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Comparative Anatomical Study on Operability in Surgical Approaches to the Anterior Part of the Third Ventricle
Accepted Manuscript Comparative Anatomical Study on Operability in Surgical Approaches to the Anterior Part of the Third Ventricle Alfio Spina, M.D, Filippo Gagliardi, M.D., Michele Bailo, M.D., Nicola Boari, M.D., Anthony J. Caputy, M.D, Pietro Mortini, M.D PII:
S1878-8750(16)30741-0
DOI:
10.1016/j.wneu.2016.08.073
Reference:
WNEU 4484
To appear in:
World Neurosurgery
Received Date: 21 April 2016 Revised Date:
15 August 2016
Accepted Date: 17 August 2016
Please cite this article as: Spina A, Gagliardi F, Bailo M, Boari N, Caputy AJ, Mortini P, Comparative Anatomical Study on Operability in Surgical Approaches to the Anterior Part of the Third Ventricle, World Neurosurgery (2016), doi: 10.1016/j.wneu.2016.08.073. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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COMPARATIVE ANATOMICAL STUDY ON OPERABILITY IN SURGICAL APPROACHES TO THE ANTERIOR PART OF THE THIRD VENTRICLE
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Alfio Spina1, M.D., Filippo Gagliardi1, M.D., Michele Bailo1, M.D., Nicola Boari1, M.D., Anthony J. Caputy2, M.D. and Pietro Mortini1, M.D. 1
Department of Neurosurgery and Gamma Knife Radiosurgery, San Raffaele Scientific Institute,
Department of Neurological Surgery, The George Washington University, Washington, District
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Vita-Salute University, Milan, Italy
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of Columbia, United States
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Corresponding Author: Alfio Spina, M.D.
Department of Neurosurgery and Gamma Knife Radiosurgery San Raffaele Scientific Institute, Vita-Salute University Via Olgettina 60, 20132 Milano, Italy. Tel: +39-02-26432396. Fax: +39-02-26437302. E-mail: [email protected] 1
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ABSTRACT
Background. Surgery of the third ventricle still represents a challenge in modern neurosurgery. To optimize the surgical planning, some aspects, related to ventricular anatomy,
evaluate these variables, to choose of a tailored surgical approach.
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have to be taken into consideration. An operability score could represent a preoperative tool to
Methods. Authors compared the transcallosal transforaminal (TCTFA) and the combined inter-hemispheric sub-commissural trans-lamina terminalis approach (CISTA), to the anterior
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part of the third ventricle, applying the operability score.
Results. Compared to the TCTFA, the CISTA provides a statistically significant
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improvement in terms of depth of surgical field, surgical angle of attack and maneuverability arc considering as four approach-related critical structures: the optic chiasm (p value: <0,0001, <0,0001, <0,0001 respectively), the anterior commissure (p value: <0,0001, <0,0001, <0,0001 respectively), the tuber cinereum (p value: <0,0001, 0,0224, 0,0173) and the inter-thalamic adhesion (p value: 0,2917, <0,0001, <0,0001 respectively).
Conclusions. Tumors originating from the anterosuperior part of the third ventricle can be
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easily approached through a transcallosal transforaminal route, whereas lesions arising from the
the CISTA.
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anteroinferior portion of the third ventricle might be safely and effectively approached through
Keywords: Corpus callosum; Lamina terminalis; Operability score; Optic chiasm; Third
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ventricle
Running title: Comparative anatomical study on surgical approaches to the anterior third ventricle.
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INTRODUCTION
Surgery of the third ventricle is still considered a challenging one. Tumors arising from this anatomical area can involve the ventricular cavity, the hypothalamic region, the optic complications.1-4
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apparatus, and the pituitary. Moreover, surgery of the third ventricle can result in life threatening
Despite the great technical advancements, the choice of the best approach still remains controversial.3, 5 Although different approaches have been described, no anatomical comparison
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of surgical approaches to this critical area has been carried out.3, 5
Two major groups of microsurgical approaches are nowadays adopted for the resection of
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the lesions affecting the anterior aspect of the ventricular cavity (Figure 1A): the transcallosal transforaminal (TCTFA) and the combined inter-hemispheric sub-commissural trans-lamina terminalis approach (CISTA).4,
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Many authors have extensively described both approaches,
nevertheless a comparative study on the advantages and drawbacks of the single approach is still lacking. The concept of operability score (OS) has been recently introduced for the quantitative assessment of the ability to reach some anatomical structures, which can be easily applied to
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comparative studies of surgical anatomy.7
The aim of this study is therefore to compare TCTFA and CISTA in approaching lesions
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of the anterior part of the third ventricle.
MATERIALS AND METHODS
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Ten cadaver specimens fixed with gluteraldehyde and injected with colored latex were
used for the anatomical dissections at the Ammermann Microsurgical Laboratory in Washington, DC (Department of Neurosurgery, George Washington University, Washington, DC). The heads were placed in surgical position, fixed in a Mayfield head-holder (Codman,
Inc., Raynham, MA). Microsurgical dissections have been performed with the microscope (Zeiss OPM 1 FC, Carl Zeiss, Oberkochen, Germany) using standard microsurgical instruments. A high-speed drill was used to perform bone drilling and craniotomy (Midas Rex, Medtronic, Fort Worth, TX, USA). 3
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For each approach we considered: a) the surgical field depth (SF), defined as the distance between the dura mater and four target points such as anatomical structures recognizable during the dissections, b) the surgical angle of attack (SAA), defined as the angle of incidence of the corridor in selected points, c) the maneuverability arc (MAC), defined as the degree of freedom defined as the area at the narrowest point of the surgical field.7
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in manipulating surgical instruments in selected points; and d) the maneuverability area (MAR),
The surgical techniques of CISTA (Figure 1 B) and TCTFA (Figure 1 C) have already been extensively described in previous reports and a brief description of them has been reported
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below.1-4, 6, 8-30
Measurements were acquired under the microscope and with the help of the endoscope,
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by using different graded scales. We selected for both approaches the same four key target points, which corresponded to the insertion of the lamina terminalis to the optic chiasm (OpCh), the tuber cinereum (TC), the anterior commissure (AC) and the inter-thalamic adhesion (IA) (Figure 1A). At these anatomical points the SF, the SAA, the MAC and MAR have been measured in both approaches (Figure 2).
Data recorded were statistically analyzed by using Prism software (version 5.0a,
Surgical technique CISTA
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GraphPad Software Inc., La Jolla, CA, USA). P-value was analyzed by using t-Test.
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The head is placed in neutral position with 20 degrees of extension. A bicoronal skin incision is performed and the skin flap is reflected anteriorly. After peforming a unilateral fronto-temporal
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craniotomy to expose the midline, the superior sagittal sinus and the Sylvian fissure laterally, an orbital osteotomy is performed on the approached side. Once opened the dura, the frontal lobe is gently separated from the falx and the contralateral mesial frontal cortex; an additional subfrontal dissection may be performed in order to increase frontal lobe retraction in order to use the frontobasal corridor. The interhemispheric dissection is continued toward the lamina terminalis by maintaining a subcommissural trajectory. At this point, the lamina terminalis, a grayish thin membrane posterior to the brighter optic chiasm, is opened both below and above the anterior communicating artery between the two A1 and A2 arteries, respectively, to access the anterior part of the third ventricle.
