Technological developments in neuroendoscopy are leading to an expansion of applications into the realm of microneurosurgical procedures. The new dimension that using an endoscope requires insight into different neuroanatomical aspects and a new kind of strategy in planning a microneurosurgical procedure. During the last century evolution of neurosurgical techniques has occurred with the aim to reduce the pre-, intra and post-operative traumatisation of patients undergoing diagnostic and therapeutic neurosurgical procedures. The results of this ongoing process can be observed in today’s microneurosurgery, which uses sophisticated microscopes, microinstruments, neuronavigation and stereotactic techniques. The improvement in diagnostic imaging enables not only precise localisation of lesions but also the accurate determination of topographical relations of specific lesions to individual anatomic variations of intracranial structures. This parallel improvement in diagnostic and surgical techniques gave rise to concept of “keyhole microneurosurgery”.[1] By choosing the correct keyhole approach to a specific lesion, it becomes possible to dramatically reduce the size of the craniotomy, and the dura opening and less brain retraction that contributes to improved post-operative results. However, keyhole approaches have a few shortcomings like narrow viewing angles, reduction of light intensity in the operating field and the necessity for almost coaxial control of the microinstruments. Advantages of endoscopes like increased light intensity while approaching an object, clear depiction of exposed (patho) anatomic structures and extended viewing angle (fisheye effect) to inspect hidden but important anatomical structures without applying additional retraction, can be used to overcome the above mentioned shortcomings of keyhole approaches.[2,3] This gave rise to the concept of endoscopy-assisted microneurosurgery. This study was undertaken to investigate the advantages and limitations of endoscopy assisted cranial microneurosurgery in non-neoplastic lesions.

This prospective observational study was carried out in the Department of Neurosurgery, from August 2016 to November 2018, after obtaining approval from the Institutional ethical Committee. Study included all the admitted patients with intracranial space occupying lesions and intracranial aneurysms who underwent which micro neurosurgical techniques during study period. Patients with contraindications to various radiological investigations which are necessary for endoscopy assisted micro neurosurgery, and unwilling patients were excluded from the study. Written informed consent was obtained from each patient prior to their enrolment in the study. Sociodemographic data of patients were noted in a predesigned proforma. Study parameters included size of craniotomy, complex anatomy incidence and identification, visualization of posterior part of aneurysm clip immediately post clip application. All the patients had undergone Neuro navigation DICOM protocol in cases of intracranial space occupying lesions, MR angiography OR 3-D CT angiography of intracranial vessels and Digital subtraction angiography in cases of intracranial aneurysms. Data thus collected was subjected to statistical analysis and results were drawn.

The mean age of study patients was 33.5 years, and majority were in the age group of 41-50 years. Of total 40 patients, 22 patients were female. In 17 cases, the pathology was located in posterior cranial fossa. In 11 patients, nature of pathology was non-neoplastic, which included aneurysms (Figure 1), A-V malformations, and neuralgias (Figure 2). (Table 1) The patients with non-neoplastic lesions were further analysed.

Table 1: Demographic and Clinical Profile of Study Patients

Figure 1: Image showing Aneurysm of anterior communicating artery

Figure 2: Endoscopic view of Trigeminal nerve compression by loop of SCA

In this study, neuronavigation was used in 15 patients, and angiogram/ venogram was used in 21 patients. Post clipping endoscopic examination of aneurysms showed re-application of clip in 2 patients, and perforator injury in 2 patients. (Figure 3) Follow-up CT angiogram was performed in 5 patients. (Table 2)

Table 2: Intra-operative and post-operative Parameters in Study Patients

Figure 3: Image showing Clipped aneurysm

The most common approach used in this study was Pterional, which was used in 12 patients. (Table 3)

Table 3: Various Surgical Corridors used in Study Patients

In 13 patients, anatomical variations on initial endoscopy were observed, details are summarized in Table 4.

Table 4: Anatomical variations in Study Patients

Intra-operative injury and associated post-operative deficit were observed in 8 patients, among which 2 patients had non-neoplastic lesion and 6 had neoplastic lesions. Details of intra-operative injury and associated post-operative deficit associated with non-neoplastic lesions are presented in Table 5.

