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1.  Anterior clinoidectomy: Description of an alternative hybrid method and a review of the current techniques with an emphasis on complication avoidance 
Background:
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.
Methods:
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.
Results:
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.
Conclusion:
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.
doi:10.4103/2152-7806.85981
PMCID: PMC3205487  PMID: 22059135
Clinoidectomy; complications; optic nerve; technical nuance
2.  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.
ABSTRACT
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.
doi:10.1055/s-0030-1247632
PMCID: PMC3023323  PMID: 21311615
Anterior clinoid process; superior orbital fissure; cavernous sinus; anterior clinoidectomy; training model
3.  Measurement of Critical Structures around Paraclinoidal Area : A Cadaveric Morphometric Study 
Objective
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.
Methods
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.
Results
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.
Conclusion
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.
doi:10.3340/jkns.2013.54.1.14
PMCID: PMC3772280  PMID: 24044074
Anterior clinoid process; Extradural anterior clinoidectomy; Optic strut; Ophthalmic segment
4.  Enhanced Exposure of Carotico-Oculomotor Triangle Following Extradural Anterior Clinoidectomy: A Comparative Anatomical Study 
Skull Base  2005;15(3):157-161.
ABSTRACT
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.
doi:10.1055/s-2005-871523
PMCID: PMC1214701  PMID: 16175225
Anterior clinoid; carotico-oculomotor triangle; clinoidectomy; extradural
5.  Posterior Clinoidectomy: Dural Tailoring Technique and Clinical Application 
Skull Base  2009;19(3):183-191.
ABSTRACT
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.
doi:10.1055/s-0028-1096196
PMCID: PMC2702194  PMID: 19881898
Posterior clinoid; clinoidectomy; dural tailoring; basilar artery; oculomotor nerve
6.  Endoscopic endonasal posterior clinoidectomy 
Background:
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.
Methods:
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.
Results:
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.
Conclusion:
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.
doi:10.4103/2152-7806.97008
PMCID: PMC3385065  PMID: 22754729
Dorsum sella; endoscopic endonasal; extradural posterior clinoidectomy; interpeduncular cistern; posterior clinoid process; skull base
7.  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.
Images
PMCID: PMC1656581  PMID: 17170983
8.  The Avoidance of Microsurgical Complications in the Extradural Anterior Clinoidectomy to Paraclinoid Aneurysms 
Objective
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.
Methods
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.
Results
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.
Conclusion
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.
doi:10.3340/jkns.2010.48.3.199
PMCID: PMC2966719  PMID: 21082045
Extradural anterior clinoidectomy; Paraclinoid aneurysm; Clinical outcomes; Surgical complications
9.  Anterior clinoid mucocele presenting with orbital apex syndrome 
Background:
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.
Conclusions:
We report a case of spontaneous anterior clinoid process mucocele presenting with orbital apex syndrome. This was treated successfully with anterior clinoidectomy for decompression.
doi:10.4103/2152-7806.111583
PMCID: PMC3680997  PMID: 23772333
Anterior clinoid process; mucocele; orbital apex syndrome
10.  Configuration of Fibrous and Adipose Tissues in the Cavernous Sinus 
PLoS ONE  2014;9(2):e89182.
Objective
Three-dimensional anatomical appreciation of the matrix of the cavernous sinus is one of the crucial necessities for a better understanding of tissue patterning and various disorders in the sinus. The purpose of this study was to reveal configuration of fibrous and adipose components in the cavernous sinus and their relationship with the cranial nerves and vessels in the sinus and meningeal sinus wall.
Materials and Methods
Nineteen cadavers (8 females and 11 males; age range, 54–89 years; mean age, 75 years) were prepared as transverse (6 sets), coronal (3 sets) and sagittal (10 sets) plastinated sections that were examined at both macroscopic and microscopic levels.