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TCTFA The head is placed in neutral position and flexed 20 degrees. A lateral-based U-shaped incision is performed, to expose the sagittal and the coronal sutures of the selected side. The skin flap is
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reflected laterally. A fronto-parietal craniotomy is carried out extending about two thirds anteriorly to the coronal suture and one third posteriorly, across the midline in order to expose the superior sagittal sinus. The dura is opened to create a medial-based flap and then reflected medially. The major bridging veins are preserved, dividing only the smallest ones, in order to widen the interhemispheric corridor. Subsequently, the interhemispheric dissection is performed
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with the help of a self-retaining retractor, to retract the mesial frontal cortex from the falx and the contralateral cortex. Once the interhemispheric dissection is completed, the corpus callosum
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come into view. After the identification of both pericallosal arteries, a callosotomy is performed at maximum 2 cm in length. The callosotomy is completed when the grayish tissue of the ventricular ependymal come into view. The ependymal layer is then opened to access to the lateral ventricle. After entering into the ventricle, the Monro foramen is identified at the floor of the ventricle, with the choroid plexus running posteriorly to it from lateral to medial and entering into the foramen, whereas the thalamostriate veins run from the lateral to the anteromedial side,
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entering the foramen. Once checked these anatomical landmarks to prevent inadvertent contralateral ventricular opening, a standard transforaminal approached is performed to access
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RESULTS
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the third ventricle from above.
The average depth of the SF at the OpCh was of 62,75 mm (range 57,8 – 67,2; DS 3,02)
for the CISTA and 76,84 mm (range 68,6 – 83,6; DS 4,26) for the TCTFA. The average depth of the SF at the AC was of 56,48 mm (range 52 – 61,8; DS 3,83) for the CISTA and 64,59 mm (range 57,7 – 69,4; DS 3,07) for the TCTFA. The average depth of the SF at the TC was of 65,03 mm (range 60 – 70; DS 2,81) for the CISTA and 78,09 mm (range 71,8 – 82,7; DS 3,56) for the TCTFA. The average depth of the SF at the IA was of 70,85 mm (range 64 – 77,2; DS 3,81) for the CISTA and 69,25 mm (range 64,9 – 73,9; DS 2,6) for the TCTFA.
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The average value of the SAA at the OpCh was 69,5° (range 66 – 73; DS 2,17) for the CISTA and 19,9° (range 14 - 40; DS 7,62) for the TCTFA. The average value of the SA at the AC was 88° (range 84 - 92; DS 2,7) for the CISTA and 47,9° (range 41 - 63; DS 7,6) for the TCTFA. The average value of the SAA at the TC was 46,2° (range 42 - 50; DS 2,82) for the
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CISTA and 40,1° (range 24 - 48; DS 7,18) for the TCTFA. The average values of the SAA of the IA was 87,9° (range 82 - 92; DS 3,14) for the CISTA and 14,6° (range 10 - 21; DS 3,5) for the TCTFA.
The average value of the MAC at the OpCh was 73,8° (range 66 – 80; DS 6,14) for the
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CISTA and 24,4° (range 14 - 40; DS 14,54) for the TCTFA. The average value of the SA at the AC was 83,5° (range 52 - 90; DS 11,6) for the CISTA and 48,3° (range 43 - 63; DS 7,67) for the
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TCTFA. The average value of the SAA at the TC was 48,6° (range 42 - 50; DS 2,95) for the CISTA and 43,2° (range 30 - 50; DS 5,8) for the TCTFA. The average values of the SA of the IA was 84,2° (range 65 - 90; DS 7,31) for the CISTA and 16,6° (range 10 - 25; DS 4,47) for the TCTFA.
The averages of the MAR were 2,12 cm2 (range: 1,5 – 2,5; DS: 0,32) for the CISTA and 1,58cm2 (range 1,4 - 2; DS 0,16) for the TCTFA. Data are summarized in Table 1.
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A value of 0 or 1 was assigned to the qualitative values. According to our previous publication, for the surgical field depth, we considered 65mm as critical limit of the length of the working channel for the optimal maneuverability of the microsurgical instrumentation (<65mm = 1, >65mm = 0). For the SAA, a value of 60° was considered (>60° = 1, <60° = 0). For the MAC
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a limit value of 45° was calculated (>45° = 1, <45° = 0).7 The OS was then calculated from the total of each score. Table 2 summarizes OS referred to specific target points inside the ATV. OpCh, AC and TC showed a lower SF in the CISTA as compared to TCTFA (p<0,0001),
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whereas the IA showed a lower SF in the TCTFA, without reaching a statistical significance. Both the SAA and MAC had significant higher values in the CISTA as compared to the TCTFA. By critically reviewing these data, it has to be noted, that the CISTA seems to be, for the
considered targets, a more direct approach, offering also a better SAA and MAC to OpCh, AC and TC. On the other hand, even if CISTA has higher values of SF to the IA, it provides a better angle of attack and maneuverability around this target. These findings can be determined by the absence in the CISTA of the callosotomy, which jeopardizes the maneuverability and SAA
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around the targets. The superior MAR also confirms this feature in the CISTA if compared to the
DISCUSSION
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TCTFA (2,12 vs. 1,58 cm2, respectively).
Since the early thirties, when Cushing and Dandy, described some key concepts, surgery in and around the third ventricle is still considered a challenge.31, 32
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The complexity of regional anatomy requires high technical skills and surgery might have a significant morbidity.2
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Endocrinological disturbances, neurological and neuropsychological deficit, such as memory loss, are the most common consequences in patients treated for tumors growing in the third ventricle region.1-3, 11, 12, 30, 33, 34
To optimize the surgical planning, some tridimensional aspects, related to the tumoral and the ventricular anatomy, should be taken into consideration, before surgery to prevent postoperative morbidity and improve the rate of a safe and radical surgical resection.34
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The operability score, as recently described, has been demonstrated to be effective in graduating both the surgical operability, and the instruments manipulation capability.7 Moreover, it is a useful tool to measure the areas that can be exposed in a single approach and their suitability for surgical manoeuvres.7
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As previously proposed, the third ventricle can be divided into an antero-superior, anteroinferior, posterior-superior and a posterior-inferior segment.18
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In this study we focused our attention in the comparison between the CISTA and the TCTFA.
The CISTA, as previously described is an antero-lateral approach, which uses multi-angle
trajectories.3 The depth of the surgical field ranges from 52 to 70 mm. As compared to the TCTFA, the anterior inter-hemispheric route is free from major draining veins, making the arachnoidal dissection safer. 20 The critical point of the surgical field, which is considered as a funnel tip, is defined by the chiasm inferiorly, the anterior commissure and anterior communicating artery superiorly and by the two anterior cerebral arteries laterally.20
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This area, represents the surgical access to the ventricular cavity, and corresponds to the narrowest cross-action area of the surgical corridor, defined as MAR. It contributes to the conizing effect (the index defined by dividing the maneuverability area and the depth of the surgical corridor) in this approach, limiting the possibility to reach the lateral portion of the ATV.
