Archives of Neurosurgery

Volume 1 Issue 1 Article 5

2020

Endoscopic–assisted surgery for cerebello pontine angle pathology: Technical note and surgical results in a series of patients

Jaime Jesus Martinez Anda Neurosurgery Department, Toluca Medical Center of Social Security Institute of the State of Mexico and Provinces, State of Mexico, Mexico, [email protected]

Pablo David Guerrero Suarez Neurosurgery Department, Toluca Medical Center of Social Security Institute of the State of Mexico, [email protected]

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Recommended Citation Martinez Anda, Jaime Jesus; Guerrero Suarez, Pablo David; Pineda Martínez, Diego; Avendaño Pradel, Rafael; Jurado Delgado, Ernesto Javier; Villlagrana Sánchez, Ricardo Santiago; Cisneros Lesser, Juan Carlos; De la Llata Segura, Carolina; and Revuelta Gutiérrez, Rogelio (2020) "Endoscopic–assisted surgery for cerebello pontine angle pathology: Technical note and surgical results in a series of patients," Archives of Neurosurgery: Vol. 1 : Iss. 1 , Article 5. Available at: https://www.ansjournal.org/home/vol1/iss1/5

This Original Research - Endoscopy is brought to you for free and open access by Archives of Neurosurgery. It has been accepted for inclusion in Archives of Neurosurgery by an authorized editor of Archives of Neurosurgery. For more information, please contact [email protected]. Endoscopic–assisted surgery for cerebello pontine angle pathology: Technical note and surgical results in a series of patients

Abstract Objectives: Endoscopic–assisted surgery combined with the operating microscope has been described for several surgical techniques and pathologies of the cerebellopontine angle (CPA). The use of an endoscope allows for a panoramic view of the CPA cistern and a high degree of maneuverability in narrow cisternal spaces that enable the surgeon to deal with most CPA lesions safely. We performed an observational study to describe the surgical anatomy and technique for endoscopic-assisted CPA surgery, describing our experience in a case series of patients with CPA pathology. Methods: Anatomical and surgical technique description of endoscopic-assisted surgery for CPA pathology, based on observations on a case series of patients surgically treated with an endoscopic–assisted keyhole retrosigmoid craniotomy. Results: Ten patients were treated with the following diagnosis: Trigeminal neuralgia (5 patients), epidermoid cyst (2 patients), hemifacial spasm (1 patient), vestibular paroxysms (1 patient), CPA neurocysticercosis (1 patient). The mean age was 48 years old, seven female and three male patients. All patients had resolution or improvement of their clinical symptoms. We describe the anatomic corridors for endoscopic–assisted surgery and surgical pearls. Conclusions: Endoscopic-assisted microsurgery of the CPA is a safe and efficient procedure that has demonstrated improved surgical results as compared to the full-microscopic technique.

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Keywords Neuroendoscopy, Cerebellopontine angle, Surgical anatomy.

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This work is licensed under a Creative Commons Attribution 4.0 License. Cover Page Footnote Founding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Conflict of Interest All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non- financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Authors Jaime Jesus Martinez Anda, Pablo David Guerrero Suarez, Diego Pineda Martínez, Rafael Avendaño Pradel, Ernesto Javier Jurado Delgado, Ricardo Santiago Villlagrana Sánchez, Juan Carlos Cisneros Lesser, Carolina De la Llata Segura, and Rogelio Revuelta Gutiérrez

This original research - endoscopy is available in Archives of Neurosurgery: https://www.ansjournal.org/home/vol1/ iss1/5 Endoscopice Assisted Surgery for Cerebello Pontine Angle Pathology: Technical Note and Surgical Results in a Series of Patients ORIGINAL RESEARCH

Jaime Jesús Martínez e Anda a,*, Pablo David Guerrero e Suarez a, Diego Pineda e Martínez b, Rafael Avendano~ e Pradel b, Ernesto Javier Delgado e Jurado a, Ricardo Santiago Villagrana - Sanchez a, Juan Carlos Cisneros e Lesser c, Carolina de la Llata Segura d, Rogelio Revuelta e Gutierrez e a Neurosurgery Department, Toluca Medical Center of Social Security Institute of the State of Mexico and Provinces, Baja Velocidad Avenue 57.5 Km, Mexico e Toluca Highway No.1519 Ote. Col. San Jeronimo Chicahualco, P.C. 52140, Metepec, Mexico b Human Biological Material Innovation Department, Faculty of Medicine, National Autonomous University of Mexico, University Campus, Coyoacan P.C. 04510, Mexico City, Mexico c Neurotology and Cranial Base Surgery Department. National Institute of Rehabilitation, Mexico-Xochimilco Avenue No. 289, Coapa, Arenal Tepepan, Tlalpan, P.C. 14389, Mexico City, Mexico d Otolaringology Department, Medica Sur Medical Center, Puente de Piedra Avenue No. 150. Col. Toriello Guerra, Tlalpan, P.C. 14050, Mexico City, Mexico e Neurosurgery Department, National Institute of Neurology and Neurosurgery, Insurgentes Sur Avenue No. 3877, La Fama, Tlalpan, P.C. 14269, Mexico City, Mexico

