Ali F. Krisht
INTRODUCTION
The pterional approach, a modification of the frontotemporal approach, was popularized by Yasargil who described the pterional craniotomy in detail and used it for different pathologies involving the frontotemporal region and basal cisterns. Recent advances in our understanding of the anatomy of the skull base region expanded our abilities with the pterional approach in the depth of the surgical field. The pterional approach is one of the most commonly used approaches by any neurosurgeon performing cranial surgery. It is centered over the Sylvian fissure region, and in its classic description, it has more frontal than temporal exposure. However, different modifications of the pterional approach with more frontal or temporal extensions help to expand the reach of the approach and help to improve our ability to maximize the potential of the approach while improving safety and minimizing risk.
HISTORY
The history of a patient needing a pterional approach or one of its variations varies significantly because of the wide spectrum of pathologies involving this region. Due to the proximity of the lesions to the sellar and parasellar region, many patients will present with visual problems. Examples are tumors such as tuberculum sellae meningiomas, pituitary adenomas, and craniopharyngiomas. Vascular lesions such as paraclinoid aneurysms may also result in visual loss. Aneurysms of the posterior communicating artery may present with third nerve palsy. Seizures may be a presentation of larger lesions in the sellar and parasellar region. Gliomas involving the temporal lobe or the limbic and paralimbic regions most commonly present with seizures. Also, pituitary endocrinopathies are a common presentation, especially in tumors arising from or compressing the pituitary gland. Large tumors may present with signs and symptoms of increased intracranial pressure such as severe headaches, papilledema, nausea, and vomiting.
PHYSICAL EXAMINATION
The physical examination of patients with pathologies that will need a pterional approach or one of its variants varies with the different disease entities being treated. Patients with meningiomas may present with visual loss and visual field deficits that vary according to the location of the origin of the meningioma. On physical examination, patients with tuberculum sellae meningioma may present with bitemporal hemianopsia. The visual loss related to some of these tumors is more pronounced on the side that is closer to where the meningioma arises. Olfactory groove meningiomas present with diminished or absent olfaction due to compression of the olfactory nerves. They may also develop psychobehavioral changes due to frontal lobe dysfunction. Proptosis is commonly seen with sphenoid wing meningiomas extending into the lateral orbital wall. Cavernous sinus meningiomas present with diplopia and sixth nerve palsy. This is more typical with meningiomas involving the posterior medial compartment of the cavernous sinus because of tumor extension into the region of Dorello's canal. Anteriorly located cavernous sinus meningiomas may present with third nerve palsy.
Patients with pituitary adenomas usually present with headaches, decreased visual acuity, and bitemporal hemianopsia on examination of the visual field. Physical changes related to hormonal hypersecretion such as Cushing's syndrome and acromegaly are found on physical examination depending on the tumor type. The physical examination of patients with craniopharyngioma is not very different from that of patients with other suprasellar tumors except some patients may not exhibit signs and symptoms of diabetes insipidus.
