area.
Eleven formalin-fixed Korean adult cadaveric heads were used and frontotemporal craniotomies were done bilaterally. The length of C6 segment of the internal carotid artery on its lateral and medial side and optic nerve length were checked before and after anterior clinoidectomy. The basal width and height of the ACP were measured. The relationships among the paraclinoidal structures were assessed. The origin and projection of the ophthalmic artery (OA) were investigated.
The mean values of intradural basal width and height of the ACP were 10.82 mm and 7.61 mm respectively. The mean length of the C6 lateral and medial side increased 49%. The mean length of optic nerve increased 97%. At the parasellar area, the lengths from the optic strut to the falciform liament, distal dural ring, origin of OA were 6.69 mm, 9.36 mm and 5.99 mm, respectively. The distance between CN III and IV was 11.06 mm.
With the removal of ACP, exposure of the C6 segments and optic nerve can expand 49% and 97%, respectively. This technique should be among a surgeon's essential skills for treating lesions around the parasellar area.
PMCID: PMC3772280  PMID: 24044074
Anterior clinoid process; Extradural anterior clinoidectomy; Optic strut; Ophthalmic segment
2.  Enhanced Exposure of Carotico-Oculomotor Triangle Following Extradural Anterior Clinoidectomy: A Comparative Anatomical Study 
Skull Base  2005;15(3):157-161.
Objective: To quantify and compare the carotico-oculomotor triangle (COT) area before and after extradural anterior clinoidectomy (AC). Methods: Ten cadaveric heads were dissected bilaterally. Before and after an extradural AC, the following points were measured: (1) the internal carotid artery (ICA) bifurcation to the tip of the anterior clinoid process (ACP) (A) and to the distal dural ring (A′), (2) the ICA bifurcation to the point where the oculomotor nerve becomes obscured by the tentorial fold (B) and to the porus oculomotoris after incision of the tentorial fold (B′), and (3) the tip of the ACP to the point where the oculomotor nerve becomes obscured by the tentorial incisura (C) and from the distal dural ring to the porus oculomotoris (C′). The area of the COT was calculated before and after AC (ΔABC and ΔA′B′C′, respectively). Results: The mean values were as follows: A: 9.15 ± 0.93 mm, A′: 13.45 ± 0.82 mm; B: 7.80 ± 1.24 mm, B′: 9.90 ± 1.21 mm; C: 7.15 ± 0.99 mm, C′: 9.3 ± 1.26 mm; ΔABC: 26.26 ± 6.05 mm2, ΔA′B′C′: 45.06 ± 8.92 mm2. Conclusions: Extradural AC enhances the exposure of the COT almost twofold. This increased exposure can be of significant help during resection of lesions of the parasellar and basilar apex regions.
PMCID: PMC1214701  PMID: 16175225
Anterior clinoid; carotico-oculomotor triangle; clinoidectomy; extradural
3.  Surgical Simulation of Extradural Anterior Clinoidectomy through the Trans-superior Orbital Fissure Approach Using a Dissectable Three-dimensional Skull Base Model with Artificial Cavernous Sinus 
Skull Base  2010;20(4):229-236.
Extradural anterior clinoidectomy via the trans-superior orbital fissure (SOF) approach can provide extensive exposure of the anterior clinoid process and safe drilling under direct view. This technique requires peeling of the dura propria of the temporal lobe from the lateral wall of the SOF. Therefore, cadaveric dissection is mandatory to acquire surgical technique. However, chances for cadaveric dissection are limited. We propose modification of our three-dimensional (3-D) skull base model made from surgically dissectable artificial bone with artificial cavernous sinus including multiple membranous layers and neurovascular structures to simulate extradural anterior clinoidectomy via the trans-SOF approach. The 3-D skull base model precisely reproduced the dura propria of the temporal lobe, periosteal bridge, and inner reticular layer in the cavernous sinus and SOF using silicone and varnish. The cranial nerves and blood vessels were made from rubber fibers and vinyl tube. Simulation of extradural anterior clinoidectomy via the trans-SOF approach could be performed on the model using a high-speed drill under the operating microscope. The steps of reconstruction of the skull base model and dissection promote clear understanding of the 3-D anatomy and techniques of extradural anterior clinoidectomy via the trans-SOF approach.
PMCID: PMC3023323  PMID: 21311615
Anterior clinoid process; superior orbital fissure; cavernous sinus; anterior clinoidectomy; training model
4.  Endoscopic endonasal posterior clinoidectomy 
Posterior clinoidectomy is a useful procedure for maximizing exposure to the interpeduncular cistern via transcranial approaches for basilar tip aneurysms and select intracranial tumors. The value of posterior clinoidectomy during endonasal endoscopic transclival surgery is not well described.
