The frontotemporal pterional craniotomy is the most frequently used and popular approach in neurosurgery. The majority of anterior circulation aneurysms can be repaired using this standard craniotomy. However, some of the complex-difficult aneurysms require skull base dissection through the orbitocranial or orbitozygomatic or transzygomatic cranial base approach. Several modifications of orbitozygomatic craniotomy have been described. Over the past three decades, the authors have been performing and teaching younger neurosurgeons «less invasive» craniotomy with minimal bone loss technique. ◘ Figure 6.11 illustrates variations of orbitozygomatic and transzygomatic approaches. In principle, the authors advocate a minimally invasive smaller bone flap. Pterion (sphenoid ridge) and anterior temporal groove drilling are performed before turning the frontotemporal bone flap. Conventional large burr holes will not be performed. In the conventional craniotomy, four or five big burr holes are made to turn the bone flap; then surgeons bite and remove the skull base bones using rongeurs and Kerrison punch, resulting in a large amount of bone loss. With the author’s less invasive method, cranial base bone is shaved first before turning the bone flap; no large perforators are used. Surgeons use only 2 mm cone-shaped cutting burr or 4 mm extra-course diamond burr to shave the subtemporal skull base areas before craniotomy. After the triangular pterional drilling is finished, orbitotemporal detachment is performed at the far anterior temporal pole under an operating microscope. The anterior basal subtemporal groove is made for 15 mm length. Making one or two small bone openings (5 mm small space) posteriorly, where the pediatric or mini craniotome footplate can pass, minimal bone loss cosmetic craniotomy can be performed. In most cases, continuous lumbar spinal drainage may be placed to facilitate extradural frontotemporal basal dura elevation. Orbital roof, sphenoid ridge, and the lateral orbital wall are shaved flat like an eggshell. ◘ Figure 6.11a illustrates a less invasive orbitocranial approach without cutting the zygomatic arch. Temporal muscle is reflected inferiorly and posteriorly using multiple blunt scalp hooks and silicon rubber bands. About 3 cm length of supraorbital bar is removed using a sagittal saw, lateral to the supraorbital foramen and medial to the frontozygomatic suture. ◘ Figure 6.11b illustrates extended orbitozygomatic craniotomy in two-piece way or in one-piece fashion. ◘ Figure 6.11c illustrates a transzygomatic cranial base approach to the subtemporal and infratemporal fossa, removing a T-bone-shaped zygomatic arch. The authors preserve the galeofascial-periosteal tissue over the zygomatic arch using the envelope method. Most of the anterior circulation giant aneurysms can be treated through the standard frontotemporal pterional approach. Even pericavernous and intracavernous aneurysms are approached via regular pterional craniotomy, because the internal carotid, A1, M1, and the cavernous carotid artery are approached with microscope viewing angle at looking down direction. Transzygomatic or orbitozygomatic approach would be used for the excessive mega-giant aneurysms or serpentine mega-sized aneurysms, where the surgeon’s viewing angle is looking upward direction toward the brain base from the skull base.

