The Combined Supraorbital Keyhole-Endoscopic ...

Technical Note 281

The Combined Supraorbital Keyhole-Endoscopic Endonasal Transsphenoidal Approach to Sellar, Perisellar and Frontal Skull Base Tumors: Surgical Technique Authors

E. J. van Lindert, J. A. Grotenhuis

A̧liation

Department of Neurosurgery, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands

Key words ̂ supraorbital approach ̎ ̂ minimally invasive surgery ̎ ̂ transsphenoidal approach ̎ ̂ neuroendoscopy ̎ ̂ combined approach ̎ ̂ extended approach ̎

Abstract & Introduction: Extended endoscopic endonasal transsphenoidal approaches (extended EETA) are increasingly being explored for lesions around the sella and the frontal skull base. These approaches, however, require signicant surgical expertise and training that can only be obtained in highvolume centers and therefore these approaches are not generalizable to the whole neurosurgical community. Also, these approaches require signicant skull base destruction and reconstruction, which comes with a high risk of CSF stulas. The aim of this article is to describe a combined supraorbital keyhole-endoscopic endonasal transsphenoidal approach as an alternative surgical strategy to the extended EETA that is

Introduction &

Bibliography DOI http://dx.doi.org/ 10.1055/s-0029-1242776 Minim Invas Neurosurg 2009; 52: 281–286 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0946-7211 Correspondence E. J. van Lindert, MD, PhD Department of Neurosurgery Radboud University Nijmegen Medical Center Postbus 9101 6500 HB Nijmegen The Netherlands Tel.: + 31/24/361 3477 Fax: + 31/24/354 1587 [email protected]

The endoscopic endonasal (transnasal) transsphenoidal approach (EETA) is increasingly replacing the standard microsurgical transseptal transsphenoidal approach for pituitary lesions. Recognized advantages of EETA over the microsurgical approach are an improved illumination of the operative eld and a much wider operative view. With these advantages more extensive surgery around the skull base becomes a possibility. With an extended EETA a wider range of lesions can be treated at the skull base including anterior skull base and suprasellar tumors. Successful removal of these tumors has been accomplished, but the possibilities for reconstructing the skull base are still limited. The result is a high rate of postoperative CSF stulas and a severely disturbed anatomy on postoperative neuroimaging [1]. An alternative to the extended EETA is the combination of a supraorbital keyhole approach and an EETA, which o̥ers minimal invasiveness with preservation of skull base anatomy. We introduce

easier to perform and that leaves the skull base anatomy more intact. Technique: Two fairly common neurosurgical approaches, the supraorbital keyhole approach and the endoscopic endonasal transsphenoidal approach, are combined into a single-stage or two-stage surgical procedure. The procedure can be performed as a single neurosurgeon-serial approach and as a two neurosurgeon-parallel simultaneous approach. The philosophy and technique of this combined approach will be described. Conclusion: The combined supraorbital keyhole-EETA approach can be used without extra surgical training or expertise and with preservation of skull base anatomy for sellar, perisellar and frontal skull base tumors.

this combined approach which can be performed as a two-stage procedure and as a single-stage procedure. In the latter case two sequential procedures (craniotomy followed by a transsphenoidal approach) by a single surgeon and a simultaneous biportal approach performed by two surgeons are optional. Our surgical philosophy and operative technique will be illustrated.

Patients and Methods & Supraorbital keyhole craniotomy The supraorbital keyhole approach is a truly minimally invasive approach. The head of the patient is xed in a Mayeld head holder with the head only slightly rotated away from the side of approach (usually 20–30 degrees). A skin incision is made just lateral to the foramen of the supraorbital nerve extending to the lateral border of the eyebrow within the hairline of the eyebrow. A small frontal muscle ap is created medial to the superior temporal line, while the

van Lindert EJ, Grotenhuis JA. The Combined Supraorbital Keyhole-Endoscopic Endonasal Transsphenoidal … Minim Invas Neurosurg 2009; 52: 281–286

282 Technical Note

temporal muscle is retracted for 1 cm laterally. A burr hole is made lateral to the superior temporal line and a small supraorbital craniotomy with a diameter of 2.5 × 1.5 cm is made. More details of this approach have been described previously [2]. The side of the supraorbital approach is dictated by the tumor extension. Parasellar tumor extension or lateral to the suprasellar space requires an ipsilateral approach. However, a suprasellar tumor part that is lateralizing within the suprasellar area may require a contralateral approach. In those cases the preoperative MRI should be carefully studied for a prexed chiasm that may hinder the approach. If the tumor is growing parasellarly into the middle cranial fossa one might opt for a small pterional approach instead of a supraorbital approach in order to improve the approach to the middle cranial fossa. The supraorbital approach allows the removal of the suprasellar tumor part, and tumor on the tuberculum sellae and anterior skull base, as well as beyond the dorsum sellae.