Table 5: Details of Intra-operative injury and Associated post-operative Neuro-deficit in Patients with Non-neoplastic lesions

The concept of neuroendoscopy is not new. L’Esoinasse a virologist from Chicago, in 1910, used a small rigid cystoscope to cauterise the choroid plexus for the treatment of congenital hydrocephalus.[4] This encouraged Walter Dandy in 1918 to develop a technique to treat communicating hydrocephalus by extirpating the choroid plexus using cystoscopes.[3] The results were disastrous but he predicted with great foresight that this would evolve into a useful diagnostic and therapeutic tool with improvement of imaging techniques. Fay and Grant in 1923, using a small cystoscope, photographed the ventricle and choroid plexus for the first time. They also attempted to create a fistula through the corpus callosum to permit the escape of ventricular fluid into the subarachnoid space. The first successful endoscopic third ventriculostomy was reported in 1923 by Jason Mixter. Over the next few years, Putnam and Scarff reported better results with endoscopic plexus coagulation.  Renewed interest in neuroendoscopy developed with improvement of illumination, magnification and computer software along with the development of a flexible fiberoptic apparatus.[5] We conducted this study to investigate the advantages and limitations of endoscopy assisted cranial microneurosurgery in non-neoplastic lesions.

Considering the fact that we were dealing with a wide variety of neurosurgical diseases, the mean age of the cohort was found to be 33.5 years. 27.5% of patients were found to be in the age group of 41 to 50 years and 20% were found in the age group of 0 to 10 years. Galzio RJ et al published their results from a 10-year long study observing 181 patients. In their study the mean age was 49.5 years, and authors attribute this variation to study population studied.[6] In our study, proportion of female was higher than males, which is in agreement with previous literature.[6] In our study, majority of patients (54.80%) had isolated posterior cranial fossa diseases, followed by middle cranial fossa lesions (32.25%), 22.5% of patients had anterior cranial fossa lesions, while 12.90% had pathology occupying middle as well as posterior cranial fossa. Attia M et al, in their study focused-on role of endoscopic micro neurosurgery in middle and posterior cranial fossa, found 33% of patients in each group of anterior, middle and posterior cranial fossae lesions.[7] Zhao JZ et al performed endoscopic assisted cranial micro neurosurgery in 89 patients and successfully clipped 88 aneurysms, among which 91% aneurysms belonged to anterior and middle cranial fossae.[8] In our study, non-neoplastic lesions (vascular and others) were found in 27.5% of patients, and neoplastic lesions were found in 72.5% of patients. Patients with non-neoplastic lesions were further analysed in detail. Of these non-neoplastic lesions, 8 patients had aneurysms of the anterior circulation. This is a first time that anybody has extended the use of endoscopic assisted micro neurosurgery to neurosurgical pathologies other than only vascular and skull base diseases.

We observed that 25% of patients had vascular pathologies, comprising aneurysms, av malformations and neuralgias. Among these vascular abnormalities, 8 cases were aneurysms while one case each were an AV malformation and a Trigeminal neuralgia. Vas Guimaraes F et al in their systemic review observed 15 cases of anterior circulation aneurysms and only 9 cases of posterior fossa aneurysms.[9] Apart from aneurysms, we enrolled one case of trigeminal neuralgia which was operated with endoscopic assisted micro neurosurgery. Kher Y et al in their study of 178 patients treated endoscopically for trigeminal neuralgia showed a superior cerebellar artery conflict in 136 cases, AICA conflict in 76 cases and a double vessel conflict in 41 cases.[10] However, in our study, only Superior cerebellar artery conflict was involved in a patient, who suffered post-operative neurological deficit involving mandibular distribution of trigeminal nerve. Yamada S et al studied the role of endoscopy in surgical treatment of arterio-venous malformations. They reported complete excision in 23 out of 25 of their cases with improved morbidity of patients.[11]

