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The Retrolabyrinthine Presigmoid Approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann Triangle
Accepted Manuscript The Retrolabyrinthine Presigmoid approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann’s Triangle Fernando Alonso, MD, Simone E. Dekker, MD, PhD, James Wright, MD, Christina Wright, MD, Andrea Alonso, BA, Margaret Carmody, MD, R. Shane Tubbs, PhD, Nicholas C. Bambakidis, MD PII:
S1878-8750(17)30669-1
DOI:
10.1016/j.wneu.2017.04.161
Reference:
WNEU 5680
To appear in:
World Neurosurgery
Received Date: 18 March 2017 Revised Date:
25 April 2017
Accepted Date: 26 April 2017
Please cite this article as: Alonso F, Dekker SE, Wright J, Wright C, Alonso A, Carmody M, Tubbs RS, Bambakidis NC, The Retrolabyrinthine Presigmoid approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann’s Triangle, World Neurosurgery (2017), doi: 10.1016/ j.wneu.2017.04.161. 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.
ACCEPTED MANUSCRIPT
The Retrolabyrinthine Presigmoid approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann’s Triangle
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Fernando Alonso MD1,2, Simone E. Dekker MD,PhD1, James Wright MD1, Christina Wright MD1, Andrea Alonso BA1, Margaret Carmody MD1, R. Shane Tubbs PhD2
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and Nicholas C. Bambakidis MD1
Department of Neurological Surgery, University Hospitals Case Medical Center,
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Cleveland, Ohio
Seattle Science Foundation, Seattle, WA
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Disclosures: The authors have no disclosures to report
Corresponding author:
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Fernando Alonso MD
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Department of Neurological Surgery, University Hospitals Case Medical Center, Cleveland, Ohio
Email: [email protected] Tel: 918-694-8208
Keywords: retrolabyrinthine; acoustic; semicircular canal, sigmoid sinus, sino-dural angle
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ABSTRACT The anatomical area exposed through the exposure of Trautmann’s triangle may not be sufficient. We studied the additional exposure provided by skeletonizing the
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sigmoid sinus. Human cadaver heads were subjected to a thin temporal bone CT scan for a total of 10 sides. The estimated surgical working angle was calculated based on the relationship of the sigmoid sinus to the posterior semicircular canal, superior
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petrosal sinus and jugular bulb on imaging. The heads were then subjected to a
mastoidectomy and remeasured with and without sigmoid sinus skeletonization.
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The working angle calculated on CT was 56 ± 11.3 degrees. Skeletonization of the sigmoid sinus increased the distance between the PSC to SS by 5 mm (p = 0.01), and LSC to SS by 4 mm (p = 0.01). Skeletonization and retraction of the SS significantly increased the distance between the PSC and LSC to the SS. On post mastoidectomy
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images, skeletonizing the sigmoid sinus helped improve anterior visibility on the majority of our samples that had a SS that was lateral to the PSC on axial imaging. In samples in which the SS is medial to the PSC or only has minimal lateral
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displacement, skeletonizing the SS did not markedly improve visibility of the
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retrolabyrinthine space. Working area and visibility improve as the PSC and SS approach the same plane on axial imaging. Preoperative evaluation of the laterality of the SS to the PSC may assist a surgeon in determining the need for skeletonizing the SS and avoiding possible vascular injuries.
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INTRODUCTION The presigmoid retrolabyrinthine approach has several advantages, such as lower morbidity than a transbyrinthine approach due to hearing preservation and a low risk
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of facial nerve injury3,5,9. However, the anatomical area uncovered through the exposure of Trautmann’s triangle (TT) may not provide a sufficient working area. Attention has been placed on the relationship of the superior jugular bulb (JB) to the
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internal auditory meatus but there is little known on the need to skeletonize the sigmoid sinus (SS) based on its relationship to the posterior semicircular canal (PSC).
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In this study, we hypothesized that an expansion of TT provides a larger exposure of lesions located at cranial nerve entry zones and the lateral brain stem. The aim of this study was to measure the additional exposure and visibility provided by skeletonizing the SS, drilling of the PSC and to determine if there are a subset of patients that would
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not benefit from exposure of the SS based on the depth of the operative field provided
METHODS
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by the relationship between the PSC and SS.
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Five adult human cadaver heads were subjected to thin cut temporal bone CT scan for a total of 10 sides. The estimated working angle was calculated based on the relationship of the SS to the PSC, superior petrosal sinus (SPS) and JB on imaging. The heads were then subjected to a mastoidectomy to calculate the following distances in the presigmoid retrolabyrintine space: external acoustic meatus (EAC) to SS, PSC to JB, PSC to SS, and lateral semicircular canal (LSC) to SS after the PSC was drilled. The SS was then skeletonized with the use of a 5mm soft touch burr and gentle retraction was applied. Measurements to the SS were then repeated. Samples
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ACCEPTED MANUSCRIPT were photographed. Measurements were also verified manually to insure correctness. Data were analyzed using IBM SPSS Statistics 23 (IBM, New York, USA). Variables were summarized as mean ± SD and the means were compared using a paired sample
<0.05 was considered to be statistically significant. RESULTS
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t test. Correlation coefficients were calculated using Pearson's correlation. A P-value
Table 1 shows the imaging and dissection measurement results. Two medial and eight
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lateral sides were included in the analysis. The distance between the EAC and SS was measured at dissection with microcalipers and was significantly correlated to the
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measured distances on imaging by placing a laterally drawn line on the SS and measuring the shortest perpendicular distance to the PSC (r = 0.82; p = 0.02) and LSC (r = 0.859; p = 0.01) on axial CT imaging. Skeletonization of the SS significantly increased the distance between the PSC to SS by 4.9 mm (13.96 ± 3.13 mm vs. 9.05 ±
= 0.01).