Results
Two types of the web-like fibrous networks were identified and localized in the cavernous sinus. A dural trabecular network constituted a skeleton-frame in the sinus and contributed to the sleeves of intracavernous cranial nerves III, IV, V1, V2 and VI. A fine trabecular network, or adipose tissue, was the matrix of the sinus and was mainly distributed along the medial side of the intracavernous cranial nerves, forming a dumbbell-shaped adipose zone in the sinus.
Conclusions
This study revealed the nature, fine architecture and localization of the fine and dural trabecular networks in the cavernous sinus and their relationship with intracavernous cranial nerves and vessels. The results may be valuable for better understanding of tissue patterning in the cranial base and better evaluation of intracavernous disorders, e.g. the growth direction and extent of intracavernous tumors.
doi:10.1371/journal.pone.0089182
PMCID: PMC3935851  PMID: 24586578
11.  Extradural Middle Fossa Approach. Proposal of a Learning Method: The “Rule of Two Fans.” Technical Note 
Skull Base  2006;16(3):181-184.
ABSTRACT
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.
doi:10.1055/s-2006-939676
PMCID: PMC1586174  PMID: 17268592
Anatomy; cavernous sinus; cranial base surgery; middle fossa approach; petrous temporal bone
12.  Transcranial approach to pituitary adenomas invading the cavernous sinus: A modification of the classical technique to be used in a low-technology environment 
Objective:
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.
Results:
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).
Conclusions:
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.
doi:10.4103/2152-7806.65054
PMCID: PMC2940085  PMID: 20847907
Cavernous sinus surgery; fronto-orbito-zygomatic craniotomy (FOZ); Hakuba’s triangle; invasive adenoma; transcranial approach
13.  A Cross-Sectional Study of Sphenoid Sinus through Gross and Endoscopic Dissection in North Karnataka, India 
Introduction: Sphenoid sinus has got importance due to trans-sphenoid approach to the pituitary gland. This study is an attempt to know the variations in North Karnataka population, through cadaveric dissection and CT scan study.
Objective: We want to study variations in sphenoid sinus and its percentage in North Karnataka population.
Material and Methods: Endoscopic examination and dissection of sphenoid sinus was carried out in 30 cadavers (three female and 27 male) using 0°, 30°, 70° rigid nasal endoscopes. Sections were then made in the sagittal plane to confirm the anatomical findings and to take the necessary measurements with millimeter strips.
Results: In six of cadavers pre-sellar, in four it was sellar and in 20 it was post-sellar while conchal type of sphenoid sinus was absent. The septa terminated on bone covering internal carotid artery (ICA) in seven cadavers while in two cadavers they terminated on the bone covering Optic nerve (ON). Findings of CT scan study were pre-sellar-8, sellar-14 and post-sellar-37 and in case of one subject left side sinus was conchal. Pneumatization of greater wing of sphenoid was observed in two sinuses, of pterygoid process in four sinuses and of anterior clinoid process in two sinuses. We also found onodi cell in one sinus.
Conclusion: Sphenoid sinus shows various types of pneumatisation, and this place the sinus in close proximity to important neurovascular structures that are present around the sinus. Newer techniques are used to confirm surgical landmarks making these techniques very safe.
doi:10.7860/JCDR/2014/7947.4243
PMCID: PMC4064884  PMID: 24959426
Sphenoid sinus; Endoscopy, Pneumatization; Optic nerve; Internal carotid artery; Trans-sphenoid hypophysectomy
14.  Microsurgical Relations between Internal Carotid Artery–Posterior Communicating Artery (ICA-PComA) Segment Aneurysms and Skull Base: An Anatomoclinical Study 
Purpose The study of the clinical, anatomic, imaging, and microsurgical characteristics of the aneurysms of the internal carotid-posterior communicating artery (ICA-PComA) segment and their relationships with the skull base structures.
Methods The anatomic relationships of PComA with neurovascular elements and skull base structures were studied in cadavers. The clinical, imaging, and microsurgical findings of 84 microsurgically treated ICA-PComA aneurysms compiled in a prospective database were reviewed.
