- Department of Neurosurgery, Hospital of the University of Pennsylvania, 3400 Spruce Street, Silverstein Pavilion 3, Philadelphia, PA 19104
- Division of Neurosurgery, Children's Hospital of Philadelphia, 3400 Civic Center Boulevard, Wood Building, Philadelphia, PA 19104
John Y.K. Lee
Department of Neurosurgery, Hospital of the University of Pennsylvania, 3400 Spruce Street, Silverstein Pavilion 3, Philadelphia, PA 19104
DOI:10.4103/2152-7806.155807Copyright: © 2015 Nayak NR. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Nayak NR, Thawani JP, Sanborn MR, Storm PB, Lee JY. Endoscopic approaches to brainstem cavernous malformations: Case series and review of the literature. Surg Neurol Int 24-Apr-2015;6:68
How to cite this URL: Nayak NR, Thawani JP, Sanborn MR, Storm PB, Lee JY. Endoscopic approaches to brainstem cavernous malformations: Case series and review of the literature. Surg Neurol Int 24-Apr-2015;6:68. Available from: http://sni.wpengine.com/surgicalint_articles/endoscopic-approaches-brainstem-cavernous-malformations-case-series-review-literature/
Background:Symptomatic cavernous malformations involving the brainstem are frequently difficult to access via traditional methods. Conventional skull-base approaches require significant brain retraction or bone removal to provide an adequate operative corridor. While there has been a trend toward limited employment of the most invasive surgical approaches, recent advances in endoscopic technology may complement existing methods to access these difficult to reach areas.
Case Descriptions:Four consecutive patients were treated for symptomatic, hemorrhagic brainstem cavernous malformations via fully endoscopic approaches (endonasal, transclival; retrosigmoid; lateral supracerebellar, infratentorial; endonasal, transclival). Together, these lesions encompassed all three segments of the brainstem. Three of the patients had complete resection of the cavernous malformation, while one patient had stable residual at long-term follow up. Associated developmental venous anomalies were preserved in the two patients where one was identified preoperatively. Three of the four patients maintained stable or improved neurological examinations following surgery, while one patient experienced ipsilateral palsies of cranial nerves VII and VIII. The first transclival approach resulted in a symptomatic cerebrospinal fluid leak requiring re-operation, but the second did not. Although there are challenges associated with endoscopic approaches, relative to our prior microsurgical experience with similar cases, visualization and illumination of the surgical corridors were superior without significant limitations on operative mobility.
Conclusion:The endoscope is a promising adjunct to the neurosurgeon's ability to approach difficult to access brainstem cavernous malformations. It allows the surgeon to achieve well-illuminated, panoramic views, and by combining approaches, can provide minimally invasive access to most regions of the brainstem.
Keywords: Brainstem, cavernoma, cavernous malformation, endoscopic, minimally invasive
Cavernous malformations (CMs) are angiographically occult vascular lesions lined with a single layer of endothelium that displace adjacent brain tissue. The prevalence of CMs is estimated to be 0.4–0.5% in the general population and present clinically with a variety of signs and symptoms including hemorrhage, headache, seizure, or focal neurologic deficit.[
Brainstem CMs are of particular concern given the eloquence of adjacent neural tissue and the high likelihood of symptomatic hemorrhage. Although most supratentorial CMs are discovered incidentally, a series by Porter et al. of 100 patients with brainstem CMs demonstrated that 97% of patients had focal neurological deficits at diagnosis.[
Surgical resection of brainstem CMs is generally considered after two or more symptomatic hemorrhages.[
Based on the two-point method, a variety of skull base approaches may be used to access the entire perimeter of the brainstem. We believe that utilization of the endoscope, in place of the standard operating microscope, improves upon the well-established surgical approaches to brainstem CMs by minimizing trauma and improving visualization. Here we present a series of four brainstem CM resections employing endoscopy as the primary visualization, magnification, and illumination tool, as well as a review of the literature of endoscopic-assisted approaches to brainstem lesions. Combined, the four cases in our series demonstrate that the endoscope can be employed to access most regions of the brainstem.