We performed endoscopic endonasal transsphenoidal extradural bilateral posterior clinoidectomy and dorsum sella removal on five silicon-injected cadaveric heads. The dorsum sella was split in the midline and removed from medial to lateral until the posterior clinoids were encountered. The posterior clinoid was dissected from the medial wall of the cavernous sinus and mobilized medially in order to detach it from the ligaments and carefully fractured it from the bony attachment to the petrous apex and carotid canal. Following this, the clival and dorsum sella dura was opened to expose the interpeduncular cistern and its contents.
The technical feasibility of endoscopic endonasal extradural posterior clinoidectomy was reproduced in all five cadaveric specimens. This technique was performed without damaging the vital structures, including preservation of the pituitary gland. After performing bilateral posterior clinoidectomy, the retrosellar dura was opened, allowing good visualization of the contents of the prepontine and interpeduncular cistern.
We describe the technique of endoscopic endonasal extradural posterior clinoidectomy. We believe this approach is best suited for retrosellar pathology located in the interpeduncular cistern and is a useful adjunct to the transclival approach to increase the field of view and maximize the extent of resection.
PMCID: PMC3385065  PMID: 22754729
Dorsum sella; endoscopic endonasal; extradural posterior clinoidectomy; interpeduncular cistern; posterior clinoid process; skull base
5.  Quantification of the Advantages of the Extended Frontal Approach to Skull Base 
Skull Base  2004;14(3):133-142.
This anatomic study evaluated the extent that a fronto-orbital osteotomy (FOO) added to a bilateral frontal craniotomy widened the exposure to the midline compartment of the anterior, middle, and posterior cranial fossae. The goal was to determine if osteotomy would significantly increase angles for two targets: the foramen magnum (FM) and anterior clinoid process (ACP). Stepwise dissections were performed on five cadaveric heads. A bilateral frontal craniotomy was made, followed by FOO. After the ethmoids were removed, the planum sphenoidale was drilled to enter the sphenoid sinus. Further drilling exposed the anterior clivus, which was drilled down to FM. Excellent exposure of the basilar artery, vertebral artery, and brain stem was achieved. With and without FOO, angles of exposure were measured for two targets: the ACP and FM. The angle of exposure after FOO increased markedly with an average gain of 76% for the ACP and of 80% for FM. Compared with a conventional bifrontal craniotomy, the addition of FOO increased the surgical exposure and minimized frontal lobe retraction for accessing lesions of the anterior, middle, and posterior cranial fossae.
PMCID: PMC1151683  PMID: 16145596
Brain tumor; extended frontal approach; operative approach; skull base; skull base tumor
6.  Posterior Clinoidectomy: Dural Tailoring Technique and Clinical Application 
Skull Base  2009;19(3):183-191.
The posterior clinoid process, a bony prominence at the superolateral aspect of the dorsum sellae, has a strategic importance in a transcavernous approach to basilar tip aneurysms. To further optimize this microsurgical technique during posterior clinoidectomy, we performed a cadaveric study of this regional anatomy, describe a technique called dural tailoring, and report initial results in the surgical treatment of upper basilar artery (BA) aneurysm. After 10 adult cadaver heads (silicone-injected) were prepared for dissection, a posterior clinoidectomy with dural tailoring was performed. The dura overlying the upper clivus was coagulated with bipolar electrocoagulation and incised. Stripping dura off the clivus and lateral reflection then exposed the ipsilateral posterior clinoid process and dorsum sellae, thus creating a dural flap. Posterior clinoidectomy with dural tailoring was then used in seven patients with upper BA aneurysms. Our stepwise modification of the posterior clinoidectomy with dural tailoring created a flap that afforded protection of the cavernous sinus and oculomotor nerve. During surgery, there were no recorded intraoperative injuries to neurovascular structures. One patient died postoperatively from morbidity related to severe-grade subarachnoid hemorrhage. Postoperative oculomotor nerve palsy occurred in 3 patients (43%). In all cases, the nerve was anatomically preserved and partial to complete recovery was recorded during the first postoperative year. This technique effectively provided exposure of retrosellar upper basilar aneurysms in seven patients (basilar tip 43% and superior cerebellar artery aneurysms 57%). Outcomes and safety are at least equivalent to or better than basilar aneurysm surgery performed without surgical adjuncts, presumably a less complex subset.
PMCID: PMC2702194  PMID: 19881898
Posterior clinoid; clinoidectomy; dural tailoring; basilar artery; oculomotor nerve
7.  Anterior clinoidectomy: Description of an alternative hybrid method and a review of the current techniques with an emphasis on complication avoidance 
Anterior clinoidectomy is a difficult but important part of surgery for a variety of parasellar, proximal carotid and central skull base pathologies. First developed intradurally nearly 60 years ago, the promotion of an extradural technique decades later offered an approach with a different set of difficulties, risks and benefits. Many recent studies have demonstrated that there is no consensus about the “correct side” of the dura from which to remove the anterior clinoid process in a number of pathologies. Here, we review and compare the current techniques for intra- and extradural clinoidectomy and describe a hybrid alternative technique.