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MAR ranges from 1,5 to 2,5 cm2 and it has to be considered that it can be further reduced by the presence of a prefixed chiasm.34
As consequence, MAC is influenced by the anatomical structures mentioned above. In the past, some authors advocated the division of the anterior communicating artery to increase it. In
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the CISTA, anterior communicating artery division is not needed, because of the three different available vascular windows, which can be used to access the ventricular cavity and the absence of
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perforating branches in this area.3, 21, 23
It has to be considered that the dissection of the lamina terminalis can present some criticisms, because it might be distorted by the ventricular content, making the optic apparatus and possibly the hypothalamus at risk of damage.13, 29
The upper view in the surgical corridor is limited by the angle made by the posteriorinferior portion of the AC. We considered this point to define one SAA. Average value of this
backward to this structure.
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angle is 88° (range 84°-92°). AC is the major limiting factor in approaching lesions that extends
One other critical aspect in the SAA is the area of the tuber cinereum. In this case the SAA is more favorable, ranging from 42° to 50° (mean 46,2°), if compared to the TCTFA.
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Lesions arising from this region are prone to be resected through this route, showing a favorable angle of SA.
Going deep into the ventricular cavity a further limiting factor in maneuverability is the
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inter-thalamic adhesion. According to Rhoton classification it represents the posterior limit of the anterior part of the third ventricle.18 Average value of MAC in this point is 87,9° (range 82°-92°). Moreover, it is possible with the CISTA to access in the posterior aspect of the third ventricle, reaching the supra pineal recess. The conizing effect of the CISTA is lower if compared to TCTFA, because of the wider maneuverability area and the shorter depth of the surgical field. The TCTFA approach is a transcallosal route, taking advantage from a dilatation of the Monro foramen to access the ventricular cavity. Although usually dilated in case of third
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ventricular tumors, the foramen represents a narrow natural corridor ranging from 3 to 7 mm in diameter.29 The diameter of the Monro foramen is essential for the feasibility of this approach.35 A wider configuration of the foramen, as it happens in case of hydrocephalus or in presence of
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lesions enlarging lesions, might increase the SAA, MAC and also the MAR. Another potential limitation of the TCTFA is the unilateral trajectory, potentially making the ipsilateral wall of the third ventricle a blind corner.35
To overcome the limits due to the foramen size, alternative variations of the transcallosal
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approach have been described, which improve the MAR.1, 2, 4, 10, 14, 15, 17, 19, 22, 24-28, 31-34, 36-42 In order to increase the opening of the Monro foramen, it is possible to make a
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transchoroidal extension, by sharply enlarging the surgical corridor, just medially to the choroid plexus and laterally to fornix, through the tenia fornicis; or alternatively a subchoroidal extension, by opening a corridor by a sharp dissection along the tenia choroidea, after displacing the choroid plexus medially from the internal cerebral veins and the posteromedial choroidal artery.29,
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Although these variants do increase the diameter of the surgical corridor at the level of the Monro foramen, they may potentially increase the approach-related morbidity as the vascular structures
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of this region, such as the internal cerebral, thalamostriate and septal vein and the posteromedial choroidal artery, might be stretched and damaged by surgical maneuvers.29, 35 Moreover one of the most critical aspects of transcallosal approaches is the right
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definition of the midline and the relation between the callosotomy and the diameter of the foramen of Monro.17, 20, 22, 24, 39, 41
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As already reported in literature in TCTFA, the risk of postoperative neurologic and neuropsychological complication due to the disconnection of the two hemispheres, is directly related to the length of the callosotomy, which should be at maximum of 2 centimeters.1, 2, 4, 14, 17, 19, 24, 26, 30, 36, 43, 44
Considering these data, the ratio between the diameter of callosotomy over
Monro foramen diameter, should be lesser than 2. To prevent a foraminal trajectory and to accomplish a midline route, a transcallosal interforniceal approach can be performed. By dissecting and retracting the bodies of the fornices together with internal cerebral veins and posteromedial choroidal arteries, this midline approach, provides the view of both walls of the third ventricle with a greater access and maneuverability as 9
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compared to a foraminal route.29, 35 Nevertheless, even this variant is not always feasible, because the length of the septum pellucidum and the adhesions between corpus callosum and fornices, might limit the dissection, contraindicating the approach.29, 35
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The maneuverability area and arc of maneuverability in TCTFA are limited by the borders of the callosotomy and the foramen of Monro; stretching of the fibers at the level of the corpus callosum might indeed cause postoperative hemiparesis, while surgical damage of the forniceal fibers might cause mnemonic impairment.2, 6, 10, 17, 33, 36 A larger craniotomy as suggested, could
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improve the conizing effect and the visibility, avoiding a wide opening of the corpus callosum.45 Compared to the CISTA, the TC could not be easily reached through the TCTFA, because of the depth of the surgical corridor. CISTA and TCTFA show statistically significant difference
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in reaching the inter-thalamic adhesion in terms of mean values.
Even if the TCTFA had a lower mean value of MAC on the TC, the likelihood to control it from above has to be considered, if the lesion or the anatomy of the OpCh-lamina terminalis do form a blind corner, making it difficult to control them through the CISTA. The OS confirms these findings, showing better results for CISTA on OpCh, TC and IA. Not surprisingly, the AC showed a higher OS in TCTFA, which is mostly due to the short distance of this target. Although
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it is not always possible to visualize AC without a dilated Monro foramen in the real scenario, this cadaveric study stressed the concept that the depth of the surgical field is essential in determining the operability of different anatomical regions during the same approach.
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Nevertheless the conizing effect of the surgical corridor in TCTFA is more unfavorable as compared to the CISTA. This is mainly due to the limit in surgical maneuverability represented
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by the callosotomy and the greater depth of the surgical field. Another important limiting point of TCTFA, is the possible presence of cortical frontal
vein draining into the superior sagittal sinus that cross the superior operative field, limiting the maneuverability of the instruments through the surgical corridor.24 The surgeon has to consider these quantitative aspects in planning a surgery in the ATV.
Moreover, it must be taken into consideration the origin, the pathology and the growth pattern of the lesion.29 As a general rule, a cadaveric study carries several limitations. Even if the main purpose of a cadaveric study is to create a setting as real as possible, in the real scenario the presence of pathology might alter the regional anatomy., This aspect has to be taken into consideration by 10
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planning the best surgical approach besides the anatomical and geometrical parameters discussed above. Furthermore, “in vivo” surgery, dealing with softer tissues, which can be more easily displaced and retracted, offers a greater maneuverability, which might influence the operability mostly on deeply seated structures. The inter-individual variability of the anatomy, such as the
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position of the optic chiasm, makes it essential an accurate preoperative planning. A prefixed or postfixed chiasm might indeed substantially change the target point corresponding to the insertion of the lamina terminalis on the optic chiasm and, more generally, the configuration of the anterior part of the third ventricle13,
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These issues can be addressed with a careful
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preoperative analysis of the imaging of the patients. On the others hand, endoscope assistance
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during surgery on deeply seated lesions, does relevantly enhance surgical visualization.7
CONCLUSIONS
Tumors originating from the anterosuperior part of the third ventricle with transforaminal extension might be approached through a transcallosal transforaminal route, whereas lesions
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arising from the anteroinferior portion of the third ventricle even in case of upper extension might be safely and effectively approached through the lamina terminalis. Due to these findings, the operability score is effective in evaluating the surgical operability, the instruments manipulation capability, and the areas that can be exposed and in quantifying how those areas are suitable for
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surgical manoeuvres.