History and clinical presentation
The patient is a 17-year-old male who presented with headache and right-sided facial numbness. Upon further workup, magnetic resonance imaging (MRI) demonstrated a lesion in the ventromedial pons consistent with a CM. The decision was made to observe the lesion given one symptomatic hemorrhage. However, over the ensuing 3 weeks, he experienced 2 additional episodes of neurological decline involving left hemiparesis, dysphagia, and right 6th cranial nerve palsy.
Given three symptomatic hemorrhages over 3 weeks, the decision was made to pursue surgical resection. The lesion measured 2.1 × 1.7 cm in the largest cross section and presented closest to the surface at the ventromedial pons near the midline [
A 2 surgeon, four-handed technique was used to perform the approach and resection. The sellar floor and basion marked the superior/inferior limits of the bony exposure, and the petrous portion of the internal carotid arteries bilaterally marked the limits of the lateral bony exposure. A midline durotomy was created and extended to the right where there was minimal discoloration of the brainstem. Stereotaxy was used to confirm the location of the lesion. A corticectomy was made and blood products expelled from the cavity [
The patient's left hemiparesis had worsened in the immediate postoperative period, as had the right-sided facial weakness. He had vertical nystagmus and restricted horizontal gaze bilaterally. He was ultimately discharged but presented one month from surgery with cerebrospinal fluid (CSF) rhinorrhea and taken back to the operating room for re-exploration and revision of nonadherent nasoseptal flaps. A ventriculostomy catheter was placed, and an endonasal revision was performed using autologous abdominal fat graft, the previously fashioned nasoseptal flaps, fibrin glue and Avitene (Davol, Warwick, RI). The ventriculostomy catheter was used for CSF drainage for an additional 5 days and subsequently removed. At 2 years follow up, his strength and ocular symptoms had improved considerably, although he continued to have mild residual deficits.
History and clinical presentation
The patient is a 39-year-old female who presented to the emergency room with acute-onset of headache, double vision, and right-sided numbness. Head computed tomography (CT) revealed hemorrhage in the dorsal midbrain and she was admitted to the intensive care unit for observation. During the first evening of her hospitalization, she developed an acute change in mental status with CT evidence of progression of hemorrhage. Clinically, she was somnolent, had difficulty focusing her gaze and had a trace right pronator drift. Subsequent MRI demonstrated a lesion measuring 1.8 × 1.3 cm in the largest cross section consistent with a CM and hematoma located primarily in the left dorsal midbrain extending anteriorly to the left cerebral peduncle and inferiorly to the left middle cerebellar peduncle [
Given progression of hemorrhage on 3 serial CT scans and 2 symptomatic hemorrhages within 3 days, the decision was made to proceed with surgical resection. She underwent a retrosigmoid craniotomy with an endoscopic lateral supracerebellar-infratentorial (SCIT) approach.
The patient was placed in the lateral position. A large, sigmoid-shaped incision was fashioned behind her ear and a 3-cm retrosigmoid craniotomy created. The dura was opened exposing the retrosigmoid area for approach to the cerebellopontine angle (CPA). Using the 2.7 mm endoscope (Karl Storz, Tuttlingen, Germany), the cerebellomedullary cistern was opened to drain CSF.
The endoscope was then inserted along the tentorium, taking care to identify, cauterize, and divide bridging veins. The Mitaka pneumatic holding arm (Mitaka Kohki, Tokyo, Japan) was used to stabilize the endoscope, and standard bimanual techniques were used to dissect the arachnoid adhesions. The 4th cranial nerve was identified and followed to its origin at the midbrain. The arachnoid over the tentorial edge on the lateral aspect of the midbrain was opened, exposing hemorrhagic staining of the leptomeninges on the lateral midbrain immediately under the tentorium and above the 4th cranial nerve [
Postoperatively the patient remained at her neurologic baseline. Postoperative MRI showed no evidence of residual lesion [
At one year follow up, she continued to have numbness of the right arm and leg without weakness. She had intact extraocular movements, and her diplopia had resolved.
History and clinical presentation
The patient is a 59-year-old female who developed hearing loss in the left ear approximately 4 weeks prior to presentation. Three weeks after the onset of symptoms, she also developed left facial paresis and was referred to a neurologist. MRI demonstrated a heterogeneous lesion measuring 1.8 × 1.4 cm in the largest cross section with mixed-age blood products and hemosiderin ring consistent with a CM of the left pons, adjacent to the root entry zones of the 7th and 8th cranial nerves [Figures
On initial neurosurgical evaluation, she had diminished hearing in the left ear and a House–Brackmann grade 3/6 left facial palsy with preserved ability to close her eye. She also had decreased left facial sensation. She maintained an intact gait with normal balance.
