Journal of Clinical Neuroscience xxx (2014) xxx–xxx
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Neuroanatomical Study
Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex Leon T. Lai a,⇑, Michael K. Morgan a, Dustin Dalgorf c, Ali Bokhari b, Peta-Lee Sacks b, Ray Sacks a, Richard J. Harvey a,b a b c
Australian School of Advanced Medicine, Macquarie University, Sydney, Australia Applied Medical Research Centre, University of New South Wales, Sydney, Australia Department of Otolaryngology, Head and Neck Surgery, University of Toronto, Canada
a r t i c l e
i n f o
Article history: Received 21 April 2013 Accepted 16 July 2013 Available online xxxx Keywords: Anterior cerebral artery Anterior communicating artery aneurysm Endoscopic endonasal approach
a b s t r a c t The endoscopic transnasal approach to the anterior communicating artery (ACoA) complex is not widely performed. This cadaveric study investigated the surgical relevance of the anterior endoscopic approach to the treatment of ACoA aneurysms. Bi-nasal endoscopic transtubercular surgery was carried out on fresh adult cadavers. Primary outcomes measures incorporated dimensions of the endonasal corridor (operative field depth, lateral limits, size of the transplanum craniotomy and dural opening); vascular exposure (proximal and distal anterior cerebral arteries [ACA], ACoA, clinoidal internal carotid artery [ICA] segment); and operative manoeuvrability defined by clip placements (ipsilateral and contralateral). Eight cadaver heads were used (mean age 84 ± 7 years, range 76–94 years, 75% female). Mean operative depth was 97 ± 4 mm. The lateral corridors were limited proximally by the alar rim openings (31 ± 2 mm), and distally by the optic nerves (22 ± 6 mm). The endonasal craniotomy dimensions were 21 ± 5 mm anteroposteriorly, and 22 ± 4 mm laterally. Vascular exposure was achieved in 100% of subjects for the ACoA segment and the ACA segments proximal to the ACoA (A1). The ACA segments distal to the ACoA (A2) were accessible only in 40% of subjects. Endonasal clip placement across the ACoA segment, clinoidal ICA, A1 and A2 were 100%, 90%, 90%, and 30%, respectively. The ventral endoscopic endonasal approach to the ACoA complex provides excellent vascular visualisation without brain retraction or gyrus rectus resection. However, the limitation in access to the A2 for temporary clip placement may prove to be a significant limitation of this approach. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Of all cerebral aneurysms, the anterior communicating artery (ACoA) aneurysm is the most frequent and represents an increased risk of rupture as compared to aneurysms in other locations [1–8]. Transcranial clip ligation (via the pterional transsylvian, supraorbital or interhemispheric corridors) presents significant technical challenges because of the deep and midline location of these lesions. Infrequently, surgical morbidity arises from the frontal lobe retraction or partial gyrectomy that are necessary to facilitate aneurysm exposure [4,9–11]. The application of endovascular techniques in recent years has provided a less invasive alternative to the management of ACoA aneurysms, but has led to an inferior durability of aneurysm repair and an increased risk for retreatment [12–16]. Cranial base approaches with clip obliteration maintain ⇑ Corresponding author. Address: Department of Neurosurgery, Level 4 East, The Royal Melbourne Hospital, Grattan Street, Parkville, Melbourne, VIC 3052, Australia. Tel.: +61 (03) 93422105. E-mail address: [email protected] (L.T. Lai).
treatment robustness but come at the expense of a greater amount of bone removal and extracranial tissue morbidity. The concept of an anterior transnasal approach to the ACoA complex is not new. Previously, the microscopic transsphenoidal approach for treatment of aneurysms around the circle of Willis has been described [17]. However, early efforts to gain direct ventral surgical access have been hindered by poor operative exposure, an inability to achieve watertight dural closure and an increased risk of postoperative cerebrospinal fluid leaks and meningitis [18–20]. The emergence of endoscopic endonasal surgery as a ventral corridor to the cranial base has brought new surgical relevance to the ACoA complex that may provide a more direct access route and minimal brain retraction. In this anatomical study, the applicability of an endoscopic transnasal access to the ACoA complex vasculature was investigated. Three outcome measures were considered for (1) the depth and lateral limitations of the endonasal corridor; (2) the degree of vascular exposure; and (3) the degree
0967-5868/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jocn.2013.07.034
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
of surgical freedom and clip placement permissible within the constraints of the endonasal corridor.
which access and manoeuvrability of clip placement was later evaluated.
2. Methods
2.4. Feasibility assessment of instrument access and clip placement
This study was approved by the local Institutional Review Board and was conducted in accordance with Ethics Committee guidelines for the use of human anatomical specimens. Adult fresh frozen cadaver heads were used. The cadaver heads were placed in the supine position slightly extended and turned 10 to 15 degrees toward the right in the horizontal plane. Zero degree endoscopes (Karl Storz and Co., Tuttlingen, Germany) that were 4 mm in diameter and 18 cm in length were used. The endoscope was connected to a light source via a fibre-optic cable and to a camera fitted with three charge-coupled device (CCD) sensors. The video camera was connected to a 21 inch monitor supporting the high resolution of the three CCD technologies.