We used a hybrid method to potentially engage the advantages of the intradural and extradural techniques. The hybrid method starts with an extradural sphenoid wing osteotomy to the level of the superior orbital fissure (SOF). The dura is then incised parallel to the sphenoid wing lateral to the SOF, and the need for further bony removal, including clinoidectomy, is assessed after gentle elevation of the frontal lobe and release of cerebrospinal fluid through opening the optico-carotid cisterns and inspection of the pathology in relation to the clinoid. Sylvian fissure may be dissected to relieve retraction on the frontal lobe.
The hybrid method allows an early identification of the optic nerve and its protection during clinoidectomy. The operator leaves the dura medial to the SOF intact and the clionoidectomy proceeds in an extradural fashion while intradural inspection periodically is performed to assess the extent of necessary extradural bony removal.
The hybrid method theoretically can be used as a versatile method under some circumstances. Cutting the dura along the sphenoid wing will prevent the dural layers from obscuring the clinoid and offers intradural visualization to monitor the lesion and potentially tailor bony removal.
PMCID: PMC3205487  PMID: 22059135
Clinoidectomy; complications; optic nerve; technical nuance
8.  Anterior clinoid mucocele presenting with orbital apex syndrome 
Pneumatized anterior clinoid process is a common anatomic variant. Mucocele formation is a known complication of clinoid drilling during certain intracranial operations; however, mucoceles of pneumatized anterior clinoid processes have been found to spontaneously occur.
Case Description:
A 44-year-old male presented with complaints of left-sided retro-orbital pain, double vision, and numbness over the upper face and scalp on the left side of 1-week duration. On examination, he was found to develop cranial nerve III, IV, and VI palsies with pupillary sparing, ophthalmic division cranial nerve V dysfunction, and eventually, the onset of vision loss.
We report a case of spontaneous anterior clinoid process mucocele presenting with orbital apex syndrome. This was treated successfully with anterior clinoidectomy for decompression.
PMCID: PMC3680997  PMID: 23772333
Anterior clinoid process; mucocele; orbital apex syndrome
9.  Microsurgical anatomical study of the frontotemporal-zygomatic arch approach to the superior petroclival region 
The aim of this study was to explore the microsurgical anatomy of the superior petroclival region, and thus provide an anatomical basis for operative approaches. The frontotemporal-orbitozygomatic approach was performed on 20 sides of 10 adult cadaver heads. In comparison to the range of the exposure with the removal of the anterior clinoid process, posterior clinoid process and part of the tip of the petrous bone, we measured the neurovascular course and their relation to the superior petroclival region. We found that the trochlear nerve goes through the edge of the tentorial marginal branch, taking 5.42 mm (4.26–6.96) away from the ophthalmic nerve. Exposing the arteria basilaris, above the middle piece the length of exposure is 15.52 mm (14.22–16.70), resulting in the posterior cerebral artery and the front part of the midbrain being completely exposed. There is little exposure on the front part of the pons and midbrain with a length of 5.6 mm (4.38–6.82). Removing the partial petrosal bones, the inferior segment of the basal artery is exposed, while 4 other nerves cab also be observed: Cranial, abducens, facial and vestibulocochlear. The frontotemporal-zygomatic arch approach can clearly expose the superior petroclival region. Obtaining more information on the relationship between the location of these structures, is therefore helpful in improving the safety and success of surgery in this region.
PMCID: PMC3440810  PMID: 22977646
frontotemporal-orbitozygomatic approach; superior petroclival region; microsurgical anatomy
10.  Extradural Total Petrous Apex Resection With Trigeminal Translocation for Improved Exposure of the Posterior Cavernous Sinus and Petroclival Region 
Skull base surgery  1996;6(2):95-103.
We have analyzed a strategy for improved exposure of the posterior cavernous sinus and petroclival region through an extradural subtemporal approach to be utilized in the removal of neoplastic processes with involvement of the apical petrous bone and posterior cavernous sinus. This surgical approach includes the following elements for improved exposure of the posterior cavernous sinus through the middle fossa corridor: (1) maximal extradural exposure and mobilization of the trigeminal nerve complex, allowing its elevation and anterior displacement, (2) complete extradural removal of the anterior petrous pyramid from the porus acousticus to the petrous apex under direct vision, (3) total exposure of the abducens nerve from the posterior fossa to its point of cross over the intracavernous carotid artery, and (4) wide extradural exposure of the cavernous carotid artery in the foramen lacerum region. This strategy can be combined with other related approaches; specifically, frontotemporal or posterior transpetrosal exposures for extensive lesions.
