Accepted Manuscript Exposure of Wide Cerebellomedullary Cisterns for Vascular Lesion Surgeries in Cerebellomedullary Cisterns: Opening of Unilateral Cerebellomedullary Fissures (unilateral trans-CMF approach) Combined with Lateral Foramen Magnum Approach Toshio Matsushima, M.D. Masatou Kawashima, M.D. Kohei Inoue, M.D. Ken Matsushima, M.D. Koichi Miki, M.D. PII:

S1878-8750(14)00447-1

DOI:

10.1016/j.wneu.2014.04.064

Reference:

WNEU 2343

To appear in:

World Neurosurgery

Received Date: 7 November 2013 Revised Date:

27 February 2014

Accepted Date: 23 April 2014

Please cite this article as: Matsushima T, Kawashima M, Inoue K, Matsushima K, Miki K, Exposure of Wide Cerebellomedullary Cisterns for Vascular Lesion Surgeries in Cerebellomedullary Cisterns: Opening of Unilateral Cerebellomedullary Fissures (unilateral trans-CMF approach) Combined with Lateral Foramen Magnum Approach, World Neurosurgery (2014), doi: 10.1016/j.wneu.2014.04.064. 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 Exposure of Wide Cerebellomedullary Cisterns for Vascular Lesion Surgeries in Cerebellomedullary Cisterns: Opening of Unilateral Cerebellomedullary Fissures (unilateral transCMF approach) Combined with Lateral Foramen Magnum Approach Toshio Matsushima, M.D.1; Masatou Kawashima, M.D.1; Kohei Inoue, M.D.1; Ken Matsushima, M.D.2; and Koichi Miki, M.D.3

Department of Neurosurgery, Faculty of Medicine, Saga University, Saga, Japan

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Department of Surgical Neurology, University of Florida, Gainesville, Florida, U.S.A.

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Department of Neurosurgery, Faculty of Medicine, Fukuoka University, Fukuoka, Japan

Correspondence and reprint requests to: Masatou Kawashima, M.D., Ph.D., Department of Neurosurgery, Faculty of Medicine, Saga University, 5-1-1 Nabeshima, Saga-shi, Saga 849-8501, Japan

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E-mail: [email protected] Tel: 81-952-34-2346; Fax: 81-952-34-2066

ABSTRACT

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BACKGROUND: Obtaining a wide surgical field is challenging in the cerebellomedullary cistern (CMC), and thus, the lateral bony wall is usually removed through lateral foramen magnum approaches. However, few studies reported methods of efficient and safe retraction of the cerebellar hemisphere, which is a medial obstacle.

OBJECTIVE: We aimed to clarify microsurgical anatomical features of the cerebellomedullary fissure (CMF), the natural cleavage plane between the cerebellum and the medulla, and its relationship to CMC. Moreover, this study describes a surgical technique that uses the unilateral trans-CMF approach for CMC surgeries.

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METHODS: In the anatomical study, 2 formalin-fixed cadaver heads were used. In the clinical study, 3 patients with vertebral artery–posterior inferior cerebellar artery aneurysms and 3 with glossopharyngeal neuralgia were surgically treated through the unilateral trans-CMF approach combined with the transcondylar fossa approach, which is a lateral foramen magnum approach. RESULTS: CMC was present at the lateral end of CMF. CMF was closed by arachnoidal adhesion, and the cerebellar hemisphere was superiorly attached to the cerebellar peduncle. After the unilateral CMF

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was completely opened, the cerebellar hemisphere was easily retracted rostrodorsally. Clinically, almost

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ACCEPTED MANUSCRIPT completely opening the unilateral CMF markedly enabled the retraction of the biventral lobule to safely obtain a wide surgical field for vascular CMC lesions. Here we present 2 representative cases. CONCLUSION: Combined unilateral trans-CMF/lateral foramen magnum approaches provided a wide and close surgical field in CMC, allowing easy and safe CMC surgery.

