Indications
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The pterional craniotomy and the transsylvian approach are the most used techniques in contemporary neurosurgery.
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The pterional craniotomy allows exposure of the frontoparietal and temporal opercula together with the basal subarachnoid cisterns ( Figure 17.1 ). This approach allows opening of the entire sylvian fissure, which allows for exposure of the circle of Willis, sphenoid wing, sella turcica, upper clivus, cavernous sinus and parasellar regions.
Figure 17.1
(A, B) The surgical window provided by a pterional approach. The craniotomy gives access to the temporo-frontal and parietal opercula and the sylvian fissure. Splitting the sylvian fissure provides a surgical corridor to access the vast majority of aneurysms of the anterior and posterior circulation and lesions of the parasellar region. T, temporal; F, frontal.
Redrawn after Potts M.B., Chang, E.F., Young W.L., et al. 2012. Transsylvian–transinsular approaches to the insula and basal ganglia: operative techniques and results with vascular lesions. Neurosurgery 70(4), 824–834.
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Extra-axial tumors of the anterior and middle cranial fossa, and intra-axial tumors of the insula and the lateral fronto-temporo-parietal subcortical areas.
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It is indicated for clipping aneurysms of the anterior and posterior circulation and resecting perisylvian arteriovenous malformations. Also, for emergent evacuation of intraparenchymal hemorrhage in that region or hemorrhage from aneurysms not amenable for treatment through an endovascular procedure.
Contraindications
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Other approaches are more suitable in treating sellar/parasellar tumors in the midline (e.g. endonasal approaches) or with superoanterior extension (e.g. bifrontal craniotomy) and distal lesions from the posterior and anterior cerebral arteries. Lesions that extend into the third ventricle may be better approached with an orbitozygomatic or transcallosal approach. This approach is contraindicated in clipping high-riding basilar aneurysms because of the lack of basilar apex visualization above the posterior clinoid.
Surgical Procedure
Patient Positioning
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The patient is placed in a supine position. The head is hyperextended, elevated and turned towards the contralateral side from 30 to 60 degrees such that the body of the zygomatic bone is the highest point in the field. The ipsilateral shoulder can be elevated to facilitate the head rotation.
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The head is fixated with a skull clamp. To avoid the Mayfield clamp blocking the access to the surgical field the paired pins are set on the ipsilateral mastoid region or further posterior, at the occipital bone. The single pin is placed in the contralateral frontal bone in the midpupillary line. Transfixation of the temporalis muscle is avoided. This position can be tailored for each lesion.
Skin Incision
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An arch line is marked with a pen from the root of the zygoma to the midline. For better cosmetic results we recommend starting the incision in between 35 and 40 mm anterior to the tragus, where the skin folds, as is done in a facial lift. The patient’s hairline is set as the anterior limit of the incision to avoid noticeable scars.
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The incision is staged into short segments and hemostasis is achieved before proceeding with the next segment. Homeostatic Raney clips are applied to the scalp edges as needed.
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The skin is incised with a No. 10 blade, starting at the anterior portion towards the superior temporal line and then curving downwards to the zygoma. From the midline to the superior temporal line, the full thickness of the scalp can be cut down to the bone, including the pericranium and galea aponeurotica (if the pericranium does not need to be preserved). From the superior temporal line to the zygoma, the skin is cut down only to the level of the superficial temporalis fascia. A two-layer dissection of the scalp is performed elevating the scalp apart from the temporalis muscle, exposing the superficial temporalis fascia to proceed with an interfascial or submuscular dissection afterwards.
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The superficial temporal artery originates from the external carotid at the level of the parotid gland. It crosses very superficially over the posterior third of the zygomatic process of the temporal bone and it divides in its frontal and parietal branches. The temporal artery can be injured at the most caudal part of the skin incision. Blunt dissection down to the level of the temporalis fascia is used in this region to preserve the superficial temporal artery. The skin flap is elevated and retracted anteriorly and the superficial temporalis fascia is exposed ( Figure 17.2 ).
Figure 17.2
Learning the surgical anatomy of the facial nerve and the superficial temporal artery is essential to avoid damage during the incision of the skin. Sacrificing the superficial temporal artery can compromise the vascularization of the skin flap. A well-vascularized skin flap is important to achieve good cosmetic results and is also important in those cases when adjuvant radiotherapy will be needed.
Reproduced with permission from Nanda, A., Javalkar, V., 2011. Paraclinoid carotid artery aneurysms. In Jandial, R., McCormick, P., Black, P. (Eds.), Core Techniques in Operative Neurosurgery. Saunders, Elsevier Inc., Philadelphia.
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Interfascial dissection: The superficial temporalis fascia covers the temporalis muscle and attaches it to the superior temporal line and to the zygomatic arch. Before attaching to the zygomatic arch the superficial temporalis fascia splits in two layers (superficial and deep). The fronto-temporal branch of the facial nerve runs in a fat pad within the two layers of the superficial temporalis fascia. With the skin flap elevation, the superficial layer of the superficial temporalis fascia and the superficial temporal fat pad are exposed. The superficial layer of the superficial temporalis fascia is incised in an arching fashion and elevated together with the underlying fat pad that contains the facial nerve. If required and if retraction on the skin flap will be prolonged, the dissection can continue down until the arch of the zygoma. Preserving the fat pad will prevent injuring the nerve from retraction pressure. Finally, the fat pad is carefully retracted anteriorly and the temporalis muscle covered by the deep layer of the superficial temporalis fascia is exposed.
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The temporalis muscle is incised along the superficial temporal line, dissected subperiostally and elevated laterally. When separating the muscle from the bone, blunt dissection is preferred and we recommend avoidance of electrocautery. It is important to keep 1 cm cuff of muscle attached to the bone for posterior reattachment.
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Another option is the submuscular dissection technique. The temporalis muscle is incised and elevated together with the superficial temporalis fascia without proceeding with the interfascial dissection. Compared with the interfascial technique, the submuscular dissection lowers the risk of facial nerve injury but restricts the working space. In both interfascial and submuscular dissections, the deep temporal artery — branch from the internal maxillary artery — may be preserved as the main blood supply for the temporalis muscle.
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The Leila bar may be used to support the hooks or sutures for the skin and muscle flaps retraction. However, any compression or ischemia of the temporalis muscle is avoided. Also, eyeball compression could cause vasovagal bradyarrhythmia and blindness by thrombosis of the central retinal vein.
Craniotomy
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Depending on the surgeon’s preferences and the tumor location, one to five burr holes are drilled for the craniotomy. We suggest placing as many as three burr holes, and under the muscle for better cosmetic results: 1. (Keyhole) Above the fronto-sphenoidal suture, below the superior temporal line and posterior to the fronto-zygomatic suture. 2: Above the root of the zygoma and posterior to the lesser wing of the sphenoid bone. 3: At the most posterior point just below the superior temporal line (and below the muscle cuff). The last one can be repositioned as superiorly as needed, as we illustrate in the accompanying video ( Figure 17.3 ).
