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- Publisher
- Oxford University Press
- Copyright
- Copyright © 2018 by the Congress of Neurological Surgeons
- ISSN
- 2332-4252
- eISSN
- 2332-4260
- D.O.I.
- 10.1093/ons/opy054
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- See Article on Publisher Site
Abstract
Abstract BACKGROUND Transorbital endoscopic approach (TOEA) to the cavernous sinus (CS) is a novel surgical technique. However, the necessity of lateral orbital rim (LOR) osteotomy is questionable. OBJECTIVE To illustrate the surgical dissection of TOEAs to CS and to investigate the additional benefit of LOR osteotomy. METHODS Anatomic dissections were carried out in 7 cadaveric heads (14 sides). The TOEAs were performed before and after LOR osteotomy; herein referred as the lateral transorbital approach (LTOA) and the lateral orbital wall approach (LOWA), respectively. The stereotactic measurements of the area of exposure, surgical freedom, and angles of attack around CS were quantified. RESULTS LOWA increased larger area of exposure than LTOA at entry site (5.3 ± 0.6 cm2 and 2.6 ± 0.6 cm2, respectively; P < .001) but both of these techniques provided similar area of exposure at the surgical target site. With regard to the surgical freedoms, those afforded by LOWA were all significantly superior at all of the surgical targets with the difference ranged from 106.6% to 172.5%. No significant differences were found between the vertical angles produced by either approach. On the other hand, the horizontal angles achieved by LOWA were significantly more favorable. CONCLUSION The TOEAs, either with or without LOR osteotomy are feasible for CS exposure. Although the incremental effect of maneuverability is attained following the LOR osteotomy, it should be performed selectively. Additional research is needed to further validate the safety and efficacy, as well as for precisely defining the clinical application of these techniques. Anatomic study, Cavernous sinus, Endoscopic surgery, Lateral orbital rim, Minimally invasive neurosurgery, Transorbital approach ABBREVIATIONS ABBREVIATIONS ACP anterior clinoid process CS cavernous sinus FO foramen ovale FR foramen rotundum FZ frontozygomatic GG gasserian ganglion GWS greater wing of the sphenoid ICA internal carotid artery IOF inferior orbital fissure LOR lateral orbital rim LOWA lateral orbital wall approach LTOA lateral transorbital approach LTW lateral wall of the orbit SOF superior orbital fissure TOEA Transorbital endoscopic approach Over the past decades, considerable efforts have been made to develop increasingly advanced minimally invasive techniques in neurosurgery, of which transorbital endoscopic approaches (TOEAs) have emerged as recent techniques of skull base surgery. With the rise of multiportal surgery, TOEAs have been efficiently combined with different approaches, enhancing access to areas otherwise difficult to reach through a single port of entry. To optimize access to various regions of the skull base, particularly when they used isolation, in monoportal technique, transorbital approaches have undergone a number of modifications, some of which have been heavily disputed. At present, primarily when approaching the cavernous sinus (CS) with the application of TOEAs, the biggest debate has centered around the effects of lateral orbital rim (LOR) osteotomy. Lately, numerous studies have reported on the perquisites of LOR preservation, while others have argued that its removal may be in fact beneficial, not only to enhance the surgical working space but also to maximize the exposure of surgical targets.1–4 In this study, we employed lateral TOEA to expose the CS both before and after LOR osteotomy; herein, referred as the lateral transorbital approach (LTOA) and the lateral orbital wall approach (LOWA), respectively. For each approach, measurements of the area of exposure and degree of surgical maneuverability were determined with stereotactic measurement and analysis was further conducted for comparison. To our knowledge, this is the first study to quantify the effects of LOR osteotomy for transorbital approaches to the CS. METHODS A total