Petroclival Epidermoid: Transtentorial Approach
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Epidermoid tumors tend to grow around the cranial nerves and often involve multiple cranial nerve complexes. They frequently occur within the cerebellopontine angle and go around the tentorium to reach their para-chiasmatic space. This video reviews a variation of a retro-sigmoid and supracerebellar approach and its modification via addition of the transtentorial route to remove epidermoid cyst that affect multiple cranial nerves. This is a 52 year old female who presented with right-sided trigeminal neuralgia and on MRI evaluation was noted to have a right-sided CP angle epidermoid tumor crossing the ventral brainstem. Also infiltrating toward this suprachiasmatic space. You can see the diffusion images definitively diagnosing the epidermoid tumor. The sole use of the retrosigmoid approach, who will remove the tumor along their subtentorial space. However, the portion of the tumor within the supratentorial compartment and the suprachiasmatic space will not be reachable. Let's go ahead and review the technical nuances for this approach. Standard curvilinear incision was used. Patient was placed in the latter position. Brainstem auditory evoked responses were monitored. You can see the transfer sinus, sigmoid sinus and their junction. The bony opening is relatively conservative. You can see the dural opening along the dural venous sinuses. Lumbar drain was installed at the beginning of the procedure. The petrous tentorial junction was exposed. Further amount of CSF was removed to achieve brain decompression. Additional dural incision was necessary to expose the lower pole of the tumor. You can see the extent of this pearly tumor. Arachnoid bands were generously opened. This perpetual sinuses was coagulated and cut. You can see the location of the fifth cranial nerve and its entry point into the Meckel's cave. Angled instruments were used. I used a piece of gel-foam soaked in papaverine solution to cover the seven and eighth cranial nerves and protect them from the thermal injury, coming from the intense light of the microscope. I attempted further resection of the tumor around the tentorium. As you can see, the angle instruments can be effective. However, the removal is quite blind. Therefore I expanded the operative corridor via a transtentorial approach and sectioning the lateral part of the tentorium, just medial to the petrous ridge. Piece of cotton was used to mobilize the occipital lobe away from the tentorium during transection of the tentorium. Obviously the fourth cranial nerve is just along the anterior edge of the incisura. And any dissection around the area should first identify the nerve. I continue with anterior sectioning of the tentorium. The tentorium can be somewhat vascular, easily coagulated. As you can see, I look both above and below the tentorium before it's sectioning. Now I find the fourth cranial nerve at the tip of my arrow before the last band of the tentorium is cut. Here I work above and below the nerve gently dissecting the nerve before the final band is severed. So here's the nerve, it's out of harm's way. I make sure that there are no further attachments to the tentorium. Now that the tentorium is cut, it retracts superiorly. My exposure is expanded toward the suprachiasmatic space. I use pituitary rongeurs to remove as much of the tumor as possible, while protecting some of the midbrain perforators. Here is the suprachiasmatic space. And this is the inferior aspect of the chiasm. Dynamic retraction is quite effective during the removal of a tumor within very small and deep operative corridors. The working distance is quite long. However, the tumor can be removed piecemeal. The flecks of the tumor are delivered into the resection cavity. This dissector has a mirror that allows visualization within the operative blind spots. Here is the third cranial nerve that was displaced inferiorly. A piece of papaverine soaked gel-foam was used a moment ago over the perforators to relieve their spasm. Here you can see the long working space toward the suprachiasmatic space. Further portions of the tumor are delivered into their resection cavity, gentle retraction of the upper brainstem allows exposure of the tumor embedded within the anterior aspect of the midbrain. The third cranial nerve is displaced inferiorly and has to be carefully protected. Now that most of the tumor in the area of intermittent brain and the suprachiasmatic space was removed, I redirected my attention between the fifth and the seventh and eighth cranial nerves, as well as just above the lower cranial nerves and worked within the available working channels within the cranial and between the cranial nerves to remove additional tumor