In the early 1980s, Dolenc in Slovenia developed a revolutionary extradural transcavernous operative method, for direct transcavernous exposure, which propagated all over the world to open the new horizon of the direct surgical access to the cavernous sinus for the management of intracavernous vascular and neoplastic lesions [10, 11]. ◘ Figures 6.12, 6.13a, b, and 6.14 illustrate details of operative method of Dolenc transcavernous techniques. The key elements of Dolenc operation are shaving of the orbital roof, removal of the sphenoid ridge and the lateral orbital wall to expose the superior orbital fissure, optic canal unroofing, and removal of the anterior clinoid process. Optic canal unroofing must be started from the distal part and from the lateral aspect. Medially, the ethmoid band should be preserved to maintain the posterior ethmoidal artery circulation. Medial to the orbit and optic canal, the ethmoid sinus and the sphenoid sinus cavities exist; therefore, optic canal unroofing must be done only through superior wall unroofing around 180° range. Shaving and removal of the anterior clinoid process and optic canal unroofing must be performed with running irrigating water to cool down the diamond drill burr and to clean up the bone dust. Removal of the anterior clinoid process, namely, anterior clinoidectomy, is the most important operative work for this approach. Using various sizes of diamond burrs (4, 3, 2 extra-course or course diamond), the first step, as illustrated in ◘ Fig. 6.12, is to shave the inside of the anterior clinoid process to make it hollow and then to remove medial half. Shave, drill, and detach the anterior clinoid medially from the optic strut (anteriorly and posteriorly). This must be done without damaging any of the extracranial optic nerve and dural membranes. Particularly, the posterior portion of the optic strut is extremely difficult to shave because it is just next to the optic nerve and carotid artery. Then, using rigid semi-sharp skull base dissectors (such as A dissector, B dissector, or D dissector), separate the lateral aspect of the anterior clinoid process off from the oculomotor nerve and toward the tip of the clinoid process. This lateral aspect of the dura is just next to the oculomotor nerve, and the surgeon must be extremely careful to perform meticulous careful and gentle dissection. Next, using a 2 mm alligator grabber forceps, slightly rotate and then remove the remaining anterior clinoid process from the C3 siphon angle (anteromedial cavernous sinus). The tip of the anterior clinoid process has a significant fibrous adhesion with the true cavernous membrane; therefore, this maneuver must be performed extremely gently. After the removal of the anterior clinoid process, the surgeon always encounters brisk venous bleeding from the anteromedial cavernous sinus (Dolenc triangle). This cavernous sinus bleeding can be easily controlled by filling the venous lake with 2 mm, 3 mm, or 4 or 5 mm adequate pieces of Surgicel and secure with Delicot cottonoids. Any cavernous sinus bleeding can be controlled in a few minutes using this method. In the author’s clinical experience of direct cavernous sinus surgery over three decades demonstrated that just optic canal unroofing and anterior clinoidectomy carry 1–2% risks of postoperative visual deficit. If surgeons do not follow this extremely careful stepwise removing method (◘ Figs. 6.12 and 6.13), visual deficit may increase to 10–30% risks. The surgeon at first needs a lot of skull base drilling exercise attending a cadaveric head hands-on microanatomy course (at least 10 times, possibly 20 times), then, learn clinical skull base practice from the expert surgeons. ◘ Figure 6.13a illustrates the location of the distal carotid fibrous ring between the intradural C2 and extradural C3 carotid segment. In the majority of cases, the ophthalmic artery is medial and intradural to this fibrous ring. However, in about 20% of the cases, the ophthalmic artery may be within the fibrous ring or at the extradural location. While controlling the cavernous sinus venous bleed with small pieces of Surgicel, if one performs very carefully, the excision of this fibrous ring, aneurysms of C3 clinoidal segment, superior hypophyseal aneurysms, dorsal or ventral paraclinoid giant aneurysms or any of the ophthalmic and paraophthalmic aneurysms become simple carotid aneurysms, such as P-com ones. ◘ Figure 6.13b demonstrates the anteromedial transcavernous exposure and access to the upper basilar trunk and basilar tip aneurysms. ◘ Figure 6.14 demonstrates the summary of the triangular operative corridors around the cavernous sinus. After learning the epidural transcavernous approach in June 1986 from Prof. Dolenc, in the following month, the author established the first systematic triangular transcavernous surgical corridors which was published in a Japanese journal (The 6th Mount Fuji Workshop, [14]). The scheme has been elaborated over the ensuing 5 years using cadaver dissection research. In 1991, with addition of the middle fossa rhomboids and premeatal and postmeatal triangles, the author established the 11 cavernous sinus triangles [14]. The author named each cavernous triangle after the pioneers who worked in this area.