of 14 orbits were dissected in 7 red- and blue-colored latex-injected human cadaveric heads. This cadaveric study received an institutional review board exemption because the dissections were performed on deidentified cadaveric specimens. The dissections were carried out in full adherance with regulations governing the use of human cadaveric tissues at our institution. Prior to anatomic dissection, specimens were submitted to fine-cut (0.5 mm slices), high-resolution computed tomographic scans; the images were later imported to a cranial navigation system platform (iNtellect - Stryker Inc, Kalamazoo, Michigan). Using frameless stereotaxy, the scans served for intraoperative confirmation of anatomic targets and determination of measurements. During the procedures, the specimens were placed on the dissection table in supine position. To simulate the condition of patients in the operating room a 3-point head clamp was used to position the cadaveric heads in slight extension and in 30° rotation away from the operator. Surgical Dissections Lateral Transorbital Approach Lateral Transorbital Approach (LTOA) was carried out with several important modifications of the methodologies described previously.5,6 Initially, a 2 cm incision was made extending posteriorly away from the lateral canthus, along a natural wrinkle (Figure 1A). Thereafter, a lateral canthotomy and cantholysis were performed, exposing the LOR superiorly from the frontozygomatic (FZ) suture, down to the level of the zygoma. The periorbita was then carefully separated from the lateral wall of the orbit (LWO) until the orbital apex was reached (Figure 1B). During this stage, akin to reports by previous publications,6–8 the maximum limit for eye globe retraction was set at <10 mm. This was performed as needed using malleable retractors. Subsequently, under endoscopic visualization, a 4 mm coarse diamond burr was used to drill the LWO from the sphenoid ridge downward to inferior orbital fissure (IOF). In similar fashion, drilling was also undertaken in a lateral trajectory, away from the superior orbital fissure (SOF), until the temporalis muscle was encountered (Figure 1C). Next, extradural elevation of the temporal lobe was carried out medially towards the CS. Then, to achieve a broad exposure of the lateral CS wall, the outer dura layer (ie, dura propria) was peeled away from the inner meningeal layer. CNs III, IV, VI, V1-3, and the intracavernous segment of ICA were thus readily exposed and identified. After the dissection was complete, stereotactic measurements were determined (Figure 1D). FIGURE 1. View largeDownload slide Demonstration of a right-sided LTOA. A, A linear incision (black line) was made along a natural skin crease of the lateral canthus. B, The periorbita was dissected from the LWO posteriorly to the orbital apex. C, Exposure of temporal dura after removing the LWO. D, Exposure of the CS and measurement of exposed area (red line). ACP = anterior clinoid process; CN = cranial nerve; GG = gasserian ganglion; ICA = internal carotid artery; IOF = inferior orbital fissure; Lat. = lateral; M. = muscle; MCF = middle cranial fossa; MOA = meningo-orbital artery; PO = periorbita; SOF = superior orbital fissure; Temp. = temporal. FIGURE 1. View largeDownload slide Demonstration of a right-sided LTOA. A, A linear incision (black line) was made along a natural skin crease of the lateral canthus. B, The periorbita was dissected from the LWO posteriorly to the orbital apex. C, Exposure of temporal dura after removing the LWO. D, Exposure of the CS and measurement of exposed area (red line). ACP = anterior clinoid process; CN = cranial nerve; GG = gasserian ganglion; ICA = internal carotid artery; IOF = inferior orbital fissure; Lat. = lateral; M. = muscle; MCF = middle cranial fossa; MOA = meningo-orbital artery; PO = periorbita; SOF = superior orbital fissure; Temp. = temporal. Lateral Orbital Wall Approach In every specimen, LOWA was carried out only after the conclusion of LTOA dissections and complete collection of measurements. To begin this approach, the temporalis muscle was first dissected away from the LOR and the greater wing of the sphenoid (GWS; Figure 2A). During this approach, no or only minimal globe retraction was necessary to reach the target. Using a high-speed drill, the LOR was osteotomized from the FZ suture to the level of the zygoma (Figure 2B). Then, the adjacent anterolateral part of GWS and the remaining portion of LWO were removed. As a result, the anterolateral part of temporal dura was broadly exposed (Figure 2C). Next, as described earlier for LTOA, the lateral wall of the CS was dissected, thus, exposing critical neurovascular structures that were then identified. Upon completion of the dissection, stereotactic measurements were acquired. FIGURE 2. View largeDownload slide Demonstration of LOR osteotomy of a right-sided LOWA. A, the LOR was cut from frontozygomatic suture to the level of zygomatic arch (dotted line) after periorbita and temporalis muscle were dissected apart from it. B, Exposure of the LWO and GWS after osteotomy of the LOR. C, Exposure of temporal dura and the orbital apex after removal of the LWO and the adjacent anterolateral segment of the GWS. GWS = greater wing of sphenoid. FIGURE 2. View largeDownload slide Demonstration of LOR osteotomy of a right-sided LOWA. A, the LOR was cut from frontozygomatic suture to the level of zygomatic arch (dotted line) after periorbita and temporalis muscle were dissected apart from it. B, Exposure of the LWO and GWS after osteotomy of the LOR. C, Exposure of temporal dura and the orbital apex after removal of the LWO and the adjacent anterolateral segment of the GWS. GWS = greater wing of sphenoid. Measurement For each procedure, measurements were obtained with neuronavigation using a similar method described previously.9–11 The dataset contained the 3D-coordinates of the anatomic target points and of the position of the proximal end of dissector representing the surgical working space. For calculation and analysis, all measurements were exported into a spreadsheet software (Microsoft Office Excel 2013; Microsoft Corp, Redmond, Washington). Area of Exposure The area of exposure was measured at 2 locations: (1) the surgical entry site and (2) the surgical target site. For the first one, the area was defined by a hexagonal-shape, bounded by far-medial, inferomedial, inferolateral, far-lateral, superolateral, and superomedial individual points, surrounding the surgical entry site of the orbit. Similarly, for the second one, the area of exposure was defined around the CS by another hexagonal-shape. However, in contrast to the first one, here the area was limited by the superior-most and inferior-most points of the orbital apex, foramen rotundum (FR), gasserian ganglion (GG) along the lateral border of CN V3, the penetrating point of CN III into CS, and the tip of the anterior clinoid process (ACP; Figure 1D). Surgical Freedom and Angles of Attack Surgical freedom was defined as the maximal permissible working area at the proximal end of a 25 cm endoscopic dissector used to manipulate a surgical target with its distal end.9 To calculate this parameter of maneuverability, coordinates of the position of the instrument were obtained, by holding the navigation probe to the proximal end of the dissector, as the latter was moved along the 6 most extreme positions in space in relation to the specimen while the distal end of the instrument was fixed over a surgical target of interest. Forming an imaginary hexagonal-shape area about the corridor's portal, 6 points were used to represent the maximal allowable working area for each approach. In this respect, the proximal end of the dissector was placed as far medially, inferomedially, inferolaterally, far-laterally, superolaterally, and superomedially as possible (Figures 3A and 3B). The surgical targets were foramen ovale (FO), FR, SOF, the tip of ACP, the posterior bend of the cavernous segment of internal carotid artery (ICA), and GG. FIGURE 3. View largeDownload slide A demonstration of the method used to collect the measurements of surgical freedom for A, LTOA and B, LOWA. Measurements were obtained by moving the proximal end of the dissector in 6 different points about the surgical corridor (red line) while fixing its distal tip at each of