Endoscopic-Assisted Microsurgery for Vestibular Schwannomas: Operative Nuances
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.319208
Source of Support: None, Conflict of Interest: None
Keywords: Endoscopic neurosurgery, intracanalicular vestibular schwannoma, meatal drilling, vestibular schwannomasKey Message: Using the best of both the microscope and endoscope while operating on vestibular schwannomas can help in achieving a safe radical tumor removal along with the advantage of minimal access surgery.
Over the last century, vestibular schwannomas surgery has evolved from finger enucleation to electro-physiologically guided microsurgical dissection to preserve hearing. Skull base surgeons the world over have toiled over decades refining the surgical approach and dissection techniques to improve patient outcomes. The introduction of the operating microscope by Theodor Kurze in the year 1957 marked the beginning of a new era in brain surgery. The next paradigm shift came in the year 1910 by Victor Lespinasse with the introduction of endoscopes for fulgurating choroid plexus in infants with hydrocephalus. With further progress endoscopes were used as inspection around the corners during microscopic surgeries. Gradually as the instrumentation and skill sets improved, surgeons started performing drilling as well as dissection under direct endoscopic vision. Intracanalicular extension often requires drilling of the posterior meatal wall to safely deliver out the tumor. This drilling risks damage to middle ear structures which are in close proximity. Smaller tumors pose further difficulty due to an acutely angled and nondilated internal auditory meatus (IAM). Additionally, vascular disruption and even damage to endolymphatic sac/duct also lead to sensorineural hearing loss even with a physically preserved cochlear nerve.
A detailed study of the preoperative temporal bone HRCT with endoscopic- assisted drilling and dissection of the meatus provides the best chances of preserving hearing while ensuring complete tumor removal.,
We present here the step-by-step approach to perform safe removal of a small right-sided vestibular schwannoma with intracanalicular extension via the endoscopic-assisted microsurgery technique.
Video link: https://youtu.be/oDsPnSNiD7g
Video timeline with audio transcript (Minutes)
In this operative video, we present to you a case of small right vestibular schwannoma operated through the endoscopic-assisted microsurgery technique. Appropriate consent was taken from the patient before publishing this video. This 40-year-old male presented with the complaint of right ear fullness for 12 months. Clinically, there were no obvious neurological deficits. [00:00:30]
Pure tone audiometry showed a mild sensory neural hearing loss in the right ear. A gadolinium-enhanced MRI revealed a small right vestibular schwannoma, mainly intracanalicular and reaching up to the fundus of the IAM, with small CSF cap. The patient was initially offered to undergo a gamma knife radiosurgery at another center which he refused and opted for observation.
He returned 3 months later with complaints of reduced hearing on the right side. Citing unwillingness to travel to another city for GKRS, the patient chose to undergo surgery. Temporal bone HRCT delineated the labyrinthine anatomy in relation to the intracanalicular tumor.
On tracing the fundus-sinus line, it was obvious that a routine craniotomy and completely microscopic approach to the fundus would cause disruption of the semicircular canal. Microscopic removal through a larger suboccipital craniotomy would require excessive cerebellar retraction. Therefore, he was planned for an endoscopic-assisted microsurgery via a mini craniectomy.
For patients with a mobile neck, supine position with head tilt is preferred, and for short-neck patients, the park bench position. The idea is that the jugular veins should be freely draining.
The skull is fixed in a three-pin clamp and the patient is strapped. We prefer a linear incision with a small oval burr hole with its long axis parallel to and its margin based on the sigmoid sinus. A curvilinear durotomy is preferred over cruciate to ensure a quick closure and reduces the chance of CSF leaks.
The patient attempt to drain CSF from the subarachnoid spaces has to be made slowly and gradually over the next few minutes. Even when the cerebellum is seen full over the durotomy, CSF can be drained in small increments with careful microdissection. Once adequate CSF has been drained, a 0 degree endoscope is introduced early to delineate the anatomy of the CP angle.