Results The most important anatomic relations of the PComA and ICA-PComA aneurysms are with the oculomotor nerve around the oculomotor triangle that forms the roof of the cavernous sinus. Aneurysms of the ICA-PComA are classified according to the orientation of the aneurysmal sac in infratentorial, supratentorial, and tentorial. Infratentorial aneurysms frequently present with subarachnoid hemorrhage (SAH) and oculomotor nerve paralysis. They have relations with skull base structures that often make it necessary to totally or partially resect the anterior clinoid process (6.7%) or anterior petroclinoid dural fold (15%). Supratentorial aneurysms course with SAH and without oculomotor nerve involvement, but they often are associated with intracranial hematoma.
Conclusion ICA-PComA aneurysms have complex anatomic relations. The orientation of the aneurysmal fundus induces relevant differences in the anatomic relations, clinical presentation, and microsurgical approach to ICA-PComA aneurysms.
doi:10.1055/s-0032-1322795
PMCID: PMC3578643  PMID: 24083126
cerebral aneurysm; internal carotid artery; posterior communicating artery aneurysm; oculomotor nerve
15.  Carotico-clinoid foramina and a double optic canal: A case report with neurosurgical implications 
Background:
The lesser wing of the sphenoid is a clinically important structure, particularly with regard to its anatomical relationship with neurovascular structures including the optic nerve, ophthalmic artery, and internal carotid artery. Anterior clinoidectomy, a neurosurgical procedure utilized to access paraclinoid aneurysms and neoplasms, is often complicated by the presence of anatomical variants including the carotico-clinoid foramen and the accessory optic canal.
Case Description:
A rare case report is presented documenting the simultaneous occurrence of bilateral carotico-clinoid foramina and a unilateral accessory optic canal.
Conclusion:
The presence of an accessory optic canal may be misconstrued as a carotico-clinoid foramen or pneumatization of the anterior clinoid process, lesser sphenoidal wing, or optic strut. The case report documents two clinically important variant structures occurring ipsilaterally, each with the potential to masquerade as the other radiographically and present complications to both neurosurgeons and radiologists. Knowledge of the unique combination of anatomical variants presented in this report may prevent adverse surgical events during anterior clinoidectomy procedures including hemorrhage of the ophthalmic artery or internal carotid artery and subsequent vision loss or death.
doi:10.4103/2152-7806.150456
PMCID: PMC4314831  PMID: 25657866
Anterior clinoidectomy; internal carotid artery; ophthalmic artery; ophthalmic foramen; optic foramen; paraclinoid aneurysm
16.  Quantification of the Advantages of the Extended Frontal Approach to Skull Base 
Skull Base  2004;14(3):133-142.
ABSTRACT
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.
doi:10.1055/s-2004-832253
PMCID: PMC1151683  PMID: 16145596
Brain tumor; extended frontal approach; operative approach; skull base; skull base tumor
17.  En Bloc Resection of the Temporal Bone by the Lateral Approach in Carcinoma of the Middle Ear Associated with Skull Base Infiltration with Reference to the Resection of the Petrous Apex 
Skull base surgery  1998;8(4):195-204.
En bloc resection of the temporal bone was performed by the lateral approach on two patients with carcinoma of the middle ear, which was associated with destruction in the temporal bone and tumor infiltration of the cranial base. In one of the patients, the petrous apex was resected along with the temporal bone.
En bloc resection on the temporal bone with the petrous apex is believed to be difficult because the internal carotid artery (ICA), cavernous sinus, and the brainstem are adjacent to each other in the petrous apex. However, the intra- and extracranial surgical procedures by this approach allow resection of the temporal bone ranging from the anterior part including the petrous apex to the posterior part including the mastoid process, the dura of the middle and posterior cranial fossae, and the sigmoid sinus, without exposure of the tumor. Special attention should be paid to the procedural points of surgery, such as, exposure of the petrous ICA, bleeding from the petrous sinus, and dural suturing in the vicinity of the apex. With regard to surgical indication, it is important to determine whether tumor infiltration is confined to the temporal bone and the dura of the middle and posterior fossa. If tumor infiltration into the petrous ICA, the dominant side of sigmoid sinus and/or the inferior cranial nerve is observed, then indication for surgery should be determined in a more critical manner.