Microsurgical dissection and morphometric analysis were performed in 20 fixed cadaver specimens for the purposes of validating the method for clinical application and determining the key elements to maximization of exposure. The trigeminal complex could be anteromedially retracted 4.8 mm ± 1.3 (range = 3 to 6 mm) without skeletonization of V2 and V3. Liberating these two divisions from their bony canals to their first peripheral branch (10.4 mm ± 2.5 and 5.4 mm ± 1.1, respectively) resulted in increased mobilization an average of 9.1 mm ± 1.7 (7 to 14 mm). Further mobilization is achieved by dividing the attachment between the trigeminal connective tissue sheath and the fibrous carotid ring at the foramen lacerum. An average of 13.0 mm ± 3.1 (7 to 20 mm) of the posterior intracavernous carotid artery was exposed. Detailed microanatomic observations and a comprehensive morphometric analysis of the relevant anatomic relationships were made.
PMCID: PMC1656581  PMID: 17170983
11.  Anatomic Variation of Sphenoid Sinus and Related Structures in Libyan Population: CT Scan Study 
The Libyan Journal of Medicine  2008;3(3):128-133.
Sphenoid sinus is the most inaccessible paranasal sinus, enclosed within the sphenoid bone and intimately related to numerous vital neural and vascular structures. Anatomic variation of the sphenoid sinus is well documented and may complicate surgery in such a place.
To outline the surgically risky anatomic variants of the sphenoid sinus as well as the variable relationships between the sinus and related neurovascular structures, for the safe removal of intrasphenoid and pituitary lesions.
Materials and Methods
We undertook a prospective review of 300 paranasal sinus CT scans of Libyan patients; coronal CT scans were obtained by special parameter techniques. We assessed pneumatization of pterygoid process (PP), anterior clinoid process (ACP), and greater wing of sphenoid (GWS); we also examined protrusion and dehiscence of internal carotid artery (ICA), optic nerve (ON), maxillary nerve (MN), and vidian nerve (VN) into the sphenoid sinus cavity.
Pneumatization of PP, ACP, and GWS were seen in 87 (29%), 46 (15.3%), and 60 patients (20%), respectively. Protrusion of ICA, ON, MN, and VN were noticed in 123 (41%), 107 (35.6%), 73 (24.3%), and 81 patients (27%), respectively; dehiscence of these structures was encountered in 90 (30%), 92 (30.6%), 39 (13%), and 111 patients (37%), respectively. Statistically, there was a highly significant association between ACP pneumatization and ICA protrusion, ACP pneumatization and ON protrusion, PP pneumatization and VN protrusion; and GWS pneumatization and MN protrusion (p-value < 0.001).
The sphenoid sinus is highly variable; this variability necessitates a comprehensive understanding of the regional sphenoid sinus anatomy by a detailed CT scan sinus examination before surgery in and around the sinus. This study indicates the possibility of a racial anatomical variation of the sphenoid sinus in the Libyan population.
PMCID: PMC3074265  PMID: 21499453
Sphenoid sinus; variation; internal carotid artery; optic nerve; maxillary nerve; vidian nerve; CT scan; Libyan
12.  The Avoidance of Microsurgical Complications in the Extradural Anterior Clinoidectomy to Paraclinoid Aneurysms 
Paraclinoid segment internal carotid artery (ICA) aneurysms have historically been a technical challenge for neurovascular surgeons. The development of microsurgical approach, advances in surgical techniques, and endovascular procedures have improved the outcome for paraclinoid aneurysms. However, many authors have reported high complication rates from microsurgical treatments. Therefore, the present study reviews the microsurgical complications of the extradural anterior clinoidectomy for treating paraclinoid aneurysms and investigates the prevention and management of observed complications.
Between January 2004 and April 2008, 22 patients with 24 paraclinoid aneurysms underwent microsurgical direct clipping by a cerebrovascular team at a regional neurosurgical center. Microsurgery was performed via an ipsilateral pterional approach with extradural anterior clinoidectomy. We retrospectively reviewed patients' medical charts, office records, radiographic studies, and operative records.
In our series, the clinical outcomes after an ipsilateral pterional approach with extradural anterior clinoidectomy for paraclinoid aneurysms were excellent or good (Glasgows Outcome Scale : GOS 5 or 4) in 87.5% of cases. The microsurgical complications related directly to the extradural anterior clinoidectomy included transient cranial nerve palsy (6), cerebrospinal fluid leak (1), worsened change in vision (1), unplanned ICA occlusion (1), and epidural hematoma (1). Only one of the complications resulted in permanent morbidity (4.2%), and none resulted in death.
Although surgical complications are still reported to occur more frequently for the treatment of paraclinoid aneurysms, the permanent morbidity and mortality resulting from a extradural anterior clinoidectomy in our series were lower than previously reported. Precise anatomical knowledge combined with several microsurgical tactics can help to achieve good outcomes with minimal complications.
