Exoscopic Supraorbital Keyhole Approach for Skull Base Lesions: An Institutional Experience

Abstract

Background In recent times, the supraorbital approach via eyebrow incision has gained tremendous popularity in targeting the anterior skull base and few middle cranial fossa lesions, over the more traditional pterional and frontotemporal approaches. However, the extremely narrow viewing angle through this approach requires frequent adjustments of the operating table and microscope for optimal visualization. Illumination via such a small opening in such deep-seated location was another limiting factor. Keeping these problems and cumbersomeness of microscope in mind, experienced surgeons gradually shifted over to purely endoscopic or endoscope-assisted supraorbital keyhole approaches. But it was also limited due to high cost, steep learning curve, and difficulties faced in blood-filled cavities. To circumvent these limitations of the microscope and endoscope, the supraorbital keyhole approach can be accomplished with an exoscope (ExSOKHA). Although various cranial procedures using exoscope have become well established in contemporary times, there is paucity of studies and literature dedicated specifically to this minimally invasive supraorbital keyhole approach using the exoscope only. Here, we aim to study the feasibility and usefulness of the exoscope in targeting skull base lesions via the supraorbital keyhole approach to determine if it can be used in learning while transitioning from the microscope to the endoscope, with the primary objective being the user friendliness of the exoscope in the SOKHA technique.

Materials and Methods This prospective observational study was conducted in the department of neurosurgery over a period of 7 years. The sample size was 50. The study utilized an exoscope and support arm—2D VITOM rigid-lens telescope (Model 28095 VA, Karl Storz Endoscopy, Tuttlingen, Germany) with a 10-mm outer diameter and a shaft length of 14 cm, light source (Xenon Nova 300, Karl Storz GmBH and Co., Tuttlingen, Germany), camera head, video display monitor, and a holding arm.

Results Out of 50 cases, the majority were pituitary adenomas (30%) and meningiomas (38%), with aneurysms comprising 6%; only 4 cases (8%) had inadvertent frontal sinus opening and 2 cases (4%) had postoperative cerebrospinal fluid (CSF) leak. The duration of surgery ranged from 2 to 4 hours, with the shortest being for aneurysm clipping/CSF rhinorrhea and the longest for meningioma and pituitary adenoma excision. Intraoperatively, exoscope repositioning for adjustment was required for a maximum of nine times, which significantly reduced the overall operative time. Eight cases had near total excision; the remaining tumors had complete excision and the aneurysms had complete clipping. Hospital stay ranged from 4 to 7 days, with mean intensive care unit (ICU) stay of 3 days. None of the patients had any surgical cosmetic deformity. The Glasgow Outcome Scale of all patients was good (4/5 or 5/5). Thus, ExSOKHA offered good results in terms of operative time, frequency of adjustments, completeness of excision and clipping, and recurrence. The results were also comparable for other parameters like inadvertent frontal sinus violation, postoperative CSF leak, hospital stay, cosmetic deformity, and outcome.

Conclusion The exoscope is a further advancement in the telescopic system, which provides a higher focal length (250–550 mm), ergonomically superior surgery with better depth illumination in skull base lesions approached via the supraorbital keyhole approach, significantly reducing operative time and improving resection margins due to increased corner visibility and easy maneuverability. It helps learn neuroendoscopy with the familiar principles of microneurosurgery, possibly shortening the learning curves. It bridges the gap between the endoscope and the microscope as the surgery is performed while viewing the screen (as in endoscope), but without needing to take the scope inside the operative field (as in microscope), making it easier to maneuver while also limiting space occupancy.

Keywords

exoscope - microneurosurgery - neuroendoscopy - skull base lesions - SOKHA

Introduction

In recent times, the supraorbital approach via eyebrow incision has gained tremendous popularity in targeting the anterior skull base and few middle cranial fossa lesions, over the more traditional pterional and frontotemporal approaches. The main objective of this approach was to facilitate adequate access to intracranial lesions while minimizing trauma to the brain, dura, bone, and skin.[1] [2] However, the extremely narrow viewing angle through this approach requires frequent adjustments of the operating table and microscope for optimal visualization. Illumination via such a small opening in such deep-seated location was another limiting factor.[3] [4] Keeping these problems and cumbersomeness of the microscope for this approach in mind, experienced surgeons gradually shifted over to purely endoscopic or endoscope-assisted supraorbital keyhole approaches. But it was also limited due to high cost, steep learning curve, and difficulties faced in blood-filled cavities. To circumvent these limitations of the microscope and endoscope, the supraorbital keyhole approach can be accomplished with exoscope (ExSOKHA). Although various cranial procedures using exoscope have become well established in contemporary times, there is paucity of studies and literature dedicated specifically to this minimally invasive supraorbital keyhole approach using the exoscope only. Here, we aim to study the feasibility and usefulness of the exoscope in targeting skull base lesions via the supraorbital keyhole approach to determine if it can be used in learning while transitioning from the microscope to the endoscope.