Instrument access and surgical manoeuvrability were measured by assessing the ability of surgical instruments to access and manipulate the proximal and distal ACA and the ACoA segment (recorded dichotomously as successful or unsuccessful from three attempts). To assess for the ability of temporary clip placements, a 10 mm window over the parasellar prominence of the ICA was drilled to expose the clinoidal ICA on each side. The Vidian canal was used as the inferior limit of this exposure, which anatomically represents the anterior genu of the petrous ICA [21]. Temporary clip placement was assessed at multiple sites, including the clinoidal ICA (Fig. 1), and proximal and distal ACA (Fig. 2, 3). Finally, the ACoA segment was evaluated for the ability of the clip to ‘‘open and close’’ over the anterior, posterior, superior and inferior surfaces. This represented the ability of clip placement for the different types of aneurysm dome projections at this region.
2.1. Surgical dissection Expanded endoscopic endonasal surgery through the planum sphenoidale and tuberculum sella was performed. The middle turbinate was lateralised or the lower half of the middle turbinate removed to facilitate visualisation of the entire sphenoid anterior wall. The sphenoid sinus was opened widely, exposing the parasellar segment of the internal carotid artery (ICA), sella and planum sphenoidale. The full width of the sphenoid from the lateral optico-carotid recess (OCR) to the contralateral OCR was exposed. A 20 mm posterior nasal septectomy was performed to allow for a binasal expanded endonasal technique. The anterior sella bone, tuberculum sella, and planum sphenoidale were removed. The bone opening of the planum was extended in the postero-anterior direction for approximately 20 mm and laterally to the optic canals. From this point, the assistant held the endoscope to allow the surgeon use of both hands. The dura mater was opened and resected maximally along the margins of the transplanum opening. The arachnoid bands forming the chiasmatic cisterns above the optic chiasm were opened using sharp dissection, upon which the anterior communicating complex vasculature was systematically identified.
2.5. Statistical analysis Descriptive data were presented as percentage and mean ± standard deviation. A paired t-test (two-tailed) was used for comparisons of paired parametric data. Student’s t-test (twotailed) was used for comparisons of unrelated groups of parametric data. The Statistical Package for the Social Sciences software (SPSS, Chicago, IL, USA) was used for statistical calculations. A p value of less than 0.05 was considered statistically significant. The modified Wald method was used to calculate the 95% confidence intervals (CI) for a proportion (GraphPad Software, La Jolla, CA, USA).
3. Results Endoscopic endonasal transtubercular exposure of the ACoA complex was performed on eight adult cadaver heads (mean age 84 ± 7 years, range 76–94 years, 75% female). One specimen had an ACoA aneurysm (Fig. 4). Transnasal and dura exposure was possible in all specimens.
2.2. Defining the endonasal dimensions The endonasal corridor was defined in mm by (1) the depth of the operative field, which was measured from the anterior choanae to the ACoA segment, and (2) the lateral limits, as defined proximally by the margins of the alar rims and more distally by the divergent margins of the optic nerves. Because the distance between the optic nerves was variable, measurement was taken at an arbitrary line that passes through the centre of the craniotomy. The extent of the transplanum and transtubercular craniotomy and dural opening (mm) were measured and recorded. Three attempts were made before a decision was agreed upon, following which the average measurement was recorded. 2.3. Exposure of the ACoA complex The degree of vascular exposure in the ACoA region above the optic chiasm was recorded as dichotomous outcomes of accessible or not. These included four sites of the left and the right proximal (A1) and distal (A2) anterior cerebral arteries (ACA). The ACoA segment itself was assessed separately and categorically divided into four surfaces (anterior, posterior, superior and inferior). These surfaces represented the hypothetical aneurysm dome projections, in
Fig. 1. Intraoperative photograph of endoscopic endonasal clip application of the right clinoidal internal carotid segment for proximal vascular control.
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Fig. 2. Intraoperative photograph of endoscopic endonasal transtubercular access and clipping of the left proximal anterior cerebral artery (A1) for proximal vascular control via a left nostril approach.
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Fig. 4. Intraoperative endoscopic endonasal view of a serendipitous discovery of an anterior communicating artery aneurysm in a cadaver specimen.
3.2. Exposure of the ACoA complex Exposure of the left and right proximal ACA (A1) and the ACoA was achieved in all subjects (100%; 95% CI 80–100). Particular to the communicating segment, it was possible to expose and visualise the anterior, superior and inferior surfaces in all subjects (Table 2). However, visualisation of the posterior surface was not possible with a 0 degree endoscope. In three out of the eight subjects, the proximal A2 was exposed and visualised (40%; 95% CI 20– 60%). 3.3. Feasibility assessment of instrument access and clip placement
Fig. 3. Intraoperative photograph of endoscopic endonasal transtubercular access and clipping of the right proximal anterior cerebral artery (A1) for proximal vascular control via a left nostril approach.