Images
PMCID: PMC1656695  PMID: 17171066
18.  The Jugular Dural Fold—A Helpful Skull Base Landmark to the Cranial Nerves 
Skull base surgery  1995;5(1):57-61.
During a retrosigmoid (or combined retrolabyrinthine-retrosigmoid) approach to the posterior fossa for vestibular neurectomy or removal of small acoustic neuromas, a white dural fold is a consistent landmark to cranial nerves VII through XII. This fold of dura appears as a white linear structure extending from the foramen magnum across the sigmoid sinus, attaching to the posterior aspect of the temporal bone, anterior to the vestibular aqueduct. The name “jugular dural fold” is suggested for this landmark. The jugular dural fold overlies the junction of the sigmoid sinus and the jugular foramen. As measured in formalin-fixed cadaver heads, the overall length of the jugular dural fold is 20.8 mm (± 2.9 mm). The cochleovestibular nerve lies 9.9 mm (± 1.5 mm) anterior to the superior aspect of the jugular dural fold, the glossopharyngeal nerve lies 9.5 mm (± 1.6 mm) anterior to the midpoint of the jugular dural fold, and the operculum of the vestibular aqueduct lies 6.6 mm (± 0.7 mm) posterior to the jugular dural fold. Intraoperative measurements in patients undergoing combined retrolabyrinthine-retrosigmoid vestibular neurectomy show an overall length of the jugular dural fold of 16.3 mm (± 1.9 mm). The cochleovestibular nerve lies 8.6 mm (± 1.3 mm) anterior to the superior aspect of the jugular dural fold, the glossopharyngeal nerve lies 8.6 mm (± 1.3 mm) anterior to the midpoint of the jugular dural fold, and the operculum lies 7.5 mm (± 0.8 mm) posterior to the jugular dural fold. The jugular dural fold can be used as a reliable landmark for rapidly locating cranial nerves in the posterior fossa.
Images
PMCID: PMC1661788  PMID: 17171158
19.  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.
doi:10.3892/etm.2011.345
PMCID: PMC3440810  PMID: 22977646
frontotemporal-orbitozygomatic approach; superior petroclival region; microsurgical anatomy
20.  Anatomic Variation of Sphenoid Sinus and Related Structures in Libyan Population: CT Scan Study 
The Libyan Journal of Medicine  2008;3(3):128-133.
Background
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.
Objective
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.
Results
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).
Conclusion
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.
doi:10.4176/080307
PMCID: PMC3074265  PMID: 21499453
Sphenoid sinus; variation; internal carotid artery; optic nerve; maxillary nerve; vidian nerve; CT scan; Libyan
21.  Internal Carotid Artery Reconstruction Using Multiple Fenestrated Clips for Complete Occlusion of Large Paraclinoid Aneurysms 
Objective
Although surgical techniques for clipping paraclinoid aneurysms have evolved significantly in recent times, direct microsurgical clipping of large and giant paraclinoid aneurysms remains a formidable surgical challenge. We review here our surgical experiences in direct surgical clipping of large and giant paraclinoid aneurysms, especially in dealing with anterior clinoidectomy, distal dural ring resection, optic canal unroofing, clipping techniques, and surgical complications.
Methods
Between September 2001 and February 2012, we directly obliterated ten large and giant paraclinoid aneurysms. In all cases, tailored orbito-zygomatic craniotomies with extradural and/or intradural clinoidectomy were performed. The efficacy of surgical clipping was evaluated with postoperative digital subtraction angiography and computed tomographic angiography.