Triangle #1: anteromedial triangle of Dolenc. Triangle #2: medial triangle of Hakuba and Dolenc. Triangle #3: superior triangle between the 3 and 4 of Fukushima triangle to make access to the C4 horizontal segment and to the meningohypophyseal branch. Triangle #4: lateral triangle of Parkinson. Triangle #5: posterolateral triangle of Glascock and Paulus. Triangle #6: posteromedial triangle of Kanzaki, Shiobara, and Kawase. Triangle #7: posteroinferior triangle of Fukushima in order to make access to the Gruber’s ligament and to the abducens nerve. Triangle #8: premeatal triangle of Day- Fukushima. Triangle #9: postmeatal triangle of Day- Fukushima. Triangle #10: anterolateral triangle of Mullan where the superior and inferior ophthalmic vein merges into the cavernous sinus. Triangle #11: lateral Vidian triangle of Dolenc, Fukushima, and Froehlich. ◘ Figure 6.15 demonstrates two typical cases of paraclinoid giant aneurysm with superior dorsal projection. Case A shows a smaller neck and case B demonstrates a wider neck. ◘ Figure 6.16 demonstrates two cases of ventral-type paraclinoid giant aneurysms. For the majority of ventral paraclinoid giant aneurysms, the surgeon needs the proximal control either at C3 segment or C6 segment or simply at the submandibular neck internal carotid artery. In general, for any cerebral aneurysms, the surgeon must be aware of the cardinal importance of the proximal control of the aneurysms to prepare for inadvertent intraoperative rupture of the aneurysm. For the majority of these paraclinoid or infraclinoid giant aneurysms, the surgeon needs careful application of various fenestrated clips: starting with a middle dome bisecting straight fenestrated clip and then applying various lengths (3, 4, 5, 6, 7 mm) of 90°-angled fenestrated clips. ◘ Figure 6.17 demonstrates two more clinical cases of extremely difficult infraclinoid giant aneurysms. Case A is a young patient, a 38-year-old female, left side. This patient’s aneurysm involved the P-com and anterior choroidal arteries; therefore, clipping was extremely difficult to preserve these vital carotid branches. Intraoperative motor-evoked potential (MEP) monitoring and intraoperative ICG control is extremely useful. Case B was a mega-giant infraclinoid aneurysm, whom the author operated in Belfast, Ireland. This patient had previous right internal carotid ligation and remaining left one carotid developed mega-size aneurysm that bled severely four times to coma. Amazingly, this patient recovered to the normal condition, and I was invited to Belfast to obliterate this complex aneurysm. Using a primitive microscope, I used all seven fenestrated clips I brought, and the surgery was successful. The author has followed this patient postoperatively for over 20 years, and the patient had no deficit from this aneurysm surgery. ◘ Figure 6.17c illustrates the typical clip arrangement for obliteration of this type of aneurysms preserving the ophthalmic artery, superior hypophyseal artery, P-com, and the anterior choroidal branches. Arrangement of the first clip being a long fenestrated dome bisecting clip and long window-locking clips (blue) to prevent slippage of the clips. ◘ Figure 6.18a–c demonstrates three cases of direct transcavernous clipping and repair of the intracavernous giant aneurysms. Using the Dolenc technique, this can be performed. However, in the initial series of the author’s direct transcavernous surgery from 1986 to 1990, this direct clipping method was performed in six patients, and I could not clip in two cases which resulted in performing interpositional saphenous vein bypass. In addition, these six cases demonstrated some degree of postoperative sequelae of persistent diplopia or facial numbness. Therefore, I abandoned direct transcavernous clipping and switched my management to the various types of microsurgical flow diversion method using skull base high-flow saphenous vein bypass.