Endoscopic temporary clip placement over the clinoidal ICA segment was achieved in 90% (95% CI 60–100%) of subjects for both the left and right nostril approach (Table 2). Endoscopic access and temporary clip placement for the distal A1 and proximal A2 were achieved in 90% (95% CI 60–100%) and 30% (95% CI 10–50%) of subjects, respectively. Surgical accesses through both ipsilateral and contralateral nostrils for clip placement was possible in 100% (95% CI 80–100%) of subjects for the superior, anterior and inferior surfaces of the ACoA segment. Clip placement was not possible in any subject for the posterior surface of the ACoA 0% (95% CI 0–20%). 4. Discussion
3.1. Endonasal dimensions Table 1 outlines the endonasal dimensions and cranial opening as achieved by the ventral endoscopic approach. The operative depth was 97 ± 4 mm (range 90–105 mm). The proximal width of the endonasal corridors (between the alar rims) was 31 ± 2 mm (range 28–35 mm). The distal lateral limits, as defined by the divergent margins of the optic nerves, were 22 ± 6 mm (range 15–32 mm). The postero-anterior distance and width of the endonasal craniotomy were 21 ± 5 mm (range 15–30 mm) and 22 ± 4 mm (range 17–30 mm), respectively. Dural opening was performed in all specimens with a mean width of 23 ± 4 mm (range 17–30 mm) and a postero-anterior distance of 21 ± 5 mm (range 15–30 mm).
The development and advancement of endoscopic surgery has emboldened neurosurgeons who are already familiar with transsphenoidal techniques to consider expanded cranial base approaches for treatment of more complex suprasellar lesions such as tuberculum sellae meningioma and craniopharyngioma [22,23]. A purely endoscopic endonasal approach for the surgical treatment of ventrally located intracranial aneurysms is a natural extension of the philosophy underlying this evolution. Vascular lesions, however, present different challenges. In the current study, we investigated the technical feasibility and limitations of the endoscopic strategy for the surgical treatment of ACoA aneurysms. Similar to the findings in our previously published work [24], the results of this study suggest that the endonasal corridor is long (10 cm) and narrow (3 cm lateral limits)
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Table 1 Dimensions of the surgical field and craniotomy as achieved by the ventral endoscopic approach Mean distance ± SD, mm (range) Endonasal corridor dimensions Operative field depth Lateral limits of endonasal corridor Between alar rims Between divergent optic nerves
97 ± 4 (90–105) 31 ± 2 (28–35) 22 ± 6 (15–32)
Transplanum craniotomy Postero-anterior length (from tuberculum sellae to proximal cribiform plate) Width (between left and right optic nerves) Dural opening Postero-anterior length Width
21 ± 5 (15–30) 22 ± 4 (17–30) 21 ± 5 (15–30) 23 ± 4 (17–30)
SD = standard deviation.
with a variable distal lateral margin as permitted by the distance between the optic nerves. Although surgical access, visualisation and clip placement over the distal A1 was achieved in all specimens, the relationship between the aneurysm and the optic chiasm remains difficult to define because of the small sample size in the present study. The relationship between the communicating arterial segment and the chiasm is an important determining factor to the success of the ventral endoscopic approach, as a more posteriorly positioned vascular complex relative to the optic chiasm (postfixed) may hinder full visualisation of the A1 vessels for proximal occlusion. Dissection of the A1 around the optic chiasm and temporary clipping was achieved in almost 90% of subjects. The proximal A2, however, was visualised in relatively few subjects (40%) with temporary clipping only possible in 30% of subjects. It is anticipated that in the presence of a large ACoA aneurysm that is anteriorly or superiorly projecting, the dome of the aneurysm will conceal the distal ACA, which presents a risk for premature bleeding. Based on our findings, the endoscopic endonasal approach provides ready access and visualisation to all surfaces of this vessel, except for the posterior surface. Although the technical challenges of a true ACoA aneurysm and its projection could not readily be studied in the present investigation, clip placement by opening and closing of the blades was achievable in all subjects for the superior, anterior and inferior surfaces. By serendipity, one of the cadaver specimens was found to have an ACoA aneurysm. Using this to our advantage, we assessed the various aneurysm projections. In this instance, endoscopic endonasal clip placement was
Fig. 5. Intraoperative photograph of endoscopic endonasal transtubercular exposure and clipping of an anterior projecting anterior communicating artery aneurysm via a left nostril approach.