KEYWORDS: Cerebellomedullary cistern, Transcerebellomedullary fissure approach, Subtonsillar approach, Telovelar approach, Vertebral artery aneurysm, Glossopharyngeal neuralgia

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RUNNING TITLE: Unilateral Trans-CMF Approach

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ACCEPTED MANUSCRIPT INTRODUCTION It is difficult to obtain a wide surgical field in the cerebellomedullary cistern (CMC) because of the very narrow space and several important structures such as lower cranial nerves (CNs). Obstacles in the approach to CMC and/or anterolateral surface of the brain stem are the jugular tubercle laterally and the biventral lobule medially. From the lateral side, the lateral bony wall of the foramen magnum has been removed through the lateral foramen magnum approaches to obtain a wide operative field.2, 8, 30, 32, 36 In addition, we have proposed the transcondylar fossa (supracondylar transjugular tubercle) approach to emphasize the importance of extradural removal of the jugular tubercle.17, 21, 24, 25 On the other hand, from

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the medial side, a few papers, including our own, have reported that the lateral cerebellomedullary fissure (CMF) opening has been primarily used for removal of tumors around the lateral recess and/or foramen of Luschka.11, 20, 39

In tumor surgeries, we can often obtain a sufficient surgical field after tumor removal. On the other

hand, in vascular diseases, it is difficult to obtain a wide surgical field in CMC. Recently, we have used almost the entire unilateral CMF opening, combined with the transcondylar fossa approach, to obtain a

wide surgical field for vascular lesions in CMC.9, 13 However, efficient procedures and safe maneuvers of

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this combined approach on the basis of anatomical characteristics of CMF have not been studied in detail. We conducted an anatomical study of the approach and surgically treated patients with vertebral artery–

posterior inferior cerebellar artery (VA–PICA) aneurysms and glossopharyngeal neuralgia (GPN) through

discuss variations of the trans-CMF approach.

MATERIALS AND METHODS

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this combined approach. In this article, we introduce this approach, describe 2 representative cases and

Two formalin-fixed cadaver heads provided materials for microsurgical anatomical studies of the lateral foramen magnum and CMF as well as the combined approach. Arteries and veins were perfused with red- and blue-colored latex, respectively, to facilitate dissection. Examined structures included neural structures of CMC and CMF and vessels in CMC and CMF. Both basic anatomy and the trans-

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CMF approach were investigated to determine how to safely obtain a wide surgical field in CMC. On the basis of anatomical studies, 3 VA–PICA aneurysm cases (2 unruptured and 1 ruptured aneurysm) and 3 cases of GPN due to vascular compression of PICA were surgically treated via through the combined approach.

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RESULTS

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ACCEPTED MANUSCRIPT I) Results of the Anatomical Study

CMC was surrounded by the jugular tubercle laterally, the medulla oblongata medially, and the flocculus and lateral recess anteriorly (Figures. 1 A–C); they were covered by the biventral lobule and a lateral part of the tonsil. Lower CNs and the 12th CN transversely crossed VA. The lateral recess and choroid plexus were situated just on nerve rootlets of the 9th and 10th CNs. The lateral recess was formed by the inferior medullary velum, tela choroidea, and rhomboid lip, which were neural tissues extending from the floor of the 4th ventricle (Figures. 1 C, D).27 The large rhomboid lip was adhered to lower CNs.5, This cistern was continuous to the premedullary cistern anteromedially and the cisterna magnum

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posteromedially.

CMF was a cleavage plane between the cerebellum and the medulla oblongata and was usually closed by arachnoid adhesion. The roof of CMF, the cerebellum, comprised the tonsil and biventral lobule, and

its floor was the inferior half of the 4th ventricular roof (the inferior medullary velum and tela choroidea) and the medulla oblongata (Figures. 1 B, C).18, 20, 27 The inferior medullary velum and tela choroidea

extended laterally from the middle portion of the rhomboid ventricular roof to form the roof of the lateral

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recess. The lateral recess, whose roof was the tela choroidea extending from the 4th ventricular roof, was a part of the CMF floor. The tonsil was superolaterally attached to the cerebellum by the tonsilar peduncle. Vessels such as PICA and vein of the CMF, coursed in the fissure, and subsequently, PICA led to choroidal arteries to the tela choroidea, whereas perforating arteries led to the medulla oblongata.