INDICATIONS
The pterional approach and its variations have the potential to safely reach numerous pathologies involving the frontotemporal region and the skull base and basal cistern region. The following is a list of the different pathologic entities that can safely and effectively be treated using the pterional approach or one of its variants:
I.Tumors
1.Extraaxial
A.Meningioma
· Lateral sphenoid wing meningioma
· Medial sphenoid wing meningioma
· Clinoidal meningioma
· Dorsum sellae meningioma
· Tuberculum sellae meningioma
· Diaphragma sellae meningioma
· Planum sphenoidale meningioma
· Olfactory groove meningioma
· Anterior tentorial meningioma
· Anterior middle fossa meningioma
· Cavernous sinus meningioma
B.Pituitary adenoma
· With significant suprasellar and parasellar extensions
· Involving the cavernous sinus
C.Craniopharyngioma
· Suprasellar craniopharyngioma
· Retrochiasmatic craniopharyngioma
D.Others
· Dermoids
· Epidermoids
· Pituicytoma
· Arachnoid cysts
· Rathke cleft cyst
2.Intraaxial
A.Gliomas
· Insular gliomas
· Fronto-orbital gliomas
· Mesial temporal gliomas
· Temporal gangliogliomas
· Hypothalamic gliomas
· Fronto-opercular gliomas
· Temporo-opercular gliomas
II.Vascular lesions
A.Aneurysms
· Middle cerebral artery
o (M1, M2, and M3 segment aneurysms)
· Internal carotid artery
o Paraclinoid
· Posterior communicating artery
· Anterior choroidal artery
· Anterior communicating artery
· Basilar apex artery
· Superior cerebellar artery
B.Vascular malformations
· Arteriovenous malformations (AVMs)
o Fronto-orbital AVM
o Insular AVM
o Fronto-opercular AVM
o Temporo-opercular AVM
o Mesiotemporal AVM
o Lateral anterior temporal AVM
o Lateral frontal AVM
· Cavernous malformations (frontal & temporal lobes)
CONTRAINDICATIONS
Given its extraordinary versatility, there are few absolute contraindications to a pterional approach. However, it is an anterolateral approach, so tumors of the anterior midline can be difficult to access completely. Also, many lesions of the posterior fossa, especially more caudal, cannot be reached through a pterional approach.
PREOPERATIVE PLANNING
The preoperative planning for patients undergoing pterional craniotomy varies with the circumstances of the involved pathology and the presence or absence of symptoms. Patients with signs and symptoms of increased intracranial pressure are usually started on IV or PO steroids in the preoperative period. Patients presenting with seizures are started on anticonvulsants. In most patients with visual symptoms, preoperative ophthalmologic evaluation with visual fields is done. Pituitary function blood tests are performed when indicated. Angiography is occasionally done, especially in patients with vascular lesions. It may also be indicated in patients with tumors to verify the flow in the cerebral vasculature and the extent of the collateral flow in cases of significant cerebral arterial stenosis or occlusion. In most patients with brain tumors, a preoperative thin-cut MRI is done for intraoperative neuronavigational guidance.
SURGICAL TECHNIQUE
Skin Incision
The skin incision for the pterional approach and its variants is planned based on two important factors: (1) the cosmetic aspect of the location of the incision as it relates to the location of the hairline in each individual patient and (2) the craniotomy site as it relates to the pathology involved. In general, trying to follow a very rigid rule about the location of the incision compromises the cosmetic result if the difference in the shape of the patient's head is not taken into account. My skin incision is usually tailored to the location of the craniotomy and its extension as is needed in every specific case. The main rule to follow is that for all pterional craniotomies, the pterion region has to be comfortably reached after reflecting the skin flap. For this reason, we make sure that a straight line connecting the beginning and the end of the skin incision is not more than 1 cm away from the junction of the root of the frontal zygoma with the orbital rim (Fig. 10.1).
FIGURE 10.1 Shows a straight line connecting the beginning and the end of the different skin incisions as indicated by the pathology. This straight line is not more than 1 cm away from the junction of the route of the frontal zygoma with the orbital rim.
In this way, the starting point of the incision at the preauricular region can extend superiorly or inferiorly based on how much temporal extension of the craniotomy is needed. The frontal end of the incision is decided based on the straight line mentioned above while at the same time achieving a good cosmetic result. In a receded hairline, the incision may need more posterior extension. When a more frontal craniotomy is needed, the skin excision is extended more frontally. Extension beyond the midline is sometimes needed if a full cranio-orbital craniotomy is needed (Fig. 10.1).