Given the progression in symptoms from hearing loss to facial paresis over several weeks, the decision was made to proceed with surgical resection.
The patient was placed in a lateral position and a sigmoid-shaped incision was fashioned behind her ear. A 3-cm retrosigmoid craniotomy was created. Both the 3D Visionsense intraoperative miniature microscope (Visionsense, New York, NY) and the 2.7 mm endoscope were used, stabilized with the Mitaka pneumatic holding arm. The cerebellomedullary cistern was opened under endoscopic visualization to facilitate drainage of CSF. The 7th and 8th nerve complex was identified. Subsequently, the 5th nerve complex and petrosal vein were identified. Old hematoma and staining was seen on the 8th nerve, tracking proximally to the pontine surface at the root entry zone of the 8th nerve [
Normally the 7th nerve sits directly deep to the 8th nerve during the retrosigmoid approach, however, in this case the 7th nerve was separated from the 8th nerve at the root entry zone by the CM. The anterior inferior cerebellar artery was dissected off of the cerebellum, which allowed access to the lesion. Bipolar electrocautery was used to gently access the lesion, at which point the encapsulated CM was encountered. Gentle pressure expelled old blood products. A combination of bipolar electrocautery and round knife was used to dissect the lesion [
Unfortunately, the patient's facial paralysis progressed to a House–Brackmann grade 6/6 postoperatively, and she had lost all hearing on her left side. Immediate postoperative MRI did not show definite residual CM and confirmed the preservation of an associated DVA.
In subsequent months, she underwent a gold weight procedure to protect her left eye, as well as facial re-animation procedures, which has led to some improvement in her facial function. Her 6-month follow up MRI, however, did show evidence of residual CM in the superior aspect of the cavity [
History and clinical presentation
The patient is a 60-year-old female with a history of a medullary brainstem glioma treated with radiation 11 years prior to presentation. Eight years following radiotherapy, she was treated with chemotherapy for neurological deterioration thought to be due to recurrence. She then experienced mild stepwise decline in neurological function culminating in an abrupt right hemiparesis rendering her wheelchair-bound. The patient's neurological examination was remarkable for 2/5 right deltoid weakness and less severe distal right upper extremity weakness. Her right lower extremity demonstrated 2/5 muscle strength throughout. She continued to have good strength on her left side, and her cranial nerves were intact.
An MRI was obtained and demonstrated a well-circumscribed, nonenhancing hemorrhagic lesion in the region of the tumor that appeared to be consistent with a radiation-induced CM. The lesion measured 8 × 9 ×10 mm and presented closest to the surface at the ventromedial cervicomedullary junction [
Given the patient's history and symptoms, the decision was made to pursue surgical resection. Using the two-point method, an endoscopic, endonasal, transclival approach was employed.
A 2 surgeon, four-handed technique was used to perform the approach and resection. Bone from the middle of the clivus down to the ring of C1 was removed using a high-speed drill. The location of the C1 arch was confirmed with both stereotactic guidance and intraoperative X-ray. A narrow, midline bony channel was then drilled to expose the dura anterior to the medulla. The exposure was widened bilaterally but remained medial to the occipital condyles. The apical ligament of the odontoid process was removed to continue the exposure inferiorly to the foramen magnum. A midline durotomy was fashioned inferior to the level of the basilar artery. A region of discoloration was noted on the pial surface [
Necrotic tissue herniated from the pial opening, and a capsule was subsequently identified and removed en bloc using a cupped forceps [
The patient's symptoms remained unchanged in the immediate postoperative period and at 3-month follow up.