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3.49 mm; p < 0.001), and the LSC to SS by 4.2 mm (16.97 ± 3.50 vs. 12.76 ± 3.83; p
After mastoidectomy, skeletonizing the SS helped improved anterior visibility on
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eight of our samples that had a SS that was lateral to the PSC on axial imaging
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(Figure 2). In samples in which the SS was medial to the PSC or only has minimal lateral displacement, skeletonizing the SS did not markedly improve visibility of the retrolabyrinthine space (Figure 4). The shortest distance between the PSC to SS and LSC to SS measured after mastoidectomy did not correlate with the perpendicular distances measured preoperatively (r = 0.63; p = 0.052, and r = 0.67; p = 0.99, respectively). Manual measurements were well correlated to imaging measurements with no statistical differences.
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ACCEPTED MANUSCRIPT DISCUSSION Background/History The retrolabyrinthine craniotomy is a workhorse approach to the cerebellopontine angle. The retrolabyrinthine approach was first described by Hitselberger and Pulec in
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1971 for a vestibular neurectomy1. It may be used for resection of vestibulocochlear and trigeminal nerves pathology, intractable Meniere’s disease, aneurysms arising
from the posterior circulation and other pathologies of the lateral brain stem2,3,4. This
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approach can be converted to a translabyrinthine approach if a more anterior exposure is required to the fundus of the internal acoustic canal (IAC) in vestibular
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schwannoma surgery5. A transcrusal exposure (partial labyrinthectomy) or petrous apicectomy may also be performed for increased visibility of the clivus6,7. TT is limited by the sinodural angle and SPS superiorly, the JB inferiorly and the PSC anteriorly (Figure 1)2,6,8. Day et al. have described the ideal composition of a cranial
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base approach- drilling or resection of bone in order to minimize retraction of the brain, a short conduit to the pathological entity, maximizes the extradural window, and allows for closure of the dural defects9.
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Anatomical findings
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We found that the shortest distance between the PSC to SS and LSC to SS measured after mastoidectomy did not correlate with the perpendicular distances measured preoperatively (r = 0.63; p = 0.052, and r = 0.67; p = 0.99, respectively). This is likely as a result of the diagonal surface of TT. The surgical depth is most shallow at the level of the SS and increases in depth in its anterior margin adjacent to the PSC. As expected, skeletonization of the SS and retraction significantly increased the distance between the PSC and SS by 4.9 mm (13.96 ± 3.13 mm vs. 9.05 ± 3.49 mm; p < 0.001), and LSC to SS by 4.2 mm (16.97 ± 3.50 vs. 12.76 ± 3.83; p = 0.01).
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ACCEPTED MANUSCRIPT Intraoperatively, this increase in distance provided a wider operative corridor for samples with a SS that was located lateral to the LSC/PSC line (Figures 1 and 2). The increase in visibility seen with our two medial samples was unremarkable (Figures 3 and 4). As expected from prior studies, drilling of the PSC in a modified partial
IAC6,10. Classification of Trautmann’s Triangle
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labyrinthectomy approach, provided an improved exposure to the fundus of the
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Tubbs et al. classified TT into three types based on area: type 1 with an area of less
than 75 mm2 (37.5%), type 2 75-149 mm2 (35%) and type 3 with an area of 150 mm2
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(27.5%) or greater2. Vachatta et al. studied the JB and its relationship to the IAC in two hundred temporal bones11. The average distance between the IAC and the JB was 7.5 +/- 2.3mm. A high JB, defined as a JB at the level of the IAC or higher, was found in 16.5% of patients. A cadaveric study found that a reference line drawn from the
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lateral semicircular canal to the posterior semicircular canal could be used to predict the area of TT12. If the SS was located lateral to the reference line, TT was found to have a smaller area and the SS was found to be superimposed over TT, severely
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limiting the operative space and possibly increasing the risk of injury to the facial
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nerve. In the medial group, the operative field was wider and less deep, making the approach less challenging. Based on these findings one can conclude that the ideal patient who would benefit from a retrolabyrinthine approach would have the following characteristics: pathology that is superficial and not centered on the fundus of the IAC, low location of the JB (below the IAC) and a medial location of the SS. Although not common, through this study we have found that this subset of patients, identified through preoperative imaging may undergo sufficient exposure of the CPA without the need for skeletonization and manipulation of the SS. On the contrary, the
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ACCEPTED MANUSCRIPT most challenging cases have a laterally displaced SS, which increased the surgical depth and reduces the area of TT and a JB that is at the level of the IAC or higher. In this latter subset of patients, additional techniques might need to be performed with more attention directed to skeletonization of the sinodural angle and SS in order to
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“expand” TT or conversion of the retrolabyrinthine craniotomy into a transcrusal or
translabyrinthine approach. Pre-operative imaging evaluation is important when the
exposure is performed in conjunction with an approach surgeon so as to establish an
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expectation of the necessary working area and depth. Sigmoid Sinus Exposure
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Unroofing the bone over the SS serves multiple purposes- it allows the surgeon to retract the sinus in order to expand the working area of TT and depress the posterior cranial fossa dura mater, therefore decreasing the depth of the surgical field3 (Figure 6). Its exposure might be required for the conversion of the retrolabyrinthine approach
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into a retrolabyrinthine-trans-sigmoid approach for treatment of vascular pathology in the vertebrobasilar circulation9,13. Posterior skeletonization of the sinus may also be conducted in order to reflect the sinus anteriorly as part of a retrolabyrinthine
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retrosigmoid approach14. The working area and visibility improves as the PSC and SS
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approach the same lateral plane on axial imaging. Preoperative evaluation of the laterality of the SS to the PSC may assist a surgeon in determining the need for skeletonizing and manipulation of the SS and avoiding possible vascular injuries. Sinus thrombosis may lead to intracranial hemorrhage, headache, visual field deficits, and increased intracranial pressure (ICP)15. Sinus thrombosis Sinus thrombosis may lead to morbidity even if the sinus is nondominant.16 In a study of 107 patients who underwent a suboccipital or translabyrinthine craniotomy, five
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ACCEPTED MANUSCRIPT patients developed pseudotumor cerebri as a result of dural sinus thrombosis16. Two patients had intraoperative iatrogenic injury to the sinus. They presented with symptomatic complaints at a median time of 17 days after surgery. Manipulation of the SS may lead to increased blood loss due to drilling injury to the SS itself or by
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avulsion of the mastoid emissary vein. Thrombosis of the SS is a well-recognized complication of surgery in the CPA. Moore et al.17 reported a case series of 43 patients who underwent resection of CPA tumors. Among those patients, 29
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underwent a translabyrinthine approach and five of those patients developed venous sinus thrombosis after resection of vestibular schwannomas.