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COMPLIANCE WITH ETHICAL STANDARDS Conflict of interest
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The authors declare that they have no conflict of interest. Financial funding
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This is an unsponsored research; the authors declare that no financial funding was received.
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ACKNOWLEDGEMENTS The authors acknowledge Alberto Gallotti, M.D., for his contribution to the preparation of the
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drawings.
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Neuro-oncology. New York: Thieme Medical Publisher; 2007:42-53. 30.
Yasargil MG, Curcic M, Kis M, Siegenthaler G, Teddy PJ, Roth P. Total removal of craniopharyngiomas: approaches and long-term results in 144 patients. J Neurosurg. 1990;73:3-11.
Carmel PW. Tumours of the third ventricle. Acta Neurochir (Wien). 1985;75:136-146.
32.
Cohen-Gadol AA, Geryk B, Binder DK, Tubbs RS. Conquering the third ventricular
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31.
chamber. J Neurosurg. 2009;111:590-599. 33.
Friedman MA, Meyers CA, Sawaya R. Neuropsychological effects of third ventricle tumor surgery. Neurosurgery. 2003;52:791-798; discussion 798. Johnson RR, Baehring J, Piepmeier J. Surgery for third ventricular tumors. Neurosurg Q.
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2003;13:207-225. 35.
Delfini R, Picchieri A. Transcallosal Approaches to Intraventricular Tumors. In:
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Cappabianca P, Califano L, Iaconetta G, eds. Cranial, Craniofacial and Skull Base Surgery. Milan: Springer-Verlag Italia; 2010:87-105.
36.
Anderson RC, Ghatan S, Feldstein NA. Surgical approaches to tumors of the lateral ventricle. Neurosurg Clin N Am. 2003;14:509-525.
37.
Hong SW, Choi HY, Koh EJ. Surgery of the Tumors in the Ventricular System. J Korean Neurosurg Soc. 2006;39:26-31.
38.
Oi S, Samii A, Samii M. Operative techniques for tumors in the third ventricle. Operat Tech Neurosurg. 2003;6:205-214.
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39.
Rosenfeld JV, Freeman JL, Harvey AS. Operative technique: the anterior transcallosal transseptal interforniceal approach to the third ventricle and resection of hypothalamic hamartomas. J Clin Neurosci. 2004;11:738-744.
40.
Timurkaynak E, Izci Y, Acar F. Transcavum septum pellucidum interforniceal approach
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for the colloid cyst of the third ventricle Operative nuance. Surg Neurol. 2006;66:544547; discussion 547. 41.
Ture U, Yasargil MG, Al-Mefty O. The transcallosal-transforaminal approach to the third ventricle with regard to the venous variations in this region. J Neurosurg. 1997;87:706-
42.
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715.
Yoshimoto K, Shono T, Matsukado K, Sasaki T. The transventricular preforniceal
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approach for exophytic chiasmatic/hypothalamic astrocytomas extending into the anterior third ventricle. Acta Neurochir (Wien). 2013;155:727-732. 43.
Apuzzo ML, Levy ML, Tung H. Surgical strategies and technical methodologies in optimal management of craniopharyngioma and masses affecting the third ventricular chamber. Acta Neurochir Suppl (Wien). 1991;53:77-88.
44.
Yamamoto I, Rhoton AL, Jr., Peace DA. Microsurgery of the Third Ventricle: Part 1:
Seeger W. Microsurgery of the Brain: Anatomical and Technical Principles. Wien:
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Springer-Verlag; 1980.
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45.
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Microsurgical Anatomy. Neurosurgery. 1981;8:334-356.
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LEGENDS FOR FIGURES
Figure 1. Anatomical dissection: Interhemispheric section (A); CISTA approach to the third
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ventricle (B); TCTFA approach to the third ventricle (C). Legend: CC: Corpus Callosum; AC: Anterior Commissure; LT: Lamina terminalis; TV: Third Ventricle; SP: Septum Pellucidum; SV: Septal Vein; MF: Monroe Foramen; ACoA: Anterior Communicating Artery; FL: Frontal Lobe; OpCh: Optic Chiasm; ON: Optic Nerve; CN: Caudate
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Nucleus; CP: Choroidal Plexus; PcA: Pericallosal Artery.
and TCTFA (B). [D: mm]
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Figure 2. Schematic drawings showing the surgical corridors and mean values for CISTA (A)
Legend: Anterior commissure (yellow point); Inter-thalamic Adhesion (green point); Tuber cinereum (Blue point); Optic chiasm (violet point); SF: Surgical field depth; SAA: Surgical angle
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of attack; MAC: Maneuverability arc.
Figure 3. Schematic drawings showing the analyzed variable of operability score: Depth of the surgical field and maneuverability arc (A); surgical angle of attack (B); maneuverability arc (C).
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Legend: SF: Surgical field depth; SAA: Surgical angle of attack; MAC: Maneuverability arc;
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MAR: Maneuverability area
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SAA
MAC
Mean
SD
p-value
Mean
Range
SD
p-value
62,75 76,84
57,8 – 67,2 68,6 – 83,6
3,02 4,26
<0,0001
69,5° 19,9°
66° - 73° 14° – 40°
2,17° 7,62°
56,48 64,59
52 – 61,8 57,7 – 69,4
3,83 3,07
<0,0001
88° 47,9°
84° – 92° 41° – 63°
2,7° 7,6°
65,03 78,09
60 – 70 71,8 – 82,7
2,81 3,56
<0,0001
46,2° 40,1°
42° – 50° 24°– 48°
70,85 69,25
64 – 77,2 64,9 – 73,9
3,81 2,6
0,2917 (ns)
87,9° 14,6°
82°– 92° 10°– 21°
Range
SD
p-value
<0,0001
73,8° 24,4°
66° - 80° 14° – 40°
6,14° 14,54°
<0,0001
<0,0001
83,5° 48,3°
52° – 90° 43° – 63°
11,6° 7,67°
<0,0001
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Mean
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OpCh CISTA TCTFA AC CISTA TCTFA TC CISTA TCTFA IA CISTA TCTFA
Depth [mm] Range
2,82° 7,18°
0,0224
48,6° 43,2°
42° – 50° 30° – 50°
2,95° 5,8°
0,0173
3,14° 3,5°
<0,0001
84,2° 16,6°
65° – 90° 10° – 25°
7,31° 4,47°
<0,0001
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Point by approach
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Table 1: Measurements. Legend. CISTA: Combined inter-hemispheric sub-commissural trans-lamina terminalis approach; TCTFA: Transcallosal transforaminal approach; OpCh: Optic Chiasm; AC: Anterior commissure; TC: Tuber cinereum; IA: Inter-thalamic Adhesion; SD: Standard deviation; Depth: Surgical field depth (millimeters); SAA: Surgical angle of attack (Grades); MAC: Maneuverability arc (Grades); ns: not statistically significant.