PMCID: PMC2966719  PMID: 21082045
Extradural anterior clinoidectomy; Paraclinoid aneurysm; Clinical outcomes; Surgical complications
13.  Extradural Middle Fossa Approach. Proposal of a Learning Method: The “Rule of Two Fans.” Technical Note 
Skull Base  2006;16(3):181-184.
The extradural middle fossa approach is used to access lesions of the petroclival and cavernous sinus regions. It may be included in combined petrosal and anterolateral transcavernous approaches. Technically, it is a demanding exposure that provides a wide extradural corridor between the 5th, 7th, and 8th cranial nerves. Its major advantages are that it offers extradural dissection, limits temporal lobe retraction, and avoids the transposition of nerves or vessels. Its disadvantages are primarily related to the complicated anatomy of the petrous apex from the middle fossa trajectory, which can be unfamiliar to neurosurgeons. To facilitate the first attempts with this relatively uncommon approach during dissections of human cadaveric injected heads and isolated temporal bones, we developed a simple learning method useful for localizing all anatomical structures. Using this “rule of two fans,” vascular, nervous, fibrous, and osseous structures are localized within two bordering fans with a 90-degree relationship to each other.
PMCID: PMC1586174  PMID: 17268592
Anatomy; cavernous sinus; cranial base surgery; middle fossa approach; petrous temporal bone
14.  The Pterional Approach and Extradural Anterior Clinoidectomy to Clip Paraclinoid Aneurysms 
The surgical clipping of paraclinoid segment internal carotid artery aneurysms is considered difficult because of the complex anatomical location and important neighboring structures. Our experiences of pterional craniotomy and extradural anterior clinoidectomy (EAC) to clip paraclinoid aneurysms are reported herein.
We present two patients with paraclinoid aneurysms who underwent surgical clipping using pterional craniotomy and EAC. The clinical results and operative techniques were reviewed from the patients' medical records.
EAC improves the surgical field in the suprasellar and periclinoid regions. Clinically, a good outcome was obtained in both cases. No surgical complications directly resulting from the EAC were observed.
Favorable surgical results can be obtained with pterional craniotomy and EAC for the clipping of paraclinoid aneurysms. EAC is advocated for the clipping of paraclinoid aneurysms.
PMCID: PMC3804669  PMID: 24167811
Paraclinoid aneurysm; Extradural; Anterior clinoidectomy; Pterional craniotomy
15.  Transcranial approach to pituitary adenomas invading the cavernous sinus: A modification of the classical technique to be used in a low-technology environment 
Pituitary adenomas invading the cavernous sinus represent a therapeutic challenge. Those tumors have been traditionally treated with incomplete surgical removal, observation and/ or adjunctive medical therapy, and radiotherapy. In relatively recent years, some authors have suggested a main direct surgical approach to cavernous sinus (CS) with the aim of complete removal of the adenoma, either by a modified trans-sphenoidal route, using or not an endoscopy-assisted approach, or by a transcranial direct approach. The latter has the advantage of allowing direct exposure of the lesion with a view of the surgical field unhindered by important neurovascular structures.
Materials and Methods:
We report a technical modification of the classical epidural approach for CS adenoma removal. This was used in 14 patients. Surgical technique included a fronto-orbito-zygomatic craniotomy with extradural anterior clinoidectomy, and intradural approach to the Hakuba’s triangle for intracavernous dissection. The tumors were removed under direct vision.
Total macroscopical removal was achieved in all but one case. This patient required postoperative radiation therapy as well as adjuvant dopaminergic regime for achieving control of preoperatively increased hormonal values. No other case required radiotherapy. Hormonal and/ or clinical control was also achieved in all the remaining cases. Out of the remaining 13 cases, all appeared to be tumor free at an average postoperative observation at 78 months (34 to 90 months). Significant surgical sequels were detected in only 1 case (persistent 3rd nerve palsy and moderate hemiparesis).
This experience, though limited, would suggest that the transcranial limited CS exposure through the Hakuba’s triangle may allow adequate removal of intracavernous pituitary adenomas with very good long-term results and acceptable complication rate.
PMCID: PMC2940085  PMID: 20847907
Cavernous sinus surgery; fronto-orbito-zygomatic craniotomy (FOZ); Hakuba’s triangle; invasive adenoma; transcranial approach
16.  Qualitative and Quantitative Radio-Anatomical Variation of the Posterior Clinoid Process 
Skull Base  2011;21(6):373-378.