achievable for a dome that projected in the superior, anterior or inferior direction (Fig. 5). Microsurgical approaches using cranial base access create a shallow and wide operative window, optimising the degree of freedom of surgical movement. Ventral endoscopic access, on the other hand, is hindered by the intradural neural and vascular structures which cannot be easily manipulated, thereby limiting the operative manoeuvrability in this field. In the current study, it was possible to pass multiple instruments, while using bimanual techniques with two operators during the extradural and intradural aspects of the procedure. The advantage of the endonasal technique is that it obviates the need for extensive dissection of the Sylvian fissure and frontal lobe retraction in order to access the ACoA complex. The endoscope also moves the lens and light source much closer to the vascular junction than conventional operative microscopy, providing superior visibility, with the ability to assess adequacy of dome occlusion and direct visualisation of small perforator vessels. A further potential technical advantage of anterior endoscopic access relates to the ability for acquiring proximal vascular control at multiple points via the same operative corridor. The ipsilateral clinoidal ICA segment may be exposed and temporarily clipped for proximal vascular control (Fig. 1). Similarly, the A1 vessels may be exposed and controlled with temporary clip occlusions. However, the inability to be confident of A2 temporary clip placement, a
Table 2 The percentage of success of vascular exposure, instrumental access, and clip placements by site in the eight cadaver heads Vascular exposure, n (%; 95% CI)
Access and clip placements, n (%; 95% CI)
Right
Left
Right
Left
Clinoidal ICA segments Anterior cerebral artery (A1 segment)
8 (100; 80–100) 8 (100; 80–100)
8 (100; 80–100) 8 (100; 80–100)
8 (100; 80–100) 7 (90; 60–100)
7 (90; 60–100) 7 (90; 60–100)
Anterior communicating artery segment Anterior surface Posterior surface Superior surface Inferior surface
8 0 8 8
8 0 8 8
8 0 8 8
8 0 8 8
Anterior cerebral artery (A2 segment)
3 (40; 20–60)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
3 (40; 20–60)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
2 (30; 10–50)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
2 (30; 10–50)
A1 = anterior cerebral artery segment proximal to the anterior communicating artery, A2 = anterior cerebral artery segment distal to the anterior communicating artery, CI = confidence interval, ICA = internal carotid artery.
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx Table 3 Endoscopic endonasal clipping of intracranial aneurysms reported in the literature Author, year
Location/Size, mm
Rupture status
Endoscopic approach
Complication
Outcome
Kassam et al. [25] Kassam et al. [26] Germanwala et al. [29] Froelich et al. [31] Ensenat et al. [28] Drazin et al. [30]
Vertebral/11 SHA/5 Paraclinoid/10 ACoA/7 Vertebral-PICA/1.2 SCA/4
Previously coiled Unruptured Ruptured Unruptured Ruptured Ruptured
Transclival Transplanum Transplanum Transplanum Transclival Transclival
CSF leak Nil Nil Nil CSF leak Nil
Independent Independent Independent Independent Independent Independent
ACoA = anterior communicating artery, CSF = cerebrospinal fluid, PICA = posterior inferior cerebellar artery, SCA = superior cerebellar artery, SHA = superior hypophyseal artery.
possible pre-condition of safe ACoA aneurysm surgery, may prove to be the limitation of this approach. In recent years, sporadic case reports have been published demonstrating the feasibility of endonasal endoscopic clip ligation on various aneurysm locations along the cranial base [25–31]. Table 3 summarises the findings in these studies. Specific to the ACoA segment, the use of an anterior transnasal approach has been described in two case reports describing the endoscopic endonasal technique for a superiorly projecting aneurysm [31] and the microsurgical transphenoidal technique for an anteriorly projecting aneurysm [27]. These cases and the findings in this study demonstrate that it is technically possible to treat an ACoA aneurysm using the endoscopic transtubercular route. However, whether the ventral endonasal route should be utilised for intracranial aneurysm surgery remains controversial and poses ethical concerns. At present, many ACoA aneurysms can be treated safely with microsurgical or endovascular techniques [16,32–34]. Microsurgery techniques are well established, enabling prompt vascular control in the case of intraoperative rupture and are associated with limited morbidity in experienced hands. The present study reports the feasibility assessment of the ventral endoscopic access to surgical treatment of ACoA aneurysm. However, its value and place in cerebrovascular neurosurgery will be defined only when improved dedicated endonasal instruments are employed and a statistically meaningful number of clinical cases have been performed. 5. Conclusion The endoscopic endonasal transtubercular approach to the ACoA complex provides excellent visualisation of the vasculature in the region with the exception of A2. A limitation of the applicability of this technique may relate to the difficulty in placing temporary clips on most A2. Further development is required to improve operative manoeuvrability and dedicated endonasal instrumentation before clinical application should be considered. Conflicts of Interest/Disclosures Richard J. Harvey has served on an advisory board for Schering Plough, NeilMed Pharmaceuticals and Glaxo-Smith-Kline. He has also acted as a consultant for Olympus and Medtronic, and on speakers’ bureau for Merek Sharp Dolme, Glaxo-Smith-Kline and Arthrocare. In addition, Dr Harvey has received grant support from NeilMed Pharmaceuticals. Dr Lai is supported by a scholarship funded by Carl Zeiss Pty Ltd. The other authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. References [1] Morita A, Kirino T, Hashi K, et al. The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 2012;366:2474–82.