anatomic targets of interest. Details are described in the methods section. C, Schematic illustration of the axial plane of skull base comparing the horizontal angle of attack achieved by LTOA (green area) and LOWA (blue area). FIGURE 3. View largeDownload slide A demonstration of the method used to collect the measurements of surgical freedom for A, LTOA and B, LOWA. Measurements were obtained by moving the proximal end of the dissector in 6 different points about the surgical corridor (red line) while fixing its distal tip at each of anatomic targets of interest. Details are described in the methods section. C, Schematic illustration of the axial plane of skull base comparing the horizontal angle of attack achieved by LTOA (green area) and LOWA (blue area). Measurements of the angles of attack were obtained using a similar method to the one described for surgical freedom.10 However, as opposed to the latter, for this one the instrument was moved as far as possible in the vertical and horizontal planes in relation to the specimen. Statistical Analysis All collected measurements were exported to statistical software (Stata Statistical Software, Release 14; StataCorp LP, College Station, Texas). Comparisons among the areas of exposure, surgical freedom, and angles of attack for each approach were carried out using a paired t-test. Statistical significance was set at P < .05. RESULTS For LTOA, the area of exposure at entry site was of 2.6 ± 0.6 cm2. This exposure was significantly expanded by LOWA to 5.3 ± 0.6 cm2 (P < .001). A similar increase in the area of exposure was also observed at the surgical target site, albeit, the difference was not statistically significant (4.08 ± 0.7 cm2 for LTOA and 4.43 ± 0.5 cm2 for LOWA; P = .25). Table 1 outlines the results of the areas of exposure for both approaches. TABLE 1. Mean Area of Exposure Provided by LTOA and LOWA Mean area of exposure (cm2)a LTOA LOWA P value Entry site 2.6 ± 0.6 5.3 ± 0.6 <.001 Target site (CS) 4.08 ± 0.7 4.43 ± 0.5 .25 Mean area of exposure (cm2)a LTOA LOWA P value Entry site 2.6 ± 0.6 5.3 ± 0.6 <.001 Target site (CS) 4.08 ± 0.7 4.43 ± 0.5 .25 aPresented as ± SD. View Large TABLE 1. Mean Area of Exposure Provided by LTOA and LOWA Mean area of exposure (cm2)a LTOA LOWA P value Entry site 2.6 ± 0.6 5.3 ± 0.6 <.001 Target site (CS) 4.08 ± 0.7 4.43 ± 0.5 .25 Mean area of exposure (cm2)a LTOA LOWA P value Entry site 2.6 ± 0.6 5.3 ± 0.6 <.001 Target site (CS) 4.08 ± 0.7 4.43 ± 0.5 .25 aPresented as ± SD. View Large When the surgical freedom at individual targets was measured, the largest values for ease of maneuverability was obtained at SOF (23.0 ± 5.7 cm2 and 49.7 ± 7.6 cm2 for LTOA and LOWA, respectively) and ACP (23.3 ± 5.4 cm2 and 40.2 ± 9.5 cm2 for LTOA and LOWA, respectively). The increased maneuverability provided by LOWA overall ranged from 106.6% to 172.5% on the targets. Of these, the greatest disparity was observed at ACP, while the smallest range was measured at FO. With regard to the mean surgical freedoms, those afforded by LOWA were all superior. Table 2 outlines the results of the surgical freedom for both approaches. TABLE 2. Mean Surgical Freedom for Each Surgical Target Provided by LTOA and LOWAa Mean surgical freedom (cm2)b LTOA LOWA P value F ovale 12.1 ± 2.8 25.0 ± 7.8 .001 F rotundum 13.3 ± 5.5 28.2 ± 8.6 <.001 SOF 23.0 ± 5.7 49.7 ± 7.6 <.001 ACP 23.3 ± 5.4 40.2 ± 9.5 .001 cICA 11.7 ± 1.7 27.1 ± 4.9 <.001 GG 12.8 ± 5.1 30.3 ± 35 <.001 Mean surgical freedom (cm2)b LTOA LOWA P value F ovale 12.1 ± 2.8 25.0 ± 7.8 .001 F rotundum 13.3 ± 5.5 28.2 ± 8.6 <.001 SOF 23.0 ± 5.7 49.7 ± 7.6 <.001 ACP 23.3 ± 5.4 40.2 ± 9.5 .001 cICA 11.7 ± 1.7 27.1 ± 4.9 <.001 GG 12.8 ± 5.1 30.3 ± 35 <.001 aLTOA = lateral transorbital approach; LOWA = lateral orbital wall approach; F = foramen; SOF = superior orbital fissure; ACP = anterior clinoid process; cICA = cavernous part of internal carotid artery; GG = gassarian ganglion. bPresented as ± SD. View Large TABLE 2. Mean Surgical Freedom for Each Surgical Target Provided by LTOA and LOWAa Mean surgical freedom (cm2)b LTOA LOWA P value F ovale 12.1 ± 2.8 25.0 ± 7.8 .001 F rotundum 13.3 ± 5.5 28.2 ± 8.6 <.001 