Abstract

Objectives: Endoscopiceassisted surgery combined with the operating microscope has been described for several surgical techniques and pathologies of the cerebellopontine angle (CPA). The use of an endoscope allows for a pano- ramic view of the CPA cistern and a high degree of maneuverability in narrow cisternal spaces that enable the surgeon to deal with most CPA lesions safely. We performed an observational study to describe the surgical anatomy and technique for endoscopic-assisted CPA surgery, describing our experience in a case series of patients with CPA pathology. Methods: Anatomical and surgical technique description of endoscopic-assisted surgery for CPA pathology, based on observations on a case series of patients surgically treated with an endoscopiceassisted keyhole retrosigmoid craniotomy. Results: Ten patients were treated with the following diagnosis: Trigeminal neuralgia (5 patients), epidermoid cyst (2 patients), hemifacial spasm (1 patient), vestibular paroxysms (1 patient), CPA neurocysticercosis (1 patient). The mean age was 48 years old, seven female and three male patients. All patients had resolution or improvement of their clinical symptoms. We describe the anatomic corridors for endoscopiceassisted surgery and surgical pearls. Conclusions: Endoscopic-assisted microsurgery of the CPA is a safe and efficient procedure that has demonstrated improved surgical results as compared to the full-microscopic technique.

Keywords: Neuroendoscopy, Cerebellopontine angle, Surgical anatomy

Received 23 May 2020; revised 11 July 2020; accepted 15 July 2020. Available online 15 April 2021

* Corresponding author. Neurosurgery Department, Toluca Medical Center of Social Security Institute of the State of Mexico and Provinces, Baja Velocidad Avenue 57.5 Km, Mexico e Toluca Highway No.1519 Ote. Col. San Jeronimo Chicahualco, P.C. 52140, Metepec. Mexico. E-mail addresses: [email protected] (J.J. Martínez e Anda), [email protected] (P.D. Guerrero e Suarez), [email protected] (D. Pineda e Martínez), [email protected] (R. Avendano~ e Pradel), [email protected] (E.J. Delgado e Jurado), [email protected] (R.S. Villagrana - Sanchez), [email protected] (J.C. Cisneros e Lesser), [email protected] (C. de la Llata Segura), [email protected] (R. Revuelta e Gutierrez).

ISSN- Pending. Published by Mexican Society of Neurological Surgery (Sociedad Mexicana de Cirugía Neurológica A.C.). © Copyright the Authors. This journal is open access. 36 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

1. Introduction Abbreviations

he retrosigmoid (RS) approach is the work- RS Retrosigmoid T horse for the surgical treatment of the cer- CPA Cerebellopontine Angle ebellopontine angle (CPA) pathologies. BNI Barrow Neurological Institute REZ Root Entry Zone Microsurgery has proven to be a major techno- CSF Cerebrospinal Fluid logical advance to increase efficacy and safety but AICA Antero e Inferior Cerebellar Artery CN Cranial Nerve has its limitations during CPA procedures. To SUCA Superior Cerebellar Artery solve some of those limitations, technical ad- PICA Postero e Inferior Cerebellar Artery vances in minimally invasive neurosurgery have enabled the use of endoscopic techniques with high definition equipment that allows the explo- 2.1. Inclusion criteria were ration of every corner in the surgical field, 1. Patients with CPA vascular syndromes where no enhancing the view and illumination [1]. Endo- vascular compression was seen on preoperative scopic techniques combined with the operating MRI or during the microscopic technique, microscope have been described for several 2. Epidermoid cysts of the CPA, and techniques and pathologies of the CPA, as it al- 3. Patients with cystic lesions of the CPA. lows for a panoramic view of the subarachnoid Clinical evaluation and follow up were made ac- cisterns and contents, having a high degree of cording to pathology, and postoperative imaging maneuverability in narrow cisternal spaces was made only in patients with cystic lesions of the enabling the surgeon to deal with most CPA le- CPA. Patients with trigeminal neuralgia were eval- sions safely. Those reports describe two tech- uated with the Barrow Neurological Institute (BNI) niques: 1) additionally to the microscope pain intensity score for trigeminal neuralgia [3]. (endoscope e assisted) and 2) entirely instead of Patients with hemifacial spasm were evaluated with the operating microscope (endoscope-controlled the severity of spasm score [4]. e microsurgery) [2]. We performed the surgical procedures in a Park Bench position, with the head fixed in a Mayfield e This study aims to describe the surgical anatomy Kees headrest on a contralateral head rotation of 60 and technique for endoscopic-assisted CPA surgery and flexion of 10. The skin incision was made 2.5 and to describe our experience in a case series of cm behind the retro auricular hairline, 2 cm over, patients. and 3 cm below the superior nuchal line. We incised the nuchal fascia in the same direction and partially 2. Material and methods dissected the sternocleidomastoid, trapezius, sple- nius capitis, longissimus capitis, and superior obli- We carried out anatomical studies at the Human que muscles from their attachments to expose the Biological Material Innovation Department of the asterion by lateral retraction. Later we made an Faculty of Medicine at the National Autonomous asterional burr-hole, completing a craniotomy of 2.5 University of Mexico. We used five preserved adult- cm in diameter; we opened the dura in “U" shape cadaver heads to analyze the endoscopic anatomy of with the base at the angle between the sigmoid and the RS approach to the CPA. We performed dis- transverse sinuses [5]. We used a Pentero micro- sections with 0 and 30 rigid endoscopes (Karl scope [Carl Zeiss(R) Meditec AG]) and a Storz Storz(R) GmbH, Tuttlingen, Germany), and micro- endoscope (Karl Storz(R) GmbH, Tuttlingen, Ger- surgery instruments. many) for the procedures. Surgical cases were selected from a series of pa- The present study was made under the interna- tients with lesions in the CPA, surgically treated tional ethical standards reviewed by our institu- with an endoscopeeassisted keyhole RS crani- tional research committee following the 1964 otomy. We collected clinical information on radio- Helsinki declaration and its later amendments or logic and operative findings, postoperative comparable ethical standards. Informed consent complications, and followeup data from the hospi- was obtained from all individuals participating in tal information system. the study. Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 37 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE

Table 1. Patients. Age Gender Diagnosis Symptoms Hospital Complications Clinical outcome stay 1 38 Female Trigeminal Grade 5* V2eV3 1 No Complete Pain Neuralgia right facial pain remission 2 45 Female Trigeminal Grade 5* V2eV3 left 1 No Complete Pain ORIGINAL RESEARCH Neuralgia facial pain remission 3 48 Male Trigeminal Grade 5* V1eV2 left 1 No Complete Pain Neuralgia facial pain remission 4 58 Female Trigeminal Grade 5* V2 left 2 No Complete Pain Neuralgia facial pain remission 5 54 Female Trigeminal Grade 5* V2eV3 1 No Complete Pain Neuralgia right facial pain remission 6 43 Male CPA Epidermoid Headache 2 No Clinical remission cyst Complete exceresis 7 47 Female CPA Epidermoid Atypical right 2 No Clinical remission cyst trigeminal neuralgia 10% Residual and vertigo tumor þ 8 61 Female Hemifacial spasm Grade 3 right 1 Transcient Complete spasm orbicularis oculis facial paresis remission spasm 9 52 Female Vestibular Bilateral tinnitus, 2 No Remission of paroxysmia paroxysmal vertigo vertigo 50% and left orbicularis recovery of oris muscle spasm tinnitus 10 36 Male CPA Right atypical 2 No Clinical remission neurocysticercosis trigeminal neuralgia and vertigo

3. Results vertigo, and hemifacial spasm at the orbicularis oris muscle (Table 1). 3.1. Clinical cases All the patients had neurophysiological moni- toring of the V and VII cranial nerve (CN) during the We included a total of 10 patients treated between procedures. We found microvascular compression January of 2018 and July of 2019 in the present study in 3 of 5 patients due by the anteroinferior cerebellar with the following diagnosis: Trigeminal neuralgia artery (AICA), all of them located at the axilla of the (5 patients), epidermoid cyst (2 patients), hemifacial nerve root entry zone (REZ), hidden from the spasm (1 patient); vestibular paroxysms (1 patient), lateral-to-medial point of view of the microscope; in CPA neurocysticercosis (1 patient). The mean age the remaining two patients, we found vascular was 48 years old, seven female and three male pa- contact by CPA veins, draining to the petrosal vein. tients. Mean followeup was eight months. A patient We found arterial vascular compression at the diagnosed with vestibular paroxysms was treated at medial face of the nerve REZ by the AICA in the the Otolaryngology service of the National Institute patient presenting with hemifacial spasm. Lastly, of Rehabilitation at Mexico City [6]; the rest of the the patient with vestibular paroxysm had a vascular patients were treated at the Neurosurgery Depart- compression by the AICA at the superior aspect of ment of Toluca Medical Center of Social Security the vestibular nerve. Institute of the State of Mexico and Provinces. Table One of the patients treated for microvascular 1 shows the clinical characteristics and outcomes of decompression of the VII CN developed a facial treated patients. paresis that recovered utterly after one month. In- All the patients with trigeminal neuralgia had a hospital stay ranged from one to two days. We score of five in facial pain according to the BNI pain observed complete facial pain remission in patients scale; a patient with hemifacial spasm had a grade with trigeminal neuralgia diagnosis and partially in III classification. One patient with an epidermoid one patient who had improved facial pain and ver- cyst had atypical trigeminal neuralgia and ipsilateral tigo after complete removal of a cystic lesion from vertigo, and the other had a headache; another pa- neurocysticercosis. From the two patients treated for tient with CPA neurocysticercosis had atypical tri- epidermoid cyst, one had complete resection of the geminal neuralgia and ipsilateral vertigo. A patient lesion, and the other had a residual tumor left with vestibular paroxysms had tinnitus, paroxysmal contralaterally to the side of the approach; both 38 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

Fig. 1. Microscopic vs. Endoscopic vision of cerebellopontine angle (A) Microscopic view and (B) endoscopic view of the trigeminal nerve. (C) Microscopic and (D) endoscopic view of the VII and VIII cranial nerves (E) Microscopic and (F) endoscopic view of a cerebellopontine angle epidermoid cyst. (G) Microscopic and (H) endoscopic view of a cerebellopontine angle cysticercosis.