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Approach
Depth
SAA
MAC
OS
OpCh
1
1
1
3
AC
1
1
1
3
TC
1
0
1
2
IA
0
1
1
2
OpCh
0
0
AC
1
0
TC
0
IA
0
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TCTFA
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CISTA
0
1
2
0
0
0
0
0
0
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0
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Table 2: Operability scores. Legend. CISTA: Combined inter-hemispheric subcommissural trans-lamina terminalis approach; TCTFA: Transcallosal transforaminal approach; OpCh: Optic Chiasm; AC: Anterior commissure; TC: Tuber cinereum; IA: Inter-thalamic Adhesion SD: Standard deviation; Depth: Surgical field depth; SAA: Surgical angle of attack; MAC: Maneuverability arc. Score values. Depth: <65mm = 1, >65mm = 0; SAA: >60° = 1, <60° = 0; MAC: >45° = 1, <45° = 0.
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ACCEPTED MANUSCRIPT Highlights: •
Surgery of the third ventricular region still represents a challenge in modern neurosurgery.
•
The operability score can be applied for the quantitative assessment of the
•
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ability to reach some anatomical structures before surgery. Depending upon tumor origins and location different surgical approaches have to be considered. •
Tumors originating from the anterosuperior part of the third ventricle with
transcallosal transforaminal route. •
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transforaminal extension might be have to be approached through a
Tumors arising from the anteroinferior portion of the third ventricle might be
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safely and effectively approached through the lamina terminalis.
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ATV: anterior third ventricle TCTA: transcallosal transforaminal approach CISTA: combined inter-hemispheric sub-commissural trans-lamina terminalis
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approach OS: operability score SF: surgical field depth SAA: surgical angle of attack
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MAC: maneuverability arc MAR: maneuverability area
TC: tuber cinereum AC: anterior commissure
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IA: inter-thalamic adhesion
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OpCh: optic chiasm
S1878-8750(16)30741-0
DOI:
10.1016/j.wneu.2016.08.073
Reference:
WNEU 4484
To appear in:
World Neurosurgery
Received Date: 21 April 2016 Revised Date:
15 August 2016
Accepted Date: 17 August 2016
Please cite this article as: Spina A, Gagliardi F, Bailo M, Boari N, Caputy AJ, Mortini P, Comparative Anatomical Study on Operability in Surgical Approaches to the Anterior Part of the Third Ventricle, World Neurosurgery (2016), doi: 10.1016/j.wneu.2016.08.073. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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COMPARATIVE ANATOMICAL STUDY ON OPERABILITY IN SURGICAL APPROACHES TO THE ANTERIOR PART OF THE THIRD VENTRICLE
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Alfio Spina1, M.D., Filippo Gagliardi1, M.D., Michele Bailo1, M.D., Nicola Boari1, M.D., Anthony J. Caputy2, M.D. and Pietro Mortini1, M.D. 1
Department of Neurosurgery and Gamma Knife Radiosurgery, San Raffaele Scientific Institute,
Department of Neurological Surgery, The George Washington University, Washington, District
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2
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Vita-Salute University, Milan, Italy
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of Columbia, United States
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Corresponding Author: Alfio Spina, M.D.
Department of Neurosurgery and Gamma Knife Radiosurgery San Raffaele Scientific Institute, Vita-Salute University Via Olgettina 60, 20132 Milano, Italy. Tel: +39-02-26432396. Fax: +39-02-26437302. E-mail: [email protected] 1
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ABSTRACT
Background. Surgery of the third ventricle still represents a challenge in modern neurosurgery. To optimize the surgical planning, some aspects, related to ventricular anatomy,
evaluate these variables, to choose of a tailored surgical approach.
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have to be taken into consideration. An operability score could represent a preoperative tool to
Methods. Authors compared the transcallosal transforaminal (TCTFA) and the combined inter-hemispheric sub-commissural trans-lamina terminalis approach (CISTA), to the anterior
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part of the third ventricle, applying the operability score.
Results. Compared to the TCTFA, the CISTA provides a statistically significant
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improvement in terms of depth of surgical field, surgical angle of attack and maneuverability arc considering as four approach-related critical structures: the optic chiasm (p value: <0,0001, <0,0001, <0,0001 respectively), the anterior commissure (p value: <0,0001, <0,0001, <0,0001 respectively), the tuber cinereum (p value: <0,0001, 0,0224, 0,0173) and the inter-thalamic adhesion (p value: 0,2917, <0,0001, <0,0001 respectively).
Conclusions. Tumors originating from the anterosuperior part of the third ventricle can be
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easily approached through a transcallosal transforaminal route, whereas lesions arising from the
the CISTA.
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anteroinferior portion of the third ventricle might be safely and effectively approached through
Keywords: Corpus callosum; Lamina terminalis; Operability score; Optic chiasm; Third
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ventricle
Running title: Comparative anatomical study on surgical approaches to the anterior third ventricle.
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INTRODUCTION
Surgery of the third ventricle is still considered a challenging one. Tumors arising from this anatomical area can involve the ventricular cavity, the hypothalamic region, the optic complications.1-4
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apparatus, and the pituitary. Moreover, surgery of the third ventricle can result in life threatening
Despite the great technical advancements, the choice of the best approach still remains controversial.3, 5 Although different approaches have been described, no anatomical comparison
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of surgical approaches to this critical area has been carried out.3, 5
Two major groups of microsurgical approaches are nowadays adopted for the resection of
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the lesions affecting the anterior aspect of the ventricular cavity (Figure 1A): the transcallosal transforaminal (TCTFA) and the combined inter-hemispheric sub-commissural trans-lamina terminalis approach (CISTA).4,
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Many authors have extensively described both approaches,
nevertheless a comparative study on the advantages and drawbacks of the single approach is still lacking. The concept of operability score (OS) has been recently introduced for the quantitative assessment of the ability to reach some anatomical structures, which can be easily applied to
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comparative studies of surgical anatomy.7
The aim of this study is therefore to compare TCTFA and CISTA in approaching lesions
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of the anterior part of the third ventricle.
MATERIALS AND METHODS
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Ten cadaver specimens fixed with gluteraldehyde and injected with colored latex were
used for the anatomical dissections at the Ammermann Microsurgical Laboratory in Washington, DC (Department of Neurosurgery, George Washington University, Washington, DC). The heads were placed in surgical position, fixed in a Mayfield head-holder (Codman,
Inc., Raynham, MA). Microsurgical dissections have been performed with the microscope (Zeiss OPM 1 FC, Carl Zeiss, Oberkochen, Germany) using standard microsurgical instruments. A high-speed drill was used to perform bone drilling and craniotomy (Midas Rex, Medtronic, Fort Worth, TX, USA). 3
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For each approach we considered: a) the surgical field depth (SF), defined as the distance between the dura mater and four target points such as anatomical structures recognizable during the dissections, b) the surgical angle of attack (SAA), defined as the angle of incidence of the corridor in selected points, c) the maneuverability arc (MAC), defined as the degree of freedom defined as the area at the narrowest point of the surgical field.7
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in manipulating surgical instruments in selected points; and d) the maneuverability area (MAR),
The surgical techniques of CISTA (Figure 1 B) and TCTFA (Figure 1 C) have already been extensively described in previous reports and a brief description of them has been reported
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below.1-4, 6, 8-30
Measurements were acquired under the microscope and with the help of the endoscope,
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by using different graded scales. We selected for both approaches the same four key target points, which corresponded to the insertion of the lamina terminalis to the optic chiasm (OpCh), the tuber cinereum (TC), the anterior commissure (AC) and the inter-thalamic adhesion (IA) (Figure 1A). At these anatomical points the SF, the SAA, the MAC and MAR have been measured in both approaches (Figure 2).