SOF 23.0 ± 5.7 49.7 ± 7.6 <.001 ACP 23.3 ± 5.4 40.2 ± 9.5 .001 cICA 11.7 ± 1.7 27.1 ± 4.9 <.001 GG 12.8 ± 5.1 30.3 ± 35 <.001 Mean surgical freedom (cm2)b LTOA LOWA P value F ovale 12.1 ± 2.8 25.0 ± 7.8 .001 F rotundum 13.3 ± 5.5 28.2 ± 8.6 <.001 SOF 23.0 ± 5.7 49.7 ± 7.6 <.001 ACP 23.3 ± 5.4 40.2 ± 9.5 .001 cICA 11.7 ± 1.7 27.1 ± 4.9 <.001 GG 12.8 ± 5.1 30.3 ± 35 <.001 aLTOA = lateral transorbital approach; LOWA = lateral orbital wall approach; F = foramen; SOF = superior orbital fissure; ACP = anterior clinoid process; cICA = cavernous part of internal carotid artery; GG = gassarian ganglion. bPresented as ± SD. View Large Furthermore, concerning the angles of attack, no significant differences were found between the mean vertical angles produced by either approach. On the other hand, compared to LTOA, the mean horizontal angles achieved by LOWA were significantly more favorable (Figure 3C). This finding, is thought to be largely a byproduct of the greater surgical freedom observed at these particular targets in LOWA. For each approach, the widest horizontal and vertical angles were obtained at ACP and SOF. Table 3 outlines the results of the angles of attack for both approaches. TABLE 3. Mean Angle of Attack for Each Surgical Target Provided by LTOA and LOWAa Vertical angle (degree)b Horizontal angle (degree)b LTOA LOWA P value LTOA LOWA P value F ovale 12.5 ± 3.8 11.8 ± 3.7 .549 8.6 ± 1.8 20.4 ± 2.9 <.001 F rotundum 16.9 ± 1.9 18.3 ± 2.9 .185 8.9 ± 2.0 21.6 ± 4.1 <.001 SOF 20.5 ± 0.3 22.9 ± 3.9 .090 13.9 ± 2.0 25.1 ± 3.2 <.001 ACP 20.9 ± 4.8 21.9 ± 5.4 .625 13.0 ± 2.1 23.8 ± 3.2 <.001 cICA 15.7 ± 2.3 16.6 ± 3.7 .248 7.2 ± 1.0 18.8 ± 2.0 <.001 GG 12.0 ± 3.0 12.8 ± 2.3 .433 11.0 ± 1.4 16.0 ± 2.2 <.001 Vertical angle (degree)b Horizontal angle (degree)b LTOA LOWA P value LTOA LOWA P value F ovale 12.5 ± 3.8 11.8 ± 3.7 .549 8.6 ± 1.8 20.4 ± 2.9 <.001 F rotundum 16.9 ± 1.9 18.3 ± 2.9 .185 8.9 ± 2.0 21.6 ± 4.1 <.001 SOF 20.5 ± 0.3 22.9 ± 3.9 .090 13.9 ± 2.0 25.1 ± 3.2 <.001 ACP 20.9 ± 4.8 21.9 ± 5.4 .625 13.0 ± 2.1 23.8 ± 3.2 <.001 cICA 15.7 ± 2.3 16.6 ± 3.7 .248 7.2 ± 1.0 18.8 ± 2.0 <.001 GG 12.0 ± 3.0 12.8 ± 2.3 .433 11.0 ± 1.4 16.0 ± 2.2 <.001 aLTOA = lateral transorbital approach; LOWA = lateral orbital wall approach; F = foramen; SOF = superior orbital fissure; ACP = anterior clinoid process; cICA = cavernous part of internal carotid artery; GG = gassarian ganglion bPresented as ± SD. View Large TABLE 3. Mean Angle of Attack for Each Surgical Target Provided by LTOA and LOWAa Vertical angle (degree)b Horizontal angle (degree)b LTOA LOWA P value LTOA LOWA P value F ovale 12.5 ± 3.8 11.8 ± 3.7 .549 8.6 ± 1.8 20.4 ± 2.9 <.001 F rotundum 16.9 ± 1.9 18.3 ± 2.9 .185 8.9 ± 2.0 21.6 ± 4.1 <.001 SOF 20.5 ± 0.3 22.9 ± 3.9 .090 13.9 ± 2.0 25.1 ± 3.2 <.001 ACP 20.9 ± 4.8 21.9 ± 5.4 .625 13.0 ± 2.1 23.8 ± 3.2 <.001 cICA 15.7 ± 2.3 16.6 ± 3.7 .248 7.2 ± 1.0 18.8 ± 2.0 <.001 GG 12.0 ± 3.0 12.8 ± 2.3 .433 11.0 ± 1.4 16.0 ± 2.2 <.001 Vertical angle (degree)b Horizontal angle (degree)b LTOA LOWA P value LTOA LOWA P value F ovale 12.5 ± 3.8 11.8 ± 3.7 .549 8.6 ± 1.8 20.4 ± 2.9 <.001 F rotundum 16.9 ± 1.9 18.3 ± 2.9 .185 8.9 ± 2.0 21.6 ± 4.1 <.001 SOF 20.5 ± 0.3 22.9 ± 3.9 .090 13.9 ± 2.0 25.1 ± 3.2 <.001 ACP 20.9 ± 4.8 21.9 ± 5.4 .625 13.0 ± 2.1 23.8 ± 3.2 <.001 cICA 15.7 ± 2.3 16.6 ± 3.7 .248 7.2 ± 1.0 18.8 ± 2.0 <.001 GG 12.0 ± 3.0 12.8 ± 2.3 .433 11.0 ± 1.4 16.0 ± 2.2 <.001 aLTOA = lateral transorbital approach; LOWA = lateral orbital wall approach; F = foramen; SOF = superior orbital fissure; ACP = anterior clinoid process; cICA = cavernous part of internal carotid artery; GG = gassarian ganglion bPresented as ± SD. View Large DISCUSSION Given its close association with critical neurovascular structures, the CS was long considered inoperable. During the past decades, the CS has been preferentially approached through transcranial approaches, for which pterional,12 subtemporal,13 zygomatic,14 orbitozygomatic,15 and combined approaches have been previously described. Currently, the interdural fronto-temporal-orbito-zygomatic approach or the extended pterional approach are considered the gold-standard.16 However, the role of CS