Temporalis Muscle Dissection
The preservation of the integrity of the temporalis muscle is of utmost importance for a good cosmetic outcome. It is very important to preserve the bulk of the temporalis muscle as well as its blood and nerve supply. The blood supply of the muscle arises from the deep temporal artery, the branches of which run along the inner surface of the muscle. This is why it is very important that the deep fascia of the temporalis muscle be dissected very carefully from the bone. This maneuver will help to preserve the underlying blood and nerve supply to the temporalis muscle. The use of cautery to elevate the temporal muscle has a higher risk of heat injury to the nerve supply of the muscles as well as compromise of the blood supply. I prefer to leave a small cuff of fascia along the superior temporal line without leaving much of the muscle fibers along its insertion, to be used for suture reconstruction of the muscle at the end of the surgery (Fig. 10.2). The muscle is reflected inferiorly and anteriorly along the course of its origin.
FIGURE 10.2 Shows the deep fascia of the right temporalis muscle being dissected sharply from the underlying bone (arrow).
Occasionally, the temporalis muscle is large, and when more temporal exposure is needed, the zygomatic arch is drilled to achieve better inferior reflection of the temporal muscle (Fig. 10.3). This maneuver can improve the exposure to lesions involving the middle temporal fossa and the region of the cavernous sinus and anterior upper one-third of the posterior fossa. It would also provide a more superior exposure to the suprasellar region from a lateral to medial projection.
FIGURE 10.3 A and B.Shows the zygomatic arch before and after drilling it. This maneuver allows more inferior reflection of the temporalis muscle for better pretemporal and subtemporal access.
The Craniotomy
The extent of the craniotomy changes with the pathology involved. There are three variations of the pterional approach craniotomy: the standard craniotomy, craniotomy with frontal extension, and craniotomy with temporal extension (Fig. 10.4).
FIGURE 10.4 Shows the three variations of the pterional approach craniotomy. The upper middle picture shows the standard pterional craniotomy. The lower left shows a pterional craniotomy with more frontal extension, and the lower right shows a pterional craniotomy with a more temporal extension.
Burr Hole
Although one burr hole may be enough to establish the needed craniotomy, it has a higher risk of tearing the dura, especially in older patients who have significant adhesions between the dura and the inner surface of the skull. I generally like to drill three burr holes as indicated in Figure 10.4, all of which would be covered by the temporalis muscle during the closure and reconstruction. The location of these burr holes will help bridge the sharp, bony prominences on the inner aspect of the skull and dissect the dura before using the craniotome to create the bone flap.
Once the burr holes are made, the craniotome is used to create the craniotomy by connecting the burr holes and drilling the medial aspect of the sphenoid wing to weaken its attachment. This allows the bone flap to be reflected easily. Hemostasis in the epidural space is then established using gel foam powder along the bone edges followed by tack-up sutures. Further work is now done under magnification using the operating microscope.
Epidural Dissection and Exposure
The extent of removal of the bone of the skull base varies with the exact location of the pathologic entity being treated. In general, to gain access to the basal cisterns and to be able to open the arachnoid over the optic nerve to release spinal fluid and achieve early brain relaxation with minimal brain retraction, the sphenoid wing has to be drilled flat with the orbital roof (Fig. 10.5). The extent of removal of the sphenoid wing varies with different pathologies. In the standard pterional approach, removal of the sphenoid wing can be stopped at the level of the meningo-orbital artery. In cases where further exposure of the temporal fossa is needed, or when the anterior clinoid process needs to be removed, the epidural dissection needs to be extended in both the subfrontal and the pretemporal regions. This is done by coagulating and cutting the meningo-orbital artery and followed by dissecting the dura propria of the temporal lobe away from the region of the superior orbital fissure (Fig. 10.6). This dissection can be extended to the lateral wall of the cavernous sinus for lesions that need to be approached either in or through the cavernous sinus (Fig. 10.7). Occasionally, during this step, brisk bleeding from the cavernous sinus may occur. This is easily controlled by injecting fibrin glue into the cavernous sinus region. When performing this step, caution should be taken to prevent reflux of fibrin glue into the Sylvian veins via the sphenoparietal sinus, which may connect to the cavernous sinus. This is done by applying pressure with the suction device or with a Cottonoid over the sphenoparietal sinus to prevent retrograde reflux of fibrin glue.
