Positioning the Patient

The patient is placed in supine position, and the head is placed in the pin head holder if the patient is older than 3 years. The horseshoe head holder is used for younger patients. A gel roll is placed under the ipsilateral shoulder, and the head is turned to the contralateral side approximately 60 degrees. The neck is slightly extended by lowering the vertex approximately 15 degrees downward, just enough to bring the zygoma to the surgeon’s eyeline and to make the zygoma the most prominent point on the midline. Lastly, the occiput is tilted slightly toward the ipsilateral shoulder ( Fig. 17.1 ). This head position places the base of the temporal fossa perpendicular to the horizontal plane. The surface of the lateral temporal lobe will be in a horizontal position, and the long axis of the hippocampus will be oriented vertically relative to the surgeon with this approach. Thus, the head position will create a good alignment of the mesial structures to the surgeon’s eyeline and will provide an excellent exposure to the uncus–amygdala complex, the whole length of hippocampus, and the lateral–basal temporal neocortex.

Scalp Incision

A smoothly curved, question mark–shaped scalp incision is drawn starting just above the zygoma and approximately 10 mm anterior to tragus, based on the location of palpated superficial temporal artery. Then the incision is extended upward such that it makes a smooth anterior turn at the upper point of the pinna by following the superior temporal line toward the keyhole. It ends approximately 3 to 4 cm behind the keyhole, depending on the patient’s hairline ( Fig. 17.1 ). Then the incision is infiltrated with 0.5% bupivacaine hydrochloride (Marcaine) diluted in 1:200.000 epinephrine solution. The superficial temporal artery is palpated and protected during the scalp incision. Some small branches of superficial temporal artery may be occasionally sacrificed, but generally the main body can be protected by dissecting and mobilizing it during the incision. Then the incision of the temporal fascia, muscle, and periosteum is also completed sharply by cutting these layers parallel to the scalp incision. Scalp, temporal fascia, muscle, and underlying periosteum are dissected subperiosteally to create a single musculocutaneous flap. The lower part of the incision is extended down to the zygoma. Having an exposure down to the zygomatic root is critical for satisfactory access to the base of the temporal fossa during the neocortical resection. The other critical point at this stage is exposure of the orbitalzygomatic ridge or the keyhole. It should be palpated, and the temporal muscle should be cut and dissected from the keyhole by retracting the scalp further and working beneath it. Then the temporal muscle is subperiosteally dissected using sharp periosteal elevators by keeping the periosteum attached to the temporal muscle as much as possible to preserve muscle innervation and vascular supply. Monopolar cautery should not be used during this dissection for the same reason. Strict adherence to this technique is critical to prevent future temporal muscle atrophy. Although application of this technique may be difficult in elderly patients, it is much easier to have an excellent subperiosteal dissection that keeps the whole periosteum intact and attached to temporal muscle in the pediatric age group. Fish hooks are then placed to reflect the musculocutaneous flap anterolaterally to expose the temporal bone widely.

Craniotomy

Three burr holes are placed with locations at the keyhole, just above the zygoma and on the superior temporal line and approximately 4 to 5 cm posterior to the burr hole on the keyhole. A free bone flap is removed after dissecting the dura with Penfield dissectors. The sphenoid ridge is removed with rongeurs to create a smooth anteriormedial bony wall. This maneuver has critical significance to have a good exposure for uncus/amygdala resection. Further bone removal is needed along the floor of the temporal fossa down to the root of the zygoma and toward the temporal tip. This will provide a comfortable access to the inferobasal neocortical region and temporal pole during the resection. Dural tack-up sutures are placed at this stage, and the epidural space at bone edges is filled with an injectable hemostatic agent, such as Surgifoam (Johnson & Johnson, Gateway, NJ, USA). Then the dura is opened C-shaped, starting from the keyhole site on frontal region and ending at temporal pole by following the craniotomy edges. The dura is folded and tacked up with 4–0 Nurolon sutures to the muscle flap over the sphenoid wing. At this stage, the exposed area in the surgical field includes the full extent of the sylvian fissure/vein, superior and middle temporal gyri, and the upper part of the inferior temporal gyrus ( Fig. 17.2 ).