Alternative inspection of the CP angle with a microscope and an endoscope helps to understand the 3D anatomical disposition of the neurovascular structures. Here, the petrous bone is seen in the superior half and the petrosal surface of the cerebellum in the lower half. The inferior surface of the tent with the petrosal vein entering at the petrotentorial junction is on the left.
Followed by the extracanalicular portion of the vestibular schwannoma. Inferiorly, the seventh to eighth nerve complex is seen being pushed posteriorly by this tumor. Next, the microscope is brought in to start the initial decompression. Some surgeons perform a completely endoscopic tumor removal. We practice a combined approach to have the best of both the visualization techniques.
The microscope provides excellent depth perception and ease of bimanual dissection. The endoscope provides a panoramic close-up view, look around the corners and work with curved instruments. For the decompression of small tumors, we prefer minimal usage of electrocautery to minimize thermal damage to overlying nerves.
These smaller tumors usually do not have large intratumoral vessels, and thus, small bleeders are easily controlled with the warm saline irrigation or a gentle pressure.
Next, dura over the posterior meatal lip is cauterized, incised, and reflected off. A 2 mm diamond drill is then used to incrementally remove bone of the posterior meatal wall. The tumor is teased out gently using a hook and small suction cannula under a low suction pressure avoiding pulling. This microscopic drilling is done till the anticipated semicircular canal is safe based on the preoperative HRCT.
Here, one can appreciate that the visible IAM is free of tumor and the seventh to eighth nerve complex is seen entering within. Thereafter, a 30 degree endoscope is introduced.
A higher-angle endoscope (45 or 75 degree) is not useful as the visualization achieved by it cannot be worked upon. This is because the angled instruments have the limitations of access and maneuverability in such tight spaces. Using an angled suction cannula at a low negative pressure, the loose tumor is gently sucked out in small bits. The suction is always introduced and moved away from the nerve to prevent any inadvertent damage.
The posterior meatal wall is further drilled incrementally with a 2 mm diamond burr till all the tumor is freed and sucked out from the IAM. During this whole process, the field needs to be kept clear of blood with generous flow of saline to maintain continuous visualization of the facial nerve.
After complete tumor removal, arachnoid in the fundus of the IAM is visible along with the neural complex. A gentle but thorough saline irrigation is done to drive out the minute tumor fragments and to confirm hemostasis. Dura is closed in a watertight fashion and skin closed in layers.
A postoperative contrast-enhanced C.T. scan done the next day shows a complete tumor removal from both intra and extracanalicular spaces. Preservation of the middle ear labyrinthine structures can be appreciated along with the drilled out posterior lip of the IAM. Postoperatively, the patient did not have any facial weakness and a 3-year follow [00:08:30] up is free of any tumor recurrence.
Surgical removal of vestibular schwannomas has evolved over the last century not only with respect to the instrumentation but also in terms of visualization, magnification, and illumination. Surgeons are using endoscopes at various levels ranging from inspection to complete endoscopic removal. We believe that a collaborative approach using the best of microscopy and endoscopy can give the best chances of functional preservation. The exclusive utilization of microscope has a poor reliability for evaluating canalicular residue. Endoscopic assistance not only decreases the amount of bone drilling in the posterior wall of the IAC, but also provides optimal views toward the fundus of the IAC to achieve complete resection safely. This is especially true with small tumors without expansion of internal auditory meatus.
A full and detailed consent from the patient/guardian has been taken. The patient's identity has been adequately anonymized. If anything related to the patient's identity is shown, adequate consent has been taken from the patient/relative/guardian. The journal will not be responsible for any medicolegal issues arising out of issues related to patient's identity or any other issues arising from the public display of the video. The journal reserves the right to withdraw or pull out the video at any point of time without providing any reason whatsoever.
Disclosure: The authors hereby certify that the work shown here is genuine, original, and not submitted anywhere, either in part or full. They transfer the full rights of the video to Neurology India. All the necessary permissions from the patient, hospital, and institution have been taken for submitting this video to Neurology India.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.