Brainstem CMs are challenging entities but can be cured with gross total resection. Given the eloquence of the nearby neural tissue, symptomatic hemorrhages tend to present fairly dramatically followed by periods of improvement. This step-wise course continues as repeat hemorrhages occur. On the other hand, some brainstem CMs have a relatively benign course and may go completely unnoticed throughout one's life. Hence the risk and benefits of surgical resection over the natural history need to be carefully weighed prior to any surgical intervention. Preoperative planning to maximize the chance of complete resection is paramount, as subtotal resection has been shown to result in repeat hemorrhage rates of 62%.[
With any brainstem lesion, we try to choose an approach that provides adequate visualization of the entire lesion, minimizes brain retraction, and provides the working angles needed for complete resection with little disruption to the adjacent parenchyma. Approaches to brainstem CMs generally start with the two-point rule, in which a line is drawn from the center of the lesion to the point where the lesion comes closest to the surface of the brain.[
The “Minimization” of brainstem CM surgery
There have been many series published on brainstem CMs using varying surgical approaches. Spetzler and colleagues were the first to describe the “minimization” of surgical approaches to brainstem CMs by largely abandoning the skull base approaches with the highest morbidity, such as the transpetrosal and subtemporal approaches.[
SCIT approach – posterior or posterolateral midbrain Orbitozygomatic approach – anterior and anterolateral midbrain, interpeduncular region, ventral pontomesencephalic junction, rostral ventral pons Midline suboccipital with or without telovelar approaches – dorsal pons, floor of the fourth ventricle, dorsal cervicomedullary junction Retrosigmoid approach – lateral and posterolateral pons, CPA, lateral middle cerebellar peduncle, rostral lateral medulla Far lateral approach – inferolateral pons, anterolateral medulla.
SCIT approach – posterior or posterolateral midbrain
Orbitozygomatic approach – anterior and anterolateral midbrain, interpeduncular region, ventral pontomesencephalic junction, rostral ventral pons
Midline suboccipital with or without telovelar approaches – dorsal pons, floor of the fourth ventricle, dorsal cervicomedullary junction
Retrosigmoid approach – lateral and posterolateral pons, CPA, lateral middle cerebellar peduncle, rostral lateral medulla
Far lateral approach – inferolateral pons, anterolateral medulla.
Aside from limiting the types of craniotomies and associated skin incisions, recent literature has focused on minimizing the pial incision used to access the CM. Mai et al. have described their operative technique utilizing diffusion tensor imaging and neuronavigation to guide a small pial incision with subsequent piecemeal resection of the CM.[
Applying endoscopic techniques
Given these challenges, we propose that the use of the endoscope can complement the above techniques by limiting the degree of boney resection and minimizing pial openings because the endoscope does not require large working spaces, can improve deep illumination and provides a panoramic view of the surgical cavity compared with the operating microscope.
Briefly, endoscopic approaches in intracranial surgery were primarily based in the treatment of hydrocephalus, and in the 1990s were largely applied to resection of pituitary lesions via transsphenoidal approaches.[
The specific use of the endoscope in surgery on CMs dates back to a 1994 case report by Otsuki et al. describing a frontal approach transcortical, endoscopic resection of a subthalamic region CM.[
For endoscopic endonasal procedures at our institution, the ear, nose, and throat (ENT) surgeon performs the approach and then moves to the patient's left side and works through the left nostril, while the neurosurgeon simultaneously stands on the patient's right side and works through the right nostril. Both surgeons operate with 2 hands. The ENT surgeon generally controls the endoscope, allowing the neurosurgeon to use both hands for dissection. In the retrosigmoid and supracerebellar/infratentorial approaches, the neurosurgeon operates alone using 2 hands for dissection. The endoscope is stabilized by the Mitaka pneumatic holder [
In both of the endonasal, transclival procedures described, exposure and cavernoma resection were performed purely endoscopically, without the use of the operating microscope. For the retrosigmoid and supracerebellar/infratentorial procedures, standard loupe magnification was used for exposure and dural opening, but the endoscope was the sole magnification tool used to approach and resect the cavernoma. While the mini-operating microscope was briefly brought into the field to compare visualization during the retrosigmoid craniotomy, the endoscope was found to provide a superior view and was therefore solely used for the rest of the procedure. It should be noted that unlike an endoscope with instrument ports, such as that used for an endoscopic third ventriculostomy, we used standard microsurgical instruments for removing the CM.
Our technique for resection of the CM itself is similar to that described by Mai et al.[
Ventral pontine and medullary lesions
Regarding the anterior midline pontine and medullary lesions in our series, we pursued a novel endoscopic, endonasal, transclival approach. We have described this approach previously and a similar approach was described by Kimball et al.[
While anterolateral approaches to ventral, medial brainstem lesions continue to be employed, there is a large risk of postoperative motor deficits due to pyramidal tracts.[
Finally, a major challenge associated with both of these cases was obtaining the appropriate reach with the endoscopic tools employed, as most endoscopic instrumentation at this institution were designed for the removal of sellar lesions. Longer instrumentation will likely be beneficial in the future.
