Extra-ventricular application of flexible neuro-endoscopy in intracranial epidermoid cyst open resection: A novel technique

Abstract

Background:

Intracranial epidermoid cysts are congenital lesions with a predilection for midline or paramedian spaces including the cerebellopontine cistern, fourth ventricle, or the interhemispheric fissure. The only effective treatment is resection. Conventionally, epidermoid cysts are resected with open transcranial approaches. The advent of neuroendoscopy has allowed for less invasive options and can assist open microneurosurgery in better visualization of the lesion around corners. As rigid neuroendoscopes are limited in accessing tight corners, flexible endoscopy has been proposed to assist neurosurgery, with the additional angles of view and the advantage of tip-steerability. We present a case of flexible endoscopy assistance in epidermoid cyst resection.

Case Description:

A 41-year-old woman presents with a posterior fossa epidermoid cyst, where suboccipital craniotomy and flexible endoscopy-assisted resection allowed for visualization of the remaining cranial portion of the tumor in the 4^th ventricle without excessive brain retraction, guide microsurgical instruments into the cavity, and confirm clearance of clots and debris in the cerebral aqueduct. A 62-year-old man presents with an interhemispheric epidermoid cyst, where bifrontal craniotomy, pure left hemispheric approach, and flexible endoscopy assistance allowed resection of cystic components in difficult areas with an acute angulation.

Conclusion:

We illustrate the novel use of flexible endoscopy to assist with the resection of a recurrent posterior fossa epidermoid cyst and an interhemispheric epidermoid cyst.

INTRODUCTION

Epidermoid cysts consist of ~1% of intracranial tumors, arising from ectodermal cells with keratin-filled epithelium.[6] Complete resection is curative but challenging due to its envelopment of cranial nerves and vasculature and multicompartmental cisternal involvement. Traditionally managed through microsurgery, neuroendoscopy offers less invasive options, especially for skull base lesions.[13] Transcranial rigid endoscope-assisted microsurgery aids visualization but is limited by linear trajectories. Flexible endoscopes enable nonlinear navigation yet remain underutilized in neurosurgery. There have been reports on its intraventricular use.[8,10,11] We illustrate flexible neuroendoscopy in resecting extraventricular posterior fossa and interhemispheric epidermoid cysts.

CASE DESCRIPTION

Case A

A 41-year-old female underwent a suboccipital craniotomy 15 years ago for a posterior fossa epidermoid cyst with medullary compression. It was subtotally removed with the adherent parts to the medulla left behind. Serial magnetic resonance imaging (MRI) showed gradual remnant enlargement, extending cranially to the cerebral aqueduct and caudally to C2 lamina, without hydrocephalus. Examination revealed bilateral horizontal nystagmus; cranial nerves were otherwise normal.

The intraoperative video illustration of case A is shown in video 1. The patient was placed in a prone position. Brainstem auditory-evoked responses, four-limbs and facial transcranial motor-evoked potential, somatosensory evoked-potential, and electromyography (EMG) of bilateral cranial nerves VII, IX-XII were monitored. The head was fixed in Mayfield pins, and the neck was semi-flexed. Medtronic StealthStation S8 EM Navigation System with malleable suction was used. The prior midline incision was reopened, and suboccipital craniotomy was performed, sparing the posterior C1 arch. The epidermoid cyst was debulked under the microscope with suction and Cavitron Ultrasonic Surgical Aspirator. The main bulk of the cyst was located between the cerebellar hemispheres, ventral to the cerebellar vermis, and dorsal to the superior and inferior medullary vela, with extension into the fourth ventricle.