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Neuroanatomical Study
Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex Leon T. Lai a,⇑, Michael K. Morgan a, Dustin Dalgorf c, Ali Bokhari b, Peta-Lee Sacks b, Ray Sacks a, Richard J. Harvey a,b a b c
Australian School of Advanced Medicine, Macquarie University, Sydney, Australia Applied Medical Research Centre, University of New South Wales, Sydney, Australia Department of Otolaryngology, Head and Neck Surgery, University of Toronto, Canada
a r t i c l e
i n f o
Article history: Received 21 April 2013 Accepted 16 July 2013 Available online xxxx Keywords: Anterior cerebral artery Anterior communicating artery aneurysm Endoscopic endonasal approach
a b s t r a c t The endoscopic transnasal approach to the anterior communicating artery (ACoA) complex is not widely performed. This cadaveric study investigated the surgical relevance of the anterior endoscopic approach to the treatment of ACoA aneurysms. Bi-nasal endoscopic transtubercular surgery was carried out on fresh adult cadavers. Primary outcomes measures incorporated dimensions of the endonasal corridor (operative field depth, lateral limits, size of the transplanum craniotomy and dural opening); vascular exposure (proximal and distal anterior cerebral arteries [ACA], ACoA, clinoidal internal carotid artery [ICA] segment); and operative manoeuvrability defined by clip placements (ipsilateral and contralateral). Eight cadaver heads were used (mean age 84 ± 7 years, range 76–94 years, 75% female). Mean operative depth was 97 ± 4 mm. The lateral corridors were limited proximally by the alar rim openings (31 ± 2 mm), and distally by the optic nerves (22 ± 6 mm). The endonasal craniotomy dimensions were 21 ± 5 mm anteroposteriorly, and 22 ± 4 mm laterally. Vascular exposure was achieved in 100% of subjects for the ACoA segment and the ACA segments proximal to the ACoA (A1). The ACA segments distal to the ACoA (A2) were accessible only in 40% of subjects. Endonasal clip placement across the ACoA segment, clinoidal ICA, A1 and A2 were 100%, 90%, 90%, and 30%, respectively. The ventral endoscopic endonasal approach to the ACoA complex provides excellent vascular visualisation without brain retraction or gyrus rectus resection. However, the limitation in access to the A2 for temporary clip placement may prove to be a significant limitation of this approach. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Of all cerebral aneurysms, the anterior communicating artery (ACoA) aneurysm is the most frequent and represents an increased risk of rupture as compared to aneurysms in other locations [1–8]. Transcranial clip ligation (via the pterional transsylvian, supraorbital or interhemispheric corridors) presents significant technical challenges because of the deep and midline location of these lesions. Infrequently, surgical morbidity arises from the frontal lobe retraction or partial gyrectomy that are necessary to facilitate aneurysm exposure [4,9–11]. The application of endovascular techniques in recent years has provided a less invasive alternative to the management of ACoA aneurysms, but has led to an inferior durability of aneurysm repair and an increased risk for retreatment [12–16]. Cranial base approaches with clip obliteration maintain ⇑ Corresponding author. Address: Department of Neurosurgery, Level 4 East, The Royal Melbourne Hospital, Grattan Street, Parkville, Melbourne, VIC 3052, Australia. Tel.: +61 (03) 93422105. E-mail address: [email protected] (L.T. Lai).
treatment robustness but come at the expense of a greater amount of bone removal and extracranial tissue morbidity. The concept of an anterior transnasal approach to the ACoA complex is not new. Previously, the microscopic transsphenoidal approach for treatment of aneurysms around the circle of Willis has been described [17]. However, early efforts to gain direct ventral surgical access have been hindered by poor operative exposure, an inability to achieve watertight dural closure and an increased risk of postoperative cerebrospinal fluid leaks and meningitis [18–20]. The emergence of endoscopic endonasal surgery as a ventral corridor to the cranial base has brought new surgical relevance to the ACoA complex that may provide a more direct access route and minimal brain retraction. In this anatomical study, the applicability of an endoscopic transnasal access to the ACoA complex vasculature was investigated. Three outcome measures were considered for (1) the depth and lateral limitations of the endonasal corridor; (2) the degree of vascular exposure; and (3) the degree
0967-5868/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jocn.2013.07.034
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
of surgical freedom and clip placement permissible within the constraints of the endonasal corridor.
which access and manoeuvrability of clip placement was later evaluated.
2. Methods
2.4. Feasibility assessment of instrument access and clip placement
This study was approved by the local Institutional Review Board and was conducted in accordance with Ethics Committee guidelines for the use of human anatomical specimens. Adult fresh frozen cadaver heads were used. The cadaver heads were placed in the supine position slightly extended and turned 10 to 15 degrees toward the right in the horizontal plane. Zero degree endoscopes (Karl Storz and Co., Tuttlingen, Germany) that were 4 mm in diameter and 18 cm in length were used. The endoscope was connected to a light source via a fibre-optic cable and to a camera fitted with three charge-coupled device (CCD) sensors. The video camera was connected to a 21 inch monitor supporting the high resolution of the three CCD technologies.