patients remained asymptomatic. The patient with The most frequent procedure for CPA surgery is hemifacial spasm had remission of dyskinetic the retrosigmoid approach. It is vital to bear in mind movements, while another patient with vestibular the anatomical references for adequate asterional paroxysms had remission of vertiginous crisis and a craniotomy. The asterion is a craniometric point 50% improvement in tinnitus (Fig. 1). located at the junction of the lambdoid, occipito- mastoid, and temporoparietal sutures situated near 3.1.1. Anatomical basis of endoscopic-assisted surgery the mastoid vein. Both references are useful land- for cerebellopontine angle pathology marks for identifying the right site for a burr-hole The cerebellopontine angle is located between the placement (keyhole-approach); surgeons are superior and inferior borders of the fissure formed encouraged to recognize these structures in the by the petrosal cerebellar surface, and opens preoperative computed tomography scan [8]. Initial medially from a lateral apex. It folds around the steps for the CPA approach begin with standard pons and middle cerebellar peduncle; the fourth microsurgical dissection of the ventral and superior through the eleventh cranial nerves are located near cerebellar surfaces to expose the dorsal petrosal or within this angular space. Professor's Rhoton Jr bone, the ventral tentorium, and the petrosal surface [7]. Masterpieces of the microsurgical anatomy of of the cerebellum. This maneuver allows cerebro- CPA are an obligated lecture for all young neuro- spinal fluid (CSF) drainage and the opening of an surgeons, as he describes all important anatomical initial corridor to reach the CPA structures by landmarks with great detail from a surgical point of endoscopy. The intracisternal endoscopic pathways view. He classifies CPA's neurovascular structures start by accessing the cerebellopontine cistern, into three complexes: located between the anterolateral surface of the pons, the middle peduncle of the cerebellum, and 1. The upper neurovascular complex consists of the the arachnoid membrane that rests on the posterior trigeminal nerve and the SUCA, located at the surface of the petrous bone. It lies in between. ventrolateral surface of the pons. 2. The middle neurovascular complex, including 1. The ambient cistern, separated by the lateral the vestibulocochlear, facial, and abducens pontomesencephalic membrane at the level of nerves accompanied by the AICA, located within the tentorium; the cerebellopontine fissure, at the petrosal 2. The cerebellomedullary cistern, separated by the surface of the cerebellum. lateral pontomedullary subarachnoid membrane 3. The lower neurovascular complex formed by the between the vestibulocochlear and glossophar- glossopharyngeal, vagus, spinal-accessory, and yngeal nerves; hypoglossal nerves and the PICA closely related 3. The prepontine cistern medially, separated by to the medulla, inferior cerebellar peduncle, and the anterior pontine membrane; and cerebellomedullary fissure. Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 39 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE

4. The cerebellar surface laterally, that wraps internal auditory meatus, the endoscope has to pass around the pons to form the cerebellopontine between the VII and VIII CN superiorly; the IX -and fissure. XI CN caudally; the jugular tubercle ventrally; and the floccule of the cerebellum dorsally. After passing To access the CPA, we need to open the outer

this window, the entire upper medullary region can ORIGINAL RESEARCH arachnoid membrane that covers the petrosal cere- be observed, with the hypoglossal nerve's roots and bellar surface. Then, three endoscopic corridors are the vertebral artery originating the PICA. identified [1]: 3.1.3. Central endoscopic corridor (Fig. 2B) 1. Inferior endoscopic corridor, by the jugular To access the central CPA corridor the outer foramen fi arachnoid membrane has to be opened at the point 2. Middle endoscopic corridor, identi ed by the of attachment to the superior petrosal vein and the internal auditory meatus fi V CN, cranially to the internal auditory meatus; this 3. Superior endoscopic corridor, identi ed by the maneuver opens a window between the VII and VIII tentorium CN caudally; V CN cranially; clivus ventrally; and fi Each corridor leads to spaces or windows to reach cerebellopontine ssure dorsally. This corridor is different structures from the CPA (Fig. 2). the widest space to access the ventral surface of the brain stem. The view through this space allows 3.1.2. Inferior endoscopic corridor (Fig. 2A) endoscopic inspection into the internal auditory To access this corridor, the outer arachnoid meatus and differentiation of vestibulocochlear and membrane has to be opened at its attachment to the facial nerves, and their relation to the premeatal jugular foramen and the internal auditory meatus; segment of AICA. Additionally, it allows the in- by moving through the inferior space inferior of the spection of the choroid plexus protruding through

Fig. 2. Surgical corridors for endoscopic-assisted approach of cerebellopontine angle. (A) Inferior corridor, endoscope inspection can be made through space (asterisk) between the IX and XI complex and jugular foramen (YF), the VII and VIII complex, and the flocculus of cerebellum (Floc); (B) central corridor: the space between the V CN, the VII and VIII complex and the cerebellopontine angle allows visualization of the ventral surface of the pons (Po), the middle third of clivus and the VI CN entrance to the Dorello's canal (DC); (C) and (D) Superior corridor entrance; on (C) microdissector separates the Petrous vein (PV) from the V CN and allows visualization of SUCA and its relation to the REZ of the V CN; (D) superior corridor, above the petrous vein (PV); this angle allows access to the tentorial edge (TE), the lateral view of cerebral peduncle (CP) and the IV CN. 40 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

the Lushcka foramen, the pontomedullary sulcus, nerve cranially, the trigeminal nerve caudally, the and the VI CN from its emergence to the Dorello's petroclival fissure ventrally, and the pons dorsally. It canal; it also provides visualization of the ventral also allows visualization of the SUCA at the tri- surface of the pons, the lower portion of the basilar geminal REZ level, the tentorial edge together with trunk and the vertebrobasilar junction, the origin of the IV CN, the entrance to the Meckel's cave, and the AICA, the caudal portion of the clivus and the the superior portion of the basilar artery. hypoglossal nerve. 3.2. Surgical technique 3.1.4. Superior corridor (Fig. 2C and D) To access this corridor the arachnoid membrane 3.2.1. Trigeminal nerve microvascular decompression that goes from the petrous vein to the V CN has to (Fig. 3) be opened; it serves as a window whose limits de- The craniotomy should be performed as high as pends on the anatomy of the petrous vein; some- possible, close to the union of transverse and sig- times the petrous vein has to be separated from the moid dural sinuses. Intradural dissection begins VCN to get through this window. The structures with conventional microsurgical technique and is that can be visualized are the tentorial edge and IV directed towards the superior corridor, looking for