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Risk factors for the development of venous sinus thrombosis as a result of intraoperative causes includes drilling injury to the SS, over manipulation of the sinus (retraction or depression in order to expand and decrease the depth of the operative field), dehydration or volume depletion as a result of intraoperative volume shifts,
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heat as a result of the surgical microscope and packing or compression of the sinus, which might be performed following iatrogenic injury or inadvertently during closure through the application of cement or substandard plating of the bony skull defect16,17.
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In this regard, the retrolabyrinthine and translabyrinthine approaches require greater
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exposure of the SS in comparison to the retrosigmoid approach17. Surgeons perform different degrees of bony unroofing of the sinus ranging from minimal removal of the sinodural angle to complete skeletonization extending into the posterior cranial fossa dura mater3.
CONCLUSIONS The retrolabyrinthine approach to the brain stem and cranial nerves is a workhorse and commonly used approach performed during a mastoidectomy. It is often performed as an initial approach before performing translabyrinthine, transotic,
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ACCEPTED MANUSCRIPT transcochlear or transpetrosal approaches. Skeletonization of the SS is frequently performed as part of the approach and serves to expand the working area of TT. A high riding JB has been defined and is identified on coronal sequences as reaching or surpassing the IAC. We describe a subset of challenging cadaveric sides with a lateral
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SS that can often cover and impede the surgeon from visualizing the dural space between the PSC and the SS. This should be identified preoperatively as this subset of patients may need an extension of the retrolabyrinthine approach in addition to a
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complete bony release of the sinodural angle and SS for its retraction. In addition, we describe a subset of cadaveric sides easily identified through imaging that may not
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need to undergo skeletonization of the SS in order to gain access to the CP angle.
REFERENCES
1. Hitselberger WE, Pulec JL. Trigeminal nerve (posterior root) retrolabyrintine
(5): 412-5.
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selective section-operative procedure for intractable pain. Arch Otolaryngol 1972; 96
2. Tubbs RS, Griessenauer C, Loukas M, Ansari SF, Fritsch MH, Cohen-Gadol AA.
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Trautmann's triangle anatomy with application to posterior transpetrosal and other
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related skull base procedures. Clin Anat. 2014 Oct; 27(7):994-8. 3. Russell SM, Roland JT Jr, Golfinos JG. Retrolabyrinthine craniectomy: the unsung hero of skull base surgery. Skull Base. 2004 Feb; 14(1):63-71. 4.Rinaldi V, Casale M, Bressi F, Potena M, Vesperini E, De Franco A, Silvestri S, Zini C, Salvinelli F. Facial nerve outcome after vestibular schwannoma surgery: our experience. J Neurol Surg B Skull Base. 2012 Feb; 73(1):21-7.
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ACCEPTED MANUSCRIPT 5. Bento RF, De Brito RV, Sanchez TG, Miniti A. The transmastoid retrolabyrinthine approach in vestibular schwannoma surgery. Otolaryngol Head Neck Surg. 2002 Nov; 127(5):437-41. 6. Sincoff EH, McMenomey SO, Delashaw JB Jr. Posterior transpetrosal approach:
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less is more. Neurosurgery. 2007 Feb; 60(2 Suppl 1):ONS53-8.
7. Chanda A, Nanda A. Partial labyrinthectomy petrous apicectomy approach to the petroclival region: an anatomic and technical study. Neurosurgery. 2002 Jul;
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51(1):147-59.
8. Cavalcanti DD, Preul MC, Kalani MY, Spetzler RF. Microsurgical anatomy of safe
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entry zones to the brainstem. J Neurosurg. 2016 May; 124(5):1359-76. 9. Day JD, Fukushima T, Giannotta SL. Cranial base approaches to posterior circulation aneurysms. J Neurosurg. 1997 Oct; 87(4):544-54.
10. Magliulo G. Modified retrolabyrinthine approach with partial labyrinthectomy:
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anatomic study. Otolaryngol Head Neck Surg. 2001 Mar; 124(3):287-91. 11. Vachata P, Petrovicky P, Sames M. An anatomical and radiological study of the high jugular bulb on high-resolution CT scans and alcohol-fixed skulls of adults. J
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Clin Neurosci. 2010 Apr; 17(4):473-8.
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12. De Melo JO, Klescoski J, Nunes CF, Cabral GA, Lapenta MA, Landeiro JA. Predicting the presigmoid retrolabyrinthine space using a sigmoid sinus tomography classification: A cadaveric study. Surg Neurol Int. 2014 Aug 30; 5:131. 13. Giannotta SL, Maceri DR. Retrolabyrinthine transsigmoid approach to basilar trunk and vertebrobasilar artery junction aneurysms. Technical note. J Neurosurg. 1988 Sep; 69(3):461-6.
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ACCEPTED MANUSCRIPT 14. Silverstein H, Nichols ML, Rosenberg S, Hoffer M, Norrell H. Combined retrolabyrinthine-retrosigmoid approach for improved exposure of the posterior fossa without cerebellar retraction. Skull Base Surg. 1995; 5(3):177-80. 15. Ohata K, Haque M, Morino M, Nagai K, Nishio A, Nishijima Y, Hakuba A.
approach. J Neurosurg. 1998 Oct; 89(4):575-84.