FIGURE 10.5 Shows the standard pterional approach before (left) and after (right) drilling of the sphenoid wing. Notice the advantage gained in accessing the subfrontal region by drilling the sphenoid wing flat with the orbital roof.
FIGURE 10.6 Shows the epidural peeling of the dura propria of the temporal lobe away from the lateral wall of the superior orbital fissure and anterior cavernous sinus region (asterisk). This will also enhance the exposure of the anterior clinoid process and put it in a more superficial location. (O, orbit; AC, anterior clinoid; FD, frontal dura; TD, temporal dura.)
FIGURE 10.7 Retouched picture of the detailed anatomy of the neurovascular structures and the lateral wall of the cavernous sinus after removal of the anterior clinoid process. (ON, optic nerve; SOF, superior orbital fissure; ICA, internal carotid artery; FD, frontal dura; TD, temporal dura; IV, trochlear nerve; III, oculomotor nerve; V1, V2, and V3 branches of the trigeminal nerve; GG, gasserian ganglion; and MC, Meckel's cave.)
During this step, a good understanding of the anatomy of the middle fossa is essential. Familiarity with the plane between the temporal lobe and the lateral wall of the cavernous sinus is crucial to avoid inadvertent entry into the cavernous sinus or into the intradural space on the temporal side.
The above-mentioned steps with dissection of the disconnected dura on the frontal side will lead to full exposure of the anterior clinoid process as far as its tip.
Removal of the Anterior Clinoid Process
Removal of the anterior clinoid process requires an in-depth understanding of its anatomy. This is very crucial because of the extensive variations of its anatomy and its relationship to the adjacent neural and vascular structures including the internal carotid artery, optic nerve, and oculomotor nerve. The anterior clinoid process has three surgical anatomic connections that need to be removed for it to be safely disconnected (Fig. 10.8). Those connections are (1) the medial sphenoid wing connection to the orbit, (2) the optic roof, and (3) the optic strut. Removal of the posterior third of the roof of the orbit will disconnect the anterior clinoid process from the sphenoid wing. This is followed by drilling the optic roof using the high-speed drill with a diamond drill bit to release the second connection. This is followed by drilling the optic strut with extra caution to avoid the clinoidal internal carotid artery and the optic nerve. This is done by using copious irrigation and frequent stops during the drilling process. During this drilling process, the bulk of the clinoid process is decreased in volume, especially in patients who have a very large and elongated clinoid (Fig. 10.9). This will render the clinoid tip free from its attachments and can easily be scooped out of its bed. In a few cases, a middle clinoid process connecting the anterior clinoid process is present and will prevent the clinoid tip from becoming mobile after disconnecting its attachments. In this case, the clinoid process should be drilled along its posterior extension toward the posterior clinoid process as needed.
FIGURE 10.8 Shows the three surgical attachments of the right anterior clinoid process. (a, sphenoid ridge; b, roof of optic canal; c, optic strut.)
FIGURE 10.9 Steps of drilling the right anterior clinoid process. A.Removal of the optic roof. B. Exposure of the anterior clinoid between the optic canal and superior orbital fissure. C. Drilling of the optic strut after unroofing the optic canal. D. View after removal of the anterior clinoid process. (ON, optic nerve; FD, frontal dura; OS, optic strut; III, oculomotor nerve; SOF, superior orbital fissure; O, orbit; ICA, internal carotid artery.)
The Dural Opening
The dural opening is tailored according to the pathology involved. For lesions needing a standard pterional approach, a C-shaped curvilinear incision of the dura with the flap reflected anteriorly over the sphenoid wing region is used. In lesions involving the sellar and parasellar regions and the clinoid and the paraclinoid regions, I prefer an incision extending along the indentation of the sphenoid wing as indicated in Figure 10.10. It is then followed by medium subfrontal and/or lateral subtemporal extensions as needed. This will allow direct access to the basal cistern area without any retraction of the brain. It will also take advantage of all of the bone work previously done to get wide access to the deeper anatomic corners.
