27 Pretemporal Approach
Abstract
The pretemporal approach is a combination of the subfrontal and transsylvian routes provided by the pterional approach described by Yasargil and the subtemporal route provided by Drake’s approach, including the temporopolar corridor. The wide opening of the Sylvian fissure and basal cisterns, including the cutting of the arachnoid in the mesial aspect of the temporal lobe and free border of the tentorium, associated with the sacrifice of small veins in the temporopolar surface, allows the displacement of the temporal lobe posteriorly and laterally, creating broad access to the interpeduncular cistern and petroclival region, as well as the sellar and parasellar regions, where tumoral and vascular lesions may be surgically treated through this approach.
In this chapter, the authors provide a stepwise description of the pretemporal approach and its variations.
Keywords: craniotomy, frontotemporal approach, half and half, microsurgery, pretemporal, pterional approach, subtemporal approach, Sylvian fissure, temporopolar approach
27.1 Introduction
The ideal neurosurgical approach provides an unobstructed view of the lesion or site of interest; has a short distance which maximizes the surgeon’s dexterity; allows a surgical field with sufficient space necessary for maneuvering of the instruments without impairing the surgeon’s vision or inadvertently injuring any tissue; renders an ergonomic environment for the surgeon during the entire procedure despite its length; causes minimal trauma to any tissue, but above all to any neurovascular structure; gives the opportunity to reconstruct any and all tissues necessary to be mobilized for its realization, restoring their natural anatomical position and physiological function; and prevents, avoids, or minimizes any postoperative complication. In this manner, the ideal neurosurgical approach is the one that allows the surgeon to master their neurosurgical skills and surgical strategy to the zenith as if, after the proposed treatment is thoroughly accomplished, it looks as if it was not even performed.
In the optimal application of these precepts, the cavernous sinus, the superior orbital fissure, the sellar, parasellar, and retrosellar areas, the interpeduncular cistern, the anterior portion of the ambient cistern, the interpeduncular fossa, the parapeduncular region, the mesial temporal region, the superior pontine area, among others, and their neurovascular contents offer extraordinary defiance for those surgeons who venture to treat lesions of these areas. To achieve these objectives, more than innovating, surgeons refine and combine different approaches in the light of the clinical, radiological, technical, and technological advances. The pretemporal approach is an example of this tendency. First mentioned by Drake, who named it the “half and half” approach, the advantages of the combining the subtemporal and pterional approaches introduced for treatment of basilar artery (BA) aneurysm (AN) were commented in the report of Samson et al.1 Influenced by Drake’s comments, Sano et al2 described the steps of this approach, naming it the “temporo-polar approach.” Derived from Yasargil’s pterional approach, the pretemporal approach was described by de Oliveira et al,3 following the concepts of Drake, Samson, and Sano.1 , 4 However, the microsurgical anatomy refinements included in de Oliveira’s description emphasized the importance of arachnoid opening on the medial temporal lobe at the level of the uncus and free edge of the tentorium and oculomotor nerve, associated with the coagulation of small bridging veins of the temporopolar region, allowing the displacement of the temporal lobe posteriorly and laterally.3 Consequently, this approach provides at least four different routes: subfrontal, transsylvian, temporopolar, and subtemporal (Fig. 27.1). Refinements of the technique and anatomical knowledge further enriched and detailed the stepwise surgical description and expanded its surgical application.
Fig. 27.1The four different corridors provided by the pretemporal approach: subfrontal, transsylvian, temporopolar, and subtemporal.
27.2 Advantages of the Pretemporal Approach
The combination of the pterional and subtemporal routes provides considerable benefits to the surgery:
●Minimizes brain retraction by wider removal of the sphenoid wing providing greater access to the frontotemporal basal angle
●Shortens the distance between the surface and the targeted lesion
●Accessing multiple surgical corridors (subfrontal, transsylvian, temporopolar, and subtemporal) provides multidirectional viewing and surgical possibilities
●Allows intradural and extradural access for unroofing the optic canal and the superior orbital fissure for further exposure and dissection of the cavernous sinus
●Allows variability in the size of the flap, either higher frontally or lower temporally, according to the lesion
●Access to the infratemporal and sphenopalatine fossa
●Possibly minimizes blood loss by early interception of the blood supply through the sphenoid ridge in the surgery of tumors
●Gives good cosmetic results
27.3 Anatomical Exposure and Surgical Access
27.4 Indications
The pretemporal approach is suitable for extradural lesions located in the parasellar and retrosellar areas, with or without extension to the cavernous sinus and superior portion of the petroclival region. It is also a choice for primary lesions in the cavernous sinus (tumors, ANs, and fistulas), anterior part of the tentorial incisura, interpeduncular fossa, and intrinsic lesions located in the medial temporal region.