The majority of subtemporal approaches can be done with the patient in the supine position and with the head rotated in a head lateral position. Mostly, a continuous lumbar spinal drainage tube is placed for relaxation of the temporal lobe and to avoid postoperative temporal lobe edema contusion or blood clot. In all cases, the temporal muscle is retracted anteriorly using multiple blunt scalp hooks in a one-layer fashion. In case of preauricular mid-subtemporal approach, temporal muscle is split in the middle and widened with a Gelpi retractor. The surgeon should know the anatomical landmarks around the anterior, middle, and posterior portion of the subtemporal cranial base, such as the foramen rotundum, Vidian loop, Ovale, MMA, and the root of zygoma. Before opening the dura, the base of the temporal lobe dura is held using a pair of 2 mm extradural rigid spatula (◘ Fig. 6.19). In recent years, an increasing number of reports appeared in the international neurosurgical meeting that some neurosurgeons advocate no use of the brain spatula. These surgeons utilize suckers and instruments to retract and jiggle the brain tissue, which will result in more damage to the brain surface. In the author’s 40 years of neurosurgical micro-operative experience, the best method of brain protection is to place on the brain surface mozaic Surgicel pieces or small collagen sheet and to cover with micro-cottonoid. Then, the brain is held gently with 2 mm tapered brain spatula preventing sagging of the brain and to provide the surgeon adequate operative space to work with his two hands freely. To perform clipping of aneurysms or to resect brain tumors, this gentle brain-holding method using one or two 2 mm tapered spatula is the best brain protection technique proven through the author’s 40 years of experience of neurosurgery. It is not recommended to perform clumsy microsurgical dissection without using this brain-holding method.

In order to make access to the deep subtemporal base, the surgeon will have a lot of advantages by using a pair of 2 mm rigid dural holders. The surgeon encounters significant amount of bleeding from the subtemporal bone and venous connection, which is controlled by diamond drill shaving, by monopolar cautery, or by using bone wax and Surgicel application. After sufficient shaving and flattening of the subtemporal base and confirmation of the foramen rotundum, ovale, and middle meningeal artery, the dura can be opened at the far deep in the subtemporal base in order to make an easier intradural subtemporal approach and to protect the temporal brain with the dural coverage. In the majority of cases, the edge of the tentorium should be retracted laterally with two sutures to the temporal basal dura that makes transtentorial exposure much wider. Occasionally, fourth nerve and oculomotor dural sleeves are opened to make much wider access for the transtentorial approach to the basilar tip and upper basilar segment aneurysms.

In some cases of difficult large aneurysms, posterior transcavernous dissection can be made. The dura propria of the temporal base is elevated from the trigeminal second and third branches using a 15-blade knife and sharp A rigid dissector, exposing the trigeminal Gasserian ganglion. Then, using a 2 mm rigid spatula, anterior translocation of the third branch and Gasserian ganglion can be made to expose the anterior petrous bone. Anterior petrosectomy exposes the posterior fossa dura through the middle fossa rhomboid construct medial to the greater superficial petrosal nerve (GSPN) and anterior to the arcuate eminence (superior semicircular canal) and geniculate ganglion (◘ Fig. 6.19). When the trigeminal dural fibrous ring is excised and the superior petrosal sinus is divided, much wider transtentorial approach can be made just through this extended middle fossa approach. ◘ Figure 6.19a demonstrates the extended middle fossa epidural exposure of the triangle complex, C6 petrous carotid, GSPN, geniculate ganglion, and the superior semicircular canal. The rhomboid (◘ Fig. 6.19a a-b-c-d) space drilling is the anterior petrosectomy (◘ Fig. 6.20b).

