Pterional

The pterional approach is one of the most versatile exposures available to the neurosurgeon. When performed properly, this approach affords the surgeon access to all aneurysms of the anterior circulation (with the exception of distal anterior and distal middle cerebral lesions) as well as most aneurysms involving the upper basilar artery. The approach also provides access to lesions involving the anterior and middle cranial fossae, including those of the cribriform plate, suprasellar cistern, and interpeduncular region.

As a general rule, the head is secured in a radiolucent frame to allow for intraoperative angiography. The malar eminence is positioned superiorly, and the head is extended slightly and rotated 30 to 45 degrees from the vertical axis depending on the exact location and orientation of the aneurysm being treated. Some of the nuances regarding positioning for particular aneurysm locations will be discussed individually in the ensuing chapters.

Several skin incisions can be utilized, although we have preferred an incision that begins in front of the ear at the level of the zygoma and stays behind the hairline, curving gently up to the midline. The temporalis fascia and muscle are divided sharply and reflected forward to expose the pterion, the orbital rim, and the frontal process of the zygoma ( Fig. 1.1A ). A cuff of fascia can be left attached to the skull to allow for resuspension of the temporalis muscle at the conclusion of the procedure.

Several burr holes are placed strategically to facilitate raising the bone flap. The exact number and location are a matter of the surgeon’s preference, although we find it helpful if one hole is placed at the “keyhole,” and as a rule, we prefer three holes, as illustrated in Fig. 1.1A .

A small bone flap, providing exposure of the frontal and temporal lobes and centered on the Sylvian fissure, suffices in most cases. Since the work in aneurysm surgery is generally being performed under the brain or through a fissure, we have avoided overly large flaps that add little to visualization and place additional exposed brain at risk for inadvertent injury. One exception is in the setting of severe subarachnoid hemorrhage (SAH), when a larger flap may be necessary for decompressive purposes and to avoid an overly swollen brain from herniating out through a small opening, obscuring visualization and precluding a safe operation.

One of the most critical aspects of the procedure is the adequate drilling of the skull base to provide a low, flat exposure without excessive brain retraction ( Fig. 1.1B ). The dura should be elevated from the lateral sphenoid wing, the orbital rim, and orbital roof. We use retractors to protect the frontal and temporal dura while aggressively drilling the lateral sphenoid wing as well as the orbital bone. At this point, the dura can be elevated from the deeper aspect of the sphenoid wing, and the medial sphenoid wing as well as a portion of the anterior clinoid process can be removed as needed. A combination of bone wax and topical hemostatic agents may be required to achieve hemostasis prior to dural opening. Of note, the surgeon should be careful to remove the prominent ridges along the orbital roof, particularly when accessing deeper, midline aneurysms, such as those of the anterior communicating and basilar arteries. Often, we end up exposing the periorbita while thinning down the orbital roof. In these instances, the periorbita should be left intact if possible. At times, the orbital fat is encountered, and we have not had any ocular complications in such cases, although the eye does tend to become more swollen in the early postoperative period.

The dura is opened in a curvilinear fashion based on the Sylvian fissure and tented up with sutures. The degrees of frontal and temporal exposure are tailored to the individual aneurysm being treated. For anterior communicating and paraclinoid lesions, a greater degree of frontal exposure is needed. For middle cerebral aneurysms, a more even exposure of the frontal and temporal lobes is appropriate.

At this point, we generally bring in the operating microscope. We have never favored using loupes in opening the Sylvian fissure or in elevating the frontal lobe, as the magnification and illumination of the microscope provide a superior alternative. The lateral aspect of the Sylvian fissure is opened to release cerebrospinal fluid (CSF) and begin the dissection ( Fig. 1.1C ). We generally use a microknife to open the arachnoid and then a pair of jeweler’s forceps to begin the dissection. Sylvian veins are preserved whenever possible.

At this point, the exact aneurysm location being treated will determine the next steps. If the aneurysm arises at the middle cerebral bifurcation, the Sylvian opening is deepened and extended as needed to achieve proximal control and expose the aneurysm. When dealing with an anterior communicating, paraclinoid, or supraclinoid internal carotid artery (ICA) aneurysm, the frontal lobe can be gently elevated to expose the optico-carotid region. Arachnoid is sharply opened as illustrated in many of the included videos, and the surgeon should patiently allow CSF to drain, providing good brain relaxation in most cases ( Fig. 1.1D ).

The key to maximizing the safety and versatility of the pterional approach is the wide opening of all necessary arachnoid membranes at this point. Arachnoid bands tether the exposed structures, including the brain itself and associated arteries, veins, and cranial nerves. When retracting on the brain, the arachnoid transmits tension to any tethered structure, potentially risking injury. To avoid this risk, the surgeon should sharply divide the arachnoid to free the exposed structures and limit the transmitted tension. First, the arachnoid over the optic nerve and ICA should be taken down. The proximal Sylvian fissure can be opened to whatever extent is needed to allow for exposure of the critical anatomy. For example, to treat a paraclinoid aneurysm, only the proximal fissure needs to be opened, whereas to reach a carotid bifurcation lesion, the fissure should be opened to expose at least the proximal M1 segment.

The optic nerve is freed of all attachments to the ipsilateral frontal lobe, being careful to protect the recurrent artery of Heubner, which may be crossing the field just deep to this point. The olfactory tract should be freed as needed to avoid injury to it. In its fullest expression, the pterional exposure affords a dramatic and wide view of numerous critical areas of the brain.

As will be described next, the use of several adjunctive measures can further widen the anatomy that can be reached through this versatile exposure.