FIGURE 10.10 Shows the different options of the dural opening depending on the different pathology involved. Left shows the opening of the pathology is more frontal and subfrontal in location. Rightshows the opening when the pathology is more centered in the approach and/or if it extends both pretemporal and subfrontal.
Intradural Steps
Once the dura is opened, the initial steps are focused on opening the arachnoid of the basal cisterns, releasing spinal fluid, and achieving brain relaxation. This is usually started by opening the arachnoid over the optic nerve followed by opening the arachnoid over the carotid cistern. Further dissection is carried out depending on the pathologies involved. In patients with subarachnoid hemorrhage, further brain relaxation is achieved by opening the lamina terminalis. In patients with anteriorly projecting anterior communicating artery aneurysms, this may not be possible, and dissection must be directed toward Liliequist's membrane to release spinal fluid from the prepontine cistern and between the internal carotid artery and oculomotor nerve.
Further dissection is carried out depending on the pathology involved. For lesions involving the region of the Sylvian fissure, the fissure will need to be opened. The extent of the opening of the Sylvian fissure also depends on the location and the size of the lesion. For example, insular gliomas need a wide opening of the Sylvian fissure, whereas a posterior communicating artery aneurysm may only need opening of the proximal aspect of the Sylvian fissure. The Sylvian fissure is best opened as described by Yasargil from inside to outside. This is usually started by finding an M4 branch of the middle cerebral artery leading to the Sylvian fissure (Fig. 10.11). The arachnoid is opened, and the dissection is carried to the depth of the Sylvian fissure in the direction of the limen insulae to find the M3 and M2 branches and then to follow the M1 branch along its proximal course in the direction of the bifurcation of the internal carotid artery. Once the deep hollow part of the fissure (the vallecula) is opened, then the dissection is carried to the more superficial part of the frontal and temporal operculae. Opening of the Sylvian fissure is a step that is essential for the safe handling of many pathologies approached through the pterional approach. The safety of the dissection is enhanced by an in-depth understanding of the vascular anatomy of the blood vessels in the Sylvian fissure and their variations.
FIGURE 10.11 Shows a left-sided Sylvian fissure and a M4 branch leading to the depth of the Sylvian fissure and the region of the M1 segment of the middle cerebral artery. (TL, temporal lobe; FL, frontal lobe.)
Pterional Transcavernous Route
The pterional approach can be used to access lesions involving the cavernous sinus region. It can also use the transcavernous route to lesions involving the suprasellar region and the interpeduncular fossa. For lesions involving the region of the cavernous sinus, a pterional approach with more temporal extension is used. The extradural dissection is performed as described above. In many pathologies, a wider extradural window is needed. This can be achieved by coagulating and cutting the attachment of the middle fossa subtemporal dura to the middle meningeal artery at the level of the foramen spinosum. This is followed by further dissection of the dura propria of the temporal lobe from the lateral wall of the cavernous sinus all the way posteriorly, over the Gasserian ganglion, and to the level of the Meckel's cave. This step provides access to most pathologies involving the cavernous sinus region, without having to open the intradural compartment.
For lesions involving the suprasellar region and the anterior superior aspect of the posterior fossa, the transcavernous route can be very valuable. This is done by combining the extradural exposure with the intradural dissections. This is further enhanced by dissecting the oculomotor nerve along its whole length from the brainstem to the superior orbital fissure. This maneuver allows the oculomotor nerve to become more mobile and enlarges the window to the interpeduncular fossa. This will provide an unobstructed view of this region with minimal to no retraction of the brain (Fig. 10.12).