Complex aneurysms of the basilar trunk, basilar tip, and the posterior cerebral artery are the most difficult to operate in neurosurgery. The deep location, complex anatomy, and the involvement of multiple cranial nerves, vessels, and the brain stem present neurosurgeons with the real challenge to achieve adequate cranial base approaches with negligible morbidity. The basilar tip and the basilar trunk can be accessed through the subtemporal transtentorial approach, through the extended middle fossa anterior petrosectomy approach, or through the retrosigmoid or transsigmoid posterior fossa approach. For the management of giant aneurysms of the basilar artery or to perform the P2 high-flow Fukushima Bypass (Type 5), the combined supra- and infratentorial transpetrosal approach is the best. In order to perform the proper combined petrosal approach with prevention of cosmetic deformity, postoperative CSF leakage or infection, very precise harvest of the STA-enhanced vascularized galeofascial pericranial flap is mandatory. ◘ Figure 6.20 demonstrates the so-called Fukushima lateral position. The important element of this Fukushima lateral positioning is bringing the patient’s shoulder and the back exactly on the edge of the surgeon’s side of the operating table. The upper shoulder and the arm need to be held 45° caudal and anterior. The upper shoulder rotates anteriorly to three-fourth lateral prone position. The patient’s hip must be in the middle of the operating table with the lower leg bent 90°. Placing a couple of large, soft pillows, the upper leg will be crossing over the lower extremity. Most of the time, in order to harvest abdominal fat, the upper hip will be rotated posteriorly to make access to the lower abdomen. The head is fixated with the Mayfield three-pin head clamp and kept horizontal, slightly vertex down (◘ Fig. 6.20a). The entire head is elevated to make sufficient space between the lower neck and the lower arm (◘ Fig. 6.20b). The face is slightly rotated toward the floor to make the external auditory canal and the mastoid bone at the highest point, and the head and neck are moderately flexed. The upper shoulder must be positioned anteriorly and caudally to make easier access to the entire retroauricular retromastoid region and the entire temporo-occipital region. The skin incision is either a postauricular large C incision or, in order to harvest an STA, enhanced highly vascularized flap; a preauricular incision is necessary in a so-called «chef hat» skin incision. ◘ Figure 6.21a illustrates the so-called chef hat scalp incision for dissection of the superficial temporal artery. ◘ Figure 6.21b illustrates the landmarks of the outer mastoid triangle, inner mastoid triangle, and the Macewen’s triangle. At first, surgeons dissect the superficial temporal artery from the preauricular inferior zygomatic point all the way along the parietal branch of the STA and also dissect the frontalis branch of the STA. Therefore, the first layer of the skin and subcutaneous tissue is retracted in the anterior inferior direction using multiple small, medium, and large blunt hooks and silicon rubber bands. When the STA branches are dissected, we can make a large galeofascial pericranial flap, the second layer with wide pedicle from STA to EAC. It is extremely important to make a very thick and wide STA-enhanced highly vascularized galeofascial and pericranial flap (second layer) which is reflected inferior posteriorly with many blunt hooks. After this second vascularized flap is elevated, then the temporal muscle will be cleanly separated from the temporal bone and reflected anteriorly. Then, the suboccipital muscles are elevated from the mastoid and retracted posteriorly and inferiorly. The surgeon should know the outer landmarks of the root of the zygoma, that is, the glenoid cap 15° to the temporal baseline. The length is about 22 mm. All bony landmarks such as the anterior temporal, pterion, superior squamosal point, middle temporal, posterior temporal, supramastoid ridge, and the occipital and suboccipital region must be secured before making a long L-shaped petrosal craniotomy. Asterion is the junction of the parietomastoid, lambdoid, and occipitomastoid sutures (◘ Fig. 6.21b). The asterion is evident in all patients and serves to identify the transverse sinus and the mastoid outer triangle. From the asterion, it passes the middle of the supramastoid crest to the posterior point of the root of the zygoma and then passes inferiorly to the spine of Henle to the mastoid tip that confirms Fukushima’s outer mastoid triangle. ◘ Figure 6.21b illustrates the outer mastoid triangle where the surgeon evenly drills the mastoid to expose the posterior temporal tegmen and transverse and sigmoid sinus and exposes the mastoid antrum, fallopian canal, and the digastric ridge as well as the stylomastoid foramen. In order