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CMF could be divided into following 3 spaces: (1) supratonsillar space between the tonsil and the inferior medullary velum; (2) uvulotonsillar space between the tonsil and the uvula; and (3) medullotonsillar space between the cerebellar hemisphere (tonsil and biventral lobule) and the medulla oblongata and tela choroidea. The medullotonsillar space was further subdivided into the medial part, surrounded by the tonsil, tela choroidea, and medulla oblongata, and the lateral part surrounded by the biventral lobule and lateral recess. The lateral part of the medullotonsillar space was superiorly blocked by the flocculus and middle cerebellar peduncle. CMF and CMC were continuous with each other with an obscure boundary, and both gradually changed from one to the other (Figures. 1 C, D).

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The procedure of opening almost the entire unilateral CMF enabled easy and safe retraction of the unilateral cerebellar hemisphere. The investigated unilateral trans-CMF approach combined with the lateral foramen magnum approach included following procedures: (1) The foramen magnum was largely opened to expose the lower margin of the unilateral cerebellar hemisphere (Figure 2 A); (2) The transcondylar fossa approach was performed to resect the lateral foramen magnum; (3) Intracranially, the unilateral CMF was first dissected, and both medullotonsillar and uvulotonsillar spaces were dissected

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and opened to some extent (Figure. 2 B); (4) The taenia and lateral recess were incised from the foramen

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of Magendie to the foramen of Luschka so that the unilateral cerebellar hemisphere (tonsil and biventral

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ACCEPTED MANUSCRIPT lobule) could be easily retracted superiorly (Figure. 2 C); (5) The choroid plexus, rhomboid lip, and/or arachnoid membrane were separated from lower CNs; and (6) After these procedures, the tonsil and biventral lobule were superiorly retracted. The unilateral trans-CMF approach combined with the transcondylar fossa approach markedly exposed the entire CMC, including the posterolateral medulla oblongata and lateral recess (Figure. 2 D). Short perforating arteries from PICA rarely restricted the superior marked retraction of the cerebellar hemisphere.

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II) Clinical Results

For the 3 patients with VA–PICA aneurysms surgically treated through the combined approach, direct clipping was easily performed uneventfully. All patients were discharged without any symptoms. For the 3 patients with GPN treated through the combined approach, the offending PICA was easily and safely decompressed, and all patients were discharged without neuralgia.

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Two Representative Cases

Case 1: 66-year-old female

A 6-mm, unruptured saccular aneurysm located at the junction of the left VA and PICA was

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accidentally revealed by 3-dimensional computed tomographic angiography (Figure. 3 A). Interventional therapy was first tried but was not completed because PICA originated from the aneurysmal neck (Figure. 3 A). The patient was referred to us for direct surgery. A surgery was performed with the patient in the right lateral recumbent position. After exposing the entire CMC through the unilateral trans-CMF approach combined with the transcondylar fossa approach, the neck of the aneurysm was directly clipped sparing PICA (Figure. 3 B). Intraoperative indocyanine green angiography revealed the patency of PICA. Step-by-step intraoperative photographs and their illustrations are presented in Figure 4 (Figures. 4 A–E). After surgery, mild difficulty in swallowing and dysarthria appeared transiently. After rehabilitation, she

Case 2: 53-year-old female

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was discharged to her home without any symptoms in the 6 weeks after surgery.

The patient visited us because of a paroxysmal violent pain in the left pharynx, particularly while drinking. On preoperative images, the left PICA with a high origin formed a loop in the supra-olivary fossette (Figures. 5 A–C). Microvascular decompression surgery for GPN was performed through the

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unilateral trans-CMF approach combined with the transcondylar fossa approach. Step-by-step

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intraoperative photographs and their illustrations are presented in Figure 6 (Figures. 6 A–D). The

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ACCEPTED MANUSCRIPT offending loop of PICA was pulled out for transposition and then fixed to the dura mater. Immediately after surgery, neuralgia completely disappeared. Notably, this case was previously reported in Neurosurgical Review from a different viewpoint.9

DISCUSSION

1. Previous Reports on Opening the Unilateral CMF Few previous papers have reported surgeries involving opening of the lateral CMF, but they were

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primarily performed for removal of tumors around the foramen of Luschka or the lateral recess.11, 39 We proposed a surgery involving opening of the unilateral CMF as a variation of the medial route of the

trans-CMF approach, i.e., the lateral recess type for removal of tumors around the lateral recess.20, 26 The

approach introduced in this paper is a little different from those in previous reports because we opened the nonpathological unilateral CMF on the lesion side almost completely to obtain a wide surgical field in CMC for vascular lesions such as VA–PICA aneurysm or GPN.