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Occlusion of the sigmoid sinus after surgery via the presigmoidal-transpetrosal
16. Keiper GL Jr, Sherman JD, Tomsick TA, Tew JM Jr. Dural sinus thrombosis and
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pseudotumor cerebri: unexpected complications of suboccipital craniotomy and translabyrinthine craniectomy. J Neurosurg. 1999 Aug; 91(2):192-7.
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17. Justin Moore, Piers Thomas, Vincent Cousins, Jeffrey V. Rosenfeld. Diagnosis and Management of Dural Sinus Thrombosis following Resection of Cerebellopontine
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Angle Tumors. J Neurol Surg B Skull Base. 2014 Dec; 75(6): 402–408.
Table 1 Legend. Pre and post mastoidectomy measurements in millimeters. EAC = external acoustic meatus; LSC = lateral semicircular canal; Perpend = Pre
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mastoidectomy measured distances by placing a laterally drawn line on the SS and
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measuring the shortest perpendicular distance to the PSC and LSC on axial CT imaging; PSC = posterior semicircular canal; SS = sigmoid sinus.
Figure Legends:
Figure 1. Left internal view of the temporal bone. The triangle represents the approximate area of Trautmann's triangle. The arrow points at the posterior semicircular canal (PSC). The horizontal semicircular canal is adjacent to the PSC.
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ACCEPTED MANUSCRIPT Figure 2. Lateral location of the SS. A line has been drawn at the angle of the LSCC and PSC. The cortical bone covering the SS is located lateral to the line and the working space appears limited. SS= Sigmoid Sinus. Arrow= Posterior Semicircular Canal.
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Figure 3.A. Lateral location of the Sigmoid Sinus. Post mastoidectomy images from two sides with a lateral SS in relation to the PSC/LSC line. The laterality and superficiality of the SS causes the sinus to appear to “override” TT. MFD= Middle
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fossa dura. SS= Sigmoid Sinus. SSC= Semicircular canals.
Figure 3.B. Lateral location of the Sigmoid Sinus. Post mastoidectomy images from
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two sides with a lateral SS in relation to the PSC/LSC line. The laterality and superficiality of the SS causes the sinus to appear to “override” TT. MFD= Middle fossa dura. SS= Sigmoid Sinus. SSC= Semicircular canals.
Figure 3.C. Lateral location of the Sigmoid Sinus. Skeletonizing and retraction of the
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SS was required in order to visualize the retrolabyrinthine space- the emissary vein can be visualized. SS= Sigmoid sinus. Arrow= Mastoid emissary vein. Figure 3.D. Lateral location of the Sigmoid Sinus. Skeletonizing and retraction of the
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SS with drilling of the PSC enlarged the area of TT and expanded the operative view.
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MFD= Middle fossa dura, SS= Sigmoid sinus, HSC= Horizontal semicircular canal, CN VII-VIII= Cranial nerve 7 and 8 complex. Figure 3.E. Lateral location of the sigmoid sinus. Skeletonizing and retraction of the SS of Figure 3.B. was needed in addition drilling of the PSC in order to visualize the retrolabyrinthine space. MFD= Middle fossa dura, SS= Sigmoid sinus, HSC= Horizontal semicircular canal, JB= Jugular Bulb. Figure 4. Medial location of the SS. A line has been drawn at the angle of the LSCC and PSC. The cortical bone covering the SS is located medial to the line and provides
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sinus, SSC=Semicircular canals, JB= Jugular Bulb.
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a medial SS in relation to the PSC/LSC line. MFD= Middle fossa dura, SS= Sigmoid
Figure 5.B. Medial location of the SS. Skeletonizing and retraction of the SS did not markedly improve visibility of the retrolabyrinthine approach. MFD= Middle fossa
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dura, SS= Sigmoid sinus, SSC=Semicircular canals, JB= Jugular Bulb.
Figure 6. Right external view of Trautmanns triangle. Complete skeletonization of the
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semicircular canals and the facial nerve. FN= facial nerve, SS= Sigmoid sinus,
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SSC=Semicircular canals, JB= Jugular Bulb.
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Table 1. Pre and post mastoidectomy measurements in millimeters Perpend
Perpend
EAC
SS (M vs L)
to SS
to SS
PSC to SS
LSC to SS
to SS
1
Lateral SS
9.6
13.6
4.4
8.8
15.3
2
Medial SS
16.3
18.5
14.3
17
19
3
Lateral SS
9.6
12.8
9
12.7
17.8
4
Lateral SS
19.7
23.1
13.4
16.9
22
5
Lateral SS
15.9
17.9
6.1
10.1
16.7
6
Lateral SS
13.7
15.1
4.7
8.1
13.4
7
Lateral SS
15.8
17.8
12.6
15.7
17.2
8
Lateral SS
12.0
14.0
8
12.1
16.2
9
Medial SS
14.0
18.0
9
13.8
16.4
10
Lateral SS
13.0
15.0
9
15.7
17.3
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LSC
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sides
to PSC
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LSC/PSC
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Cadaver
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EAC = external acoustic meatus; LSC = lateral semicircular canal; Perpend = Pre mastoidectomy measured distances by placing a laterally drawn line on the SS and
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measuring the shortest perpendicular distance to the PSC and LSC on axial CT imaging; PSC = posterior semicircular canal; SS = sigmoid sinus.
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1. In temporal bones in which the sigmoid sinus is medial to the posterior semicircular canal or only has minimal lateral displacement, skeletonizing the sigmoid sinus does not significantly improve visibility of the retrolabyrinthine space. 2. Working area and visibility improve as the posterior semicircular canal and the sigmoid sinus approach the same plane on axial imaging. 3. A subset of temporal bones that can be easily identified through imaging may not need to undergo skeletonization of the sigmoid sinus in order to gain access to the cerebellopontine angle.