Instrument access and surgical manoeuvrability were measured by assessing the ability of surgical instruments to access and manipulate the proximal and distal ACA and the ACoA segment (recorded dichotomously as successful or unsuccessful from three attempts). To assess for the ability of temporary clip placements, a 10 mm window over the parasellar prominence of the ICA was drilled to expose the clinoidal ICA on each side. The Vidian canal was used as the inferior limit of this exposure, which anatomically represents the anterior genu of the petrous ICA [21]. Temporary clip placement was assessed at multiple sites, including the clinoidal ICA (Fig. 1), and proximal and distal ACA (Fig. 2, 3). Finally, the ACoA segment was evaluated for the ability of the clip to ‘‘open and close’’ over the anterior, posterior, superior and inferior surfaces. This represented the ability of clip placement for the different types of aneurysm dome projections at this region.
2.1. Surgical dissection Expanded endoscopic endonasal surgery through the planum sphenoidale and tuberculum sella was performed. The middle turbinate was lateralised or the lower half of the middle turbinate removed to facilitate visualisation of the entire sphenoid anterior wall. The sphenoid sinus was opened widely, exposing the parasellar segment of the internal carotid artery (ICA), sella and planum sphenoidale. The full width of the sphenoid from the lateral optico-carotid recess (OCR) to the contralateral OCR was exposed. A 20 mm posterior nasal septectomy was performed to allow for a binasal expanded endonasal technique. The anterior sella bone, tuberculum sella, and planum sphenoidale were removed. The bone opening of the planum was extended in the postero-anterior direction for approximately 20 mm and laterally to the optic canals. From this point, the assistant held the endoscope to allow the surgeon use of both hands. The dura mater was opened and resected maximally along the margins of the transplanum opening. The arachnoid bands forming the chiasmatic cisterns above the optic chiasm were opened using sharp dissection, upon which the anterior communicating complex vasculature was systematically identified.
2.5. Statistical analysis Descriptive data were presented as percentage and mean ± standard deviation. A paired t-test (two-tailed) was used for comparisons of paired parametric data. Student’s t-test (twotailed) was used for comparisons of unrelated groups of parametric data. The Statistical Package for the Social Sciences software (SPSS, Chicago, IL, USA) was used for statistical calculations. A p value of less than 0.05 was considered statistically significant. The modified Wald method was used to calculate the 95% confidence intervals (CI) for a proportion (GraphPad Software, La Jolla, CA, USA).
3. Results Endoscopic endonasal transtubercular exposure of the ACoA complex was performed on eight adult cadaver heads (mean age 84 ± 7 years, range 76–94 years, 75% female). One specimen had an ACoA aneurysm (Fig. 4). Transnasal and dura exposure was possible in all specimens.
2.2. Defining the endonasal dimensions The endonasal corridor was defined in mm by (1) the depth of the operative field, which was measured from the anterior choanae to the ACoA segment, and (2) the lateral limits, as defined proximally by the margins of the alar rims and more distally by the divergent margins of the optic nerves. Because the distance between the optic nerves was variable, measurement was taken at an arbitrary line that passes through the centre of the craniotomy. The extent of the transplanum and transtubercular craniotomy and dural opening (mm) were measured and recorded. Three attempts were made before a decision was agreed upon, following which the average measurement was recorded. 2.3. Exposure of the ACoA complex The degree of vascular exposure in the ACoA region above the optic chiasm was recorded as dichotomous outcomes of accessible or not. These included four sites of the left and the right proximal (A1) and distal (A2) anterior cerebral arteries (ACA). The ACoA segment itself was assessed separately and categorically divided into four surfaces (anterior, posterior, superior and inferior). These surfaces represented the hypothetical aneurysm dome projections, in
Fig. 1. Intraoperative photograph of endoscopic endonasal clip application of the right clinoidal internal carotid segment for proximal vascular control.
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Fig. 2. Intraoperative photograph of endoscopic endonasal transtubercular access and clipping of the left proximal anterior cerebral artery (A1) for proximal vascular control via a left nostril approach.
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Fig. 4. Intraoperative endoscopic endonasal view of a serendipitous discovery of an anterior communicating artery aneurysm in a cadaver specimen.
3.2. Exposure of the ACoA complex Exposure of the left and right proximal ACA (A1) and the ACoA was achieved in all subjects (100%; 95% CI 80–100). Particular to the communicating segment, it was possible to expose and visualise the anterior, superior and inferior surfaces in all subjects (Table 2). However, visualisation of the posterior surface was not possible with a 0 degree endoscope. In three out of the eight subjects, the proximal A2 was exposed and visualised (40%; 95% CI 20– 60%). 3.3. Feasibility assessment of instrument access and clip placement
Fig. 3. Intraoperative photograph of endoscopic endonasal transtubercular access and clipping of the right proximal anterior cerebral artery (A1) for proximal vascular control via a left nostril approach.