Aims and objectives: The aims and objectives of the study were to assess the operated cases of skull base lesions via the supraorbital keyhole approach performed using only exoscope for visualization.

Materials and Methods

A prospective observational study was conducted in the department of neurosurgery of a tertiary care referral center over a period of 7 years.

The sample size was 50.

The inclusion criteria were the following: diagnosed cases of sellar suprasellar lesions, anterior skull base meningioma, anterior circulation aneurysm, and cerebrospinal fluid (CSF) rhinorrhea

The exclusion criteria were the following: previously operated cases, large frontal sinus, and cases lost to follow-up.

Surgical technique: The transciliary supraorbital keyhole approach performed in our study was done as per the standard literary description. The patient was placed in the supine position with a 30-degree head elevation and turned between 15 and 60 degrees to the contralateral side of the incision, which was modified depending on the location of the lesion. Neck extension was such that the zygomatic arch was the highest point to facilitate gravity-assisted retraction of the frontal lobes. Skin incision was taken just above the eyebrow, lateral to the supraorbital notch and extending laterally up to the keyhole of McCartey. Subcutaneous dissection was done from the supraorbital notch to the frontozygomatic suture, protecting the supraorbital neurovascular bundle and frontal branches of the facial nerve, followed by subperiosteal dissection of the temporalis muscle exposing the keyhole burr site. A 25- to 30-mm-wide and 20- to 25-mm high craniotomy was fashioned with high-speed drill with the medial inferior edge around the level of the base and lateral edge up to the sphenoid wing. Inadvertent entry into the frontal sinus was managed by its exteriorization and covering with the periosteal flap. Semicircular durotomy with the frontal base was done. The traditional microsurgical technique using an exoscope was implemented. After watertight dural closure, the bone flap was fixed with miniplates and muscle and fascia sutured to the pericranium, with subcuticular skin closure.

The study utilized an exoscope and support arm—two-dimensional (2D) VITOM consisting of rigid-lens telescope (Model 28095 VA, Karl Storz Endoscopy, Tuttlingen, Germany) with a 10-mm outer diameter and shaft length of 14 cm, light source (Xenon Nova 300, Karl Storz GmBH and Co., Tuttlingen, Germany), camera head, video display monitor, and holding arm with a wide range of motion ([Fig. 1]).

Fig. 1 2D exoscope parts. (A) Exoscope. (B) Clamping jaw. (C) Holding arm. (D) Camera head. (E) Light source cable. (F) Intraoperative setup.

Data collection and analysis: Preoperative data collection included demographic data, clinical presentation, Glasgow Coma Scale, lesion morphology, and frontal sinus. Intraoperative data collection included the duration of surgery from incision to last skin suture, violation of the frontal sinus, difficulty in access and excision, frequency of adjustments, and completeness of excision. Postoperative data collection over a follow-up period of 4 years included complete excision on follow-up MRI at 3 months postoperatively, CSF leakage, cosmetic deformity, hospital stay, outcome at 3 months postoperatively in terms of Glasgow Outcome Scale (GOS),[5] and recurrence. The variables were tested for normality with the Shapiro–Wilk test for normality, Q-Q plots, visual inspection of the histograms, and the z-scores for the degree of skewness and kurtosis. The difference in proportions of categorical variables was determined using the chi-squared or Fisher's exact test. The difference in means of paired quantitative variables was determined using Student's paired t-test or Wilcoxon signed-rank test. Scatter diagrams were used to describe the relationship between two quantitative variables. The correlation coefficient was used to find out the strength of the correlation between two variables. Not all variables met the assumptions required for parametric tests; therefore, nonparametric tests (i.e., Mann–Whitney test, Spearman's correlation) were used for all analyses for consistency. A p-value of less than 0.05 was considered significant.