Fig. 3. Surgical technique for trigeminal nerve endoscopic e assisted microvascular decompression. (A) and (B) endoscopic view of a left approach to the V CN: dissection of the petrous vein (PV) from the V CN can be done with microdissectors (Md) and microsurgical scissors (Sc), and this allows to amplify the space to completely explore the V CN; (C) and (D) after the space between the petrous vein (PV) and the V CN is opened, the V CN can be explored from the root entry zone (asterisk) to its entrance to the Mackel's cave (MC), this should allow the identification of the site of vessel contact, that is usually located in the root entry zone, and comes from the SUCA (white arrow); (E) closing - up to the site of compression at the root entry zone of the V CN by a loop of the SUCA (white arrow); (F) 30 angled endoscopic view of a right approach to the V CN: when there is doubt of the site of vascular contact, a 30 angled endoscope can be used to corroborate the site of compression. Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 41 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE

the corner between the tentorium and the dorsal vascular contact is seen with 0 endoscope, a 30 surface of the petrosal bone. The outer arachnoid endoscope should be used to carefully explore the membrane is opened at the point of attachment to medial face of the nerve, before concluding that the superior petrosal vein, cranially to the internal there is no arterial loop in the axilla of the nerve.

auditory meatus. Once CSF is drained, no cerebellar Compression and distortion of the V CN by the ORIGINAL RESEARCH retraction is needed, and a 4 mm endoscope can be surrounding veins are less frequent than arterial introduced for the next steps. In our experience, compression but can be the source of neuralgia there is no need to coagulate the petrosal vein; the when no arterial contact is found. Petrosal veins endoscope allows the view of its entire track from its draining into the superior petrosal sinus are most origin to the superior petrosal dural sinus, it can be frequently encountered compressing V CN. The safely dissected from its arachnoid attachments to superior petrosal vein can be a single vein or a the V CN (Fig. 3A and B). This maneuver is a major complex of veins that drain tributaries from the difference with conventional microsurgical tech- transverse pontine and pontotrigeminal veins, cer- nique, where the petrosal vein is coagulated to allow ebellopontine fissure veins, middle cerebellar an adequate view of VCN, especially when no peduncle veins, and veins draining lateral part of offending arterial vessel is identified [7,9,10]. We the cerebellar hemisphere. This complex anatomy strongly suggest complete dissection of the petrosal may distort the V CN through direct vascular con- vein from V CN as it allows full view of its trajectory tact or by arachnoidal attachments; therefore, when from its emergence at the ventrolateral surface of venous compression is suspected, the petrosal the pons, to its entrance to the Meckel's cave (Fig. venous complex has to be entirely dissected, and a 3C). Circumferential exploration of the V CN by Teflon sponge should be interposed between the 0 and 30 endoscopes identifies the site of vascular vein and the nerve. contact (Fig. 3D); the most common finding is a SUCA segment compressing the trigeminal nerve 3.2.2. Vascular syndromes of the VII and VIII complex near or at the nerve REZ (Fig. 3E). The SUCA can (Fig. 4) easily be followed from its origin in the basilar ar- The site of craniotomy should be 5 mm lower to tery, through the cerebello-mesencephalic fissure, the trigeminal nerve approach and extended running together with the distal portion of the caudally. Once CSF is drained, the central corridor trochlear nerve above the trigeminal nerve, where it is followed, and the outer arachnoid is opened from makes a caudal loop and courses inferiorly for a jugular foramen to the internal auditory canal. The variable distance on the lateral side of the pons, endoscope is directed straight to the internal where contact between the artery and the trigeminal auditory meatus to reach the VII and VIII CN(Fig. nerve occurs, at the superior or superomedial aspect 4A); the lower CNs should also be identified. The of the nerve. In this case, a Teflon fragment is space above and below the internal acoustic meatus inserted after microsurgical arachnoidal attach- is used to access and explore those nerves; we ments dissection between the artery and the nerve; suggest the use of a 30 endoscope to visualize however, sometimes, the SUCA lies down in be- them from their REZ to the entrance to the CAI tween the medial side of the nerve the pons (Fig. (Fig. 4B). It also allows visualization of the AICA 3D). Another variant is the contact of the nerve close from its origin at the basilar artery and can be to the brainstem at the cerebello e mesencephalic followed to its meatal segment where the acoustic fissure (Fig. 3E). Other sites of compression are seen artery originates (Fig. 4B). AICA causes arterial depending on how far distal the artery bifurcates compression of facial and vestibulocochlear nerves about the trigeminal nerve; if it bifurcates to close to in most cases; the offending artery may be located the basilar artery, one of the trunks arising from the on the superior or inferior aspect of the REZ of the SUCA may compress the nerve at its axilla (Fig. 3F). facial nerve (Fig. 4C). Dissecting the artery to the A less frequent source of compression is the AICA VII CN can be difficult as it makes a loop at the that usually passes around the pons below the tri- level of the meatus that could be located between geminal nerve; however, it may have a high origin facial en vestibular nerves (Fig. 4D). The loop of the and loop upward to indent the medial or lower AICA can join the VII CN to its entrance to the surface of the trigeminal nerve. The basilar artery CAI, making it difficult to visualize. The PICA can also may wander laterally and compress the medial also be the offending vessel, as its proximal part face of the nerve. More infrequently, the PICA may passes around the brainstem below the VII and VIII reach and groove the undersurface of the trigeminal CN, and can loop superiorly toward them before nerve. The vascular variant giving compression to descending to pass between the lower cranial the V CN may not be easily visible, so when no nerves. This trajectory can also be challenging to 42 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