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Abbreviations: CT Computed Tomography PSC Posterior Semicircular Canal
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LSC Lateral Semicircular Canal SS Sigmoid Sinus TT Trautmann’s triangle JB Jugular Bulb
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SPS Superior Petrosal Sinus EAC External Acoustic Meatus
CPA Cerebellopontine Angle
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ICP Intracranial Pressure
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IAC Internal Acoustic Canal
S1878-8750(17)30669-1
DOI:
10.1016/j.wneu.2017.04.161
Reference:
WNEU 5680
To appear in:
World Neurosurgery
Received Date: 18 March 2017 Revised Date:
25 April 2017
Accepted Date: 26 April 2017
Please cite this article as: Alonso F, Dekker SE, Wright J, Wright C, Alonso A, Carmody M, Tubbs RS, Bambakidis NC, The Retrolabyrinthine Presigmoid approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann’s Triangle, World Neurosurgery (2017), doi: 10.1016/ j.wneu.2017.04.161. 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.
ACCEPTED MANUSCRIPT
The Retrolabyrinthine Presigmoid approach to the Anterior Cerebellopontine Region: Expanding the Limits of Trautmann’s Triangle
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Fernando Alonso MD1,2, Simone E. Dekker MD,PhD1, James Wright MD1, Christina Wright MD1, Andrea Alonso BA1, Margaret Carmody MD1, R. Shane Tubbs PhD2
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and Nicholas C. Bambakidis MD1
Department of Neurological Surgery, University Hospitals Case Medical Center,
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Cleveland, Ohio
Seattle Science Foundation, Seattle, WA
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Disclosures: The authors have no disclosures to report
Corresponding author:
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Fernando Alonso MD
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Department of Neurological Surgery, University Hospitals Case Medical Center, Cleveland, Ohio
Email: [email protected] Tel: 918-694-8208
Keywords: retrolabyrinthine; acoustic; semicircular canal, sigmoid sinus, sino-dural angle
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ABSTRACT The anatomical area exposed through the exposure of Trautmann’s triangle may not be sufficient. We studied the additional exposure provided by skeletonizing the
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sigmoid sinus. Human cadaver heads were subjected to a thin temporal bone CT scan for a total of 10 sides. The estimated surgical working angle was calculated based on the relationship of the sigmoid sinus to the posterior semicircular canal, superior
SC
petrosal sinus and jugular bulb on imaging. The heads were then subjected to a
mastoidectomy and remeasured with and without sigmoid sinus skeletonization.
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The working angle calculated on CT was 56 ± 11.3 degrees. Skeletonization of the sigmoid sinus increased the distance between the PSC to SS by 5 mm (p = 0.01), and LSC to SS by 4 mm (p = 0.01). Skeletonization and retraction of the SS significantly increased the distance between the PSC and LSC to the SS. On post mastoidectomy
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images, skeletonizing the sigmoid sinus helped improve anterior visibility on the majority of our samples that had a SS that was lateral to the PSC on axial imaging. In samples in which the SS is medial to the PSC or only has minimal lateral
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displacement, skeletonizing the SS did not markedly improve visibility of the
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retrolabyrinthine space. Working area and visibility improve as the PSC and SS approach the same plane on axial imaging. Preoperative evaluation of the laterality of the SS to the PSC may assist a surgeon in determining the need for skeletonizing the SS and avoiding possible vascular injuries.
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INTRODUCTION The presigmoid retrolabyrinthine approach has several advantages, such as lower morbidity than a transbyrinthine approach due to hearing preservation and a low risk
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of facial nerve injury3,5,9. However, the anatomical area uncovered through the exposure of Trautmann’s triangle (TT) may not provide a sufficient working area. Attention has been placed on the relationship of the superior jugular bulb (JB) to the
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internal auditory meatus but there is little known on the need to skeletonize the sigmoid sinus (SS) based on its relationship to the posterior semicircular canal (PSC).
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In this study, we hypothesized that an expansion of TT provides a larger exposure of lesions located at cranial nerve entry zones and the lateral brain stem. The aim of this study was to measure the additional exposure and visibility provided by skeletonizing the SS, drilling of the PSC and to determine if there are a subset of patients that would
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not benefit from exposure of the SS based on the depth of the operative field provided
METHODS
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by the relationship between the PSC and SS.
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Five adult human cadaver heads were subjected to thin cut temporal bone CT scan for a total of 10 sides. The estimated working angle was calculated based on the relationship of the SS to the PSC, superior petrosal sinus (SPS) and JB on imaging. The heads were then subjected to a mastoidectomy to calculate the following distances in the presigmoid retrolabyrintine space: external acoustic meatus (EAC) to SS, PSC to JB, PSC to SS, and lateral semicircular canal (LSC) to SS after the PSC was drilled. The SS was then skeletonized with the use of a 5mm soft touch burr and gentle retraction was applied. Measurements to the SS were then repeated. Samples
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ACCEPTED MANUSCRIPT were photographed. Measurements were also verified manually to insure correctness. Data were analyzed using IBM SPSS Statistics 23 (IBM, New York, USA). Variables were summarized as mean ± SD and the means were compared using a paired sample
<0.05 was considered to be statistically significant. RESULTS
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t test. Correlation coefficients were calculated using Pearson's correlation. A P-value
Table 1 shows the imaging and dissection measurement results. Two medial and eight
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lateral sides were included in the analysis. The distance between the EAC and SS was measured at dissection with microcalipers and was significantly correlated to the
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measured distances on imaging by placing a laterally drawn line on the SS and measuring the shortest perpendicular distance to the PSC (r = 0.82; p = 0.02) and LSC (r = 0.859; p = 0.01) on axial CT imaging. Skeletonization of the SS significantly increased the distance between the PSC to SS by 4.9 mm (13.96 ± 3.13 mm vs. 9.05 ±
= 0.01).