Results
Of the ten cases reported, five each were of ruptured and unruptured aneurysms. Five aneurysms occurred in the carotid cave, two in the superior hypophyseal artery, two in the intracavernous, and one in the posterior wall. The mean diameter of the aneurysms sac was 18.8 mm in the greatest dimension. All large and giant paraclinoid aneurysms were obliterated with direct neck clipping without bypass. With the exception of the one intracavenous aneurysm, all large and giant paraclinoid aneurysms were occluded completely.
Conclusion
The key features of successful surgical clipping of large and giant paraclinoid aneurysms include enhancing exposure of proximal neck of aneurysms, establishing proximal control, and completely obliterating aneurysms with minimal manipulation of the optic nerve. Our results suggest that internal carotid artery reconstruction using multiple fenestrated clips without bypass may potentially achieve complete occlusion of large paraclinoid aneurysms.
doi:10.3340/jkns.2013.54.6.477
PMCID: PMC3921274  PMID: 24527189
Clinoidectomy; Orbito-zygomatic craniotomy; Paraclinoid aneurysm; Large and giant; Microsurgical clipping
22.  Classification system of foramen magnum meningiomas 
Background:
Foramen magnum meningiomas (FMMs) are challenging tumors. We report a classification system based on our experience of 107 tumors.
Materials and Methods:
The three main algorithm criteria included the compartment of development of the tumor, its dural insertion, and its relation to the vertebral artery.
Results:
The compartment of development was most of the time intradural (101/107, 94.4%) and less frequently extradural (3/107, 2.8%) or both intra-extradural. (3/107, 2.8%). When developed inside the intradural compartment, FMMs were subdivided into posterior (6/104, 5.8%), lateral (57/104, 54.8%), and anterior (41/104, 39.4%), if their insertion was respectively posterior to the dentate ligament, anterior to the dentate ligament without or with extension over the midline. Anterior and lateral intradural lesions grew below (77/98, 78.6%), above (16/98, 16.3%), or on both sides (5/98, 5.1%) of the VA. Only three cases of extraduralFMMs (3/107, 2.8%) were resected by an antero-lateral approach while all the other ones (104/107, 97.2%) were removed successfully by a postero-lateral approach. Lower cranial nerves were displaced superiorly in FMM growing below the VA but their position cannot be anticipated in other situations.
Conclusions:
This classification system helps for defining the best surgical approach but also for anticipating the position of the lower cranial nerves and therefore for reducing the surgical morbidity.
doi:10.4103/0974-8237.65476
PMCID: PMC2944858  PMID: 20890409
Classification; foramen magnum; meningioma; surgical approach; tumor - vertebral artery
23.  Reducing the cervical flexion tear-drop fracture with a posterior approach and plating technique: an original method 
European Spine Journal  1999;8(2):110-116.
Flexion tear-drop fractures (FTDF) in the cervical spine constitute a highly unstable condition with a high incidence of neurological complications due to posterior displacement of the fractured vertebra in the spinal canal. The widely accepted surgical management for this condition includes complete excision and grafting of the vertebral body through an anterior approach. Thorough radiological and CT analysis of FTDF shows that the vertebral body is often separated into two parts by a sagittal plane fracture, but remains continuous through the pedicle and anterior arch of the vertebral foramen with the lateral mass and the articular processes. We therefore hypothesized that reduction would be possible by acting on the articular process through a posterior approach with a particular plating technique. Eight patients with FTDF were operated on with the technique we describe. Three had complete tetraplegia, four had incomplete tetraplegia and one was normal. A preoperative CT scan was made in all patients. Local kyphosis, posterior displacement of the vertebral body, and general lordosis in the cervical spine were recorded. In all cases, a satisfactory reduction was achieved on the postoperative radiographs and at the mean follow-up of 18.6 ± 12.1 months, with residual posterior displacement being less than 1 mm. No complication occurred. Out of seven neurologically impaired patients, five showed some motor recovery at the latest follow-up. The posterior technique is described, and the rationale and pros and cons are discussed. The study showed that posterior reduction and fixation of flexion tear-drop fracture is not only possible, but permits an accurate restoration of the anatomy of the fractured cervical spine.
doi:10.1007/s005860050138
PMCID: PMC3611153  PMID: 10333149
Key words Cervical spine; Sinal injury; Tear-drop fracture; Posterior plating
24.  Trans-Sinusal Frontal Approach for Olfactory Groove Meningiomas 
Skull Base  2001;11(1):35-46.