Fig. 4. Surgical technique for endoscopiceassisted approach of the VII and VIII cranial nerves. (A) 0 endoscope view of the VII and VIII complex at the entrance to the internal auditory canal (B) 30 angled endoscope view through central corridor, between the VII and VIII CN and the V CN: ful trajectory from the antero-inferior cerebellar artery (AICA) can be seen, form its origin at the basilar artery (BA) to the meatal segment, joining the VII and VIII CN's. Vascular contact is seen at the origin of the VII CN at most lateral part of the pontomedullary sulcus (asterisk). The VIII and VII CN's can be differentiated. Note how the VI CN trajectory is altered by the AICA. (C) Closing -up to site of vascular contact between the AICA and VII CN (asterisk). This is the most common site of vascular contact in vascular syndromes of the VII CN. (D) Closing up to the internal auditory canal. Relation of meatal segment of the AICA and the VII and VIII cranial nerves is seen. A loop of the AICA can surround the VII CN at this site, as seen in the image (asterisk).

see but can be identified with a 30 endoscope 3.2.3. Epidermoid cyst at CPA (Fig. 5) through the space between meatus and lower cra- Most epidermoid cysts at the CPA grow between nial nerves. Jannetta [9] and Gardner [11] described the outer arachnoid layer, and arachnoid mem- that the arterial compression of VII and VIII CN branes on the lateral surface of the brain stem, and must occur in a right angle to the nerve at the REZ, as the cyst grows, they fill the space and fissures and exploration can be done with a 30 endoscope between cranial nerves and brains stem, from the through the space inferior to the meatus, as foramen magnum to the tentorium incisura, and as sometimes the REZ is hidden by the flocculus of far as the perimesencephalic cisterns and the the cerebellum or the choroid plexus. If no supratentorial spaces. Posteriorly and superiorly, compression is seen at this location, AICA must be the tumor can extend between the tentorium and followed to the CAI, and a PICA rostral located the upper surface of the cerebellum; medially it can loop must be sought at the REZ. Venous compress the brainstem or cerebellar hemispheres; compression is rare at this location and must be superiorly it can reach the ambient cistern via the looked for at the pontomedullary sulcus or adjacent hiatus of the cerebellar tentorium; and inferiorly, it to the cerebellum's olive. Facial nerve monitoring is can surround the lower cranial nerves [13]. Their mandatory, and abnormal muscular responses can consistency is soft and can be easily aspirated (Fig. be used as an indicator of the effectiveness of the 5A and B), even though they can adhere to vascular procedure [12]. Also, the surgeon must be aware of and nervous structures. The first steps include potential thermal injury to the VII, and VIII CN by opening the outer arachnoid membrane from ten- the endoscope, so prolonged contact must be torium to lower cranial nerves. The cyst's growth avoided. displaces CN laterally, AICA and SUCA against the brain stem and cerebellar petrous surface, and Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 43 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE ORIGINAL RESEARCH

Fig. 5. Surgical technique for endoscopic-assisted resection of epidermoid cyst (A) and (B) Endoscopic view of a right cerebellopontine approach for resection of an epidermoid cyst; access through the superior corridor; cyst content is able to be aspired, so bimanual technique can be used, with one hand holding-up the endoscope, and the other hand using the aspirator. (C) A common site of residual tumor (asterisk) hidden from microscope view is medial to the IX and XI CN. (D) endoscopic view with 30 endoscope: residual tumor hidden medial to the IX and XI CN's, between medulla (Me) and Lower clivus (LC) can be seen with 30 angled endoscope through inferior corridor. (E) Superior corridor is used to explore the cavity of the cyst; entrance window between the V CN, the petrous vein (PV) and the tentorial edge (TE) is widened by tumor growth; residual tumor is seen in the cerebellopontine fissure (black asterisk), and between pons (Po) and middle clivus (MC) (white asterisk). (F) Aspiration of residual tumor described in Fig. 4E allows visualization of basilar artery (BA) and complete surface of the pons (Po).

basilar and vertebral arteries contralateral. For the approach; after initial decompression, the endo- cyst's initial approach, it is advisable to begin scope is advanced through the window that is wider through the wider corridor, which is usually the for initial exploration of cyst cavity; at this point windows above the meatus, between the tentorium aspiration of the cyst's content must be careful, as and VII and VIII CN (Fig. 5A). It is advisable to the cyst's walls can be adherent to vascular and debulk the lesion as in the classical microscopical nervous structures. Residuary content should be 44 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