A single-use flexible endoscope (Karl Storz GmbH, Item 091361-01, 3.5 mm outer diameter, 1.2 mm working channel, 65 cm working length, resolution 400 × 400 pixels) with a 300W Xenon light source was used for visualization of the tumor and suction through the working channel and assistance. The working channel was connected to controlled intermittent suction and assisted in suction of the tumor. We confirmed caudal gross total resection, visualizing C1-C2 nerve roots and accessory nerve. Cranially, it assisted cyst removal by applying gentle traction with direct suction force and provided visualization for guidance of microsurgical instruments (including malleable suction devices (Integra MicroFrance, Item MCEN347), angled-tip bipolars, and the Medtronic malleable suction tip with electromagnetic navigation (Medtronic, Item 9735015, 14.5 cm length) for resection. “Torque” maneuvers, rotating the endoscope shaft while flexing the tip, achieved more degrees of freedom at the tip with flexible viewing trajectories. The cerebral aqueduct was clearly visualized and confirmed to be free of obstructive clots or debris. Hydrocortisone solution (100 mg diluted in 1L of Hartmann’s solution) was used to irrigate the surgical field. A small part of the cranial part of tumor was left behind due to sustained signal from the facial EMG. Postoperatively, she had diplopia, with partial right abducens nerve dysfunction that improved at 1-month follow-up. A week-long dexamethasone course was given, and there were no signs or symptoms of Mollaret’s meningitis. She had minimal neck pain at discharge without the need for analgesics. 3-month postoperative MRI confirmed satisfactory brainstem decompression with subtotal resection [Figure 1].

Figure 1:

Magnetic resonance imaging (MRI), diffusion-weighted imaging sequence for Case A. (a) the preoperative MRI showing an epidermoid cyst in the posterior fossa, between the two cerebellar hemispheres. (b) the postoperative MRI, which shows the near-total removal of the lesion.

Case B

A 62-year-old male presented with a 1-year history of progressive cognitive decline. There were no focal neurological deficits. Brain MRI showed a 6 cm interhemispheric T1-hypointense and T2-hyperintense epidermoid cyst. It led to entrapment of the left occipital horn and trigone, exerting mass effect onto the body and splenium of corpus callosum.

The patient was placed supine with the head in Mayfield pins, slightly flexed. Linear left frontal incision was made crossing midline. Medtronic StealthStation S8 EM Navigation System was used. Bi-frontal craniotomy was fashioned, 55 mm in size, just anterior to the coronal suture, predominantly on left-sided exposure with unroofing of the superior sagittal sinus. As the cyst’s left side was larger, we adopted a left anterior interhemispheric approach. After microsurgical removal of the left-sided component, the falx was coagulated and cut. Most of the right-sided component was removed under the microscope. However, the right superior portion was difficult to access with microscopic view, due to a “down-and-up” angulated viewing trajectory. Flexible endoscopy was used to resect this component with similar techniques to the first case. Retro-flexing the tip of the endoscope, analogous to the “J-maneuver” in esophagogastroduodenoscopy, provided good visualization. Irrigation with hydrocortisone solution was performed. The patient had no added deficits or features of aseptic meningitis. 3-month postoperative MRI confirmed satisfactory removal [Figure 2].

Figure 2:

Magnetic resonance imaging (MRI), T2 FLAIR sequence for Case B. (a) the preoperative MRI showing a large 6 cm T2-hyperintense epidermoid cyst with restricted diffusion in the interhemispheric fissure. It led to entrapment of the left occipital horn and trigone and exerted mass effect onto the body and splenium of corpus callosum. (b) the postoperative MRI, which showed the extent of removal of the cyst.

For both patients, the procedures were included in routine care and therefore ethics approval was not required. The patients gave informed consent.

DISCUSSION

Complete resection of epidermoid cysts is crucial to reduce recurrence rates. We report the first use of flexible endoscopy for extraventricular epidermoid cyst resection. Its steerable flexible endoscope navigates tight, curved spaces like ventricles or cisterns, minimizing tissue trauma, with an imaging system and working channels for micro-instruments (e.g., biopsy forceps, suction). Traditional fiber-optic flexible endoscopes have lower resolution than rigid endoscopes.[4] However, advances like camera-on-a-chip endoscopes provide higher resolution and wider fields of view by capturing digital images at the tip of the scope, enhancing visualization of neurovascular structures in confined spaces.[3]

In both cases, we employed the camera-on-a-chip flexible endoscope. In Case A, it enabled visualization and dissection of the tumor’s cranial portion without brain retraction. We preserved the posterior C1 arch, minimizing dissection of nuchal musculature to reduce refractory postoperative neck pain. In Case B, since the lesion had crossed the midline, a bilateral interhemispheric approach would be required, which would involve cortical manipulation and possible dysfunction. Using flexible neuroendoscopy to access the right superior portion of the tumor with the “J-maneuver” [Figure 3] enabled a pure left anterior interhemispheric approach, a technique not previously reported in neurosurgical literature.