Endoscopic temporary clip placement over the clinoidal ICA segment was achieved in 90% (95% CI 60–100%) of subjects for both the left and right nostril approach (Table 2). Endoscopic access and temporary clip placement for the distal A1 and proximal A2 were achieved in 90% (95% CI 60–100%) and 30% (95% CI 10–50%) of subjects, respectively. Surgical accesses through both ipsilateral and contralateral nostrils for clip placement was possible in 100% (95% CI 80–100%) of subjects for the superior, anterior and inferior surfaces of the ACoA segment. Clip placement was not possible in any subject for the posterior surface of the ACoA 0% (95% CI 0–20%). 4. Discussion
3.1. Endonasal dimensions Table 1 outlines the endonasal dimensions and cranial opening as achieved by the ventral endoscopic approach. The operative depth was 97 ± 4 mm (range 90–105 mm). The proximal width of the endonasal corridors (between the alar rims) was 31 ± 2 mm (range 28–35 mm). The distal lateral limits, as defined by the divergent margins of the optic nerves, were 22 ± 6 mm (range 15–32 mm). The postero-anterior distance and width of the endonasal craniotomy were 21 ± 5 mm (range 15–30 mm) and 22 ± 4 mm (range 17–30 mm), respectively. Dural opening was performed in all specimens with a mean width of 23 ± 4 mm (range 17–30 mm) and a postero-anterior distance of 21 ± 5 mm (range 15–30 mm).
The development and advancement of endoscopic surgery has emboldened neurosurgeons who are already familiar with transsphenoidal techniques to consider expanded cranial base approaches for treatment of more complex suprasellar lesions such as tuberculum sellae meningioma and craniopharyngioma [22,23]. A purely endoscopic endonasal approach for the surgical treatment of ventrally located intracranial aneurysms is a natural extension of the philosophy underlying this evolution. Vascular lesions, however, present different challenges. In the current study, we investigated the technical feasibility and limitations of the endoscopic strategy for the surgical treatment of ACoA aneurysms. Similar to the findings in our previously published work [24], the results of this study suggest that the endonasal corridor is long (10 cm) and narrow (3 cm lateral limits)
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Table 1 Dimensions of the surgical field and craniotomy as achieved by the ventral endoscopic approach Mean distance ± SD, mm (range) Endonasal corridor dimensions Operative field depth Lateral limits of endonasal corridor Between alar rims Between divergent optic nerves
97 ± 4 (90–105) 31 ± 2 (28–35) 22 ± 6 (15–32)
Transplanum craniotomy Postero-anterior length (from tuberculum sellae to proximal cribiform plate) Width (between left and right optic nerves) Dural opening Postero-anterior length Width
21 ± 5 (15–30) 22 ± 4 (17–30) 21 ± 5 (15–30) 23 ± 4 (17–30)
SD = standard deviation.
with a variable distal lateral margin as permitted by the distance between the optic nerves. Although surgical access, visualisation and clip placement over the distal A1 was achieved in all specimens, the relationship between the aneurysm and the optic chiasm remains difficult to define because of the small sample size in the present study. The relationship between the communicating arterial segment and the chiasm is an important determining factor to the success of the ventral endoscopic approach, as a more posteriorly positioned vascular complex relative to the optic chiasm (postfixed) may hinder full visualisation of the A1 vessels for proximal occlusion. Dissection of the A1 around the optic chiasm and temporary clipping was achieved in almost 90% of subjects. The proximal A2, however, was visualised in relatively few subjects (40%) with temporary clipping only possible in 30% of subjects. It is anticipated that in the presence of a large ACoA aneurysm that is anteriorly or superiorly projecting, the dome of the aneurysm will conceal the distal ACA, which presents a risk for premature bleeding. Based on our findings, the endoscopic endonasal approach provides ready access and visualisation to all surfaces of this vessel, except for the posterior surface. Although the technical challenges of a true ACoA aneurysm and its projection could not readily be studied in the present investigation, clip placement by opening and closing of the blades was achievable in all subjects for the superior, anterior and inferior surfaces. By serendipity, one of the cadaver specimens was found to have an ACoA aneurysm. Using this to our advantage, we assessed the various aneurysm projections. In this instance, endoscopic endonasal clip placement was
Fig. 5. Intraoperative photograph of endoscopic endonasal transtubercular exposure and clipping of an anterior projecting anterior communicating artery aneurysm via a left nostril approach.