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2. Techniques for Lifting of the Unilateral Cerebellar Hemisphere on the Basis of Anatomical Characteristics

The conventional lateral suboccipital approach is used to naturally retract the lateral cerebellar hemisphere through a small opening in CMF, and in such situations, it is too difficult and risky to

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markedly shift the lateral cerebellar hemisphere. Lifting of the whole unilateral cerebellar hemisphere after almost completely opening the ipsilateral CMF is safer and more effective compared with retraction of a part of the biventral lobule through a small opening in CMF. The tonsil and biventral lobule are just adherent to the uvula medially and to the medulla oblongata inferiorly by arachnoid adhesion. Therefore, when uvulotonsilar and medullotonsilar spaces are dissected and opened, the tonsil and biventral lobule are free from the uvula and medulla oblongata, and the unilateral cerebellar hemisphere can then be easily lifted superiorly.

However, several vessels, including PICA, choroidal arteries, and vein of the CMF, course in

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uvulotonsilar and medullotonsilar spaces. Therefore, instead of complete dissection of these spaces, the taenia, which is an attachment of the tela choroidea to the medulla oblongata, is incised from the foramen of Magendie to the foramen of Luschka.16, 20 After incision of the whole taenia and a part of the tela choroidea, the tonsil and/or biventral lobule can be easily retracted superiorly with the reflexed tela choroidea and choroid plexus together. In few cases, although PICA may be an obstacle, this method is

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well oriented and easier and provides the same effect as complete opening of CMF.

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3. Variations of the Trans-CMF Approach: Previous Reports and Recent Application

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ACCEPTED MANUSCRIPT Since our proposal of opening CMF instead of splitting the inferior vermis, it is well known that opening of CMF creates a wide surgical field around the 4th ventricle and decreases the incidence of the vermian splitting syndrome and residual tumors in the lateral recess.4, 7, 10, 14, 18, 20, 31, 33 In addition, effects of opening of CMF have been evaluated by cadaveric studies.3, 28, 34 Approaches and procedures have been described by various names because they were applied to different kinds of lesions in different areas of the 4th ventricle, and various CMF portions were opened. These approaches include the median inferior suboccipital transfissual,37, 38 CMF,14 subtonsillar–transcerebellomedullary fissure,39 telo–velo,28 and subtonsillar approaches.11, 35 Although these approaches differ in a few ways, they are considered to be variations of the trans-CMF approach because they use opening of a part of CMF during surgery.

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We have developed the trans-CMF approach gradually.6, 9, 10, 12, 13, 15, 16, 18, 19, 20, 22, 23, 26 Initially, we

began to use it for the medial route after the midline suboccipital approach and then found it to be useful

in the lateral route combined with the transcondylar fossa approach from the lateral foramen magnum side. Recently, we used the approach for surgeries of vascular lesions in CMC. Procedures and techniques of

opening CMF are similar in all these applications, but the exposed surgical field differs depending on the opening portion of CMF. Currently, we use opening of CMF for 4 different regions: A, the interior of

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CMF, which means the outside of the ventricle; B, the intra-fourth ventricle, particularly in the medial

portion; C, the region across from CMF to CMC through and/or around the lateral recess; and D, only in CMC (Figure. 7). In the intra-CMF (region A), occipital artery–PICA anastomosis with the opening of CMF was recently reported.1 In both CMF and CMC around the lateral recess (region C), some tumors

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such as ependymoma, choroids plexus papilloma, lower CN neurinoma, and jugular tubercle meningioma have been surgically treated.12, 15, 26 In CMC (region D) alone, we have experienced VA–PICA aneurysms and GPNs.9, 13 Because we are unaware of any reports on variations for region D, we reported detailed procedures and maneuvers of the combined approach for region D in this article.