FIGURE 10.12 Shows the extent of the exposure achieved by adding the intradural dissections with a transcavernous route to the right pterional approach. Notice the wide exposure of the depth of the surgical field in the region of the interpeduncular fossa. (III, oculomotor nerves; An, aneurysm; P1, posterior segment of the posterior cerebral artery on the right side.)
Closure
Attention to the closure of the pterional craniotomy should be as important as the attention to the opening. Tack-up sutures are applied at the edges of the craniotomy to avoid excessive collection of blood in the epidural space. In cases where the pretemporal space is dissected along the lateral wall of the cavernous sinus, pretemporal tack-up sutures are applied. This would prevent the occurrence of a pretemporal hematoma. The closure of the dura should be watertight. In many cases when the anterior clinoid process is removed and the clinoidal dura is excised, a defect remains in the dura which usually spans the space between the optic nerve medially and the oculomotor nerve latterly. I usually close this defect with either a piece of temporalis muscle or a piece of adipose tissue harvested from the subcutaneous tissue of the abdomen. While performing this closure and in patients in whom the sphenoid sinus has been opened while removing the anterior clinoid process, extra attention is paid to obliterate the window to the sphenoid sinus between the optic nerve and the internal carotid artery. This is important to prevent any leakage of cerebral spinal fluid. Along the same lines, in patients who undergo a pterional craniotomy with a more median extension, the frontal sinus may be opened. In such cases, it is important to cranialize the sinus by stripping the mucosa of the sinus and then obliterating the sinus either with bone wax, if the window to the sinus is small, or with subcutaneous adipose tissue, if the opening in the sinus is wide. The closure is usually reinforced by reflecting and rotating a pericranial flap over the obliterated opening.
The bone reconstruction after a pterional approach is also important to be attended to in order to avoid any cosmetic defects in the region of the temporalis muscle. This is especially so when the junction of the zygoma and the orbital rim is drilled flat with the orbital roof and after removing the sphenoid ridge. The combination of reconstructing this defect and preservation of the integrity of the temporalis muscle leads to an excellent cosmetic result (Fig. 10.13).
FIGURE 10.13 Shows the closure and reconstruction of the bone of the region of the junction of the frontal zygoma, the orbital rim, and the sphenoid wing region with the orbital roof.
Following this step, the temporalis muscle is sutured back to the superior temporal line from where it was detached as described earlier. This is followed by good approximation of the galea and subcutaneous tissue to establish good hemostasis. For this reason, I do not use any subcutaneous drains in our patients.
The skin is closed with either staples or 3-0 nylon sutures. The sutures are usually removed two weeks from the day of the surgery, and the incision is kept dry during this period of time.
POSTOPERATIVE MANAGEMENT
In the postoperative period, patients are kept for one or two nights in the intensive care unit to monitor their neurologic status, fluid input/output balance, and vital signs. Antibiotics are started an hour before surgery and continued for 24 hours when the surgical procedure is shorter than 4 hours and 48 hours if it is longer than 4 hours. The antibiotics of choice should include coverage for Gram-positive cocci. Nafcillin is one choice in patients who have no penicillin allergy; otherwise, vancomycin is used. For patients in whom the skull base air sinuses are violated, ceftazidime is added for broader spectrum coverage. In the majority of patients, periorbital edema is commonly seen. It is usually treated with cold compresses and by elevating the head of the bed.
On the first postoperative day, patients are moved to a chair, and their Foley catheter is discontinued unless closer monitoring of urine output is indicated. Patients are started on PO diets and advanced as tolerated. Early ambulation is encouraged, and the majority of patients are transferred out of the intensive care unit to a regular room on the second day after surgery.