surgery has been faded because of surgical morbidity17 as well as the excellent outcome of stereotactic radiosurgery.16 In recent years, minimally invasive techniques to the CS have been developed, including the keyhole concept18,19 and the endoscopic techniques.20–22; thus eventually giving rise to various strategies. According to previous data, this approach achieves comparable outcomes to those of conventional open craniotomies with considerably less morbidity.23,24 Transorbital endoscopic surgery is one of the innovative skull base operative concepts. The past 5 yr have observed a dramatic surge of knowledge in the field associated with the innovative description of transorbital neuroendoscopic techniques that can be employed for tumors within the anterior and middle skull bases. Its indications may vary from simple biopsies up to attempting a complete surgical resection.7,8,25 Recent studies have demonstrated the feasibility of using the lateral orbital corridor to gain CS access.6,17,26,27 Perhaps among the main advantages offered by TOEAs to the CS are the ability to provide the surgeon with a direct visualization of its lateral wall, the significantly shorter distance of the incision site to the targets, and its minimal need for brain and neurovascular manipulation. Altogether, these features yield a considerable decrease in the operating time combined with minimal anatomic disruption; hence, there is a high likelihood of improved postoperative functional outcomes.6,17 Additionally, several cosmetic techniques have been used to expose the lateral orbit, consisting of transcutaneous incisions, such as Krönlein and Stallard-Wright incisions, and transconjunctival incisions.27–29 In this study, a lateral canthotomy, previously reported as an excellent LOR exposure and cosmetic technique,3,17 was applied for CS access. At present, accomplishing full CS exposure by transorbital techniques through the lateral orbital corridor remains controversial. Often, LOR osteotomy (ie, LOWA) is exercised in some centers with the idea that it grants broad CS exposure.3,17,30 Additionally, it has been proposed by some studies that by LOR removal the need for retraction of orbital contents is reduced significantly, simultaneously allowing for enhanced instrument maneuverability.3,17,30 However, LOR removal warrants surgical reconstruction, which may be associated with poor cosmetic outcomes.6,31 Moreover, for the bony defect that is left following GWS removal, judicious patching with a fat graft is required to reduce the chance of the patient developing postoperative enophthalmos.8,27,32 For these and other drawbacks, several groups now opt instead for LOR preservation (ie, LTOA).8,26,33 Moreover, recent reports have demonstrated that despite LOR preservation, adequate surgical exposure and acceptable manipulation of CS lesions is still possible.5,6,34 Despite these claims, the available studies have not quantitatively established the precise surgical benefits and disadvantages of LOR removal or preservation in a manner that permits comparison. The findings presented in this study demonstrate that both of these lateral transorbital techniques offer comparable CS exposures (4.08 ± 0.7 cm2 vs 4.43 ± 0.5 cm2). Nevertheless, LOR removal enhances surgical freedom in approaches to the CS, as occurred for each of the target points investigated here. When the LOR is removed, the magnitude of surgical maneuverability among the same targets ranged from 106.6% to 172.5%. Moreover, although the attack angles in the vertical plane afforded by each approach were not significantly different for any of the targets, the attack angles in the horizontal plane were significantly increased. These results were influenced by the exposure gained at the surgical entry site, following the dissection of the temporalis muscle and the removal of the adjacent GWS. Given these findings, it can be inferred that LTOA may be an adequate option to address small CS lesions, whereas the application of LOWA may be reasonable for highly selected cases involving larger lesions, although in such instances more extensive manipulation of targets may be required.3 