Last Updated: March 31, 2020
The pterional or frontotemporal craniotomy is the workhorse of the supratentorial approaches. Because of its simplicity, flexibility, efficiency, and familiarity to neurosurgeons, this corridor is the most commonly used surgical route to lesions along the anterior and middle skull base.
I use the extended pterional approach, defined as a standard pterional craniotomy supplemented and expanded by
- Osteotomy along the lateral sphenoid wing to the level of the superior orbital fissure
- Drilling along the roof of the orbit to flatten its surface.
- If necessary, roungering temporal squama towards the floor of the middle fossa.
These modifications provide unobstructed operative working angles toward the parasellar and subfrontal targets.
I consider this extended modification a skull base approach. The additional bone removal at the sphenoid wing and orbital roof expands the subfrontal operative trajectories toward the midline skull base while reducing retraction on the frontal lobe. The osteotomy along the roof of the orbit provides some of the advantages of an orbitozygomatic craniotomy, but it is more efficient and associated with less cosmetic deformity.
The extended pterional craniotomy must be tailored to the specific underlying pathology. The following steps describe the general principles of this approach, whereas the other relevant chapters review tailored exposures and intradural dissection via this route.
Recently, a supraorbital craniotomy through the eyebrow incision has been used as part of the minimally invasive keyhole concept to parasellar and midline anterior skull base pathologies. Using the same concept, a minipterional approach has also been described, which is predominantly centered on the main axis of the sylvian fissure and results in a similar exposure to the one afforded via the standard pterional approach. The ultimate choice of exposure must be minimally disruptive and allow flexible operative working angles to handle the lesion safely and efficiently.
Most importantly, the exposure should provide appropriate working space to handle potentially catastrophic situations such as massive intraoperative hemorrhage from aneurysms and vascular tumors. Therefore, routine indiscriminate use of one approach should be avoided. The operator should be intimately familiar with all modifications of the exposures to the subfrontal corridor and their advantages and limitations.
Indications for the Approach
The extended pterional approach has replaced the bifrontal craniotomy for giant midline anterior cranial fossa intradural lesions (ie olfactory and cribriform plate meningiomas) in my practice. With the exception of extradural skull base tumors extending into the intradural space (i.e. esthesioneuroblastomas, chondrosarcomas and other sinus malignancies), the unilateral lateral supraorbital or pterional exposure offers numerous advantages and no compromise in the necessary operative working angles.
I occasionally use the pterional route to reach contralateral lesions in very select cases such as contralateral ophthalmic, MCA and P1 artery aneurysms.
I do not use this route for purely third ventricular tumors, especially craniopharyngiomas. The endoscopic endonasal route provides excellent working angles along the long axis of the ventricle and most parasellar tumors and facilitates dissection without excessive brain manipulation. For the past decade, through the use of endoscopic endonasal techniques, I have not approached any pituitary tumor (regardless of its size or texture) through the transcranial route.
I use antiepileptic medications for patients who are not suffering from preoperative seizures, and I terminate these medications 7 days after surgery in the absence of any seizure during the immediate postoperative period. A lumbar drain is placed for cerebrospinal fluid (CSF) drainage and facilitation of brain relaxation in select patients who harbor large skull base lesions filling the basal cisterns. Such lesions block CSF pathways along these cisterns and prevent adequate cerebral relaxation during opening of the corresponding arachnoid membranes.
Depending on the degree of mass effect caused by the tumor, mannitol may be administered prior to the craniotomy. Dexamethasone is used in patients with significant vasogenic edema.
I use embolization sparingly in patients with an AVMs or meningiomas. Neuronavigation is usually used. Electroencephalography may be used for confirmation of burst suppression during clip ligation of aneurysms that are expected to require temporary parent vessel occlusion. I keep the patient normotensive throughout surgery, except patients with AVMs, for whom the systolic blood pressure is kept ~20-30% below their corresponding preoperative blood pressure.
Relevant anatomy for performing an adequate pterional craniotomy involves knowledge of the scalp and temporal connective tissue layers and the keyhole site. Over the scalp, five concentric layers are easily recognized, namely the skin, the subcutaneous tissue, the galea aponeurotica, the loose connective tissue and the pericranium.