Neocortical Resection

The previously planned resection length of the lateral temporal neocortex is measured and marked on the cortex at this stage. The tip of the temporal pole can be seen easily seen with the help of a cortical ribbon placed on a Cottonoid over the middle temporal gyrus. A predetermined 3.5- or 5-cm resection length (depends on being on the dominant or nondominant side) from the tip of the temporal lobe is measured along the middle temporal gyrus and marked on the cortex with bipolar coagulation. The resection line starts at the medial edge of the temporal pole and turns toward the middle temporal gyrus approximately 2 cm behind the temporal tip ( Fig. 17.2 ). The remaining part of the incision continues along the upper border of the middle temporal gyrus to spare most of the superior temporal gyrus posteriorly. This resection line is marked on the pia-arachnoid of the superior and middle temporal gyri with a fine-tip bipolar coagulator staying parallel and 5 to 6 mm below the sylvian vein or superior temporal sulcus. After coagulation of the pia-arachnoid over the gyri, it is incised with micro-scissors throughout the length of the marked incision line. After completing the incision, the pia-arachnoid adjacent to sylvian vein is coagulated thoroughly to create an appropriate handle to hold during the subpial dissection of superior and middle temporal gyri. Then cortex is subpially dissected from pia of the sylvian fissure anteriorly and from the superior temporal sulcus posteriorly. Meticulous subpial dissection technique is used to avoid injury to the middle cerebral artery (MCA) branches in the sylvian fissure ( Fig. 17.3A ) and to protect the vascular supply of the unresected part superior temporal gyrus by leaving both pial layers of the superior temporal sulcus undisrupted on the lower bank of the superior temporal gyrus. Some bleeding is generally encountered while peeling the cortex from pia that can be easily controlled by placing Surgifoam and Cottonoid patties. We would like to remind the reader that subpial dissection is much more challenging in pediatric patients than adults because of the very thin and fragile nature of the pia at this age. Appropriate application of this technique may not be feasible in very young children.

The next critical step is finding the temporal horn. There are several approaches for this and a close review of the patient’s MRI, especially coronal spoiled gradient recalled (SPGR) cuts, will be helpful to determine the best approach. The temporal horn starts approximately 3 cm behind the temporal tip, and the average distance between the surface of superior temporal gyrus and the ventricle is approximately 31 to 34 mm.32,33 We prefer to perform our dissection to reach the temporal horn at a point on the superior temporal sulcus approximately 3.5 cm behind the tip of the temporal pole. Frequently, the T1 sulcus (superior temporal sulcus) directly brings the surgeon into the temporal horn. This can be done through an intrasulcal approach or by remaining subpial and following either the inferior wall of the superior temporal gyrus or superior wall of the middle temporal gyrus, which we prefer. The bottom of the sulcus can be easily recognized by visualizing the end of the pial bank at first. Then the ependyma can be appreciated after deepening the same incision approximately 11 to 12 mm further.33 This distance can be measured case by case on MRI coronal cuts easily. The ependyma can be opened with Penfield #4 dissector (Codman, MA) and cerebrospinal fluid will verify the intraventricular location. If the surgeon passes the estimated distance and the temporal horn is not in sight, the best strategy is to redirect the dissection. The most common two reasons for not being able to find the ventricle are either placing the entry point of the dissection too anteriorly or directing the dissection either too medially or too laterally. At this stage, the appropriate strategy is to redirect the dissection toward the floor of the middle fossa but not medially. The dissection is then deepened toward the floor of the middle fossa until gray matter is encountered on the adjacent occipitotemporal (or fusiform) gyrus. Then the dissection is redirected again, this time medially into the white matter until temporal horn is entered. Deepening the dissection medially to search the temporal horn without taking the aforementioned strategies may easily lead the surgeon into the temporal stem and basal ganglia and may cause significant complications. Therefore redirecting the dissection intentionally too laterally initially is a much safer approach, as defined very clearly by Wen et al.32 When we enter into the ventricle, we place a tiny cottonoid patty in it to prevent blood contamination and then subpially dissect first the superior wall of the medial temporal gyrus and then sylvian pia anteriorly to the temporal pole using microsuction in a low setting and a Penfield dissector. This subpial dissection is performed down to the ependymal level throughout the sulcus. Then the ependyma is easily opened using a bipolar coagulator, the temporal horn is unroofed all the way to its tip, and a small cotton ball is placed into the temporal horn toward the atrium to avoid intraventricular dissemination of blood products.

Several other approaches to the temporal horn exist. One is to follow the collateral sulcus. This approach is only feasible after completing the second cortical incision, which will be described in the following paragraphs. Alternatively, the temporal horn can be found after completing the resection of the anterolateral temporal lobe without locating the temporal horn. In this case, the uncus is located first by following the tentorial edge anteromedially. When removal of the uncus is completed, its posterior segment will open and expose the tip of the temporal horn automatically. Lastly, the use of a neuronavigation system to assist the localization of the temporal horn is an option.

The second cortical incision line starts from the most posterior extent of the first incision and is directed perpendicularly toward the floor of temporal fossa ( Fig. 17.2 ). The posterior line of the neocortical resection extends inferiorly traversing the superior, middle, inferior temporal, and fusiform gyri, respectively, and ends at the collateral sulcus. The temporal horn is located generally just dorsal to the base of the collateral sulcus and can be found by following the collateral sulcus pia as described previously. The average distance from the depth of the collateral sulcus to the temporal horn is 3 to 6 mm.33 Thus, the posterior end of the first incision and superior end of the second incision lines intersect at the temporal horn. A third incision is directed to the collateral sulcus by cutting across the temporal stem and the white matter of the basal temporal lobe. This third incision disconnects the temporal neocortex from parahippocampus/hippocampus and completes the lateral neocortical temporal resection by dividing the collateral sulcus from its posterior end to the tip of the temporal horn at rhinal sulcus level. The entire lateral neocortex is removed as an en bloc specimen ( Fig. 17.3A,B ).