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Petroclival Epidermoid: Posterior Fossa and Pterional Craniotomies

February 03, 2016


Let's review this interesting case which involves resection of a multicompartmental epidermal tumor. This is a young patient who presented with hemifacial spasm on the left side. MRI evaluation revealed a sizable epidermoid cyst within the CP angle, herniating all the way and extending into the medial temporal lobe. On flare images, you can see the location on the mass, around the seventh and eighth cranial nerve complex, all the way along the anterior midbrain into the medial aspect of the temporal lobe. This tumor was approached through two different operations. One first via a retromastoid craniotomy, and the second stage via a pterional craniotomy. I do not believe there is a single complex skull-based approach, which would allow a resection of the mass in one stage. Let's go ahead and review the first stage of the operation when the symptomatic part of the tumor was addressed. A high resolution MRI again, demonstrates the location of the mass around the seventh and eighth cranial nerves, extending all the way superiorly around the medial temporal lobe. Diffusion weighted images also confirm the character of the mass as an epidermoid cyst. Here's the first stage as discussed. Left sided, retromastoid craniotomy. Sigmoid sinus, transverse sinus. The dura was incised along the dural venous sinuses. Early on the petral, then dural junction was identified. The superior petrosal vein was sacrificed and here's the tumor. Capsule of the tumor was entered, and the flakes or pearls of the tumor were removed piecemeal. The cranial nerves were identified as early as possible. These flakes are very easy to remove via pituitary rounders. Encasing neurovascular structures have to be protected. Here are the lower cranial nerves. Here's the ninth cranial nerve that is being separated from the tumor mass. Again, working within operative corridors between the cranial nerves to remove the tumor. Any part of the capsule that's very adherent to the cranial nerves is left behind. Here's the area of the anterior bonds. Seven and eighth cranial nerves. Here's the sixth cranial nerve. Again, here's the sixth cranial nerve entering the dorellos canal. Capsule of the tumor is generously dissected. Here's the basilar artery. The arachnoid bands around the tumor are also dissected. Here's the seven and eighth cranial nerves. The brainstem auditory evoke responses were monitored during the procedure. Here's the fifth cranial nerve. Now working between the fifth and seventh and eighth cranial nerves to remove the residual portions of the mass. Here's the tentorium, if cranial nerve relatively forgiving, when it's manipulated. Here's the portion of the tumor along the anterior bonds. Here is tumor on the contralateral aspect of the basilar artery. The capsule of the tumor adherent to the fifth cranial nerve is micro surgically dissected. Obviously there is tumor herniating along the incisura, toward the medial temporal lobe. Now, a trans-tentorial window is created to see if I can remove more of the tumor herniating toward the superior tentorial space. The fourth nerve at the level of the incisura is protected. Here you can see the nerve here. This trans-tentorial window is further expanded toward the petrous apex. One has to be very careful where the fourth cranial nerve enters the tentorium at the area of the petrous apex. Now you can see the tumor along the posterior basal temporal lobe. Here's the fourth nerve. I work within the superal trochlear working angles to remove the tumor. Here's the portion of the mass, just anterior to the midbrain. Here's the contralateral oculomotor nerve. Again, the contralateral oculomotor nerve is apparent. I remove as much of the tumor as possible via this corridor. This portion of the tumor again, is along the medial temporal lobe. I believe this is as far as I can get using this operative corridor, in terms of removing the tumor. And the fourth nerve, fifth nerve, seven and eighth cranial nerves, as well as the contralateral oculomotor nerve. Tumor along the anterior midbrain is removed. Some of the septations of the tumor are dissected and a small piece of the tumor hiding within the septation along the anterior brain stem is also evacuated. Further inspection of the posterior fossa contents reveals nodes of residual tumor. I'm satisfied with this portion of the operation. Second stage was conducted about 10 days later. Patient made an excellent recovery from the initial operation. A transsylvian corridor was selected again, a left front temporal craniotomy. Temporal lobe, frontal lobe, transsylvian corridor, MCA branches. Sylvian fissure is split more anteriorly. Here's this sphenoidal segment of the fissure that is being opened. Here's the optic nerve. The subfrontal area is being released from the nerve through arachnoidal dissection. Here are the MCA branches. The insular. Now, the anterior aspect of the insula or Lyman insula was entered to remove the tumor. Here's the tumor itself. The ventricle was also entered. The tumor fragments were followed until gross total removal of the mass was accomplished. Here is the capsule of the tumor. The tricky part is removal of the posterior pole of the tumor. A mirror was used to inspect the posterior aspect of the resection cavity. It appears relatively clean. Here is a more demagnified view of the operative corridor, left transsylvian approach. Postoperative MRI demonstrated gross total resection of the mass. No residual tumor is evident on diffusion weighted images. This patient made an excellent recovery and his hemifacial spasms completely resolved after the surgery. Thank you.

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