Endoscopic endonasal transsphenoidal approach (EETA) Although several di̥erent endoscopic techniques are being developed in parallel, our technique is based on the pioneering work of Jho et al. and later Cappabianca et al. [3–6]. However, we modied the technique by using a binostril, transsphenoidal, endoscopic approach to the sella turcica in which the endoscope is handheld in the majority of cases. For endonasal pituitary surgery we use a 0 ° endoscope with an optic diameter of 4 mm with a separate shaft that allows easy and comfortable holding, while o̥ering a suction-irrigation system for cleaning of the lens (Karl Storz, Tuttlingen, Germany). The maximal outer diameter of the oval-shaped shaft is 6.3 mm. A 30 ° optic is available for use in specic situations. The camera used is the Endovision TRICAM® SLII three-chip camera (Karl Storz, Tuttlingen, Germany) connected to EndoSite 3Di Digital (Viking Systems, Westborough, MA, USA) and projected on a head-mounted display (HMD) that is worn by the surgeon during all phases of the surgery. The endoscopic picture is projected onto the LCD-screens from the HMD with a resolution of 800 × 600 pixels. The instruments used are principally the same as with the microsurgical technique. In the case of large tumors that destroy the sellar oor, invade the cavernous sinus and ll up the sphenoid sinus, electromagnetic (EM) navigation is used, because the usual anatomic landmarks are absent or poorly demarcated. This enhances the safety and radicality of tumor removal.

Combined approach The combined supraorbital keyhole-endoscopic endonasal transsphenoidal approach can be used in two di̥erent ways: two sequential approaches by one surgeon or a parallel biportal approach by two surgeons. The combined approach is chosen if the neurosurgeon considers a single transsphenoidal approach (without extensive skull base dissection) insu̦cient for complete removal of a suprasellar tumor part or inappropriate if adhesion of the tumor to suprasellar anatomic structures is suspected. This is only the case in a minority of the tumors of this region, since more than 90 % of these tumors are primarily operated upon by the endonasal transsphenoidal approach. In the sequential approach we opt for a supraorbital approach rst, since this is sterile, unlike the transsphenoidal approach. The suprasellar part can be removed safely without the blind traction to structures that may occur with a transsphenoidal approach.

If the side of approach does not matter, we prefer a left-sided supraorbital approach, because the head is then turned 20 ° to the right and xed in a Mayeld head holder. In this position no repositioning of the head for the endonasal transsphenoidal approach is required, since the (right-handed) surgeon is positioned at the right shoulder of the patient for that approach. The endonasal transsphenoidal approach is only started after completely nishing the supraorbital approach. For the endonasal approach the patient is draped separately, and cottonoids drenched in a cocaine hydrochloride/epinephrine solution for decongestion of the nasal mucosa are installed after the supraorbital approach and before draping. The simultaneous biportal approach requires two surgeons, both experienced in performing the supraorbital keyhole ̂ Fig. 1). If the supratentorial tumor approach and the EETA (̎ extension allows it, a left-sided supraorbital approach is preferred for the reasons described above. Both approaches are performed in the usual manner and may require sequential maneuvers instead of simultaneous maneuvers. During this approach one benets from the use of a HMD. Normally a monitor for the endoscopic picture is placed at the head of the patient, but now the microscope used for the supraorbital approach blocks that position. The HMD overcomes this problem. By using the picture-in-picture mode of the HMD the neurosurgeon performing the EETA is able to see the microsurgical view of the other surgeon simultaneously with the endoscopic view. This enhances the cooperation between the surgeons during the use of four microinstruments in two pairs of hands. Two di̥erent sets of instruments on two di̥erent tables are used for the sterile transcranial approach and the non-sterile transsphenoidal approach. In all cases of a combined approach a transsphenoidal CSF leakage will occur intraoperatively. This is treated with a small intrasellar fat graft, a tissue sealant and lumbar CSF drainage for three days. The sphenoid sinus usually requires no packing.