CMF in the lower posterior cranial fossa serves a purpose similar to that of the Sylvian fissure in the frontotemporal region. Because opening of the Sylvian fissure is very useful for supratentorial surgeries, even if a lesion is not present in the fissure, opening of CMF is also very useful for several kinds of

CONCLUSION

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surgeries in the lower posterior cranial fossa.

The procedure involving almost complete opening of the unilateral CMF provides a wide surgical field in CMC and enables a gentle cerebellar retraction. Moreover, the unilateral trans-CMF approach combined with the lateral foramen magnum approach yields a wide and close surgical field in CMC,

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which enables easy and safe surgeries in CMC.

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ACCEPTED MANUSCRIPT ACKNOWLEDGMENTS We would like to express our gratitude to Dr. Albert L. Rhoton, Jr. (University of Florida) for providing us opportunities to study the microsurgical anatomy of the posterior fossa and for his continuous teaching and guidance. In addition, we thank Mrs. Sumiko Matsushima, Mrs. Yumiko Ohishi,

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and Mrs. Takako Shiga for preparing the manuscript and illustrations.

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ACCEPTED MANUSCRIPT References 1) Abe H, Harashina J, Fukuda K, Hatayama S, Hamada O, Ogata T, Iwaasa M, Nonaka M, Higashi T, Inoue T, (2013) Surgical treatment of VA-PICA aneurysms using OA-PICA anastomosis, The 42nd annual meeting of Japanese society on surgery for cerebral stroke, Abstract ( in Japanese ) 2) Bertalanffy H, Seeger W (1991) The dorsolateral, suboccipital, transcondylar approach to the lower clivus and anterior portion of the craniocervical junction. Neurosurgery 29: 815-821 3) Deshmukh VR, Figueiredo EG, Deshmukh P, Crawford NR, Preul MC, Spetzler RF (2006) Quantification and comparison of telovelar and transvermian approaches to the fourth

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ventricle. Neurosurgery 58:ons202-ons207 4) El-Bahy K (2005) Telovelar approach to the fourth ventricle: operative findings and results in 16 cases. Acta Neurochir (Wien) 147:137-142

5) Funaki T, Matsushima T, Masuoka J, Nakahara Y, Takase Y, Kawashima M (2010) Adhesion of rhomboid lip to lower cranial nerves as special consideration in microvascular decompression for hemifacial spasm: Report of two cases. Surg Neurol Int. 18;1:71

6) Haga S, Sakata S, Isido K, Nakazaki K, Matsushima T (2002) Transcerebellomedullary fissure

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approach to the aneurysms of the distal posterior inferior cerebellar artery. Jpn J Neurosurg 11:39-744. (in Japanese).

7) Han S, Wang Z, Wang Y, Wu A (2013) Transcerebellomedullary fissure approach to lesions of the

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fourth ventricle: less is more? Acta Neurochirurgica 155, Issue 6, pp 1011-1016

8) Heros RC (1986) Lateral suboccipital approach for vertebral and vertebrobasilar artery lesion. J Neurosurg 64: 559-562

9) Hiraishi T, Matsushima T, Kawashima M, Nakahara Y, Takahashi Y, Ito H, Oishi M, Fujii Y (2013) 3D computer graphics simulation to obtain optimal surgical exposure during microvascular decompression of the glossopharyngeal nerve. Neurosurgical Review 36:629-635

10) Inoue T, Matsushima T, Inamura T, Kawamura T, Ishihara S, Fukui M (1998) Surgical approach to the mesencephalic vascular malformation. Surg Cereb Stroke 26:287-291 (in Japanese with English abstract)