Results

All 50 cases were preoperatively evaluated in respect to the location and size of the lesion as described in [Table 1]. Intraoperatively, the parameters studied were frontal sinus violation, duration of surgery from skin incision to closure, frequency of adjustments required, and completeness of excision, as described in [Table 2]. Postoperative parameters like completeness of excision/clipping on imaging after 3 months, CSF leak, hospital stay, cosmetic deformity, and GOS are as described in [Table 3].

Table 1 Preoperative parameters

Lesion	Location	Average size (cm3)	Cases (n = 50)
Craniopharyngioma	Sellar suprasellar region	4	10 (20%)
Pituitary adenoma	With suprasellar and parasellar extension	5	15 (30%)
Epidermoid	Suprasellar	6	2 (4%)
Meningioma	Olfactory groove	5	5 (10%)
	Tuberculum sella	4	8 (16%)
	Planum sphenoidal	5	6 (12%)
Aneurysm	Anterior communicating	0.5	3 (6%)
CSF rhinorrhea	Cribriform plate	–	1 (2%)
Total			50 (100%)

Abbreviation: CSF, cerebrospinal fluid.

Table 2 Intraoperative parameters

Lesion	Frontal sinus violation cases	Average duration of surgery (h)	Average frequency of adjustments	Completeness of excision
Craniopharyngioma (n = 10)	0	3	8	Near total: 3 Complete: 7
Pituitary adenoma (n = 15)	2	4	9	Near total: 4 Complete: 11
Suprasellar epidermoid (n = 2)	1	3	8	Near total: 1 Complete: 1
Olfactory groove meningioma (n = 5)	0	4	7	Complete
Tuberculum sella meningioma (n = 8)	0	4	7	Complete
Planum sphenoidal meningioma (n = 6)	0	4	6	Complete
Acom aneurysm (n = 3)	1	2	4	Complete clipping
CSF rhinorrhea (n = 1)	0	2	5	Complete repair

Abbreviation: CSF, cerebrospinal fluid.

Table 3 Postoperative parameters

Lesion	Complete excision/clipping/repair cases (on imaging at 3 mo)	CSF leak cases	Average hospital stay (d)	Cosmetic deformity cases	Average GOS
Craniopharyngioma (n = 10)	7 (70%)	0	7	0	4
Pituitary adenoma (n = 15)	11 (73%)	1	7	0	5
Suprasellar epidermoid (n = 2)	1 (50%)	1	6	0	5
Olfactory groove meningioma (n = 5)	5 (100%)	0	5	0	5
Tuberculum sella meningioma (n = 8)	8 (100%)	0	5	0	5
Planum sphenoidal meningioma (n = 6)	6 (100%)	0	5	0	5
Acom aneurysm (n = 3)	3 (100%)	0	4	0	4
CSF rhinorrhea (n = 1)	1 (100%)	0	7	0	5

Abbreviations: CSF, cerebrospinal fluid; GOS, Glasgow Outcome Scale.

Discussion

The supraorbital keyhole approach is being increasingly preferred over traditional pterional and frontotemporal approaches,[6] due to its advantages like smaller incision, avoiding complete sylvian fissure dissection, better cosmetic results, avoiding temporalis muscle dissection, smaller bone window, and lesser brain retraction with similar outcomes on GOS.[7] In available literature, this approach has been executed using either a microscope or an endoscope or both. Usually, the training in neurosurgery starts with a microscope, and hence most surgeons are comfortable with the microscopic supraorbital approach. Despite its multiple advantages in cranial and spinal surgeries, the supraorbital approach is challenging and technically demanding, and using a microscope makes it even more difficult owing to its limited focal length, inability to see around corners, decreased depth illumination, potentially uncomfortable surgical positions, and bulky size, making frequent adjustments in positions cumbersome. To circumvent these disadvantages of the microscope, endoscopes are used to enhance the reach and visualization, which allow for better views and access to the pituitary fossa, the region under the ipsilateral optic nerve, contralateral segments of the circle of Willis, the anterior third ventricle, the anterior interhemispheric fissure, the upper third of the clivus, the interpeduncular cistern, and the medial aspect of the ipsilateral middle cranial fossa and temporal lobe.[8] The endoscopic-assisted supraorbital approach appeared to be associated with similar effectiveness and safety compared with microscopic alternatives.[9] However, as most neurosurgical trainings are conducted under the operative microscope, it leads to difficulty in suddenly shifting from microneurosurgery to endoneurosurgery, especially for narrow corridor approaches like this one, due to lack of hand–eye coordination, small-diameter delicate endoscope with a very short focal distance, unfamiliar instruments that often collide with the endoscope, frequent lens fogging, visual obscuration, narrow working space, and unfamiliarity in the 2D view.[10] The exoscope, being a hybrid instrument between the two, ameliorates the disadvantages of both in performing this approach. Its usefulness has been well established in routine cranial and spinal surgeries.[11] [12] [13] However, there is limited literature on the exoscopic supraorbital keyhole approach. There is no study demonstrating the outcomes of this approach using an exoscope.