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3.49 mm; p < 0.001), and the LSC to SS by 4.2 mm (16.97 ± 3.50 vs. 12.76 ± 3.83; p
After mastoidectomy, skeletonizing the SS helped improved anterior visibility on
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eight of our samples that had a SS that was lateral to the PSC on axial imaging
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(Figure 2). In samples in which the SS was medial to the PSC or only has minimal lateral displacement, skeletonizing the SS did not markedly improve visibility of the retrolabyrinthine space (Figure 4). The shortest distance between the PSC to SS and LSC to SS measured after mastoidectomy did not correlate with the perpendicular distances measured preoperatively (r = 0.63; p = 0.052, and r = 0.67; p = 0.99, respectively). Manual measurements were well correlated to imaging measurements with no statistical differences.
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ACCEPTED MANUSCRIPT DISCUSSION Background/History The retrolabyrinthine craniotomy is a workhorse approach to the cerebellopontine angle. The retrolabyrinthine approach was first described by Hitselberger and Pulec in
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1971 for a vestibular neurectomy1. It may be used for resection of vestibulocochlear and trigeminal nerves pathology, intractable Meniere’s disease, aneurysms arising
from the posterior circulation and other pathologies of the lateral brain stem2,3,4. This
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approach can be converted to a translabyrinthine approach if a more anterior exposure is required to the fundus of the internal acoustic canal (IAC) in vestibular
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schwannoma surgery5. A transcrusal exposure (partial labyrinthectomy) or petrous apicectomy may also be performed for increased visibility of the clivus6,7. TT is limited by the sinodural angle and SPS superiorly, the JB inferiorly and the PSC anteriorly (Figure 1)2,6,8. Day et al. have described the ideal composition of a cranial
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base approach- drilling or resection of bone in order to minimize retraction of the brain, a short conduit to the pathological entity, maximizes the extradural window, and allows for closure of the dural defects9.
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Anatomical findings
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We found that the shortest distance between the PSC to SS and LSC to SS measured after mastoidectomy did not correlate with the perpendicular distances measured preoperatively (r = 0.63; p = 0.052, and r = 0.67; p = 0.99, respectively). This is likely as a result of the diagonal surface of TT. The surgical depth is most shallow at the level of the SS and increases in depth in its anterior margin adjacent to the PSC. As expected, skeletonization of the SS and retraction significantly increased the distance between the PSC and SS by 4.9 mm (13.96 ± 3.13 mm vs. 9.05 ± 3.49 mm; p < 0.001), and LSC to SS by 4.2 mm (16.97 ± 3.50 vs. 12.76 ± 3.83; p = 0.01).
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ACCEPTED MANUSCRIPT Intraoperatively, this increase in distance provided a wider operative corridor for samples with a SS that was located lateral to the LSC/PSC line (Figures 1 and 2). The increase in visibility seen with our two medial samples was unremarkable (Figures 3 and 4). As expected from prior studies, drilling of the PSC in a modified partial
IAC6,10. Classification of Trautmann’s Triangle
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labyrinthectomy approach, provided an improved exposure to the fundus of the
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Tubbs et al. classified TT into three types based on area: type 1 with an area of less
than 75 mm2 (37.5%), type 2 75-149 mm2 (35%) and type 3 with an area of 150 mm2
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(27.5%) or greater2. Vachatta et al. studied the JB and its relationship to the IAC in two hundred temporal bones11. The average distance between the IAC and the JB was 7.5 +/- 2.3mm. A high JB, defined as a JB at the level of the IAC or higher, was found in 16.5% of patients. A cadaveric study found that a reference line drawn from the
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lateral semicircular canal to the posterior semicircular canal could be used to predict the area of TT12. If the SS was located lateral to the reference line, TT was found to have a smaller area and the SS was found to be superimposed over TT, severely
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limiting the operative space and possibly increasing the risk of injury to the facial
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nerve. In the medial group, the operative field was wider and less deep, making the approach less challenging. Based on these findings one can conclude that the ideal patient who would benefit from a retrolabyrinthine approach would have the following characteristics: pathology that is superficial and not centered on the fundus of the IAC, low location of the JB (below the IAC) and a medial location of the SS. Although not common, through this study we have found that this subset of patients, identified through preoperative imaging may undergo sufficient exposure of the CPA without the need for skeletonization and manipulation of the SS. On the contrary, the
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ACCEPTED MANUSCRIPT most challenging cases have a laterally displaced SS, which increased the surgical depth and reduces the area of TT and a JB that is at the level of the IAC or higher. In this latter subset of patients, additional techniques might need to be performed with more attention directed to skeletonization of the sinodural angle and SS in order to
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“expand” TT or conversion of the retrolabyrinthine craniotomy into a transcrusal or
translabyrinthine approach. Pre-operative imaging evaluation is important when the
exposure is performed in conjunction with an approach surgeon so as to establish an
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expectation of the necessary working area and depth. Sigmoid Sinus Exposure
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Unroofing the bone over the SS serves multiple purposes- it allows the surgeon to retract the sinus in order to expand the working area of TT and depress the posterior cranial fossa dura mater, therefore decreasing the depth of the surgical field3 (Figure 6). Its exposure might be required for the conversion of the retrolabyrinthine approach
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into a retrolabyrinthine-trans-sigmoid approach for treatment of vascular pathology in the vertebrobasilar circulation9,13. Posterior skeletonization of the sinus may also be conducted in order to reflect the sinus anteriorly as part of a retrolabyrinthine
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retrosigmoid approach14. The working area and visibility improves as the PSC and SS
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approach the same lateral plane on axial imaging. Preoperative evaluation of the laterality of the SS to the PSC may assist a surgeon in determining the need for skeletonizing and manipulation of the SS and avoiding possible vascular injuries. Sinus thrombosis may lead to intracranial hemorrhage, headache, visual field deficits, and increased intracranial pressure (ICP)15. Sinus thrombosis Sinus thrombosis may lead to morbidity even if the sinus is nondominant.16 In a study of 107 patients who underwent a suboccipital or translabyrinthine craniotomy, five
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ACCEPTED MANUSCRIPT patients developed pseudotumor cerebri as a result of dural sinus thrombosis16. Two patients had intraoperative iatrogenic injury to the sinus. They presented with symptomatic complaints at a median time of 17 days after surgery. Manipulation of the SS may lead to increased blood loss due to drilling injury to the SS itself or by
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avulsion of the mastoid emissary vein. Thrombosis of the SS is a well-recognized complication of surgery in the CPA. Moore et al.17 reported a case series of 43 patients who underwent resection of CPA tumors. Among those patients, 29
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underwent a translabyrinthine approach and five of those patients developed venous sinus thrombosis after resection of vestibular schwannomas.