Case illustrations Case 1 A 55-year-old female patient came to the attention of an endocrinologist with irregular menses, fatigue, increased perspiration and an increase in shoe size. Analysis revealed an acromegaly with a growth hormone (GH) level of 3 mU/L, a paradoxical increase of GH in an oral glucose tolerance test (OGTT) and an increased IGF-1 of 59.5 nmol/L. LH and FSH levels were consistent with a postmenopausal state, while the other pituitary axes were intact. MRI of the brain revealed a right intrasellar microadenoma, but also a tuberculum sellae meningioma and a small meningioma at the lamina cribrosa. An opthalmological evaluation showed normal visual acuity and normal visual eld in Goldman perimetry. Since we routinely pretreat patients with acromegaly before surgery with a somatostatin-analogue for several months, we rst planned a supraorbital approach for the tuberculum sellae meningioma to be followed at a later date by transsphenoidal surgery. Both meningiomas were removed through a left supraorbital approach (Simpson grade II resection). Four months later an EETA was performed in which a macroscopically radical adenoma resection was carried out. Both procedures were without complications, with hospital duration times of 4 and 7 days, respectively. The postoperative IGF-1 level normalized to 16.1 nmol/L and in an OGTT the GH level was suppressed below 1 mU/L. An endocrinological cure was thus


Technical Note 283

Fig. 1 a, b, c Preoperative T1-weighted gadolinium enhanced sagittal and coronal MRI depicting two meningiomas and an intrasellar microadenoma. d, e Postoperative T1-weighted gadolinium enhanced sagittal and coronal MRI revealing no tumor remnants.

Fig. 2 a, b, c Preoperative T1-weighted gadolinium enhanced sagittal and coronal MRI showing an intra- and suprasellar tumor with compression of the chiasm. d, e, f Postoperative T1-weighted, gadolinium enhanced sagittal and coronal MRI showing macroscopic radical tumor resection.

achieved. Postoperative MRI revealed total resection of the men̂ Fig. 2). ingiomas and the adenoma (̎

Case 2 A 16-year-old female patient complained of headaches, nausea and fatigue, and had primary amenorrhea as well as an increase in the size of both hands and feet. Endocrinological evaluation revealed a GH plasma level of 45 mU/L, IGF-1 of 100.9 nmol/L


284 Technical Note

Fig. 3 a Photograph of the intraoperative setting of a single stage/parallel procedure with one surgeon performing a left supraorbital microsurgical keyhole approach and the other surgeon performing an EETA with the aid of a head-mounted display. b, c Intraoperative view of both surgeons with picturein-picture view of both the microscope and the endoscope.

(greatly increased) and a prolactin of 1894 mU/L (moderate increase). It was concluded that the patient had acromegaly but possibly also some prolactin hypersecretion. The MRI is shown ̂ Fig. 3. It shows a macroadenoma extending suprasellarly in ̎ between both optic nerves and before the chiasm and lying on the tuberculum sellae. Because of this extension we concluded that it seemed unlikely (although not impossible) for the suprasellar tumor part to descend completely into the sella upon transsphenoidal tumor resection. Therefore a single stage combined approach was planned. First a right supraorbital craniotomy was performed with the head xed in a Mayeld head holder with 20 ° rotation to the left, after which the suprasellar tumor part could easily be removed as well as part of the diaphragm. Hemostasis of the intrasellar tumor remnant was achieved with Floseal® after which the craniotomy was closed. The patient was then slightly repositioned by turning the Mayeld head holder to the right. After installation of nasal cottonoids drenched in cocaine hydrochloride and epinephrine and new sterile draping, an EETA was performed. The intrasellar tumor part was macroscopically completely removed. Due to CSF leakage, which was expected and is a consequence of the biportal approach, the sella was packed with autologous fat and secured with a brin sealant. The postoperative course was uneventful. A transient diabetes insipidus improved over several weeks. Histological examination showed an adenoma with both GH and PRL expression immunohistologically. The initial postoperative GH was 10 mU/L and IGF-1 46.9 nmol/L. Endocrinologically this means no cure and thus the patient was further treated with a somatostatin analogue with which a normalized IGF-1 (17.5 nmol/L) was achieved. A postoperative MRI did not delineate a tumor remnant and therefore revision surgery was not considered, thus avoiding endangering pituitary function and fertility in this young woman.