sought at fissures between the cerebellum and the trigeminal nerve could be the cause of trigeminal brain stem, especially within the space between the neuralgia [16], a theory that was later demonstrated flocculus and the lower cranial nerves (Fig. 5Cand by Jannetta [9] using magnification provided by the D), at the cerebellopontine fissure, and in the space operating microscope. One of the putative advan- between the brainstem, the basilar/vertebral ar- tages of the endoscope as compared with the mi- teries, and the clivus (Fig. 5E and F). croscope is that hidden compression may be identified [17]. There is an estimation that in 3.1%e 4. Discussion 17% of trigeminal neuralgia cases, no vascular compression was found; therefore, these patients Since the onset of neurosurgery, there has been an are a medical and surgical challenge. There are accepted hypothesis that is exposing the brain tissue surgical options when no vascular compression is by any approach during surgery for several hours, found, as the root compression technique described will always translate into brain surface injury. With by Professor Revuelta e Gutierrez et al. [10], with the advent of the surgical microscope, keyhole cra- good surgical results, but high recurrence rates. niotomies emerged as a concept for almost every Radiosurgery is a valid option when a surgical neurosurgical approach, minimizing the size of procedure is not suited, but surgery background craniotomies. As those approaches proved their diminishes good results [18]. Multiple groups have safety and efficacy, it became evident that the loss of demonstrated that endoscopic-assisted approaches, intraoperative light and sight through the limited where the bulk of the procedure is done with the craniotomy caused significantly reduced optical operating microscope, and an endoscope is used to control during surgery. Endoscopic-assisted micro- inspect the nerve before and after decompression, surgery brought 1) increased light intensity, 2) lead to increased identification of vascular contact extended viewing angle, and 3) a clear depiction of and compression, which were not appreciated with details in close-up positions [14]. microscope alone [17]. Teo et al. reported in their Most neurosurgeons prefer the retromastoid series of endoscopiceassisted microvascular suboccipital craniotomy for CPA pathology because decompression that they identified vascular of its familiarity; however, it has its own limitations. compression in all patients with the aid of the The use of endoscope allows for a panoramic view endoscope; in 8% of the cases, no vessel was iden- of the cerebellopontine cistern, which would other- tified with the microscope but was identified with wise be difficult. A high degree of maneuverability the endoscope [19]. Lee et al. reported that in 10% of in narrow cisternal spaces provided by the endo- patients with trigeminal neuralgia, they did not scope enables the surgeon to deal with CPA pa- found vascular compression with a fully endoscopic thology safely. However, with growing experience, technique, but had an 8% improvement in visuali- case selection is of the utmost importance because zation of the offending vessel compared with pre- benign tumors and vascular loops allow dissection vious results with a fully microscopic technique by and decompression without significant hazards by the same group [17]. We found an arterial vessel classical approaches [15]. Our experience on offending the trigeminal nerve in three of five pa- endoscopy-assisted microsurgery is limited to CPA tients treated by endoscopic-assistance when no vascular compression syndromes and cystic lesions. artery was found during microscope inspection. In We use the same surgical position and technique the other two patients, we found vascular contact like the one described for microsurgical approaches, with veins draining to the petrosal venous complex, and we added the endoscope as a tool in cases when performing microdissection to separate arachnoid we did not find the vascular compression by the adhesions to the nerve. All the patients had remis- surgical microscopy view, or when we had limita- sion of facial pain with no recurrence during follow- tions in the surgical field view suspecting incom- up. Another advantage of this technique is that plete resection of CPA cysts contents. there is no need to coagulate the petrous venous Microvascular decompression of the trigeminal complex for complete exploration of trigeminal nerve is the most durable and efficacious treatment nerve; even this is frequently done for CPA surgery for trigeminal neuralgia. Dandy postulated in 1934 and has proved to be safe, we can not forget the risk that arterial compression and distortion of of ischemic complications in the brain stem [5,20]. Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 45 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE

4.1. Surgical techniques for microvascular in every case could not be possible due to tumor decompression of the VII and capsule adherence to surrounding nerves, blood vessels, brain surface, and anatomical gaps. By the VIII CN have evolved in hand with techniques for time they are identified, the forcible stripping of the trigeminal neuralgia. Studies carried out by Jannetta

tumor capsule may cause surgical bleeding and ORIGINAL RESEARCH [21] demonstrated that vascular contact with facial postoperative neurologic dysfunction; therefore, nerve could be an etiology of hemifacial spasm, and sites, where the capsule firmly adheres to the ner- had successful results with microvascular decom- vous or vascular structures, no attempt to remove pression. On the other hand, surgical results with the entire capsule, is suggested. microvascular decompression techniques for Several studies are reporting the use of endo- vestibular nerve pathology as vestibular paroxysms scopic-assisted surgery for CPA schwannomas and are variable and highly depend on selection criteria. meningiomas; it has been used mainly as an adju- In most cases, the offending vessel is the AICA or vant tool for visualization and resection of the tumor PICA, and the site of vascular contact is at the nerve in microscopy blind spots and around corners and REZ. The classical surgical approach allows com- has been useful in improving percentages of tumor plete remission of facial spasm in 80% of cases [22]; resection and predicting the extent of resection although no arterial vessel is found in 10e28.5% of when a residual tumor was left [26]. cases; where visualization advantages with an Complications associated with endoscopic-assis- endoscope can increase the possibility of founding ted procedures of CPA are related to surgical the offending vessel in up to 8% of procedures for bleeding and manipulation of nerve tissue struc- vascular syndromes related to the VII CN [12]. The tures. In order to avoid complications and surgical space and angle for endoscopic access to the VII and bleeding, preventive measures are. VIII complex are more limited than those used for the V CN decompression, and endoscopic-assisted 1. Surgical training, maneuvers could have a higher risk of VII CN 2. To avoid forced lateral movements of the endo- associated complications due to manipulation. We scope when attempting to obtain a certain angle had a transient facial paresis in the patient treated of vision, for hemifacial spasm, and it was probably related to 3. To place and remove the surgical instruments manipulation. and endoscope in the field of vision, Epidermoid Cyst is the third most common tumor 4. To minimize the retraction of the cerebellar that occurs in the CPA; due to its slow growth, an hemisphere during the procedure, epidermoid cyst can remain clinically silent for a 5. To perform neurophysiologic monitoring of long time, and diagnosis is only made when the cranial nerves, and lesion involves the sulci and cisterns that surrounds 6. To avoid traction of venous vessels during sur- the nerves and blood vessels, and complete resec- gical maneuvers. tion of the tumor is highly challenging. A remnant fi tumor is often observed following microsurgical As a result of advanced technologies, the eld of e resection of a CPA epidermoid cyst due to the so- endoscopic assisted surgery is continuously called blind spots in the microscopic field of vision growing, and the advantages in the treatment of [13]. Neuroendoscopic approaches provide superior CPA lesions are well acknowledged. Further inno- illumination and better magnification, and all the vation aims to reduce technical limitations and features of tumor-related anatomy can be clearly render the procedure safer and direct in this noble visualized. Their soft consistency facilitates its area. The characteristics of microscopes and endo- aspiration by a bimanual endoscopic technique, scopes complement one another. The intraoperative with one hand sustaining the endoscope, and the combination of these two powerful visualization e other hand, aspirating the content (Fig. 5A and B). tools in the direction of an endoscopic assisted Angled endoscopes and endoscopic instruments technique expands the effectiveness of microsur- maximize the visualization area, and the full cyst gical procedures in the CPA and can further contents are accessible through the spaces previ- improve surgical results [27]. ously referred (Fig. 5CeF). Complete excision by conventional surgical approaches has been reported 5. Conclusions from 18 to 80% [23,24]. By the endoscopic-assisted Endoscopic-assisted microsurgery of CPA is a safe procedure, complete excision can reach higher rates and efficient procedure that has demonstrated util- and reduce tumor recurrence and postoperative ity as it: 1) extends the surgical field into additional complications [13,25]. Even-so, complete resection 46 JAIME JESÚS MARTINEZ - ANDA ET AL Archives of Neurosurgery ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE 2021;1(1):35e47 RGNLRESEARCH ORIGINAL