While the endoscopic, endonasal transclival approach has potential to resect ventral pontine and medullary lesions, it is critical that the surgeon have significant experience with the relevant anatomy, endoscopic techniques and instrumentation, and a plan to prevent potential postoperative CSF leaks.
Lateral midbrain lesion
A direct midline approach is useful for approaches to the quadrigeminal plate and pineal region,[
Another major benefit of the SCIT approach is the possibility of extending the approach to resect lesions via a transtentorial approach.[
Lateral pontine lesion
A direct retrosigmoid approach was used to resect the lateral pontine lesion. While this approach can be routinely performed with either a microscope or endoscope, the benefit of the endoscope is that extended approaches can potentially be exploited. For example, Samii et al. originally described a suprameatal extension of the retrosigmoid craniotomy, which can be useful to resect lesions extending through Meckel's cave into the antero-medial middle fossa.[
We have described a series of 4 brainstem CMs resected using endoscopic techniques. The endonasal, transclival approach is a technique that we believe provides the most direct approach to midline anterior pontine and medullary lesions. In other regions of the brainstem, the endoscope serves as an adjunct to standard open approaches in order to limit craniotomy size, minimize brain retraction and improve visualization. However, surgeon experience and skill in endoscopic techniques are a high priority before embarking on these approaches, and further refinements in endoscopic tools and techniques are necessary for them to become standard of care.
1. Abla AA, Lekovic GP, Turner JD, de Oliveira JG, Porter R, Spetzler RF. Advances in the treatment and outcome of brainstem cavernous malformation surgery: A single-center case series of 300 surgically treated patients. Neurosurgery. 2011. 68: 403-14
2. Abla AA, Spetzler RF. Brainstem Cavernoma Surgery: The state of the art. World Neurosurg. 2013. 80: 44-6
3. Abla AA, Turner JD, Mitha AP, Lekovic G, Spetzler RF. Surgical approaches to brainstem cavernous malformations. Neurosurg Focus. 2010. 29: E8-
4. Bertalanffy H, Benes L, Miyazawa T, Alberti O, Siegel AM, Sure U. Cerebral cavernomas in the adult. Review of the literature and analysis of 72 surgically treated patients. Neurosurg Rev. 2002. 25: 1-53
5. Brown AP, Thompson BG, Spetzler RF. The two-point method: Evaluating brain stem lesions. BNI Q. 1996. 12: 20-4
6. Cappabianca P, Alfieri A, de Divitiis E. Endoscopic endonasal transsphenoidal approach to the sella: Towards functional endoscopic pituitary surgery (FEPS). Minim Invasive Neurosurg. 1998. 41: 66-73
7. Cappabianca P, Cavallo LM, Esposito F, de Divitiis E, Tschabitscher M. Endoscopic examination of the cerebellar pontine angle. Clin Neurol Neurosurg. 2002. 104: 387-91
8. Chen LH, Zhang HT, Chen L, Liu LX, Xu R ×. Minimally invasive resection of brainstem cavernous malformations: Surgical approaches and clinical experiences with 38 patients. Clin Neurol Neurosurg. 2014. 116: 72-9
9. Cinalli G, Spennato P, Columbano L, Ruggiero C, Aliberti F, Trischitta V. Neuroendoscopic treatment of arachnoid cysts of the quadrigeminal cistern: A series of 14 cases. J Neurosurg Pediatr. 2010. 6: 489-97
10. de Divitiis O, Conti A, Angileri FF, Cardali S, La Torre D, Tschabitscher M. Endoscopic transoral-transclival approach to the brainstem and surrounding cisternal space: Anatomic study. Neurosurgery. 2004. 54: 125-30