Discussion & The microsurgical transsphenoidal approach has been a standard approach to lesions of the sella for decades. Even lesions extending beyond the sella can be treated through this approach in the majority of cases. In the case of very large tumors extending intracranially, a primary transcranial approach (e. g., the pterional approach) is chosen, followed eventually by a secondary transsphenoidal approach for intrasellar or infrasellar tumor remnants. Occasionally, a transsphenoidal approach has to be converted into a transcranial approach in a second stage procedure because of incomplete tumor removal. The use of a nasal speculum, however, creates a corridor that limits the size of the anatomic region that can be visualized. The introduction of endoscopic endonasal transsphenoidal surgery in the 1990s allowed for a broader eld of view and improved visualization while preserving minimal invasiveness. The popularization of this relatively new surgical technique, with which very good clinical results have been achieved, together with excellent anatomic studies in human cadavers that have enabled the limits of this approach to be explored, and encouraged the extension of the approach beyond the limits of the microsurgical approach. Many groups are now exploring the limits of this extended endoscopic endonasal transsphenoidal approach to cover all sorts of lesions around the anterior cranial base, the tuberculum sellae, the sellar and suprasellar region and the clivus down to the foramen magnum [7–12]. The majority of reports concern tumors, but encephaloceles, dural stulas, aneurysms and AVM’s have also been treated by this approach [13–15].

Extended EETA The extended EETA is usually considered as a minimally invasive approach, because it leaves no scars or supercial wounds and avoids brain retraction. The latter is regarded as a big advantage over a transcranial approach, and has also been used as an argu-


Technical Note 285

ment in favor of large skull base approaches over standard craniotomies such as the pterional craniotomy. The use of an endoscope seems to automatically (and wrongfully) suggest minimal invasiveness, no matter what is done during surgery. In an extended EETA lesions of the skull base are approached from their “safe” side, that is, the side from which no critical structures are encountered on the way to the lesion. However, this automatically means that all relevant anatomic structures that may be in close contact with the lesion (frontal lobe, carotid arteries, ACoA complex, optic nerves and chiasm, pituitary stalk) are behind the lesion and can only be controlled in the last phase of the removal of the lesion. In cases in which these anatomic structures adhere to a tumor, bimanual microsurgical dissection is more di̦cult with the two-dimensional endoscopic view. Fortunately, lesions such as meningiomas and adenomas often have a good dissecting plane of arachnoid, so that this approach can be performed successfully in many cases. To be able to treat intracranial lesions the skull and the dura mater need to be opened. In a craniotomy, reconstruction of the dura mater and the skull is relatively easy and the nal result is a near normal anatomy of those structures. In extended EETA this is di̥erent. The opening of the skull base is a destructive procedure with removal of bone with no option to perform a craniotomy. In the case of a small bone window in the sellar oor this hardly constitutes a problem. However, a large bone defect becomes a problem if a rm underlay for reconstruction of the dura is required, e. g., for anchoring a dura substitute. The largest problem associated with the extended EETA is the reconstruction of the dura. Primary closure of the dura is never possible and thus several techniques have been developed. They usually consist of the use of a dura substitute in a monolayer or double layer fashion, the use of additional autologous grafts (fat, muscle, and fascia), tissue sealants and sometimes bone substitutes in combination with external lumbar CSF-drainage (ELD) [1, 16, 17]. The ethmoid and sphenoid sinuses may become completely obliterated. Even then there is a relatively high risk of CSF leakage and consecutive meningitis, as well as pneumencephaly and a need for repeat surgery to deal with these problems [1]. As a result of the ELD immobilization of the patient there is an associated risk of thromboembolic complications. Altogether the hospital stay may thus be prolonged. To reduce the risk of CSF stulas after the extended EETA, a vascularized endonasal mucosa ap has been developed and is increasingly used [17, 18]. This has successfully reduced the number of postoperative CSF stulas. Nevertheless, we consider this technique to cause a signicant disturbance of endonasal anatomy, which may also lead to nasal airway complaints. This can hardly be considered minimally invasive. Regarding the destruction of the anatomy of the skull base, we conclude that the extended EETA might be considered a maximally invasive approach. For many patients this may not cause any signicant problems or complaints, but it may have more signicance in cases of tumor recurrence. Redo surgery after extensive skull base reconstruction is a problem because of the loss of anatomy and signicant scarring due to the use of (autologous) implants [19]. The extended EETA requires special expertise and training and a signicant learning curve, which can only be obtained with a signicant annual case load [12]. Therefore this specic approach may not be suitable for low to average case load centers. Furthermore, at least two experienced surgeons are required: one dedicated endoscopist and one surgeon for bimanual dissection

[12]. The extended EETA may therefore be successfully used in a small number of highly specialized multidisciplinary teams with a high case load, but the technique may not be generalizable to the average neurosurgical community.