Figure 3:

A schematic showing the “J”-maneuver used for flexible neuroendoscopy.

Flexible endoscopy has previously been used for a range of indications in the literature, from intraventricular surgery, to emergency surgery including clot evacuation of subacute subdural hematomas,[5,7] both as a standalone tool and assisting open surgery. A systematic review and meta-analysis on rigid and flexible neuroendoscopy utilization for endoscopic third ventriculostomy (ETV) in pediatric hydrocephalus showed that there was no significant difference in ETV success and complication rates,[9] illustrating the efficacy and safety of flexible neuroendoscopy in intraventricular surgery. Moreover, Feletti et al. described the use of flexible endoscopy to clear aqueductal clots after posterior fossa ependymoma resection through fourth ventricle access, using a syringe through the endoscope’s channel.[2] Similarly, in Case A, we accessed the tumor’s cranial portion in the fourth ventricle, confirming clot clearance in the aqueduct. Flexible endoscopy has also been used as an adjunct to extra-ventricular pathologies such as vestibular schwannoma, where it was deployed in the internal acoustic canal to detect any residual tumor. However, in this case, it was not directly involved in the resection of the tumor.[1]

Our case series identified key challenges with flexible neuroendoscopy. Its nonlinear approach creates a steep learning curve, risking operator disorientation compared with linear views of the rigid endoscope. Neuronavigation can mitigate this by tracking the endoscope tip in real-time using electromagnetic glidewires.[12] Moreover, avoiding withdrawal in a bent configuration after employing the “J-maneuver” was essential to protect neurovascular structures. In addition, we noted intraoperative electrophysiological monitoring caused intermittent video quality interference. Nonetheless, we also considered a 45° or 70° rigid endoscope for assistance in the surgeries, with a larger optic channel size, visual field, and resolution. However, unlike flexible neuroendoscopy, it may not fully access areas such as the 4^th ventricle in the posterior fossa surgery or other deep spaces with tight corners without placing pressure on the adjacent brain. Therefore, the flexible neuroendoscope has proved to be a beneficial tool in assisting open craniotomy for extra-ventricular indications.

Flexible neuroendoscopy’s limited adoption in neurosurgery stems from several challenges. The lack of specialized tools for the working channel, currently limited to micro-graspers and a monopolar probe, restricts surgical maneuvers; custom microscissors and dissectors could enhance capabilities. Yang et al. demonstrated the use of cup biopsy forceps (commonly used in uroscopic procedures) for biopsy of a tectal lesion in endoscopic intraventricular surgery, with the advantage of a larger biopsy sample due to the oval cup, with a flexible shaft, resulting in less friction in the working channel with minimal manipulation of the flexible endoscope position.[14] In our cases, flexible neuroendoscopy mainly served to guide malleable instruments into deep corners of the surgical cavity, and we did not pass tools through its working channel. In addition, bimanual dissection is not feasible, hindering intricate work on structures like cranial nerves or perforators. Monopolar electrocautery is the only hemostatic option in flexible endoscopy and is less effective than microsurgery, making flexible endoscopy best suited for avascular pathologies like epidermoid cysts.

Advances in technology facilitate flexible endoscopy as a valuable adjunct for accessing confined spaces like the posterior fossa or ventricles, compared to traditional microscopes or rigid endoscopy. Our novel extraventricular application highlights its potential, which could expand with surgeon expertise and specially-designed instruments.

CONCLUSION

We describe the use of flexible neuroendoscopy as a novel surgical adjunct in the excision of posterior fossa and interhemispheric epidermoid cysts. Expansion of specially designed surgical tools can expand its application to wider pathologies. We believe the flexible endoscope can represent a new, versatile tool in the neurosurgeon’s armamentarium.

Ethical approval:

Institutional review board approval is not required.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Video available on:

https://doi.org/10.25259/SNI_939_2025

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