Data recorded were statistically analyzed by using Prism software (version 5.0a,
Surgical technique CISTA
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GraphPad Software Inc., La Jolla, CA, USA). P-value was analyzed by using t-Test.
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The head is placed in neutral position with 20 degrees of extension. A bicoronal skin incision is performed and the skin flap is reflected anteriorly. After peforming a unilateral fronto-temporal
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craniotomy to expose the midline, the superior sagittal sinus and the Sylvian fissure laterally, an orbital osteotomy is performed on the approached side. Once opened the dura, the frontal lobe is gently separated from the falx and the contralateral mesial frontal cortex; an additional subfrontal dissection may be performed in order to increase frontal lobe retraction in order to use the frontobasal corridor. The interhemispheric dissection is continued toward the lamina terminalis by maintaining a subcommissural trajectory. At this point, the lamina terminalis, a grayish thin membrane posterior to the brighter optic chiasm, is opened both below and above the anterior communicating artery between the two A1 and A2 arteries, respectively, to access the anterior part of the third ventricle.
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TCTFA The head is placed in neutral position and flexed 20 degrees. A lateral-based U-shaped incision is performed, to expose the sagittal and the coronal sutures of the selected side. The skin flap is
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reflected laterally. A fronto-parietal craniotomy is carried out extending about two thirds anteriorly to the coronal suture and one third posteriorly, across the midline in order to expose the superior sagittal sinus. The dura is opened to create a medial-based flap and then reflected medially. The major bridging veins are preserved, dividing only the smallest ones, in order to widen the interhemispheric corridor. Subsequently, the interhemispheric dissection is performed
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with the help of a self-retaining retractor, to retract the mesial frontal cortex from the falx and the contralateral cortex. Once the interhemispheric dissection is completed, the corpus callosum
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come into view. After the identification of both pericallosal arteries, a callosotomy is performed at maximum 2 cm in length. The callosotomy is completed when the grayish tissue of the ventricular ependymal come into view. The ependymal layer is then opened to access to the lateral ventricle. After entering into the ventricle, the Monro foramen is identified at the floor of the ventricle, with the choroid plexus running posteriorly to it from lateral to medial and entering into the foramen, whereas the thalamostriate veins run from the lateral to the anteromedial side,
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entering the foramen. Once checked these anatomical landmarks to prevent inadvertent contralateral ventricular opening, a standard transforaminal approached is performed to access
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RESULTS
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the third ventricle from above.
The average depth of the SF at the OpCh was of 62,75 mm (range 57,8 – 67,2; DS 3,02)
for the CISTA and 76,84 mm (range 68,6 – 83,6; DS 4,26) for the TCTFA. The average depth of the SF at the AC was of 56,48 mm (range 52 – 61,8; DS 3,83) for the CISTA and 64,59 mm (range 57,7 – 69,4; DS 3,07) for the TCTFA. The average depth of the SF at the TC was of 65,03 mm (range 60 – 70; DS 2,81) for the CISTA and 78,09 mm (range 71,8 – 82,7; DS 3,56) for the TCTFA. The average depth of the SF at the IA was of 70,85 mm (range 64 – 77,2; DS 3,81) for the CISTA and 69,25 mm (range 64,9 – 73,9; DS 2,6) for the TCTFA.
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The average value of the SAA at the OpCh was 69,5° (range 66 – 73; DS 2,17) for the CISTA and 19,9° (range 14 - 40; DS 7,62) for the TCTFA. The average value of the SA at the AC was 88° (range 84 - 92; DS 2,7) for the CISTA and 47,9° (range 41 - 63; DS 7,6) for the TCTFA. The average value of the SAA at the TC was 46,2° (range 42 - 50; DS 2,82) for the
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CISTA and 40,1° (range 24 - 48; DS 7,18) for the TCTFA. The average values of the SAA of the IA was 87,9° (range 82 - 92; DS 3,14) for the CISTA and 14,6° (range 10 - 21; DS 3,5) for the TCTFA.
The average value of the MAC at the OpCh was 73,8° (range 66 – 80; DS 6,14) for the
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CISTA and 24,4° (range 14 - 40; DS 14,54) for the TCTFA. The average value of the SA at the AC was 83,5° (range 52 - 90; DS 11,6) for the CISTA and 48,3° (range 43 - 63; DS 7,67) for the
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TCTFA. The average value of the SAA at the TC was 48,6° (range 42 - 50; DS 2,95) for the CISTA and 43,2° (range 30 - 50; DS 5,8) for the TCTFA. The average values of the SA of the IA was 84,2° (range 65 - 90; DS 7,31) for the CISTA and 16,6° (range 10 - 25; DS 4,47) for the TCTFA.
The averages of the MAR were 2,12 cm2 (range: 1,5 – 2,5; DS: 0,32) for the CISTA and 1,58cm2 (range 1,4 - 2; DS 0,16) for the TCTFA. Data are summarized in Table 1.
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A value of 0 or 1 was assigned to the qualitative values. According to our previous publication, for the surgical field depth, we considered 65mm as critical limit of the length of the working channel for the optimal maneuverability of the microsurgical instrumentation (<65mm = 1, >65mm = 0). For the SAA, a value of 60° was considered (>60° = 1, <60° = 0). For the MAC
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a limit value of 45° was calculated (>45° = 1, <45° = 0).7 The OS was then calculated from the total of each score. Table 2 summarizes OS referred to specific target points inside the ATV. OpCh, AC and TC showed a lower SF in the CISTA as compared to TCTFA (p<0,0001),
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whereas the IA showed a lower SF in the TCTFA, without reaching a statistical significance. Both the SAA and MAC had significant higher values in the CISTA as compared to the TCTFA. By critically reviewing these data, it has to be noted, that the CISTA seems to be, for the
considered targets, a more direct approach, offering also a better SAA and MAC to OpCh, AC and TC. On the other hand, even if CISTA has higher values of SF to the IA, it provides a better angle of attack and maneuverability around this target. These findings can be determined by the absence in the CISTA of the callosotomy, which jeopardizes the maneuverability and SAA
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around the targets. The superior MAR also confirms this feature in the CISTA if compared to the
DISCUSSION
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TCTFA (2,12 vs. 1,58 cm2, respectively).