Combined supraorbital keyhole-endoscopic endonasal transsphenoidal approach The microsurgical transsphenoidal operation for pituitary tumors avoids a craniotomy with large wounds and brain retraction and leads to good results with minimal morbidity and discomfort to the patient in comparison to the large craniotomies that have been performed in the past. However, with small or keyhole craniotomies the surgical wound, discomfort from wound pain, morbidity and brain retraction have all been minimized and thus the di̥erence between a transsphenoidal approach and a keyhole transcranial approach has been largely overcome. Nowadays, we even dare to say that a supraorbital keyhole craniotomy causes no more morbidity than an endoscopic transsphenoidal approach. The little brain retraction that is required during this procedure hardly ever causes serious morbidity and therefore cannot be regarded as an argument against this transcranial approach. There have been di̥erent descriptions of this approach in the literature, but the procedures are more or less identical: supraorbital keyhole craniotomy [2, 20], supraciliary frontolateral keyhole craniotomy [21], transciliary subfrontal craniotomy [22], eyebrow keyhole approach [23], and pterional keyhole approach [24]. Recently, a fully endoscopic supraorbital approach to tumors of the middle cranial fossa has been described, further reducing surgical trauma [25]. Sequential transsphenoidal and transcranial approaches in multistage procedures are a fairly common surgical routine in the case of very large tumors. A simultaneous approach, however, is relatively unusual. Alleyne et al. described a combined transsphenoidal and pterional craniotomy approach to giant pituitary tumors and used this approach with success in 10 patients [26]. The combination of a supraorbital keyhole approach and an EETA, whether performed sequentially or simultaneously, allows two minimally invasive procedures to optimize tumor removal without extensive skull base dissection. Most morbidity is the result of immobilization of the patient after ELD placement. However, with the small skull base defect CSF drainage can be limited to three days. This, however, does not prolong hospitalization. The combined approach comprises two fairly routine approaches. The EETA is becoming a standard approach for “normal” pituitary adenomas. A su̦cient case load to obtain acceptable surgical experience with this approach can occur even in moderate size neurosurgical departments. The supraorbital keyhole approach can be used for a broad range of indications, e. g., aneurysms of the anterior circulation, tumors of the suprasellar area (tuberculum sellae meningiomas, craniopharyngeomas), frontal skull base tumors, and (Sylvian) arachnoid cysts. Therefore, this approach can be practiced on a regular basis. In a center with a small to average size case load of frontal skull base and perisellar tumors the surgeon may be more accustomed to combining two di̥erent approaches with which he is familiar, than trying to adopt a completely new surgical approach, which he will not practice frequently enough to gain su̦cient experience. Here the adage “the simpler, the better” may apply. This also counts when a simultaneous biportal approach is per-


286 Technical Note

formed by two neurosurgeons. It is easier to gain enough experience with common approaches that are used on a regular basis, than with a rarely indicated approach. Since the anatomy is more or less preserved, prevention of CSF leakage is relatively simple and surgical morbidity is minimal. The preservation of the anatomy also confers the advantage of relatively easy and straightforward redo surgery in cases of tumor recurrence. Based on the surgical principles of the combined approach described here, one might predict that in specic cases of tumor around the sella and frontal skull base the surgical morbidity caused by the two approaches is likely to be less than that of a single extended EETA.

Conclusion & A minimally invasive combined approach of a supraorbital keyhole craniotomy and an EETA is a good alternative to extensive transcranial skull base approaches or an extended EETA for lesions around the sella and anterior skull base.