to perform this transmastoid retrolabyrinthine or infralabyrinthine drilling, the neurosurgeon needs a lot of temporal bone dissection exercises and understanding of all neuro-otologic structures. At a minimum, it is recommended for younger neurosurgeons to practice 20 temporal bone dissections to become a skull base expert. ◘ Figure 6.22 demonstrates the retrolabyrinthine and infralabyrinthine temporal bone dissection, exposing the posterior temporal tegmen, sinodural angle, and transverse and sigmoid sinus, down to the jugular dome. The most important is the confirmation of the lateral semicircular canal (9 mm length and 15° angle to the basal temporal line), which is easily identified in the mastoid antrum. Anteriorly, the entry corridor to the middle ear named aditus, short process of incus, malleus head, the facial recess, the genu of the facial nerve, and the descending segment of the fallopian canal as well as the stylomastoid foramen must be identified. In most cases, 12–15 mm of presigmoid dura can be exposed. We can perform presigmoid approach, retrosigmoid approach, or transsigmoid wider exposure. ◘ Figure 6.19a demonstrates the middle fossa dissection of the rhomboid construct, posterior to the trigeminal complex, medial to the greater superficial petrosal nerve (GSPN), and the petrous segment of the carotid artery, anterior to the geniculate ganglion and the posterior semicircular canal. About 5 mm of petrous ridge can be drilled away, and the anterior petrosectomy will expose from the internal auditory canal, postmeatal and premeatal triangle, and all the way to the posterior fossa dura toward the abducens nerve (◘ Fig. 6.19). ◘ Figure 6.19b demonstrates the completion of the extradural dissection, exposure of the middle fossa rhomboid construct, and anterior petrosectomy. ◘ Figure 6.23 illustrates the retrolabyrinthine-combined supra- and infratentorial exposure to identify cranial nerves III, IV, V, VI, VII, VIII, IX, and X and vascular structures. The red line arrow from the superior petrosal sinus along the transverse sinus, this dura must not be incised to protect the vein of Labbe. The combined petrosal dural incision is from the presigmoid to the temporal base dural incision and resection of the superior petrosal sinus and the tentorium. The superior petrosal sinus should be double ligated 10 mm off the transverse sigmoid sinus junction.

Management of aneurysms located on the vertebral artery, PICA, and vertebrobasilar junction can be operated through the so-called far lateral ELITE approach . This extreme lateral infrajugular transcondylar exposure was developed by Hakuba and Fukushima simultaneously in 1987 in Japan. Fukushima elaborated this ELITE approach to two types of exposure, dorsolateral transcondylar approach and anterolateral transcondylar approach, which is combined with the transjugular and the high cervical exposure.

The transcondylar and transjugular tubercle approach was first described in anatomy research by Prof. Seeger in 1976. Later, his pupil Prof. Bertalanffy performed the first clinical operative series in the mid-1980s. ◘ Figure 6.24a demonstrates the lazy S curvilinear incision 2–3 cm posterior to the body of the mastoid line. Figure 6.24b illustrates the inferior retrosigmoid point; opening of the foramen magnum lateral edge; exposure of the C1 lamina upper edge, C1 condyle J groove, and occipital C1 facet; and identification of the hypoglossal canal and the triangular concept of the condylar triangle as well as the jugular tubercle triangle. In front of the C1 dura, when the occipital condyle is drilled away, for superior medial portion (about 30% of the condylar bone), hypoglossal canal can be exposed slightly cephalad parallel to the facet line and anterior to the C1 dura. From this hypoglossal canal under the jugular bulb, the jugular tubercle extends 25 mm long toward the inferior clivus. Removal of this jugular tubercle is a key step to make flat access to the ventral medulla and to the vertebrobasilar junction. This drilling exercise is extremely difficult not to violate the ninth and tenth lower cranial nerves. Surgeons need microanatomy dissection practice in the laboratory (at least on 10 to 20 specimens). The author performed the ELITE far lateral approach in three cases of basilar trunk giant aneurysm clipping and 25 cases of vertebral artery giant aneurysm. The majority of vertebral artery giant aneurysms are fusiform, either atherosclerotic origin or dissecans type. Some reports assume of unknown vasculopathies or vascular inflammatory etiology. ◘ Figure 6.25 illustrates two cases of clipping of the vertebral artery giant aneurysms. ◘ Figure 6.26 demonstrates three cases of vertebral artery giant aneurysm clipping. ◘ Figure 6.27 demonstrates three cases of resection of the vertebral giant aneurysm and aneurysmorrhaphy with 7-0 Prolene sutures.