COMPLICATIONS
The pterional approach and its variants have been well established, and when properly done with minimal trauma to the tissues and attention to preservation of the blood supply to the tissue, they are approaches with a very low complication rate. When proper dissection of the subcutaneous layer is performed, the frontalis branch of the facial nerve achieves full recovery even if a temporary weakness occurs from stretching the nerve or postoperative edema. When significant drilling of the sphenoid wing region is indicated and done, inadequate reconstruction of the pterional bony defect can lead to a postoperative disfiguring depression at the site of the craniotomy. This may be further exaggerated if atrophy of the temporalis muscle occurs due to poor handling of its blood supply. Complications related to vascular, parenchymal, or cranial nerve injuries are in general avoidable using the proper microsurgical technique and an in-depth understanding of both normal anatomy and distorted pathologic anatomy. Obviously, the chance of complications varies with the complexity of the lesions involved.
The reconstruction of the skull base is of utmost importance in avoiding complications such as cerebrospinal fluid leaks leading to rhinorrhea or otorrhea. This is best avoided by in-depth knowledge of the bony anatomy of the skull base and the region of the anterior clinoidal process and its variations especially as it relates to the air sinuses. Adequate reconstruction of the defects in the skull base is best achieved by obliterating the windows leading to the air sinuses as mentioned earlier. This is best done either using subcutaneous adipose tissue harvested from the abdomen or, for a small defect, using a small piece of temporalis muscle and/or fascia.
RESULTS
An in-depth understanding of the pterional approach and its variations is essential for every neurosurgeon performing cranial procedures. It provides access to a wide intracranial region that harbors a long list of pathologic processes. Mastering this approach and understanding the variations of the bony, vascular, and neural anatomy involved with this approach are essential for the safe and effective treatment of these pathologies.
The results of pterional and orbitopterional craniotomy for many cranial lesions have been well described in the literature. These approaches represent the most commonly performed techniques for clipping all anterior circulation and many aneurysms of the posterior circulation. This has created the standard against which all other results are measured, including endovascular treatment. Sphenoid wing meningiomas, suprasellar tumors, and lesions of the cavernous sinus and interpeduncular cistern have all been approached with ease and success via these approaches with little approach-related morbidity.
PEARLS
· The pterional craniotomy may be modified with different frontal or temporal exposure as needed, depending on the location of the pathology.
· The anterior clinoid can be exposed with careful interdural dissection deep to the meningo-orbital artery.
· The anterior clinoid process should be disconnected from the medial sphenoid wing, optic roof, and optic strut. Copious irrigation should be employed during drilling.
· The Sylvian fissure should be split from the inside to outside, identifying proximal MCA and ICA branches before separating the operculae.
PITFALLS
· During subcutaneous dissection, the adipose tissue pad superficial to the temporalis fascia should be separated from the underlying fascia or the fascia brought up with it in order to avoid injury to the frontalis branch of the facial nerve, which runs superficial to it.
· Drilling of the optic strut carries the risk of injury to the internal carotid artery and the optic nerve and should be done slowly and carefully.
INSTRUMENTS TO HAVE AVAILABLE
· Standard craniotomy instruments
· Variable length bipolar forceps
· Variable-sized suction tips
· Microdissectors
· Microknives
· Microscissors
· Microforceps
SUGGESTED READING
Yasargil MG, Antic J, Laciga R, et al. Microsurgical pterional approach to aneurysm of the basilar bifurcation. Surg Neurol 1976;6:83–91.
Yasargil MG, Smith RD, Young PH, et al. Interfascial pterional craniotomy. In Yasargil MG, ed. Microneurosurgery, Vol. 1. Thieme, Stuttgart, 1984:215–233.
Yasargil MG, Krisht AF, Ture U, et al. Microsurgery of insular gliomas, part II: opening of the sylvian fissure. Contemporary Neurosurgery 2002;24(8):1–6.
Krisht AF. Transcavernous approach to diseases of the anterior upper third of the posterior fossa. Neurosurg Focus 2005;19:1–10.
Krayenbuhl N, Hafez A, Hernesniemi J, et al. Taming the cavernous sinus: technique of hemostasis using fibrin glue. Neurosurgery 2007;61(3):ONS-E52.