Furthermore, TOEAs to the CS are not without disadvantages. The crowding of surgical instruments forces the surgeon to become accustomed to uncomfortable technical maneuvers as a result of the exceptionally narrow working corridor.3,32 It may be difficult to undertake these techniques under a bloody field, especially when ICA control is necessary. Moreover, it may preclude achieving tight dural closure following the resection of large lesions, increasing the likelihood of CSF leak.3,33 Moreover, when viewed endoscopically, the anatomy of the orbit differs significantly from that, which is encountered with the standard craniotomies. Thus, for becoming familiar with transorbital approaches, it is beneficial to spend long hours of thorough practice in a cadaver dissection lab. Limitations As a full cadaveric study, several limitations were encountered. These include the limited number of specimens, the absence of physiological and presence of anatomic conditions resulting postmortem, as well as the employment of cadavers free from skull base or intracranial disease. All of which may prevent adequate extrapolation of the results into clinical practice. However, we hope that the data presented here will serve as a framework that can be relied upon by future studies. CONCLUSION Obtaining adequate CS exposure is feasible both before and after LOR osteotomy when approaching this region endoscopically through the lateral orbital corridor. Consistent with prior studies, improved instrument maneuverability at targets within the CS is attained following LOR osteotomy. However, despite these enhancements, LOR removal has some inherent disadvantages and therefore should be performed selectively. Still, strategies for CS lesions should continue to be tailored to the individual patient and lesion characteristics; this should always be the cornerstone of treatment. To further validate our results, clinical studies to better define the safety, efficacy, and limitations of transorbital endoscopic techniques to the CS are necessary. Disclosures This study was performed at ALT-VISION at The Ohio State University. This laboratory receives educational support from the following companies: Carl Zeiss Microscopy, Intuitive Surgical Corp, KLS Martin Corp, Karl Storz Endoscopy, Leica Microsystems, Medtronic Corp, Stryker Corp, and Vycor Medical. Dr Prevedello is a consultant for Stryker Corp, Medtronic Corp, and Codman, has received honorarium from Leica Microsystem, and has received royalties from KLS-Martin. Dr Carrau is a consultant for Medtronic Corp. 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Transorbital endoscopic approaches to the skull base: current concepts and future perspectives . J Neurosurg Sci . 2016 ; 60 ( 4 ): 514 - 525 . Google Scholar PubMed 33. Chen HI , Bohman L-E , Emery L et al. Lateral transorbital endoscopic access to the hippocampus, amygdala, and entorhinal cortex: initial clinical experience . ORL J Otorhinolaryngol Relat Spec . 2015 ; 77 ( 6 ): 321 - 332 . Google Scholar CrossRef Search ADS PubMed 34. Dallan I , Di Somma A , Prats-Galino A et al. Endoscopic transorbital route to the cavernous sinus through the meningo-orbital band: a descriptive anatomical study . J Neurosurg . 2016 ; 127 ( 3 ): 622 - 629 . Google Scholar CrossRef Search ADS PubMed COMMENT Using measurements of cadaveric dissections, the authors make comparisons between transorbital endoscopic approaches (TOEA) to the cavernous sinus with or without the use of a lateral orbital rim (LOR) osteotomy. The authors quantify the difference in the exposure and surgical maneuverability achieved using these 2 different approaches. The study adds useful information to the body of knowledge on these techniques, although, of course, with the uncertain applicability of these cadaveric findings to the “real world” of surgery on living patients. Nonetheless, I think these findings are instructive to surgeons utilizing these approaches. Michael Chicoine St. Louis, Missouri Copyright © 2018 by the Congress of Neurological Surgeons
Journal
Operative Neurosurgery – Oxford University Press
Published: Apr 26, 2018
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