In this study, out of 50 cases, the majority were pituitary adenomas (30%) and meningiomas (38%), with aneurysms comprising 6% ([Fig. 2] and [Fig. 3]). This case selection profile was similar to that described in the literature by Ndlovu et al using this approach.[14] The pituitary adenomas were subjected to SOKHA in place of the regular transsphenoidal approach as they had normal sella with a larger suprasellar component as well as significant parasellar extension. Of them, only four cases (8%) had inadvertent frontal sinus opening and postoperative CSF leak in two cases (4%), which resolved on conservative management. Our complication rate was lesser than that described by Ndlovu et al.[14] The duration of surgery ranged from 2 to 4 hours, with the shortest being for aneurysm clipping/CSF rhinorrhea and the longest for meningioma and pituitary adenoma excision. Intraoperatively, exoscope repositioning for adjustment was required for a maximum of nine times in the cases illustrated in [Table 2], which significantly reduced the overall operative time. Of all 50 cases, only 8 cases had near total excision, where the lesion was invading into the cavernous sinus, who then underwent a postoperative Gamma Knife therapy. The rest of the tumors had complete excision and aneurysms had complete clipping with preservation of the branching vessels and perforators, which was corroborated on postoperative MRI of the brain done after 3 months. Hospital stay ranged from 4 to 7 days, with mean intensive care unit (ICU) stay of 3 days, which was slightly more as compared to the study by Ndlovu et al (mean ICU stay: 2.2 days).[14] None of the patients had any cosmetic deformity around the surgical site. The GOS of all patients was good (4/5 or 5/5).

Fig. 2 Illustrative case 1: A 40-year-old woman with tuberculum sella meningioma approached via the right supraorbital keyhole craniotomy. (A) Contrast-enhanced MRI of the brain, (B) intraoperative exoscopic view showing meningioma being dissected off from optic nerve, and (C) immediate postoperative contrast-enhanced CT of the brain showing complete excision. ICA, internal carotid artery.

Fig. 3 Illustrative case 2. A 50-year-old man having sellar epidermoid with parasellar and suprasellar extension approached via the right supraorbital keyhole craniotomy. (A) MRI T2 coronal view, (B) Diffusion-weighted imaging (DWI) axial view and (C) T1 sagittal view showing epidermoid lesion (green arrowhead). (D) Immediate postoperative contrast CT (brain) showing complete excision of the lesion (orange arrows) and (E) intraoperative image of the lesion and surrounding structures. ACA, anterior cerebral artery; ICA, internal carotid artery; MCA, middle cerebral artery.

Thus, ExSOKHA offered good results in terms of operative time, frequency of adjustments, completeness of excision and clipping, and recurrence. The results were also comparable for other parameters like inadvertent frontal sinus violation, postoperative CSF leak, hospital stay, cosmetic deformity, and outcome.[14]

Furthermore, everyone in the operating room, including assistants, trainees, and staff, can appreciate the same quality of images as those of the surgeon.[15] Limitations include a lack of stereopsis in 2D exoscopes, although this has been resolved with 3D models, physical discomfort from prolonged usage of 3D glasses, and difficult repositioning, although this has also been addressed with models that include a foot-pedal controller and sterile pilot unit.

Conclusion

The exoscope is a further advancement in the telescopic system, which provides higher focal length (250–550 mm), ergonomically superior surgery with better depth illumination in skull base lesions approached via the supraorbital keyhole approach, significantly reducing the operative time and improving the resection margins due to increased corner visibility and easy maneuverability. It helps in learning neuroendoscopy with the familiar principles of microneurosurgery, possibly shortening the learning curves.

Conflict of Interest

None declared.

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Publication History

Article published online:
18 March 2025