During the course of study, 8 aneurysms were clipped, among which 50% were of anterior communicating artery, 25% were of ICA bifurcation and one each from Distal anterior cerebral circulation and Middle cerebral artery bifurcation aneurysm. Yoshioka H et al in their study of neuroendoscopy in cerebral aneurysms observed 34% of their cases to be of anterior communicating aneurysms, and 7% were of posterior circulation aneurysms.[12] A key development in modern neurosurgery is Frameless Neuronavigation, which aids in accurately localizing pathologies within the skull and provides real-time imaging, though it doesn't account for brain shift, a critical factor. In our study, neuronavigation was used in 37.5% of cases, particularly for deep-seated pathologies like lateral and third ventricular tumors and sellar tumors, leading to reduced patient morbidity. Schroeder HW et al highlighted the benefits of frameless neuronavigation suggesting that it improves surgical outcomes by enhancing accuracy and reducing patient morbidity.[13]

The study cohort underwent conventional or MRI-based angiography/venography as needed, with patients having vascular pathologies receiving Digital Subtraction Angiography (DSA). Among the cohort, 52% underwent angiograms, of which 42.85% had conventional DSA. Yamada S et al highlighted the benefits of angiography in managing vascular pathologies and emphasized the importance of multimodal evaluation, including intra-operative endoscopic assessment of the vascular system.[11] We addressed a wide range of pathologies, employing various surgical corridors, and the most frequently used approach was Pterional Craniotomy (30%). Other commonly utilized corridors included retro mastoid sub-occipital, midline occipital sub-occipital, and combinations of different approaches. Menovasky et al highlighted the effectiveness of supraorbital keyhole endoscopic-assisted micro neurosurgery for interpeduncular fossa lesions, including retro sellar epidermoid tumors, aneurysms, and a body tumor.[14] Profeta G et al advocated the use of endoscopic-assisted cranial micro neurosurgery through Pterional craniotomy for anterior circulation aneurysms, particularly those located at the internal carotid artery-anterior communicating artery (ICA-ACOMA).[57]

We observed that endoscopic-assisted surgeries not only improved the delineation of pathologies but also revealed anatomical variations. We found anatomical variations in 30% of study patients. We operated on one patient with a middle cerebral artery bifurcation aneurysm, where a long ipsilateral M1 segment was found, with the aneurysm in the temporal lobe and lenticulostriate perforators originating from the distal M1 segment. Endoscopic evaluation of a right middle cerebral artery aneurysm revealed a long M1 segment with distal perforators near the aneurysm. Ture U et al highlighted the surgical significance of both short and long M1 segments, which impact surgical approach and perforator orientation.[16] Pai SB et al found that perforators in the Indian population originated from the inferomedial surface of M1, equally distributed between proximal and distal origins.[17] We performed post clipping endoscopic evaluation in 8 cases and observed that 25% need clip reapplication and 25% showed perforator injury. Fischer G et al in their study of 1380 aneurysms, performed endoscopic inspection post clipping in 130 procedures with a clip reapplication rate of 20%.[18]

In endoscope-assisted microsurgery, most of the procedure is performed under a microscopic view because of the better image quality. However, endoscopic approaches are used in certain steps. The endoscope is mostly used to look around bony or dural corners, as well as neurovascular structures, to avoid retraction and extensive skull base drilling. Frequently, the endoscope is simply used freehand for inspection. However, when bimanual dissection is required, the endoscope is fixed to a self-retaining holding device, and the surgeon has both hands free for manipulation. Addition of endoscope to neurosurgeon’s armamentarium offers the surgeon a freedom to look beyond the scope of the traditional microneurosurgery.