The temporal region has a much more complex anatomical relationship. Beneath the skin and subcutaneous tissue, the temporoparietal fascia comprises an extension of the galea over the temporal area. It is commonly included within the skin flap during surgical procedures. The next layer is the loose connective areolar tissue, which is commonly used to develop the dissection plane towards the zygomatic arch. This plane is followed to the inferior temporal septum where three fascial layers get fused (temporoparietal fascia, loose areolar tissue and temporal fascia). At that level, the temporal fascia splits into two layers, the deep and superficial laminae that involve the superficial temporal fat pad before adhering to the superior margin of the zygomatic arch. The temporal fascia is the last layer over the temporal muscle and is in continuity with pericranium above superior temporal line. The frontotemporal branches of the facial nerve are found in the fatty-fibrous tissue in front of the septum. At this stage, preservation of such branches involves performing interfascial or subfascial dissection.
The patient is placed in the supine position with knees flexed and the head of the table elevated approximately 15-20 degrees. The head is immobilized in a skull clamp, turned (20-45 degrees) away from the side of the approach, and moderately hyperextended to allow the frontal lobes to fall away from the floor of the anterior cranial fossa. The latter maneuver requires the malar eminence to be the highest point on the head. The closer the pathology to the midline and the further anteriorly the lesion is located, the less I turn the head. For example, I turn the head ~30 and ~45 degrees for an anterior communicating artery and middle cerebral artery aneurysm, respectively.
Other colleagues use other parameters to position the head. More basal pathologies such as ophthalmic and posterior communicating artery aneurysms as well as cavernous sinus masses require little head deflection and greater head rotation so that the orbital ridge is left in the superior plane. On the other hand, middle cerebral and carotid bifurcation artery aneurysms as well as suprasellar tumors with more superior extension benefit from a greater head deflection and minimal head rotation, allowing the malar prominence to stay in the superior plane.
I reflect the myocutaneous flap in one layer and do not leave a cuff of muscle behind along the superior temporal line. The muscle should be mobilized as anteroinferiorly as possible to reveal the pterion. When securing the flap with fish-hook retractors, I place a rolled-up gauze underneath the flap to prevent the kinking of the scalp and its subsequent ischemic damage.
The anteromedial aspect of the craniotomy may violate the frontal sinus, so this bony area should be carefully inspected. Although the supraorbital notch has been cited as a landmark for defining the lateral aspect of the frontal sinus, this landmark is variable. Preoperative imaging and intraoperative navigation can help identify the lateral extent of the frontal sinus. If the frontal sinus is exposed, it should be exenterated, its mucosa removed and packed with muscle or bone wax.
Dissection of the Fat Pad via the Interfascial and Subfascial Techniques
The following two images demonstrate the techniques of interfascial and subfascial dissection of the fat pad to minimize the risk of frontalis palsy.
Pearls and Pitfalls
- I use the extended pterional approach, defined as a standard pterional craniotomy supplemented and expanded by aggressive osteotomy along the lateral sphenoid wing and roof of the orbit, to provide unobstructed operative working angles toward the parasellar area.
- The osteotomy along the roof of the orbit provides some of the advantages of orbitozygomatic craniotomy while being more efficient and associated with less cosmetic deformity.
Orbital and sphenoid wing meningiomas lead to orbital roof and sphenoid wing hyperostosis. Any intentional fracture over the lateral sphenoid wing during bone flap elevation can unintentionally extend to the optic canal and lead to blindness.
- The use of a pterional craniotomy for fibrous superior petroclival meningiomas and other large clival tumors is not advised. Petrosal osteotomies provide more expanded and safer approaches to these tumors.
Contributor: Marcus A. Acioly, MD, PhD
Figueiredo EG, Deshmukh P, Nakaji P, Crusius MU, Crawford N, Spetzler RF, Preul MC. The minipterional craniotomy: technical description and anatomic assessment. Neurosurgery. 2007;61(5 Suppl 2):256-265.
Krayenbühl N, Isolan GR, Hafez A, Yasargil MG. The relationship of the fronto-temporal branches of the facial nerve to the fascias of the temporal region: a literature review applied to practical anatomical dissection. Neurosurg Rev. 2007;30(1):8-15.
Shimizu S, Tanriover N, Rhoton AL Jr, Yoshioka N, Fujii K. MacCarty keyhole and inferior orbital fissure in orbitozygomatic craniotomy. Neurosurgery. 2005;57(1 Suppl):152-159.
Yasargil MG (ed) Microneurosurgery, vol I., Georg Thieme Verlag, New York, pp 217–220, 1984.
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