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11) Jean WC, Aziz KMA, Keller JT, Loveren HR (2003) Subtonsillar approach to the foramen of Luschka: An anatomic and clinical study. Neurosurgery 52:860-866 12) Kawashima M, Matsushima T, Nakahara Y, Takase Y, Masuoka J, Ohata K (2009) Transcerebellomedullary fissure approach with special reference to lateral route. Neurosurg Rev 32:457-464 13) Kawashima M, Takase Y, Matsushima T (2013) Surgical treatment for vertebral artery – posterior inferior cerebellar artery aneurysms: special reference to the importance of the CMF dissection. J

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Neurosurg 118:460-464

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ACCEPTED MANUSCRIPT 14) Kellogg JX, Piatt JH Jr (1997) Resection of fourth ventricle tumours without splitting the vermis: The cerebellomedullary fissure approach. Pediatr Neurosurg 27:28-33 15) Matsushima T (2006) Microsurgical anatomy and surgery of the posterior fossa. Scimed Publications, Tokyo, (in Japanese) 16) Matsushima T, Abe H, Kawashima M, Inoue T (2012) Exposure of the wide interior of the fourth ventricle without splitting the vermis: importance of cutting procedures for the tela choroidea Neurosurg Rev 35:563-572 17) Matsushima T, Fukui M (1996) Lateral approaches to the foramen magnum: with special reference to

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the transcondylar fossa approach and the transcondylar approach. Neurological Surgery 24: 119-124 (in Japanese)

18) Matsushima T, Fukui M, Inoue T, Natori Y, Baba T, Fujii K (1992) Microsurgical and magnetic

resonance imaging anatomy of the CMF and its application during fourth ventricle surgery. Neurosurgery 30:325-330

19) Matsushima T, Ikezaki K, Inoue T, Fukui M (1998) Surgery of ependymoma in the fourth ventricle. In: Shibata S (ed) Surgery of glioma. Medicus Shuppan, Suita City, pp 54-62 (in Japanese with English

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abstract)

20) Matsushima T, Inoue T, Inamura T, Natori Y, Ikezaki K, Fukui M (2001) Transcerebellomedullary fissure approach with special reference to methods of dissecting the fissure. J Neurosurg 94:257-264 21) Matsushima T, Kawashima M, Masuoka J, Mineta T, Inoue T (2010) Transcondylar Fossa Approach

and surgical experiences. Skull Base 20:83-92

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22) Matsushima T, Matsukado K, Inamura T, Natori Y, Inoue T, Ikezaki K, Fukui M (2000) Approach to the fourth ventricle: midline suboccipital approaches- special reference to trans-cerebellomedullary fissure approach. In: Saeki N (ed) Surgical anatomy for microneurosurgery, 11th edn. Scimed, Tokyo, pp 99-110 (in Japanese with English abstract)

23) Matsushima T, Matsukado K, Inoue T, Fukui M (2000) Part 5: trans-cerebellomedullary fissure approach. Nerv Syst Child 25:173-177 (in Japanese with English abstract)

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24) Matsushima T, Matsukado K, Natori Y, Inamura T, Hitotsumatsu T, Fukui M (2001) Surgery on a saccular vertebral artery-posterior inferior cerebellar artery aneurysm via the transcondylar fossa (supracondylar transjugular tubercle) approach or the transcondylar approach: surgical results and indications for using two different lateral skull base approaches. J Neurosurg 95: 268-274 25) Matsushima T, Natori Y, Katsuta T, Ikezaki K, Fukui M, Rhoton AL Jr (1998) Microsurgical anatomy for lateral approaches to the foramen magnum with special reference to transcondylar fossa

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(Supracondylar transjugular tubercle) approach. Skull Base Surgery 8: 119-125

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ACCEPTED MANUSCRIPT 26) Matsushima T, Ohata K (2005) Anatomy of the fourth ventricle and trans-cerebellomedullary fissure approach: medial route and lateral route. In: Hongo K (ed) Surgical anatomy for microneurosurgery, 18th edn. Scimed, Tokyo, pp 39-48 (in Japanese with English abstract) 27) Matsushima T, Rhoton AL Jr, Lenkey C (1982) Microsurgery of the fourth ventricle: part 1. Microsurgical anatomy. Neurosurgery 11:631-667 28) Mussi AC, Rhoton AL Jr (2000) Telovelar approach to the fourth ventricle: microsurgical anatomy. J Neurosurg 92:812-823 29) Nakahara Y, Matsushima T, Hiraishi T, Takao T, Funaki T, Masuoka J, Kawashima M 2013

spasm. J Neurosurg DOI:10.3171/2013.4.JNS 121546

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Importance of awareness of the rhomboid lip in microvascular decompression surgery for hemifacial