11. de Oliveira JG, Lekovic GP, Safavi-Abbasi S, Reis CV, Hanel RA, Porter RW. Supracerebellar infratentorial approach to cavernous malformations of the brainstem: Surgical variants and clinical experience with 45 patients. Neurosurgery. 2010. 66: 389-99
12. de Oliveira JG, Parraga RG, Chaddad-Neto F, Ribas GC, de Oliveira EP. Supracerebellar transtentorial approach-resection of the tentorium instead of an opening-to provide broad exposure of the mediobasal temporal lobe: Anatomical aspects and surgical applications: Clinical article. J Neurosurg. 2012. 116: 764-72
13. Del Curling O, Kelly DL, Elster AD, Craven TE. An analysis of the natural history of cavernous angiomas. J Neurosurg. 1991. 75: 702-8
14. Ebner FH, Koerbel A, Kirschniak A, Roser F, Kaminsky J, Tatagiba M. Endoscope-assisted retrosigmoid intradural suprameatal approach to the middle fossa: Anatomical and surgical considerations. Eur J Surg Oncol. 2007. 33: 109-13
15. Francois P, Ben Ismail M, Hamel O, Bataille B, Jan M, Velut S. Anterior transpetrosal and subtemporal transtentorial approaches for pontine cavernomas. Acta Neurochir (Wien). 2010. 152: 1321-9
16. Gangemi M, Maiuri F, Colella G, Magro F. Endoscopic treatment of quadrigeminal cistern arachnoid cysts. Minim Invasive Neurosurg. 2005. 48: 289-92
17. Garrett M, Spetzler RF. Surgical treatment of brainstem cavernous malformations. Surg Neurol. 2009. 72: S3-9
18. Gore PA, Gonzalez LF, Rekate HL, Nakaji P. Endoscopic supracerebellar infratentorial approach for pineal cyst resection: Technical case report. Neurosurgery. 2008. 62: S108-9
19. Gross BA, Batjer HH, Awad IA, Bendok BR. Brainstem cavernous malformations. Neurosurgery. 2009. 64: E805-18
20. Gross BA, Batjer HH, Awad IA, Bendok BR, Du R. Brainstem Cavernous Malformations: 1390 Surgical Cases from the Literature. World Neurosurg. 2013. 80: 89-93
21. Gross BA, Lin N, Du R, Day AL. The natural history of intracranial cavernous malformations. Neurosurg Focus. 2011. 30: E24-
22. Hadad G, Bassagasteguy L, Carrau RL, Mataza JC, Kassam A, Snyderman CH. A novel reconstructive technique after endoscopic expanded endonasal approaches: Vascular pedicle nasoseptal flap. Laryngoscope. 2006. 116: 1882-6
23. Hauck EF, Barnett SL, White JA, Samson D. The presigmoid approach to anterolateral pontine cavernomas. Clinical article. J Neurosurg. 2010. 113: 701-8
24. Hayashi N, Cohen AR. Endoscope-assisted far-lateral transcondylar approach to the skull base. Minim Invasive Neurosurg. 2002. 45: 132-5
25. Hebb MO, Spetzler RF. Lateral transpeduncular approach to intrinsic lesions of the rostral pons. Neurosurgery. 2010. 66: S26-9
26. Jho HD, Carrau RL. Endoscopic endonasal transsphenoidal surgery: Experience with 50 patients. J Neurosurg. 1997. 87: 44-51
27. Kassam AB, Thomas A, Carrau RL, Snyderman CH, Vescan A, Prevedello D. Endoscopic reconstruction of the cranial base using a pedicled nasoseptal flap. Neurosurgery. 2008. 63: ONS44-52
28. Kimball MM, Lewis SB, Werning JW, Mocco JD. Resection of a pontine cavernous malformation via an endoscopic endonasal approach: A case report. Neurosurgery. 2012. 71: S186-93
29. Lang SS, Chen HI, Lee JY. Endoscopic Microvascular Decompression: A Stepwise Operative Technique. ORL J Otorhinolaryngol Relat Spec. 2012. 74: 293-8
30. Li D, Hao SY, Jia GJ, Wu Z, Zhang LW, Zhang JT. Hemorrhage risks and functional outcomes of untreated brainstem cavernous malformations. J Neurosurg. 2014. 121: 32-41
31. Mai JC, Ramanathan D, Kim LJ, Sekhar LN. Surgical resection of cavernous malformations of the brainstem: Evolution of a minimally invasive technique. World Neurosurg. 2013. 79: 691-703
