Endoscope-Assisted Retromastoid Intradural Suprameatal Approach for Trigeminal Schwannoma
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.299137
Source of Support: None, Conflict of Interest: None
Keywords: 5th nerve, operative video, retromastoid, schwannoma, trigeminal nerve
Trigeminal schwannomas (TSs) are the most common non-vestibular intracranial schwannomas accounting for 0.8% to 8% of all intracranial schwannomas., It is usually seen in the age group of 20 to 50 years, presenting in 70% of patients with trigeminal sensory symptoms. It can extend into different intracranial and extracranial compartments depending on the parts of the trigeminal nerve involved. It can arise from the trigeminal root, Gasserian ganglion More Details, or one of the peripheral branches. The surgical approach is decided based on the location and size of the tumor. Of late numerous surgical techniques have evolved, leading to improved chances of gross or near-total excision.,,, Herein, we demonstrate surgical decompression through Endoscopic Assisted Retrosigmoid Intradural Suprameatal Approach (EA-RISA).
Herein, we are describing a case of a 29-year-old male patient presenting with progressive left facial sensory disturbances, headache, difficulty in chewing, swallowing difficulties, and imbalance while walking for 2 years. On examination, the patient had impaired tandem gait, reduced facial sensation to a light touch on the left side. There were no other neurological deficits. He was evaluated with contrast-enhanced magnetic resonance imaging (MRI) brain, which revealed 4.8 × 2.6 × 2.4 cm homogenously enhancing extra-axial dumbbell-shaped mass lesion in the left cerebellopontine angle with extension into Meckel's cave with predominant posterior fossa component.
Based on the clinical signs and symptoms and radiological findings, the possibility of a TS was considered.
The video in this article demonstrates endoscope assisted microsurgical excision of left trigeminal dumbbell schwannoma operated through the left RISA. Though multiple skull base approaches are available for excision of TS, a single posterior approach can be used to remove tumors, especially if the posterior fossa component is predominant. Besides, the use of an endoscope further enhances the possibility of complete removal through the posterior approach.
Left Retromastoid Suboccipital Intradural Suprameatal Approach was considered as the tumor had a predominant posterior fossa component with a small middle fossa component (Samii's type C1). The patient was positioned in the right lateral position with the head fixed by three-point fixation and rotated, flexed, and laterally flexed so as the left mastoid is at the highest point. Intra-op neuromonitoring was done using brainstem auditory evoked response (BAER). The skin incision marked two fingerbreadths behind the auricle. Left retromastoid suboccipital craniotomy performed, dura opened K-shaped and raised based on the transverse and sigmoid sinus. Cerebrospinal fluid (CSF) was released from the cisterns to relax the cerebellum. Tumor internal decompression, mobilization, and piece-meal excision done keeping the arachnoid plane intact. Near-total excision was done by endoscope-assisted microsurgery. An endoscope was used after adequate microsurgical decompression, to identify a small residual lesion in the postero-lateral aspect of Meckel's cave behind the trigeminal nerve. The postoperative scan revealed a small residual lesion in Meckel's cave region, which is planned for Gamma Knife Radiosurgery (GKRS). A step by step video description is given below.
Video Link: https://www.youtube.com/watch?v=0bxZ3X_R09w
Video timeline with audio transcript:
0.01 s: This is an interesting case of a trigeminal schwannoma operated using the endoscope-assisted microsurgery.
0.09 s: This was a 29-year-old male who had a small schwannoma diagnosed 3 years ago, and which grew rapidly and had sensory changes, difficulty walking, and swallowing problems.
0.23 s: You can approach this tumor either anteriorly or posteriorly. The component posteriorly was fairly large, and hence going retromastoid was considered better.
0.33 s: So, we planned to do a retromastoid craniotomy in the lateral position, much like an acoustic. I just tilt the head a little bit lower to get a better view of the tentorium. This is the generous burr hole and the craniotomy, and we would like to see the transverse and sigmoid sinus. It is ideal to use neuronavigation in all cases.
0.53 s: You can see the tumor, the tentorium, and the petrous bone marked here, and also clear that this is not a meningioma. This appears more likely a cystic trigeminal schwannoma. So here are the seventh and eighth cranial nerves seen for the first time. I opened the arachnoid next to it, and we dive into the tumor going layer by layer. This is where I think the Cavitron Ultrasonic Surgical Aspirator (CUSA) has been a big advantage. So here, we are using the CUSA to decompress tumors and bipolarizing the bleeders as we go. We got a frozen section which confirmed schwannoma. A portion of the tumor specimen was also taken for final histopathology. Here we are using the flat knife to go within the tumor.