References 1 de Divitiis DE, Esposito F, Cappabianca P et al. Tuberculum sellae meningiomas: high route or low route? A series of 51 consecutive cases. Neurosurgery 2008; 62: 556–563 2 van Lindert EJ, Perneczky A, Fries G et al. The supraorbital keyhole approach to supratentorial aneurysms: concept and technique. Surg Neurol 1998; 49: 481–489 3 Cappabianca P, Aleri A, de Divitiis DE. Endoscopic endonasal transsphenoidal approach to the sella: towards functional endoscopic pituitary surgery (FEPS). Minim Invas Neurosurg 1998; 41: 66–73 4 Cappabianca P, Aleri A, Thermes S et al. Instruments for endoscopic endonasal transsphenoidal surgery. Neurosurgery 1999; 45: 392–395 5 Jho HD, Carrau RL. Endoscopic endonasal transsphenoidal surgery: experience with 50 patients. J Neurosurg 1997; 87: 44–51 6 Jho HD, Aleri A. Endoscopic transsphenoidal pituitary surgery: various surgical techniques and recommended steps for procedural transition. Br J Neurosurg 2000; 14: 432–440 7 Dave SP, Bared A, Casiano RR. Surgical outcomes and safety of transnasal endoscopic resection for anterior skull tumors. Otolaryngol Head Neck Surg 2007; 136: 920–927 8 de Divitiis DE, Cavallo LM, Cappabianca P et al. Extended endoscopic endonasal transsphenoidal approach for the removal of suprasellar tumors: Part 2. Neurosurgery 2007; 60: 46–58

9 Kassam A, Thomas AJ, Snyderman C et al. Fully endoscopic expanded endonasal approach treating skull base lesions in pediatric patients. J Neurosurg 2007; 106: 75–86 10 Kassam A, Snyderman CH, Mintz A. Expanded endonasal approach: the rostrocaudal axis Part I. Crista galli to the sella turcica. Neurosurg Focus 2005; 19: E3 11 Laufer I, Anand VK, Schwartz TH. Endoscopic, endonasal extended transsphenoidal, transplanum transtuberculum approach for resection of suprasellar lesions. J Neurosurg 2007; 106: 400–406 12 Prevedello D, Kassam A, Snyderman C et al. Endoscopic Cranial Base Surgery: Ready for Prime Time? Clin Neurosurgery 2007; 54: 48–57 13 Prevedello DM, Thomas A, Gardner P et al. Endoscopic endonasal resection of a synchronous pituitary adenoma and a tuberculum sellae meningioma: technical case report. Neurosurgery 2007; 60: E401 14 Kassam AB, Thomas AJ, Zimmer LA et al. Expanded endonasal approach: a fully endoscopic completely transnasal resection of a skull base arteriovenous malformation. Childs Nerv Syst 2007; 23: 491–498 15 Frank G, Sciarretta V, Calbucci F et al. The endoscopic transnasal transsphenoidal approach for the treatment of cranial base chordomas and chondrosarcomas. Neurosurgery 2006; 59: ONS50–ONS57 16 Cavallo LM, Messina A, Esposito F et al. Skull base reconstruction in the extended endoscopic transsphenoidal approach for suprasellar lesions. J Neurosurg 2007; 107: 713–720 17 Snyderman CH, Kassam AB, Carrau R et al. Endoscopic reconstruction of cranial base defects following endonasal skull base surgery. Skull Base 2007; 17: 73–78 18 Hadad G, Bassagasteguy L, Carrau RL et al. A novel reconstructive technique after endoscopic expanded endonasal approaches: vascular pedicle nasoseptal ap. Laryngoscope 2006; 116: 1882–1886 19 El-Banhawy OA, Halaka AN, Ayad H et al. Long-term endonasal endoscopic review of successful duraplasty after endonasal endoscopic skull base surgery. Am J Rhinol 2008; 22: 175–181 20 Reisch R, Perneczky A. Ten-year experience with the supraorbital subfrontal approach through an eyebrow skin incision. Neurosurgery 2005; 57: 242–255 21 Jallo GI, Bognar L. Eyebrow surgery: the supraciliary craniotomy: technical note. Neurosurgery 2006; 59: ONSE157–ONSE158 22 Sanchez-Vazquez MA, Barrera-Calatayud P, Mejia-Villela M et al. Transciliary subfrontal craniotomy for anterior skull base lesions. Technical note. J Neurosurg 1999; 91: 892–896 23 Paladino J, Pirker N, Stimac D et al. Eyebrow keyhole approach in vascular neurosurgery. Minim Invas Neurosurg 1998; 41: 200–203 24 Mori K, Osada H, Yamamoto T et al. Pterional keyhole approach to middle cerebral artery aneurysms through an outer canthal skin incision. Minim Invas Neurosurg 2007; 50: 195–201 25 Kabil MS, Shahinian HK. The endoscopic supraorbital approach to tumors of the middle cranial base. Surg Neurol 2006; 66: 396–401 26 Alleyne CH Jr, Barrow DL, Oyesiku NM. Combined transsphenoidal and pterional craniotomy approach to giant pituitary tumors. Surg Neurol 2002; 57: 380–390