27.5 Step-by-Step Procedure
27.5.1 Patient Positioning
For the pretemporal approach, the patient is placed in a supine position. The patient’s trunk and head are elevated about 20 degrees, i.e., above the heart’s level, to facilitate the venous return. The head is then fixed in the three-point head-holder, taking care to keep the pins away, far posterior to the incision’s planned site (Fig. 27.2). Care must be taken to avoid positions that compress the trachea, jugular vein, carotid, or vertebral arteries. The head is careful hyperextended, rotated away from the side of the lesion, and deflected to place the malar eminence at the most superior point of the operative field. This sets the sphenoidal ridge vertically and the Sylvian fissure perpendicularly to the surgeon’s view, facilitating the opening of the fissure and the exposure of the basal cisterns and exposition of the proximal segment of the intradural ICA, ICA bifurcation, and A1 and M1 segments. The head’s deflection also allows better exposure of the middle fossa without the need for temporal lobe retraction.
Fig. 27.2 (a–c) Patient positioning with the head fixed by a three-point Mayfield head-holder and the hair shaved only in the area of the skin incision.
27.5.2 Skin Incision
There are variations in the incision location from patient to patient depending on the intracranial site of interest, the skull morphology and frontal sinus topography, and the hairline position. As a general rule, a curvilinear frontotemporal skin incision extends from the superior border of the zygomatic arch, beginning 1 cm anterior to the tragal cartilage, and extending behind the hairline toward the ipsilateral pupil, midline, or contralateral pupil depending on the lesion extension and need of exposure on the anterior fossa (Fig. 27.3). If the middle fossa and petroclival region’s exposition is necessary, an extended incision over the rim of the external ear is carried out. The skin incision is made with meticulous dissection to prevent injury of the superficial temporal artery (STA) and the branches of the facial nerve that pass anterior to it.
Fig. 27.3Incision options: up to the midline (blue line) or crossing the midline up to the contralateral pupillary line (red line).
Fig. 27.4 (a–c) Skin incision and preservation of the superficial temporal artery (STA) and its branches.
27.5.3 Preservation of the STA
The skin incision starts higher in the temporal area and advances downward toward the tragus. The STA is identified distally and separated from the skin by dissection in the subcutaneous plane. Its attachment to the muscle is preserved, and it is not raised with the skin flap, as is commonly practiced. After sharp dissection of the galea, the scalp flap is reflected anteriorly, leaving thick areolar tissue with a pericranial layer adhering to the calvaria. The STA’s anterior branch can be cut distally and displaced with the scalp flap, while the posterior branch should remain adherent to the temporalis muscle (Fig. 27.4).
27.5.4 Facial Nerve Branches Preservation
The frontotemporal branches of the facial nerve innervate the frontal belly of the frontalis muscle, the orbicularis oculi, and corrugator supercilii muscles.5 These branches run within the plane between the superficial temporal fascia and the galea aponeurotica (Fig. 27.5), and their preservation will increase the chances of excellent functional and postoperative cosmetic results. Yasargil reported the first attempt of atraumatic mobilization by the so-called interfascial dissection technique, interfascial pterional (frontotemporosphenoidal) craniotomy, describing the mobilization of the superficial layer of temporal fascia along with the fat pad between the superficial and deep layers of the temporal fascia6 (Fig. 27.6).
In case of a more extensive deflection of the skin flap anteriorly, as in orbital rim removal, the described subfascial dissection maneuver, by Al-Mefty,7 , 8 consisting of mobilization of both, the superficial and deep layers of the temporalis fascia, is anatomically more appropriate. On this, the layers are incised 1- to 2-cm posterior to the orbital rim until the muscle fibers are visualized, posterior and parallel to the course of the facial branches, towards the most posterior aspect of the root of the zygoma, facilitating the subperiosteal exposure of the zygomatic arch and lateral orbital rim (Fig. 27.7).
Fig. 27.5Cadaveric specimen dissection demonstrating the anatomical relationship of the superficial temporal artery (STA), facial nerve branches, and zygomatic arch.
Fig. 27.6 (a) Subcutaneous dissection. (b) Pericranial flap used for skull base dural reconstruction. (c, d) Interfascial dissection of the temporal muscle.
27.5.5 Mobilization of the Temporal Muscle
The temporal muscle derives its blood supply from the middle temporal artery (MTA), a branch of the STA, and from the anterior and posterior deep temporal arteries (DTAs), which are branches of the internal maxillary artery (IMA). The innervation of the temporal muscle derives from the anterior division of the mandibular nerve (V3—the third division of the trigeminal nerve), which, through its buccal and masseteric rami, gives the nerve supply to the different muscular components of the muscle by the ramification of the anterior, middle, and posterior deep temporal nerves. Both main vascular and nerve supplies are contained within the deep temporal fascia, which is how the periosteum is named at the region covered by the temporal muscle.