The authors report on their experience with the trans-sinusal frontal approach in removing olfactory groove meningiomas. Six tumors were operated on by the trans-sinusal frontal approach, using a bicoronal incision; two tumors developed on one side, and there were four bilateral olfactosellar tumors. Osteotomy of the anterior wall of the frontal sinus was performed with an oscillating saw without any burr hole. The posterior wall of the sinus was resected and the tumor was attacked through a real subfrontal route along the plane of the anterior skull base. Ethmoidal blood supply was controlled at the initial stages of the operation, allowing avascular tumor debulking. Olfactory nerves, invaded by the tumor, were removed along with the tumor. Tumor extensions toward the sella and the optic canals were removed without brain retraction, opening of the Sylvian fissure, or dissection of the carotid arteries. All patients made a good neurologic recovery; intellectual impairment disappeared within 1 month, and visual acuity normalized within 2 weeks. Olfactory nets were preserved on the contralateral side in unilateral tumors. The trans-sinusal frontal approach is technically easy and safe to achieve. Osteotomy and replacement of the anterior wall of the frontal sinus are rapidly performed. When the frontal sinus is small, imageguided surgery allows precise deliniation of its limits and the free bone flap, including the calvarial outer layer, tangentially cut from one supraorbital canal to the other. The cosmetic result is perfect, as the normal contour of the forehead is maintained without any scar or visible burr hole. The trans-sinusal frontal approach gives access to the orbital roofs and to the central anterior skull base from the crista galli to the tuberculum sellae and the anterior clinoid processes. The trans-sinusal frontal approach represents an alternative to conventional craniotomies for tumors developed in the central anterior skull base, especially for olfactory groove meningiomas, whatever their size.
Images
PMCID: PMC1656832  PMID: 17167602
Anterior skull base; olfactory groove meningioma; frontal sinus approach
25.  Dorello's Canal for Laymen: A Lego-Like Presentation 
Objective Dorello's canal was first described by Gruber in 1859, and later by Dorello. Vail also described the anatomy of Dorello's canal. In the preceding century, Dorello's canal was clinically important, in understanding sixth nerve palsy and nowadays it is mostly important for skull base surgery. The understanding of the three dimensional anatomy, of this canal is very difficult to understand, and there is no simple explanation for its anatomy and its relationship with adjacent structures. We present a simple, Lego-like, presentation of Dorello's canal, in a stepwise manner.
Materials and Methods Dorello's canal was dissected in five formalin-fixed cadaver specimens (10 sides). The craniotomy was performed, while preserving the neural and vascular structures associated with the canal. A 3D model was created, to explain the canal's anatomy.
Results Using the petrous pyramid, the sixth nerve, the cavernous sinus, the trigeminal ganglion, the petorclival ligament and the posterior clinoid, the three-dimensional structure of Dorello's canal was defined. This simple representation aids in understanding the three dimensional relationship of Dorello's canal to its neighboring structures.
Conclusion Dorello's canal with its three dimensional structure and relationship to its neighboring anatomical structures could be reconstructed using a few anatomical building blocks. This method simplifies the understanding of this complex anatomical structure, and could be used for teaching purposes for aspiring neurosurgeons, and anatomy students.
doi:10.1055/s-0032-1311753
PMCID: PMC3424015  PMID: 23730547
Dorello's canal; anatomy; 3D; skull base

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