32. Mizoguchi M, Inamura T, Hikita T, Cheng CL, Ohgami S. Neuroendoscopic biopsy of tectal glioma: A case report. Minim Invasive Neurosurg. 2000. 43: 53-5
33. Morota N, Deletis V, Lee M, Epstein FJ. Functional anatomic relationship between brain-stem tumors and cranial motor nuclei. Neurosurgery. 1996. 39: 787-93
34. Ochalski PG, Fernandez-Miranda JC, Prevedello DM, Pollack IF, Engh JA. Endoscopic port surgery for resection of lesions of the cerebellar peduncles: Technical note. Neurosurgery. 2011. 68: 1444-50
35. Oka K, Kin Y, Go Y, Ueno Y, Hirakawa K, Tomonaga M. Neuroendoscopic approach to tectal tumors: A consecutive series. J Neurosurg. 1999. 91: 964-70
36. Otsuki T, Yoshimoto T. Endoscopic resection of a subthalamic cavernous angioma: Technical case report. Neurosurgery. 1994. 35: 751-3
37. Otten P, Pizzolato GP, Rilliet B, Berney J. 131 cases of cavernous angioma (cavernomas) of the CNS, discovered by retrospective analysis of 24,535 autopsies. Neurochirurgie. 1989. 35: 82-3
38. Porter RW, Detwiler PW, Spetzler RF, Lawton MT, Baskin JJ, Derksen PT. Cavernous malformations of the brainstem: Experience with 100 patients. J Neurosurg. 1999. 90: 50-8
39. Prat R, Galeano I. Endoscopic resection of cavernoma of foramen of Monro in a patient with familial multiple cavernomatosis. Clin Neurol Neurosurg. 2008. 110: 834-7
40. Quinones-Hinojosa A, Chang EF, Lawton MT. The extended retrosigmoid approach: An alternative to radical cranial base approaches for posterior fossa lesions. Neurosurgery. 2006. 58:
41. Recalde RJ, Figueiredo EG, de Oliveira E. Microsurgical anatomy of the safe entry zones on the anterolateral brainstem related to surgical approaches to cavernous malformations. Neurosurgery. 2008. 62: S9-15
42. Reisch R, Bettag M, Perneczky A. Transoral transclival removal of anteriorly placed cavernous malformations of the brainstem. Surg Neurol. 2001. 56: 106-15
43. Robinson JR, Awad IA, Little JR. Natural history of the cavernous angioma. J Neurosurg. 1991. 75: 709-14
44. Samii M, Tatagiba M, Carvalho GA. Retrosigmoid intradural suprameatal approach to Meckel's cave and the middle fossa: Surgical technique and outcome. J Neurosurg. 2000. 92: 235-41
45. Sanborn MR, Kramarz MJ, Storm PB, Adappa ND, Palmer JN, Lee JY. Endoscopic, endonasal, transclival resection of a pontine cavernoma: Case report. Neurosurgery. 2012. 71: S198-203
46. Sandalcioglu IE, Wiedemayer H, Secer S, Asgari S, Stolke D. Surgical removal of brain stem cavernous malformations: Surgical indications, technical considerations, and results. J Neurol Neurosurg Psychiatry. 2002. 72: 351-5
47. Schroeder HW, Oertel J, Gaab MR. Endoscope-assisted microsurgical resection of epidermoid tumors of the cerebellopontine angle. J Neurosurg. 2004. 101: 227-32
48. Shahinian H, Ra Y. Fully Endoscopic Resection of Pineal Region Tumors. J Neurol Surg B Skull Base. 2013. 74: 114-7
49. Shahinian HK, Eby JB, Ocon M. Fully endoscopic excision of vestibular schwannomas. Minim Invasive Neurosurg. 2004. 47: 329-32
50. Shahinian HK, Ra Y. 527 fully endoscopic resections of vestibular schwannomas. Minim Invasive Neurosurg. 2011. 54: 61-7
51. Steiger HJ, Hanggi D, Stummer W, Winkler PA. Custom-tailored transdural anterior transpetrosal approach to ventral pons and retroclival regions. J Neurosurg. 2006. 104: 38-46
52. Uschold T, Abla AA, Fusco D, Bristol RE, Nakaji P. Supracerebellar infratentorial endoscopically controlled resection of pineal lesions: Case series and operative technique. J Neurosurg Pediatr. 2011. 8: 554-64