2.00 min: Now, we are going near the superior pole to mobilize the tumor. Typically, you encounter a petrous vein here, which I usually coagulate. You can see the edge of the tentorium here, and you can also visualize the fourth cranial nerve coming into sight. We have cleared the arachnoid and tumor adhesion from the nerve. Sometimes even when you touch these nerves, you can get a fourth our palsy, so I am always very cautious.
2.54 min: Here, you can see the arachnoid plane. That is very important. Just like acoustics, you are going to stay on that plane. Though tumors can be suctioned coming from anterior, it would have been difficult in this case as this is not one of those soft tumors that suctions out. It is adherent, and the plane was deceptive. So, removing this tumor from anteriorly would not be easy. Here we are on the brain stem, and a thin wisp of the fifth cranial nerve can be visualized. Now in the tumor-brainstem interface. I am being very cautious there.
4.00 min: Here, you can see the seventh and eighth cranial nerve at the lower pole of the tumor. As you separate and mobilize the lower pole, you will observe the sixth cranial nerve. The arachnoid plane, sixth nerve and the seventh-eighth cranial nerve complex, and fifth cranial nerve can be seen clearly as we decompress more tumor. The tumor is completely mobilized from the brainstem, and it is nice to have the insulated bipolar, which does not dissipate the heat to surrounding structures. Notice that we do not touch the sixth nerve. This patient's only deficit postoperatively was the sixth nerve palsy, which was completely resolved. It is difficult to remove the tumor inside the Meckel's cave at this stage. You can see the brainstem clearly at the end of the decompression.
6.00 min: At this stage, we use the endoscope to make sure that we have not left any tumor residue. Here you can see a small tumor residual. We could go back and remove some of those residual tumors from behind the fifth cranial nerve. Some argue that you should drill out the petrous bone and get into the Meckel's cave or even go with an extended craniotomy. However, I do not recommend that.
7.08 min: Brain stem and cerebellum looks relaxed. We did a watertight closure of dura after filling the cavity with saline and replaced the bone flap. We closed the skin in layers with nylon.
7.45 min: You can see the postoperative MRI showing a small residual within the Meckel's cave which we will consider for GKRS. He had a sixth nerve palsy, which resolved completely at follow-up.
7.55 min: So, in conclusion, we believe that the retromastoid approach works very well in most cases with the predominant posterior fossa component. The endoscope can help visualize the residual tumor, for residual tumors consider gamma knife radiosurgery.
The patient recovered uneventfully following surgery and was discharged home on postoperative day 6. Postoperative MRI brain showed a residual lesion measuring 7 mm × 15.4 mm × 19.1 mm within the Meckel's cave. Histopathology was consistent with schwannoma, WHO grade 1. The patient had transient left sixth nerve palsy, which recovered over the next few weeks. He is planned for a repeat MRI brain at 6 months to consider GKRS for the residual lesion.
Initial internal decompression allows the mobilization of the tumor from all the direction. Keeping the arachnoid plane around the tumor intact throughout is crucial to prevent inadvertent damage to cranial nerves, brainstem, and their blood vessels. Avoid as much as possible, the manipulation of cranial nerves during surgery. Use endoscope to identify residual tumor in blinded areas around cranial nerves, brainstem, and Meckel's cave. Residual tumors either adherent to important neurovascular structures or inaccessible can be considered for GKRS.
The video highlights key steps in the decompression of TS through a single approach. Different surgical techniques and approaches have been described like Lateral Subtemporal, Fronto-Temporal Extradural, Kawase's Approach, Retrosigmoid, Presigmoid, Combined Subtemporal, RISAEA-RISA, and Endoscopic Transnasal Approach. Endoscopic assistance helps to visualize and resect dumbbell schwannomas.
The choice of approach depends on the size of the tumor, location, extent, and surgeon's preference and expertise. Our case had a dumbbell schwannoma with a predominant posterior fossa component and a smaller Meckel's cave component without extension into the cavernous sinus, consistent with modified Samii's type C1. Through a combined approach that was considered ideal in many dumbbell tumors, the use of an endoscope precludes the necessity for it.
GKRS can be considered for small primary TSs, residual tumor after surgery, and primary tumors involving the cavernous sinus.
We have presented a video of EA-RISA and near-total decompression of TS. We have shown and discussed the operative nuances, aiming younger neurosurgeons and residents.
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