This study was conducted to investigate the radiological anatomy of the posterior clinoid process (PCP) to highlight preoperative awareness of its variations and its relationships to other skull base landmarks. The PCPs of 36, three-dimensional computed tomographic cadaveric heads were evaluated by studying the gross anatomy of the PCP and by measuring the distances between the PCP and other skull base anatomical landmarks relevant to transnasal or transcranial skull base approaches. PCP variations were found in five specimens (14%): in two the dorsum sellae was absent, in one the PCP and the anterior clinoid process (ACP) were connected unilaterally and in two bilaterally. The mean distance between the right/left PCP and the crista galli was 45.14 ± 4.0 standard deviation (SD_/46.24 ± 4.5 SD, respectively, while the distance to the middle point of the basion at the level of the foramen magnum was 40.41 ± 5.1 SD/41.0 ± 5.2 SD, respectively. The mean distance between the PCP and the ACP was 12.03 ± 3.18 SD on the right side and 12.11 ± 2.77 SD on the left. The data provided highlights the importance of careful preoperative evaluation of the PCP and of its relationships to other commonly encountered skull base landmarks. This information may give an idea of the exposure achievable through different transcranial and transnasal approaches. This is especially relevant when neuronavigation is not available.
PMCID: PMC3312125  PMID: 22547963
Radio-anatomical study; posterior clinoid processes; skull base surgery; transnasal approaches
17.  Accessing the Basilar Artery Apex: Is the Temporopolar Transcavernous Route an Anatomically Advantageous Alternative? 
Skull Base  2011;21(1):23-30.
The restricted operative field, difficulty of obtaining proximal vascular control, and close relationship to important anatomic structures limit approaches to basilar apex aneurysms. We used a cadaveric model to compare three surgical transcavernous routes to the basilar apex in the neutral configuration. Five cadaveric heads were dissected and analyzed. Working areas and length of exposure provided by the transcavernous (TC) approach via pterional, orbitozygomatic, and temporopolar (TP) routes were measured along with assessment of anatomic variation for the basilar apex region. In the pterional TC and orbitozygomatic TC approaches, the mean length of exposure of the basilar artery measured 6.9 and 7.2 mm, respectively (p = NS). The mean length of exposure in a TP TC approach increased to 9.3 mm (p < 0.05). Compared with the pterional and orbitozygomatic approaches, the TP TC approach provided a larger peribasilar area of exposure ipsilaterally and contralaterally (p < 0.05). The multiplanar working area related to the TP TC approach was 77.7 and 69.5% wider than for the pterional TC and orbitozygomatic TC, respectively. For a basilar apex in the neutral position, the TP TC approach may be advantageous, providing a wider working area for the basilar apex region, improving maneuverability for clip application, fine visualization of perforators, and better proximal control.
PMCID: PMC3312409  PMID: 22451796
Basilar artery aneurysm; transcavernous approach; temporopolar approach; pterional approach; orbitozygomatic approach; anatomic study
18.  Anatomical Variations of Anterior Communicating Artery 
Introduction: The Circle of Willis is a vascular network formed at the base of skull in the interpeduncular fossa. Its anterior part is formed by the anterior cerebral artery, from either side. Anterior communicating artery connects the right and left anterior cerebral arteries. Posteriorly, the basilar artery divides into right and left posterior cerebral arteries and each joins to ipsilateral internal carotid artery through a posterior communicating artery. Anterior communicating artery, an important component of circle of Willis, acts as collateral channel to stabilize blood flow. In the present study, anatomical variations in the anterior communicating artery were noted.
Material and Methods: One hundred apparently normal formalin fixed brain specimens were collected from human cadavers. Normal anatomical pattern and variations of anterior communicating artery were studied. The anterior communicating arteries were then coloured, photographed, numbered and the abnormalities, if any, were noted.
Result: Thity eight variant anterior communicating arteries were noted. The most common variation observed in the anterior communicating artery was its duplication in 10 subjects, followed by its absence in 8 subjects. Some variations like plexus formation, median artery were found in adults, because of persistence of embryonic pattern.
Conclusion: Knowledge on variations in the anterior communicating artery is of clinical significance, as it is one of the components of circle of Willis which stabilizes cerebral blood flow when principle conduits fail.
PMCID: PMC3919289  PMID: 24551604
Anterior communicating artery; Circle of Willis; Cerebral supply; Hypoplastic
19.  Radiographic Imaging of the Distal Dural Ring for Determining the Intradural or Extradural Location of Aneurysms 
Skull Base  2005;15(4):253-262.
The effectiveness of several anatomical and radiological landmarks proposed to determine whether an aneurysm is located intradurally or extradurally is still debated. In anatomical and radiological studies, we examined the relationships of the distal dural ring (DDR) to the internal carotid artery (ICA) and surrounding bony structures to aid in the localization of aneurysms near the DDR. Anatomical relationships were examined by performing dissections on 10 specimens (5 formalin-fixed cadaveric heads). After the position of the DDR, optic nerve, and tuberculum sellae were marked with surgical steel wire, radiographs were taken in multiple projections. The only bony landmark consistently visible on radiographs was the planum sphenoidale. The superior border of the DDR is located at or below the level of the tuberculum sellae, which laterally becomes the superomedial aspect of the optic strut; thus, the optic strut marks the dorsal limit of the DDR. On 50 dry skulls, we measured the vertical distance between the planum sphenoidale and medial aspect of the optic strut (5.0 ± 0.4 mm), the interoptic strut distance (14.4 ± 1.4 mm), and the linear distance between the most posterior aspect of the planum sphenoidale (limbus sphenoidale) and the tuberculum sellae (6.0 ± 0.5 mm). Using these measurements and the planum sphenoidale, tuberculum sellae, and optic strut as reference landmarks, we determined the location of the aneurysm relative to the DDR on angiographic images. In this way, we were able to identify whether lesions were intra- or extradural.