30) Perneczky A (1986) The posterolateral approach to the foramen magnum. in Samii M (ed): Surgery In and Around the Brain Stem and Third Ventricle: Anatomy, Pathology, Neuro-physiology, Diagnosis, Treatment. Berlin: Springer-Verlag, pp 460-466

31) Rajesh BJ, Rao BRM, Menon G, Abraham M, Easwer HV, Nair S (2007) Telovelar approach: technical issues for large fourth ventricle tumours. Childs Nerv Syst 23:555-558

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32) Sen CN, Sekhar LN (1990) An extreme lateral approach to intradural lesions of the cervical spine and foramen magnum. Neurosurgery 27: 197-204

33) Shimoji K, Miyajima M, Karagiozov K, Yatomi K, Matsushima T, Arai H (2009) Surgical

focus. Childs Nerv Syst 25:1221-1228

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consideration of fourth ventricular ependymoma with the transcerebellomedullary fissure approach in

34) Tanriover N, Ulm AJ, Rhoton AL Jr, Yasuda A (2004) Comparison of the transvermian and telovelar approaches to the fourth ventricle. J Neurosurg 101:484-498

35) Tatagiba M, Koerbel A, Roser F. (2006) The midline suboccipital subtonsillar approach to the hypoglossal canal: surgical anatomy and clinical application. Acta Neurochir (Wien) 148(9):965-9 36) Wen HT, Rhoton AL Jr, Katsuta T, de OLIVEIRA E (1997) Microsurgical anatomy of the transcondylar, supracondylar, and paracondylar extensions of the far-lateral approach. J Neurosurg 87: 555-585

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37) Yasargil MG (1996) Chapter 3. tonsillar uveal sulcus, Microneurosurgery IVB. Microneurosurgery of CNS Tumors. Georg Thieme Verlag, Stuttgart

New York, pp63-64

38) Yasargil MG (1996) Chapter 19. Median inferior suboccipital transfissual Approach, Microneurosurgery IVB. Microneurosurgery of CNS Tumors. Georg Thieme Verlag, Stuttgart York, pp315

39) Ziyal M, Sekhar LN, Salas E (1999) Subtonsillar-

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transcerebellomedullary approach to lesions involving the fourth

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ventricle, the C and the lateral brainstem. Br J of Neurosurg 13:276-284

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ACCEPTED MANUSCRIPT Figure Legends

Figure. 1: Anatomical characteristics of CMC and CMF. 1-A: The suboccipital cerebellar surface. Neither CMF nor CMC can be visualized because they are hidden by the tonsil and biventral lobule. The uvulotonsilar and medullotonsilar spaces are closed. 1-B:Left CMF and the cerebellomedullary cistern are exposed after removal of the left cerebellum. 1-C: CMF and CMC after removal of the left cerebellar hemisphere. The middle cerebellar peduncle, flocculus, and lateral recess can be observed. In CMC, PICA originates

ventricle. 1-D: Illustration presenting territories of CMC and CMF. The green circled area represents CMC, and the pink area represents CMF.

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from VA and meanders in CMC to reach the posterior surface of the medulla oblongata and the 4th

Figure. 2: Dissection of a cadaveric specimen, revealing anatomical characteristics of the left unilateral

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CMF and CMC and how to open and expose them. The posterior view is presented.

2-A: The state of the left CMC after the transcondylar fossa approach. The biventral lobule is retracted without opening CMF.

2-B: Partial opening of the left CMF. Uvulotonsillar and medullotonsillar spaces have been dissected and

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opened; the roof of the 4th ventricle and lateral recess can then be visualized.

2-C: Opening of the roof of the 4th ventricle. The taenia and lateral recess on the left side were incised to open the left half of the roof of the 4th ventricle. Thereafter, it becomes easier to retract the unilateral cerebellar hemisphere.