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Risk factors for the development of venous sinus thrombosis as a result of intraoperative causes includes drilling injury to the SS, over manipulation of the sinus (retraction or depression in order to expand and decrease the depth of the operative field), dehydration or volume depletion as a result of intraoperative volume shifts,
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heat as a result of the surgical microscope and packing or compression of the sinus, which might be performed following iatrogenic injury or inadvertently during closure through the application of cement or substandard plating of the bony skull defect16,17.
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In this regard, the retrolabyrinthine and translabyrinthine approaches require greater
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exposure of the SS in comparison to the retrosigmoid approach17. Surgeons perform different degrees of bony unroofing of the sinus ranging from minimal removal of the sinodural angle to complete skeletonization extending into the posterior cranial fossa dura mater3.
CONCLUSIONS The retrolabyrinthine approach to the brain stem and cranial nerves is a workhorse and commonly used approach performed during a mastoidectomy. It is often performed as an initial approach before performing translabyrinthine, transotic,
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ACCEPTED MANUSCRIPT transcochlear or transpetrosal approaches. Skeletonization of the SS is frequently performed as part of the approach and serves to expand the working area of TT. A high riding JB has been defined and is identified on coronal sequences as reaching or surpassing the IAC. We describe a subset of challenging cadaveric sides with a lateral
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SS that can often cover and impede the surgeon from visualizing the dural space between the PSC and the SS. This should be identified preoperatively as this subset of patients may need an extension of the retrolabyrinthine approach in addition to a
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complete bony release of the sinodural angle and SS for its retraction. In addition, we describe a subset of cadaveric sides easily identified through imaging that may not
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need to undergo skeletonization of the SS in order to gain access to the CP angle.
REFERENCES
1. Hitselberger WE, Pulec JL. Trigeminal nerve (posterior root) retrolabyrintine
(5): 412-5.
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selective section-operative procedure for intractable pain. Arch Otolaryngol 1972; 96
2. Tubbs RS, Griessenauer C, Loukas M, Ansari SF, Fritsch MH, Cohen-Gadol AA.
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Trautmann's triangle anatomy with application to posterior transpetrosal and other
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related skull base procedures. Clin Anat. 2014 Oct; 27(7):994-8. 3. Russell SM, Roland JT Jr, Golfinos JG. Retrolabyrinthine craniectomy: the unsung hero of skull base surgery. Skull Base. 2004 Feb; 14(1):63-71. 4.Rinaldi V, Casale M, Bressi F, Potena M, Vesperini E, De Franco A, Silvestri S, Zini C, Salvinelli F. Facial nerve outcome after vestibular schwannoma surgery: our experience. J Neurol Surg B Skull Base. 2012 Feb; 73(1):21-7.
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ACCEPTED MANUSCRIPT 5. Bento RF, De Brito RV, Sanchez TG, Miniti A. The transmastoid retrolabyrinthine approach in vestibular schwannoma surgery. Otolaryngol Head Neck Surg. 2002 Nov; 127(5):437-41. 6. Sincoff EH, McMenomey SO, Delashaw JB Jr. Posterior transpetrosal approach:
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less is more. Neurosurgery. 2007 Feb; 60(2 Suppl 1):ONS53-8.
7. Chanda A, Nanda A. Partial labyrinthectomy petrous apicectomy approach to the petroclival region: an anatomic and technical study. Neurosurgery. 2002 Jul;
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51(1):147-59.
8. Cavalcanti DD, Preul MC, Kalani MY, Spetzler RF. Microsurgical anatomy of safe
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entry zones to the brainstem. J Neurosurg. 2016 May; 124(5):1359-76. 9. Day JD, Fukushima T, Giannotta SL. Cranial base approaches to posterior circulation aneurysms. J Neurosurg. 1997 Oct; 87(4):544-54.
10. Magliulo G. Modified retrolabyrinthine approach with partial labyrinthectomy:
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anatomic study. Otolaryngol Head Neck Surg. 2001 Mar; 124(3):287-91. 11. Vachata P, Petrovicky P, Sames M. An anatomical and radiological study of the high jugular bulb on high-resolution CT scans and alcohol-fixed skulls of adults. J
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Clin Neurosci. 2010 Apr; 17(4):473-8.
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12. De Melo JO, Klescoski J, Nunes CF, Cabral GA, Lapenta MA, Landeiro JA. Predicting the presigmoid retrolabyrinthine space using a sigmoid sinus tomography classification: A cadaveric study. Surg Neurol Int. 2014 Aug 30; 5:131. 13. Giannotta SL, Maceri DR. Retrolabyrinthine transsigmoid approach to basilar trunk and vertebrobasilar artery junction aneurysms. Technical note. J Neurosurg. 1988 Sep; 69(3):461-6.
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ACCEPTED MANUSCRIPT 14. Silverstein H, Nichols ML, Rosenberg S, Hoffer M, Norrell H. Combined retrolabyrinthine-retrosigmoid approach for improved exposure of the posterior fossa without cerebellar retraction. Skull Base Surg. 1995; 5(3):177-80. 15. Ohata K, Haque M, Morino M, Nagai K, Nishio A, Nishijima Y, Hakuba A.
approach. J Neurosurg. 1998 Oct; 89(4):575-84.