PMCID: PMC1380264  PMID: 16648887
Tuberculum sellae; planum sphenoidale; optic strut; distal dural ring; aneurysms
20.  Possibility of Middle Meningeal Artery-to-Petrous Internal Carotid Artery Bypass: An Anatomic Study 
Skull Base  2004;14(3):153-156.
The possibility of creating a middle meningeal artery (MMA)-to-petrous internal carotid artery (ICA) bypass was investigated in six cadavers (bilaterally). Such a procedure could be used to treat patients with high cervical vascular lesions and those with tumors of the infratemporal fossa invading the high cervical ICA. After a frontotemporal craniotomy, the foramen spinosum and foramen ovale were exposed extradurally. Immediately posterior to the foramen ovale and medial to the foramen spinosum, the petrous portion of the ICA was exposed with a diamond-tipped drill. The MMA was lifted from its groove, and a sufficient length was transected to perform a bypass with the petrous ICA medially. The mean width of the MMA at the site of anastomosis was 2.3 ± 0.35 mm. The mean length of MMA from the foramen spinosum to the site of the anastomosis was 9.6 ± 1.7 mm. Based on these measurements, width and length of MMA appear to be sufficient for a bypass with petrous ICA.
PMCID: PMC1151685  PMID: 16145598
Middle meningeal artery; internal carotid artery; bypass procedure; angiography
21.  Abnormal Course of the Oculomotor Nerve on the Clivus Combined with a Petroclival Meningioma 
Skull Base  2002;12(3):141-144.
The course of the oculomotor nerve on the clivus was abnormal in a patient with petroclival meningioma. He complained of gait disturbance. A gadolinium-enhanced magnetic resonance image demonstrated a 4.4-cm enhancing mass in the petroclival region. The tumor was removed via an anterior transpetrosal-transtentorial approach. Normally, the oculomotor nerve originates from the brainstem and enters the oculomotor trigone. In this patient, the oculomotor nerve entered the dura mater at the upper clivus, behind the posterior clinoid process, and coursed parallel to the basilar artery. This entrance is lower than the normal entry point of the oculomotor nerve. The abnormal entrance of the oculomotor nerve may reflect an atypical developmental relationship among the cranial nerves, meninges, and bones during embryogenesis.
PMCID: PMC1656935  PMID: 17167668
Petroclival meningioma; anatomical variation; oculomotor nerve; microanatomy; anterior transpetrosal-transtentorial approach
22.  A Case of Large Anterior Paraclinoid Aneurysm with Intraoperative Premature Rupture 
We report here troubleshooting of intraoperative premature rupture with large anterior paraclinoid aneurysm, which was successfully clipped. A 61-year-old woman with left nasal hemianopia was referred to our institute. Preoperative three-dimensional computed tomography angiography and a left internal carotid artery angiogram showed a large left anterior clinoid aneurysm adjacent to the anterior clinoid process. Aneurysm was ruptured prematurely and tentative clipping of the dome of the aneurysm was done incidentally to stop bleeding and to reduce the volume of the aneurysm. The anterior clinoid process and superior wall of the orbit were drilled out safely, since the tentative clipping had created sufficient space between the aneurysm and the anterior clinoid process to perform the procedure. The proximal neck was observed and tandem clipping was applied to the aneurysm. Intraoperative and postoperative angiography revealed complete disappearance of the aneurysm.
PMCID: PMC3658651  PMID: 23946926
anterior clinoid process; anterior paraclinoid aneurysm; premature rupture; saccular aneurysm; tentative clipping
23.  The So-Called Anterior Meningeal Artery: an Anatomic Study for Treatment Modalities 
Interventional Neuroradiology  2005;10(4):293-299.
The so called anterior meningeal artery (AMA) is a branch of the vertebral artery (VA), which had been interpreted as a supplying vessel of the dura in the foramen magnum and upper cervical level.
In this study, we examined the anatomy of this artery and relationships to its surrounding structures for treatment modalities. With the aid of magnification, five adult cadaveric head and neck complex and five cervical spines were examined after perfusion of the vessels with colored silicone.
The AMA arose from the VA between the C2 and C3 level, and passed medially through the intrervertebral foramen anterior to the dural sheath of the third cervical nerve root. It ran upwards dorsal to the deep layer of the posterior longitudinal ligament (PLL) with anterior internal vertebral venous plexus. Rostrally, it formed an arcade above the apex of the odontoid process with its contralateral mate.