2-D: Exposure of the left CMC with retraction of the biventral lobule after opening of the left unilateral CMF.

Figure. 3: Preoperative and postoperative images of Case 1 (left VA–PICA aneurysm)

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3-A: Preoperative MRA revealing the VA–PICA aneurysm. The posteromedial view is presented. A saccular aneurysm is located at the junction of VA and the origin of PICA. PICA originates from the aneurysmal neck.

3-B: Postoperative 3D-CT image. The posterior view is presented. The aneurysm is completely clipped.

Figure. 4: Intraoperative photographs of step-by-step procedures and their illustrations for Case 1

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4-A: Exposure of the inferior margin of the left cerebellar hemisphere and the foramen of Magendie after

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opening the dura mater.

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ACCEPTED MANUSCRIPT 4-B: Separation of the medullotonsillar space on the left side. After dissecting the uvulotonsillar space, the left tonsil is lifted superolaterally, and the arachnoidal adhesion is dissected in the left medullotonsillar space. The tela choroidea and roof of the 4th ventricle can be visualized. 4-C: Incision of the left taenia and roof of the lateral recess. The taenia is incised from the foramen of Magendie to the left lateral recess. Because the roof of the lateral recess is incised, the interior of the lateral recess can be visualized. 4-D: The surgical field in the cerebellomedullary cistern after opening the left unilateral CMF. The biventral lobule is retracted after opening the left unilateral CMF, and then a wide surgical field is obtained. The whole CMC and a part of the lateral recess with choroid plexus can be visualized. In

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addition, the VA–PICA aneurysm and the origin of PICA are visible through the space between the 10th and 11th CNs.

4-E: Clipping of the VA–PICA aneurysm. The neck of the aneurysm is clipped and PICA is spared.

Figure. 5: Preoperative images of Case 2 (left glossopharyngeal neuralgia)

5-A, B: Preoperative magnetic resonance images and axial view T2-weighted images demonstrating an

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offending PICA and its upward loop. The 9th CN can be visualized. PICA originating from VA forms a loop in the left supraolivary fossette.

5-C: Preoperative 3D-CT image. The lateral view from the midline is presented. PICA, with a high origin,

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forms an upward loop above the jugular tubercle.

Figure. 6: Intraoperative photographs of step-by-step procedures and their illustrations of Case 2. 6-A: State after opening the left CMF. After opening CMF, the left biventral lobule is retracted superiorly to expose the left CMC. The choroid plexus, 9th and 10th CNs, and 4th ventricle are visible. The loop of the left PICA pushes up and compresses nerve rootlets of the 9th and 10th CNs (from Hiraishi T. et al9 with permission).

6-B: Pulling out the PICA loop. The PICA loop is pulled out after absence of perforating arteries is confirmed.

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6-C: Decompressive state after pulling out the PICA loop (from Hiraishi T. et al9 with permission). 6-D: Fixation of the PICA loop using the stitched sling technique (from Hiraishi T. et al9 with permission).

Figure.7 Illustration presenting 4 different regions approached after opening CMF (through the transCMF approach).

A: Sky blue circle indicates the interior of CMF, which is the outside of the ventricle;

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B: Pink circle indicates the interior of the 4th ventricle, particularly in the medial portion;

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ACCEPTED MANUSCRIPT C: Purple circle indicates regions in both CMF and CMC (C-1: a primary lesion in CMF; C-2: a primary lesion in CMC);

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D: Green circle indicates region only in CMC.

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ACCEPTED MANUSCRIPT Abbreviations

cerebellomedullary cistern (CMC), cerebellomedullary fissure (CMF), cranial nerves (CNs),

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glossopharyngeal neuralgia (GPN), vertebral artery–posterior inferior cerebellar artery (VA–PICA)

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Exposure of wide cerebellomedullary cisterns for vascular lesion surgeries in cerebellomedullary cisterns: opening of unilateral cerebellomedullary fissures combined with lateral foramen magnum approach.

To clarify microsurgical anatomic features of the cerebellomedullary fissure (CMF), the natural cleavage plane between the cerebellum and the medulla,...
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