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Occlusion of the sigmoid sinus after surgery via the presigmoidal-transpetrosal
16. Keiper GL Jr, Sherman JD, Tomsick TA, Tew JM Jr. Dural sinus thrombosis and
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pseudotumor cerebri: unexpected complications of suboccipital craniotomy and translabyrinthine craniectomy. J Neurosurg. 1999 Aug; 91(2):192-7.
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17. Justin Moore, Piers Thomas, Vincent Cousins, Jeffrey V. Rosenfeld. Diagnosis and Management of Dural Sinus Thrombosis following Resection of Cerebellopontine
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Angle Tumors. J Neurol Surg B Skull Base. 2014 Dec; 75(6): 402–408.
Table 1 Legend. Pre and post mastoidectomy measurements in millimeters. EAC = external acoustic meatus; LSC = lateral semicircular canal; Perpend = Pre
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mastoidectomy measured distances by placing a laterally drawn line on the SS and
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measuring the shortest perpendicular distance to the PSC and LSC on axial CT imaging; PSC = posterior semicircular canal; SS = sigmoid sinus.
Figure Legends:
Figure 1. Left internal view of the temporal bone. The triangle represents the approximate area of Trautmann's triangle. The arrow points at the posterior semicircular canal (PSC). The horizontal semicircular canal is adjacent to the PSC.
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Figure 3.A. Lateral location of the Sigmoid Sinus. Post mastoidectomy images from two sides with a lateral SS in relation to the PSC/LSC line. The laterality and superficiality of the SS causes the sinus to appear to “override” TT. MFD= Middle
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fossa dura. SS= Sigmoid Sinus. SSC= Semicircular canals.
Figure 3.B. Lateral location of the Sigmoid Sinus. Post mastoidectomy images from
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two sides with a lateral SS in relation to the PSC/LSC line. The laterality and superficiality of the SS causes the sinus to appear to “override” TT. MFD= Middle fossa dura. SS= Sigmoid Sinus. SSC= Semicircular canals.
Figure 3.C. Lateral location of the Sigmoid Sinus. Skeletonizing and retraction of the
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SS was required in order to visualize the retrolabyrinthine space- the emissary vein can be visualized. SS= Sigmoid sinus. Arrow= Mastoid emissary vein. Figure 3.D. Lateral location of the Sigmoid Sinus. Skeletonizing and retraction of the
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SS with drilling of the PSC enlarged the area of TT and expanded the operative view.
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MFD= Middle fossa dura, SS= Sigmoid sinus, HSC= Horizontal semicircular canal, CN VII-VIII= Cranial nerve 7 and 8 complex. Figure 3.E. Lateral location of the sigmoid sinus. Skeletonizing and retraction of the SS of Figure 3.B. was needed in addition drilling of the PSC in order to visualize the retrolabyrinthine space. MFD= Middle fossa dura, SS= Sigmoid sinus, HSC= Horizontal semicircular canal, JB= Jugular Bulb. Figure 4. Medial location of the SS. A line has been drawn at the angle of the LSCC and PSC. The cortical bone covering the SS is located medial to the line and provides
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sinus, SSC=Semicircular canals, JB= Jugular Bulb.
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a medial SS in relation to the PSC/LSC line. MFD= Middle fossa dura, SS= Sigmoid
Figure 5.B. Medial location of the SS. Skeletonizing and retraction of the SS did not markedly improve visibility of the retrolabyrinthine approach. MFD= Middle fossa
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dura, SS= Sigmoid sinus, SSC=Semicircular canals, JB= Jugular Bulb.
Figure 6. Right external view of Trautmanns triangle. Complete skeletonization of the
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semicircular canals and the facial nerve. FN= facial nerve, SS= Sigmoid sinus,
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Table 1. Pre and post mastoidectomy measurements in millimeters Perpend
Perpend
EAC
SS (M vs L)
to SS
to SS
PSC to SS
LSC to SS
to SS
1
Lateral SS
9.6
13.6
4.4
8.8
15.3
2
Medial SS
16.3
18.5
14.3
17
19
3
Lateral SS
9.6
12.8
9
12.7
17.8
4
Lateral SS
19.7
23.1
13.4
16.9
22
5
Lateral SS
15.9
17.9
6.1
10.1
16.7
6
Lateral SS
13.7
15.1
4.7
8.1
13.4
7
Lateral SS
15.8
17.8
12.6
15.7
17.2
8
Lateral SS
12.0
14.0
8
12.1
16.2
9
Medial SS
14.0
18.0
9
13.8
16.4
10
Lateral SS
13.0
15.0
9
15.7
17.3
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LSC
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to PSC
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EAC = external acoustic meatus; LSC = lateral semicircular canal; Perpend = Pre mastoidectomy measured distances by placing a laterally drawn line on the SS and
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measuring the shortest perpendicular distance to the PSC and LSC on axial CT imaging; PSC = posterior semicircular canal; SS = sigmoid sinus.
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Highlights:
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1. In temporal bones in which the sigmoid sinus is medial to the posterior semicircular canal or only has minimal lateral displacement, skeletonizing the sigmoid sinus does not significantly improve visibility of the retrolabyrinthine space. 2. Working area and visibility improve as the posterior semicircular canal and the sigmoid sinus approach the same plane on axial imaging. 3. A subset of temporal bones that can be easily identified through imaging may not need to undergo skeletonization of the sigmoid sinus in order to gain access to the cerebellopontine angle.
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Abbreviations: CT Computed Tomography PSC Posterior Semicircular Canal
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LSC Lateral Semicircular Canal SS Sigmoid Sinus TT Trautmann’s triangle JB Jugular Bulb
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SPS Superior Petrosal Sinus EAC External Acoustic Meatus
CPA Cerebellopontine Angle
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ICP Intracranial Pressure
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IAC Internal Acoustic Canal