Since the early thirties, when Cushing and Dandy, described some key concepts, surgery in and around the third ventricle is still considered a challenge.31, 32
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The complexity of regional anatomy requires high technical skills and surgery might have a significant morbidity.2
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Endocrinological disturbances, neurological and neuropsychological deficit, such as memory loss, are the most common consequences in patients treated for tumors growing in the third ventricle region.1-3, 11, 12, 30, 33, 34
To optimize the surgical planning, some tridimensional aspects, related to the tumoral and the ventricular anatomy, should be taken into consideration, before surgery to prevent postoperative morbidity and improve the rate of a safe and radical surgical resection.34
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The operability score, as recently described, has been demonstrated to be effective in graduating both the surgical operability, and the instruments manipulation capability.7 Moreover, it is a useful tool to measure the areas that can be exposed in a single approach and their suitability for surgical manoeuvres.7
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As previously proposed, the third ventricle can be divided into an antero-superior, anteroinferior, posterior-superior and a posterior-inferior segment.18
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In this study we focused our attention in the comparison between the CISTA and the TCTFA.
The CISTA, as previously described is an antero-lateral approach, which uses multi-angle
trajectories.3 The depth of the surgical field ranges from 52 to 70 mm. As compared to the TCTFA, the anterior inter-hemispheric route is free from major draining veins, making the arachnoidal dissection safer. 20 The critical point of the surgical field, which is considered as a funnel tip, is defined by the chiasm inferiorly, the anterior commissure and anterior communicating artery superiorly and by the two anterior cerebral arteries laterally.20
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This area, represents the surgical access to the ventricular cavity, and corresponds to the narrowest cross-action area of the surgical corridor, defined as MAR. It contributes to the conizing effect (the index defined by dividing the maneuverability area and the depth of the surgical corridor) in this approach, limiting the possibility to reach the lateral portion of the ATV.
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MAR ranges from 1,5 to 2,5 cm2 and it has to be considered that it can be further reduced by the presence of a prefixed chiasm.34
As consequence, MAC is influenced by the anatomical structures mentioned above. In the past, some authors advocated the division of the anterior communicating artery to increase it. In
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the CISTA, anterior communicating artery division is not needed, because of the three different available vascular windows, which can be used to access the ventricular cavity and the absence of
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perforating branches in this area.3, 21, 23
It has to be considered that the dissection of the lamina terminalis can present some criticisms, because it might be distorted by the ventricular content, making the optic apparatus and possibly the hypothalamus at risk of damage.13, 29
The upper view in the surgical corridor is limited by the angle made by the posteriorinferior portion of the AC. We considered this point to define one SAA. Average value of this
backward to this structure.
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angle is 88° (range 84°-92°). AC is the major limiting factor in approaching lesions that extends
One other critical aspect in the SAA is the area of the tuber cinereum. In this case the SAA is more favorable, ranging from 42° to 50° (mean 46,2°), if compared to the TCTFA.
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Lesions arising from this region are prone to be resected through this route, showing a favorable angle of SA.
Going deep into the ventricular cavity a further limiting factor in maneuverability is the
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inter-thalamic adhesion. According to Rhoton classification it represents the posterior limit of the anterior part of the third ventricle.18 Average value of MAC in this point is 87,9° (range 82°-92°). Moreover, it is possible with the CISTA to access in the posterior aspect of the third ventricle, reaching the supra pineal recess. The conizing effect of the CISTA is lower if compared to TCTFA, because of the wider maneuverability area and the shorter depth of the surgical field. The TCTFA approach is a transcallosal route, taking advantage from a dilatation of the Monro foramen to access the ventricular cavity. Although usually dilated in case of third
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ventricular tumors, the foramen represents a narrow natural corridor ranging from 3 to 7 mm in diameter.29 The diameter of the Monro foramen is essential for the feasibility of this approach.35 A wider configuration of the foramen, as it happens in case of hydrocephalus or in presence of
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lesions enlarging lesions, might increase the SAA, MAC and also the MAR. Another potential limitation of the TCTFA is the unilateral trajectory, potentially making the ipsilateral wall of the third ventricle a blind corner.35
To overcome the limits due to the foramen size, alternative variations of the transcallosal
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approach have been described, which improve the MAR.1, 2, 4, 10, 14, 15, 17, 19, 22, 24-28, 31-34, 36-42 In order to increase the opening of the Monro foramen, it is possible to make a
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transchoroidal extension, by sharply enlarging the surgical corridor, just medially to the choroid plexus and laterally to fornix, through the tenia fornicis; or alternatively a subchoroidal extension, by opening a corridor by a sharp dissection along the tenia choroidea, after displacing the choroid plexus medially from the internal cerebral veins and the posteromedial choroidal artery.29,
35
Although these variants do increase the diameter of the surgical corridor at the level of the Monro foramen, they may potentially increase the approach-related morbidity as the vascular structures
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of this region, such as the internal cerebral, thalamostriate and septal vein and the posteromedial choroidal artery, might be stretched and damaged by surgical maneuvers.29, 35 Moreover one of the most critical aspects of transcallosal approaches is the right
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definition of the midline and the relation between the callosotomy and the diameter of the foramen of Monro.17, 20, 22, 24, 39, 41
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As already reported in literature in TCTFA, the risk of postoperative neurologic and neuropsychological complication due to the disconnection of the two hemispheres, is directly related to the length of the callosotomy, which should be at maximum of 2 centimeters.1, 2, 4, 14, 17, 19, 24, 26, 30, 36, 43, 44
Considering these data, the ratio between the diameter of callosotomy over
Monro foramen diameter, should be lesser than 2. To prevent a foraminal trajectory and to accomplish a midline route, a transcallosal interforniceal approach can be performed. By dissecting and retracting the bodies of the fornices together with internal cerebral veins and posteromedial choroidal arteries, this midline approach, provides the view of both walls of the third ventricle with a greater access and maneuverability as 9
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compared to a foraminal route.29, 35 Nevertheless, even this variant is not always feasible, because the length of the septum pellucidum and the adhesions between corpus callosum and fornices, might limit the dissection, contraindicating the approach.29, 35
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The maneuverability area and arc of maneuverability in TCTFA are limited by the borders of the callosotomy and the foramen of Monro; stretching of the fibers at the level of the corpus callosum might indeed cause postoperative hemiparesis, while surgical damage of the forniceal fibers might cause mnemonic impairment.2, 6, 10, 17, 33, 36 A larger craniotomy as suggested, could
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improve the conizing effect and the visibility, avoiding a wide opening of the corpus callosum.45 Compared to the CISTA, the TC could not be easily reached through the TCTFA, because of the depth of the surgical corridor. CISTA and TCTFA show statistically significant difference
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in reaching the inter-thalamic adhesion in terms of mean values.
Even if the TCTFA had a lower mean value of MAC on the TC, the likelihood to control it from above has to be considered, if the lesion or the anatomy of the OpCh-lamina terminalis do form a blind corner, making it difficult to control them through the CISTA. The OS confirms these findings, showing better results for CISTA on OpCh, TC and IA. Not surprisingly, the AC showed a higher OS in TCTFA, which is mostly due to the short distance of this target. Although
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it is not always possible to visualize AC without a dilated Monro foramen in the real scenario, this cadaveric study stressed the concept that the depth of the surgical field is essential in determining the operability of different anatomical regions during the same approach.
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Nevertheless the conizing effect of the surgical corridor in TCTFA is more unfavorable as compared to the CISTA. This is mainly due to the limit in surgical maneuverability represented
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by the callosotomy and the greater depth of the surgical field. Another important limiting point of TCTFA, is the possible presence of cortical frontal
vein draining into the superior sagittal sinus that cross the superior operative field, limiting the maneuverability of the instruments through the surgical corridor.24 The surgeon has to consider these quantitative aspects in planning a surgery in the ATV.