The AMA gave off several tiny branches to the deep layer of the PLL, ligaments and soft tissues above the apex of the odontoid process, and vertebral bodies of the axis. At the level of the foramen magnum, it ended in several small twigs to the dura. Anastomoses between the AMA system and adjacent vessels were observed. One was directed through the hypoglossal canal to the ascending pharyngeal artery and the other was with the V3 segment of the VA. The origin and course of the two AMA, and anastomoses were symmetric. Although the AMA feeds the ventral dura of the foramen magnum, the perfusion area is larger than its name suggests, including the bony and ligamentous structures in the craniovertebral junction.
Anatomical knowledge of the AMA, including its anastomoses and layer relationships to the surrounding structures, may help to perform treatment modalities in this region rationally.
PMCID: PMC3463288  PMID: 20587212
anatomy, anterior meningeal artery, craniovertebral junction, vertebral artery
24.  Microsurgical and Endoscopic Approaches to the Basilar Bifurcation 
Skull Base  2001;11(2):93-97.
To determine the most effective route to the upper third of the basilar artery, 10 cadaver dissections were performed comparing the exposure gained using the combined pterional/anterior temporal approach and the orbitozygomatic extended approach. Endoscopic evaluation through an eyebrow incision in each dissection helped determine whether any advantage was conferred by the cranial base approach. This also served to assess the benefit of using the endoscope as an adjunct to open procedures in evaluating the opticocarotid and retrocarotid routes to the basilar artery. The results of cadaveric dissections suggest that compared with the exposure afforded by the combined pterional/anterior temporal approach, the orbitozygomatic extended approach yields an increase of 8 cm in the anteroposterior axis and 10 cm in the superoinferior axis. Furthermore, as expected, the increases in visibility were directed anteriorly and posteriorly. When employed through the craniotomy site during aneurysm clipping, endoscopy was found to be potentially useful in assessing the contralateral elements of the upper basilar complex.
PMCID: PMC1656798  PMID: 17167607
Basilar artery; aneurysm; orbitozygomatic; endoscope; pterion
25.  Microanatomy and Surgical Approaches to the Infratemporal Fossa: An Anaglyphic Three-Dimensional Stereoscopic Printing Study 
Skull Base  2007;17(5):285-302.
Objective: The infratemporal fossa (ITF) is a continuation of the temporal fossa between the internal surface of the zygoma and the external surface of the temporal bone and greater wing of the sphenoid bone that is sitting deep to the ramus of the mandible. The principal structure to understanding its relationships is the lateral pterygoid muscle. Other important structures are the medial pterygoid muscle, the maxillary artery, the pterygoid venous plexus, the otic ganglion, the chorda tympani nerve and the mandibular nerve. In this study, we describe the microsurgical anatomy of the ITF, as viewed by step-by-step anatomical dissection and also through the perspective of three lateral approaches and one anterior surgical approach. Methods: Eight cadaver specimens were dissected. In one side of all specimens, an anatomical dissection was done in which a wide preauricular incision from the neck on the anterior border of the sternoclidomastoid muscle at the level of the cricoid cartilage to the superior temporal line was made. The flap was displaced anteriorly and the structures of the neck were dissected followed by a zygomatic osteotomy and dissection of the ITF structures. On the other side were the surgical approaches to the ITF. The combined infratemporal and posterior fossa approach was done in two specimens, the subtemporal preauricular infratemporal fossa approach in two, the zygomatic approach in two, and the lateral transantral maxillotomy in two. The anatomical dissections were documented on the three-dimensional (3D) anaglyphic method to produce stereoscopic prints. Results: The lateral pterygoid muscle is one of the principal structures to enable understanding of the relationships into the ITF. The tendon of the temporal muscle inserts in the coronoid process at the ITF. The maxillary artery is the terminal branch of the external carotid artery that originates at the neck of the mandible and runs into the parotid gland. In our dissections the maxillary artery was lateral to the buccal, lingual, and inferior alveolar nerves. We found the second part of the maxillary artery superficial to the lateral pterygoid muscle in all specimens The anterior and posterior branches of the deep temporal artery supply the temporal muscle. In two cases we found a middle deep temporal artery. The different approaches that we used provided different views of the same anatomical landmarks and this provides not only safer surgery but also the best choice to approach the ITF according with the pathology extension. Conclusions: The ITF is a complex region on the skull base that is affected by benign and malignant tumors. The study through different routes is helpful to disclose the relationship among the anatomical structures. Although the authors have shown four approaches, there are a variety of approaches and even a combination of these can be used. This type of anatomical knowledge is essential to choosing the best approach to treat lesions in this area.
PMCID: PMC2095118  PMID: 18330427
Infratemporal fossa; surgical anatomy; approaches; paraganglioma; mandibular nerve

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