achievable for a dome that projected in the superior, anterior or inferior direction (Fig. 5). Microsurgical approaches using cranial base access create a shallow and wide operative window, optimising the degree of freedom of surgical movement. Ventral endoscopic access, on the other hand, is hindered by the intradural neural and vascular structures which cannot be easily manipulated, thereby limiting the operative manoeuvrability in this field. In the current study, it was possible to pass multiple instruments, while using bimanual techniques with two operators during the extradural and intradural aspects of the procedure. The advantage of the endonasal technique is that it obviates the need for extensive dissection of the Sylvian fissure and frontal lobe retraction in order to access the ACoA complex. The endoscope also moves the lens and light source much closer to the vascular junction than conventional operative microscopy, providing superior visibility, with the ability to assess adequacy of dome occlusion and direct visualisation of small perforator vessels. A further potential technical advantage of anterior endoscopic access relates to the ability for acquiring proximal vascular control at multiple points via the same operative corridor. The ipsilateral clinoidal ICA segment may be exposed and temporarily clipped for proximal vascular control (Fig. 1). Similarly, the A1 vessels may be exposed and controlled with temporary clip occlusions. However, the inability to be confident of A2 temporary clip placement, a
Table 2 The percentage of success of vascular exposure, instrumental access, and clip placements by site in the eight cadaver heads Vascular exposure, n (%; 95% CI)
Access and clip placements, n (%; 95% CI)
Right
Left
Right
Left
Clinoidal ICA segments Anterior cerebral artery (A1 segment)
8 (100; 80–100) 8 (100; 80–100)
8 (100; 80–100) 8 (100; 80–100)
8 (100; 80–100) 7 (90; 60–100)
7 (90; 60–100) 7 (90; 60–100)
Anterior communicating artery segment Anterior surface Posterior surface Superior surface Inferior surface
8 0 8 8
8 0 8 8
8 0 8 8
8 0 8 8
Anterior cerebral artery (A2 segment)
3 (40; 20–60)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
3 (40; 20–60)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
2 (30; 10–50)
(100; 80–100) (0; 0–20) (100; 80–100) (100; 80–100)
2 (30; 10–50)
A1 = anterior cerebral artery segment proximal to the anterior communicating artery, A2 = anterior cerebral artery segment distal to the anterior communicating artery, CI = confidence interval, ICA = internal carotid artery.
Please cite this article in press as: Lai LT et al. Cadaveric study of the endoscopic endonasal transtubercular approach to the anterior communicating artery complex. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.07.034
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L.T. Lai et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx Table 3 Endoscopic endonasal clipping of intracranial aneurysms reported in the literature Author, year
Location/Size, mm
Rupture status
Endoscopic approach
Complication
Outcome
Kassam et al. [25] Kassam et al. [26] Germanwala et al. [29] Froelich et al. [31] Ensenat et al. [28] Drazin et al. [30]
Vertebral/11 SHA/5 Paraclinoid/10 ACoA/7 Vertebral-PICA/1.2 SCA/4
Previously coiled Unruptured Ruptured Unruptured Ruptured Ruptured
Transclival Transplanum Transplanum Transplanum Transclival Transclival
CSF leak Nil Nil Nil CSF leak Nil
Independent Independent Independent Independent Independent Independent
ACoA = anterior communicating artery, CSF = cerebrospinal fluid, PICA = posterior inferior cerebellar artery, SCA = superior cerebellar artery, SHA = superior hypophyseal artery.
possible pre-condition of safe ACoA aneurysm surgery, may prove to be the limitation of this approach. In recent years, sporadic case reports have been published demonstrating the feasibility of endonasal endoscopic clip ligation on various aneurysm locations along the cranial base [25–31]. Table 3 summarises the findings in these studies. Specific to the ACoA segment, the use of an anterior transnasal approach has been described in two case reports describing the endoscopic endonasal technique for a superiorly projecting aneurysm [31] and the microsurgical transphenoidal technique for an anteriorly projecting aneurysm [27]. These cases and the findings in this study demonstrate that it is technically possible to treat an ACoA aneurysm using the endoscopic transtubercular route. However, whether the ventral endonasal route should be utilised for intracranial aneurysm surgery remains controversial and poses ethical concerns. At present, many ACoA aneurysms can be treated safely with microsurgical or endovascular techniques [16,32–34]. Microsurgery techniques are well established, enabling prompt vascular control in the case of intraoperative rupture and are associated with limited morbidity in experienced hands. The present study reports the feasibility assessment of the ventral endoscopic access to surgical treatment of ACoA aneurysm. However, its value and place in cerebrovascular neurosurgery will be defined only when improved dedicated endonasal instruments are employed and a statistically meaningful number of clinical cases have been performed. 5. Conclusion The endoscopic endonasal transtubercular approach to the ACoA complex provides excellent visualisation of the vasculature in the region with the exception of A2. A limitation of the applicability of this technique may relate to the difficulty in placing temporary clips on most A2. Further development is required to improve operative manoeuvrability and dedicated endonasal instrumentation before clinical application should be considered. Conflicts of Interest/Disclosures Richard J. Harvey has served on an advisory board for Schering Plough, NeilMed Pharmaceuticals and Glaxo-Smith-Kline. He has also acted as a consultant for Olympus and Medtronic, and on speakers’ bureau for Merek Sharp Dolme, Glaxo-Smith-Kline and Arthrocare. In addition, Dr Harvey has received grant support from NeilMed Pharmaceuticals. Dr Lai is supported by a scholarship funded by Carl Zeiss Pty Ltd. The other authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. References [1] Morita A, Kirino T, Hashi K, et al. The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 2012;366:2474–82.
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