flecks. Here you can see a perforating vessel adherent to the capsule of the tumor that will be dissected in a moment. First, the tumor is generously de-bulked. The arachnoid bands within the tumor are dissected. The sixth cranial nerve will be entering the Laurer's canal in this area. Here is my small working channel between the fifth and seventh and eighth cranial nerves. I exploit as much of the space as available between the fifth and the seventh and eighth complex to remove the tumor that appears to be very adherent to the anterior aspect of these nerves. Sharp dissection exposes some of the arachnoid bands that are trapping the tumor flecks. Here's working on both sides of the seventh and eighth cranial nerves to deliver additional sections of the tumor. In this area where the tumor is adherent to the anterior aspect of the facial nerve. You can see that I'm gently mobilizing the tumor while tearing the arachnoid bands toward the nerve to prevent undue traction on the facial nerve. This maneuver is very important in a atraumatic to protect the cranial nerves that are very sensitive. Any manipulation of the nerve is avoided. Here's the perforator that was previously noted to be adherent to the capsule of the tumor that is being carefully dissected away. Here is some of the tumor capsule that is being mobilized. Here's the third cranial nerve. Here's the fifth cranial nerve for your orientation. You can see that the third cranial nerve was very inferiorly mobilized, or displaced by the tumor. And a portion of the tumor was very adherent to the inferior aspect of the nerve. You can see that the majority of manipulation is exerted on the tumor and not on the nerve. Despite this manipulation, the patient, awoke from the anesthesia without any extra acral movement abnormalities. Further tumor de-bulking facilitates it's mobilization away from the nerve without undue traction on the nerve. Here's another piece of the tumor delivered. Further work along the anterior aspect of the fifth cranial nerve is performed. You can see the sixth cranial nerve. A portion of the tumor is embedded within the brainstem along the sixth cranial nerve. This small portion of the tumor was left behind to avoid any injury to the sixth cranial nerve. This tumor fragment is just anterior to the fifth cranial nerve. The arachnoid bands are being dissected. You can see the sixth cranial nerve at the depth of our resection cavity. As much of the tumor that is extra-axial is removed, small portion of the tumor that is embedded in the brainstem at the level of the sixth cranial nerve, again is left behind. Working between the nerves to extract more tumor fragments. There are numerous operative blind spots, and the surgeon should continue to use dynamic retraction to find these blind spots. Here is the third cranial nerve. Again, additional tumor anterior to it is circumferentially dissected. This tumor is quite complex, affecting multiple cranial nerves, which is not unusual in epidermoid tumors that grow around the nerves, as compared to dermoid tumors, that are more solid and typically displace the surrounding neurovascular structures. Small amount of tumor that was embedded within the posterior aspect of the nerve and the root entry zone of the fifth cranial nerve is being removed. The fifth cranial nerve is most forgiving and therefore it's manipulation is exploited to expand the operative corridor, both in the supratrigeminal and infra-trigeminal triangles. Here's the sixth cranial nerve. Here's the entry aspect of the brainstem all the way across the basilar artery. No residual tumor is apparent. In here is the clival dura. Further inspection reveals no evidence of obvious residual tumor except a small piece here that will be removed. Ample amount of irrigation will be used to further deliver any tumor flecks into the resection cavity. Here's the posterior subtemporal space above the tentorium. Ample amount of irrigation is used as previously mentioned. Here again is the clival dura. And looking across the brainstem, to assure gross store remove of the tumor besides the small amount of epidermoid cyst affecting the brainstem at the level of the sixth cranial nerve. Postoperative MRI demonstrates adequate removal of the tumor as expected. Small amount of epidermoid tumor was infiltrating the brainstem at the root exit zone of the sixth cranial nerve and was left alone. The rest of the tumor is removed. You can see that the suprachiasmatic space is generously decompressed and there's no residual tumor apparent. This patient's preoperative pain disappeared. She did not have any post-operative extra-acral movement abnormalities, and has since returned to work without any untoward side effect. Thank you.
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