intracranial compartments; 2) allows visualization Publication comment #2 and resection of residual tumor not adequately visualized with the microscope; 3) improves the The authors present their experience using prediction of the extent of the resection; and 4) in- endoscope-assisted microsurgery in pathologies of creases the visualization of the vascular structures the cerebellopontine angle. They report their results improving surgical outcomes for vascular syn- in 10 patients with diverse lesions, including mainly dromes of the cranial nerves. vascular compression syndromes and cystic lesions, showing a favorable outcome after surgery without Funding complications. Additionally, they describe the fi anatomical corridors of this region from an endo- This research did not receive any speci c grant scopic point of view in a simple and understandable from funding agencies in the public, commercial, or fi manner. not-for-pro t sectors. The advantages of using the endoscope consist fl mainly of an enhanced vision and illumination of Con icts of interest the deepest regions with minimal - if any- cere- All authors certify that they have no affiliations with bellar retraction. It allows for close inspection of or involvement in any organization or entity with any areas that cannot be otherwise visualized with the financial interest (such as honoraria; educational microscope alone, such as the root entry zones or grants; participation in speakers’ bureaus; member- proximal vascular structures, as well as an angled ship, employment, consultancies, stock ownership, or vision with different lenses, as the authors show in other equity interest; and expert testimony or patent- their report. Another important application of this licensing arrangements), or non-financial interest technique that is not present in this paper is the (such as personal or professional relationships, affili- resection of tumors like meningiomas or schwan- ations, knowledge or beliefs) in the subject matter or nomas in "blind spots" that cannot be visualized materials discussed in this manuscript. using only the microscope. However, we must acknowledge the limitations fi Publication comment and dif culties that may arise with the use of the endoscope in such narrow corridors full of essential Publication comment #1 and delicate structures. The endoscope's view lies at the tip of the rod, so there exists a risk of injury The authors present a well-documented paper on behind the lens if care is not taken when moving the the usefulness of endoscope assistance in micro- endoscope. The use of this tool can lead to better scopic surgery of the cerebellopontine angle. They surgical outcomes in experienced hands and proper have performed anatomical dissections using the technique, but it requires training and a learning endoscope and present the technique's usefulness curve. in 10 patients where they used the endoscope. The paper is well illustrated with excellent quality Diego Mendez Rosito photos that show the widest angle of view when Professor of Neurosurgery using the endoscope. Neurosurgery Department, National Medical Center In my opinion, the assistance of the endoscope in November 20th, Institute of Social Security and Services microscopic surgery, especially at the posterior fossa for State Workers, CDMX, Mexico level, is of great help to the surgeon. I congratulate the authors for their work, as they demonstrate in a References very didactic and convincing way the usefulness of endoscope-assisted surgery. [1] Kurucz P, Baksa G, Patonay L, Thaher F, Buchfelder M, Ganslandt O. Endoscopic approach-routes in the posterior fossa cisterns through the retrosigmoid keyhole craniotomy: Alvaro Campero, MD, PhD an anatomical study. Neurosurg Rev 2017;40:427e48. https:// Professor doi.org/10.1007/s10143-016-0800-1. Neurosurgery Department [2] Hopf NJ, Perneczky A. Endoscopic neurosurgery and endo- scope-assisted microneurosurgery for the treatment of The Padilla Hospital of Tucuman, Argentina e intracranial cysts. Neurosurgery 1998;43:1330 6. discussion Tucuman, Argentina 1336-1337. Archives of Neurosurgery JAIME JESÚS MARTINEZ - ANDA ET AL 47 2021;1(1):35e47 ENDOSCOPIC SURGERY OF CEREBELLO PONTINE ANGLE

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