An inferior-to-superior and posterior-to-anterior, called retrograde maneuver, is applied to mobilize the muscle and prevent secondary injury to its innervation and vascularization, ensuring that the subperiosteal plane is maintained and the use of electrocautery is avoided (Fig. 27.8). The muscle is completely detached from the superior temporal line avoiding cutting in the fibers of the temporal muscle (Fig. 27.9). A piece or cuff of deinnervated or devascularized muscle left attached to the bone could contribute to poor postoperative cosmetic result, secondary to the muscular atrophy and the disfiguring temporal hollow. At the reconstruction step of the surgery, the superior part of the muscle is sutured directly to the bone through a series of holes made in the bone along the superior temporal line.
Fig. 27.7Subfascial dissection on a cadaver specimen. (a–e) Identification and cutting of the temporal muscle’s deep superficial fascia with muscle fibers’ observation. (f) Subfascial dissection with the exposition of the lateral wall of the orbit and the zygomatic arch.
27.5.6 Craniotomy
The craniotomy used in this procedure is an extended pterional craniotomy with a temporal extension. In general, three burr holes, or even two depending on the bone–dura interface dissection, are sufficient (Fig. 27.10). Eventually, four or more burr holes may be necessary to maintain the dura mater integrity and optimize the dissection’s extradural step. The initial burr hole is placed just posterior to the frontozygomatic suture under the superior temporal line. A second hole is placed just below the superior temporal line, variably behind the coronal suture, depending on the posterior extension of the site of interest. The third hole is placed over the squamous part of the temporal bone at the junction with the posterior root of the zygomatic arch as flush as possible to the temporal fossa floor. We often avoid placing a frontal burr hole for cosmetic reasons, but if necessary, we try to respect the frontal sinus’s limits.
The dura mater is then gently and carefully separated from the bone with different angulated periosteal elevators to preserve the dural integrity. The high-speed drill’s foot attachment connects the burr holes and is advanced through the inferior burr anteriorly, as flush as possible to the temporal fossa floor, until the sphenoid ridge is reached. The most lateral portion of the greater wing of the sphenoid, still holding the bone flat, is then grooved with the drill to allow an atraumatic and limited fracture across the sphenoid ridge, and the flap is finally raised. If any remaining temporal squama obstructs a perpendicular view of the temporal fossa, it is drilled away until the temporal lobe tip is visualized.
The bone dust is saved to fill up the holes in the reconstruction step of the procedure. The presenting rough bony hills of the posterolateral aspect of the orbit are shaved carefully with the drill to prevent any inadvertent violation of the orbital content and secondary extravasation of the periorbital fat. Similarly, the sphenoidal ridge is progressively and extensively drilled away until the orbital-meningeal artery, an anastomotic branch of the ophthalmic to the middle meningeal artery, which is the lateral limit of the superior orbital fissure, is reached. The remaining ridge of bone represents the most lateral aspect of the lesser wing, guiding the dissection medially toward the anterior clinoid process. To facilitate the subsequent step, which is removing the anterior clinoid process, the posterior third of the lateral and superior orbital can be removed during this step, preserving the periorbita.
27.5.7 Variations and Alternative Routes
Zygomatic Osteotomy
An osteotomy of the zygomatic arch is highly recommended in patients with bulky temporal muscle, especially if access to the lower temporal fossa is anticipated. Further retraction downward of the temporal muscle prevents brain retraction and unhindered exposure of the temporal lobe. It allows a better view without excessive retraction of the muscle, which could injure the muscle fibers and integrity of vascularization and innervation. The posterior deep temporal and masseteric nerves are related to the posterior root of the zygoma. To prevent injury to these nerves, the temporal muscle is protected from the cutting tool by a spatula applied between the muscle and the zygoma. The osteotomy is performed with oblique cuts anteriorly through the malar eminence and posteriorly through the zygoma root, drawing a “V”-shaped zygomatic arch flap (Fig. 27.11) that keeps its vascularization attached to the masseteric muscle. Because of its shape, the zygomatic flap arch is easily reattached. One maneuver to achieve the best possible anatomical realignment is to place the microplate burrs before detaching the flap. An alternative to the zygomatic osteotomy is to drill the superior aspect of the zygomatic arch at the level of the zygomatic notch (the junction of the frontal and temporal zygomatic arches), achieving an inferior reflection of the muscle somehow similar to the osteotomy.9 , 10