Moreover, it must be taken into consideration the origin, the pathology and the growth pattern of the lesion.29 As a general rule, a cadaveric study carries several limitations. Even if the main purpose of a cadaveric study is to create a setting as real as possible, in the real scenario the presence of pathology might alter the regional anatomy., This aspect has to be taken into consideration by 10
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planning the best surgical approach besides the anatomical and geometrical parameters discussed above. Furthermore, “in vivo” surgery, dealing with softer tissues, which can be more easily displaced and retracted, offers a greater maneuverability, which might influence the operability mostly on deeply seated structures. The inter-individual variability of the anatomy, such as the
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position of the optic chiasm, makes it essential an accurate preoperative planning. A prefixed or postfixed chiasm might indeed substantially change the target point corresponding to the insertion of the lamina terminalis on the optic chiasm and, more generally, the configuration of the anterior part of the third ventricle13,
29
These issues can be addressed with a careful
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preoperative analysis of the imaging of the patients. On the others hand, endoscope assistance
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during surgery on deeply seated lesions, does relevantly enhance surgical visualization.7
CONCLUSIONS
Tumors originating from the anterosuperior part of the third ventricle with transforaminal extension might be approached through a transcallosal transforaminal route, whereas lesions
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arising from the anteroinferior portion of the third ventricle even in case of upper extension might be safely and effectively approached through the lamina terminalis. Due to these findings, the operability score is effective in evaluating the surgical operability, the instruments manipulation capability, and the areas that can be exposed and in quantifying how those areas are suitable for
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surgical manoeuvres.
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COMPLIANCE WITH ETHICAL STANDARDS Conflict of interest
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The authors declare that they have no conflict of interest. Financial funding
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This is an unsponsored research; the authors declare that no financial funding was received.
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ACKNOWLEDGEMENTS The authors acknowledge Alberto Gallotti, M.D., for his contribution to the preparation of the
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drawings.
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LEGENDS FOR FIGURES
Figure 1. Anatomical dissection: Interhemispheric section (A); CISTA approach to the third
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ventricle (B); TCTFA approach to the third ventricle (C). Legend: CC: Corpus Callosum; AC: Anterior Commissure; LT: Lamina terminalis; TV: Third Ventricle; SP: Septum Pellucidum; SV: Septal Vein; MF: Monroe Foramen; ACoA: Anterior Communicating Artery; FL: Frontal Lobe; OpCh: Optic Chiasm; ON: Optic Nerve; CN: Caudate
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Nucleus; CP: Choroidal Plexus; PcA: Pericallosal Artery.
and TCTFA (B). [D: mm]
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Figure 2. Schematic drawings showing the surgical corridors and mean values for CISTA (A)
Legend: Anterior commissure (yellow point); Inter-thalamic Adhesion (green point); Tuber cinereum (Blue point); Optic chiasm (violet point); SF: Surgical field depth; SAA: Surgical angle
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of attack; MAC: Maneuverability arc.
Figure 3. Schematic drawings showing the analyzed variable of operability score: Depth of the surgical field and maneuverability arc (A); surgical angle of attack (B); maneuverability arc (C).
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Legend: SF: Surgical field depth; SAA: Surgical angle of attack; MAC: Maneuverability arc;
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MAR: Maneuverability area
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SAA
MAC
Mean
SD
p-value
Mean
Range
SD
p-value
62,75 76,84
57,8 – 67,2 68,6 – 83,6
3,02 4,26
<0,0001
69,5° 19,9°
66° - 73° 14° – 40°
2,17° 7,62°
56,48 64,59
52 – 61,8 57,7 – 69,4
3,83 3,07
<0,0001
88° 47,9°
84° – 92° 41° – 63°
2,7° 7,6°
65,03 78,09
60 – 70 71,8 – 82,7
2,81 3,56
<0,0001
46,2° 40,1°
42° – 50° 24°– 48°
70,85 69,25
64 – 77,2 64,9 – 73,9
3,81 2,6
0,2917 (ns)
87,9° 14,6°
82°– 92° 10°– 21°
Range
SD
p-value
<0,0001
73,8° 24,4°
66° - 80° 14° – 40°
6,14° 14,54°
<0,0001
<0,0001
83,5° 48,3°
52° – 90° 43° – 63°
11,6° 7,67°
<0,0001
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Mean
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OpCh CISTA TCTFA AC CISTA TCTFA TC CISTA TCTFA IA CISTA TCTFA
Depth [mm] Range
2,82° 7,18°
0,0224
48,6° 43,2°
42° – 50° 30° – 50°
2,95° 5,8°
0,0173
3,14° 3,5°
<0,0001
84,2° 16,6°
65° – 90° 10° – 25°
7,31° 4,47°
<0,0001
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Point by approach
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Table 1: Measurements. Legend. CISTA: Combined inter-hemispheric sub-commissural trans-lamina terminalis approach; TCTFA: Transcallosal transforaminal approach; OpCh: Optic Chiasm; AC: Anterior commissure; TC: Tuber cinereum; IA: Inter-thalamic Adhesion; SD: Standard deviation; Depth: Surgical field depth (millimeters); SAA: Surgical angle of attack (Grades); MAC: Maneuverability arc (Grades); ns: not statistically significant.
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Approach
Depth
SAA
MAC
OS
OpCh
1
1
1
3
AC
1
1
1
3
TC
1
0
1
2
IA
0
1
1
2
OpCh
0
0
AC
1
0
TC
0
IA
0
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TCTFA
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CISTA
0
1
2
0
0
0
0
0
0
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Table 2: Operability scores. Legend. CISTA: Combined inter-hemispheric subcommissural trans-lamina terminalis approach; TCTFA: Transcallosal transforaminal approach; OpCh: Optic Chiasm; AC: Anterior commissure; TC: Tuber cinereum; IA: Inter-thalamic Adhesion SD: Standard deviation; Depth: Surgical field depth; SAA: Surgical angle of attack; MAC: Maneuverability arc. Score values. Depth: <65mm = 1, >65mm = 0; SAA: >60° = 1, <60° = 0; MAC: >45° = 1, <45° = 0.
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ACCEPTED MANUSCRIPT Highlights: •
Surgery of the third ventricular region still represents a challenge in modern neurosurgery.
•
The operability score can be applied for the quantitative assessment of the
•
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ability to reach some anatomical structures before surgery. Depending upon tumor origins and location different surgical approaches have to be considered. •
Tumors originating from the anterosuperior part of the third ventricle with
transcallosal transforaminal route. •
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transforaminal extension might be have to be approached through a
Tumors arising from the anteroinferior portion of the third ventricle might be
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safely and effectively approached through the lamina terminalis.
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ATV: anterior third ventricle TCTA: transcallosal transforaminal approach CISTA: combined inter-hemispheric sub-commissural trans-lamina terminalis
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approach OS: operability score SF: surgical field depth SAA: surgical angle of attack
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MAC: maneuverability arc MAR: maneuverability area
TC: tuber cinereum AC: anterior commissure
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IA: inter-thalamic adhesion
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OpCh: optic chiasm