1. Axel Perneczky, George Fries. Endoscope assisted brain surgery Part I/II-Evolution, basis concept and current Neurosurgery. 1998;42:219−32.
2. Auer LM, Holzer P, Ascher PW, Heppner F (1988) Endoscopic neurosurgery. Acta Neurochir (Wien) 90: 1–14
3. Dandy WE (1922) Cerebral Johns Hopkins Hosp Bull 33: 189
4. L'Espinasse VL: In: Davis E (ed) Neurological surgery, 2nd Lea and Febinger, Philadelphia, 442 pp
5. Endoscopic Neurosurgery (Ramamurthy textbook of neurosurgery) Association of Neurological Surgeons, 1992.
6. Takaishi Y, Yamashita H, Tamaki N. Cadaveric and clinical study of endoscope-assisted microneurosurgery for cerebral aneurysms using angle- type rigid endoscope. Kobe J Med Sci. 2002 Apr;48(1-2):1-11. PubMed PMID: 11912349.
7. Attia, , Alaghoy,I., El Hawary, M. and Abo-Shosha, M.(2018) Endoscopic Assisted Microscopic Skull Base Surgery. Open Journal of Modern Neurosurgery, 8, 187-200. https://doi.org/10.4236/ojmn.2018.82016
8. Zhao JZ, Wang S, Wang YG, Zhao YL, Yu SQ, Wang R, Wang DJ, Zhang D, Li Y.[Application of the neuro-endoscope to the intracranial aneurismal surgery].Zhonghua Yi Xue Za Zhi. 2004 May 17;84(10):799-802. Chinese. PubMed PMID:15200879.
9. Vaz-Guimaraes F, GARDNERl PA, Fernandez-Miranda JC, Wang E, Snyderman Endoscopic endonasal skull base surgery for vascular lesions: a systematic review of the literature. J Neurosurg Sci. 2016 Dec;60(4):503-13. Epub 2016 Jun 21. Review. PubMed PMID: 27327518.
10. Kher Y, Yadav N, Yadav YR, Parihar V, Ratre S, Bajaj J. Endoscopic Vascular Decompression in Trigeminal Neuralgia. Turk Neurosurg. 2017;27(6):998-1006. doi: 10.5137/1019-5149.JTN.17046-16.1. PubMed PMID: 27593827.
11. Yamada S, Iacono RP, Mandybur GT, Anton R, Lonser R, Yamada S, Haugen GE.Endoscopic procedures for resection of arteriovenous malformations. Surg Neurol. 1999 Jun;51(6):641-9. PubMed PMID: 10369233
12. Yoshioka H, Kinouchi H. The Roles of Endoscope in Aneurysmal Surgery. Neurol Med Chir (Tokyo). 2015;55(6):469-78. doi: 10.2176/nmc.ra.2014- 0428. Epub 2015 Jun Review. PubMed PMID: 26041623; PubMed Central PMCID: PMC4628198.
13. Schroeder HW, Wagner W, Tschiltschke W, Gaab MR. Frameless neuronavigation in intracranial endoscopic neurosurgery. J Neurosurg. 2001 Jan;94(1):72-9. PubMed PMID: 11147902.
14. Patra Charalampaki, Ronald Filippi, Stefan Welschehold, Jens Conrad, Axel Perneczky; Tumors of the Lateral and Third Ventricle: Removal under Endoscope-assisted Keyhole Conditions, Operative Neurosurgery, Volume 57, Issue  suppl_4,  1  October  2005,  Pages  ONS–302–ONS–311, https://doi.org/10.1227/01.NEU.0000176638.86772.2D
15. Profeta G, De Falco R, Ambrosio G, Profeta L. Endoscope-assisted microneurosurgery for anterior circulation aneurysms using the angle-type rigid endoscope over a 3-year period. Childs Nerv Syst. 2004 Nov;20(11- 12):811-5. Epub 2004 Jun 23. PubMed PMID: 15221249
16. Türe U, Yaşargil MG, Al-Mefty O, Yaşargil DC. Arteries of the insula. J Neurosurg. 2000 Apr;92(4):676-87. PubMed PMID: 10761659
17. Pai SB, Varma RG, Kulkarni RN. Microsurgical anatomy of the middle cerebral artery. Neurol India. 2005 Jun;53(2):186-90. PubMed PMID:
18. Fischer G, Oertel J, Perneczky A. Endoscopy in aneurysm surgery. Neurosurgery. 2012 Jun;70(2 Suppl Operative):184-90; discussion 190-1. doi:10.1227/NEU.0b013e3182376a36.

PubMed PMID: 21937925