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Recurrent Epidermoid: Anterior Petrosal Approach

January 15, 2016


Let's review application of anterior petrosal approach for resection of a recurrent superior petroclival epidermoid cyst. This is a 29 year old female who presented with a recurrent left-sided superior petroclival epidermoid, seven years following her retromastoid craniotomy for primarily a CP angle epidermoid tumor. This is her initial MRI at the time of her presentation about seven years ago. You can see the tumor is primarily within the CP angle, around the seventh and eighth cranial nerves, extending to the level of the tentorial incisura. She underwent a reasonable resection, however, a small piece of the tumor was unreachable through the retromastoid approach, and this tumor continued to grow. And few years later, the tumor was noted to causing some compression of the brain stem leading to progressive double vision and slight gait difficulty. You can see that the tumor goes over the edge of the tentorium to the level of the middle fossa. And the tumor is primarily based along the petroclival region and a superior location of the mass makes it suitable for anterior petrosal approach. Patient was placed in the supine position. The head is turned generously, brainstem auditory evoked responses, as well as facial nerve monitoring in this case was used. Here you can see the linear incision. Temporalis muscle, palpation is followed to identify the root of zygoma. If the root of zygoma is not easily palpable the incision is extended more inferiorly, and the temporalis muscle is mobilized using a T-shaped incision. The T-shaped incision is quite effective, more than a linear incision, to mobilize the temporalis muscle and expose a generous section of the bone for craniotomy. A burr hole was placed at the root of the zygoma, after the temporalis muscle is generously elevated. The root of zygoma is exposed as you can see here. Again, we're on the left side, the ear is over here. Fish hooks are used, here is again, the root of zygoma. Self-retaining retractors as you can see amplify the exposure. A burr hole was placed at the base of the zygoma, just above the middle fossa floor. You can see the outer cortex is first removed, followed by the cancellous and inner cortex of the calvarium. A generous craniotomy is elevated. The route of zygoma is used as a landmark for the middle fossa floor. The middle fossa floor, essentially slopes somewhat inferiorly in the posterior to anterior direction. Now the craniotomy is complete. The dura is mobilized along the lateral aspect of the middle fossa floor. It is important to note that a lumbar drain was used at the beginning of the procedure to achieve generous dural decompression at this stage of the operation. I drained 10cc aliquots and up to 60cc of CSF if necessary or more. This is another important technique. The edge of the craniotomy, it's lower edge is generously drilled so that the edge of the craniotomy is reduced to the level of the middle fossa floor. The mastoid air cells are entered and should be waxed. One should not compromise the anterior or posterior level of the craniotomy. Here you can see that air cell there. I make sure the craniotomy is white. Bone wax is used to seal off the air cells. You can see the level of the bone parallel to the floor of the middle fossa. Here's the middle meningeal artery entering the foramen spinosum. It is isolated, coagulated and cut and bone wax with surgicel is used to seal off the foramen spinosum. The dural is mobilized in the posterior to enter a direction, to protect the GSPN as much as possible. Here is some bleeding from the middle meningeal artery at the level of the dura. Here you can see the elevation of the dural from the posterior to anterior direction. This patient had a very unusual osteology or morphology of bone at the level of the middle fossa floor. The edges of the petrous bone are carefully identified Micro Doppler ultrasound device may be used to locate the internal carotid artery associated potentially with an incompetent bony roof. This patient also harbored a very unusual piece of bone penetrating the third division of the trigeminal nerve. Now the bone over the quasi triangle is drilled away. Self retaining retractors are necessary, drilling is continued, Our ENT colleagues are intimately associated with the performance of this part of the operation the IEC is protected. Neural navigation using skull-based CT helps the operator with the extent of bony removal. Again, the floor of the middle fossa is reduced as much as possible to provide additional viewing angles. The tumor in this case, extended more posteriorly and again, these gyrations of bone were reduced, to provide additional viewing angles. The semicircular canals are not entered, here you can see the dura over the middle fossa in this location and the dura over the posterior fossa. Here's the initial dural opening. In this case, the dura was quite thick. Here you can see that dura over the posterior fossa, the dura over the middle fossa is here. The dura is first incised over the middle fossa then over the posterior fossa and these two incisions are connected along the posterior aspect of the cavernous sinus and the fifth nerve. I elevated the temporal lobe and identified the edges of the incisura in order to protect the fourth cranial nerve as you can see here. It was just about to be cut, if I wasn't very careful. The tumor is encountered because I wasn't very sure about the location of the nerve. I initially elevated a lobe, identified the location of the nerve and then rediverted my attention more laterally, where the dura was cut just lateral to the fifth nerve. You can see the venous bleeding from the posterior aspect of the cavernous sinus. This can be quite vigorous and gel foam soaked in thrombin is used to seal off the bleeding using gentle tamper knot. Bipolar coagulation is often unsuccessful and will lead to additional tears and further bleeding. The dura over the middle fossa is further cut. The fifth nerve is obviously intimately associated with this dura and the root of the fifth nerve has to be carefully protected. I continue to gently work medially and laterally and cut the dura around the fifth nerve. Here you can see part of the trigeminal nerve that is very much thinned out over the pool of the tumor. I continued to cut the dura more posterior to the nerve. The fourth nerve is protected as much as possible. Continue to work on both sides of the nerve to remove as much of the tumor as possible. Here you can see the tumor being mobilized just medial to the nerve. Here is other fast close of the trigeminal nerve that are being protected. Here you can see the fourth nerve that has to be gently mobilized so that the tumor fragments are removed. The medial arachnoid bands are identified. They are opened, so some of the other tumor fragments are not overlooked. You can see the arachnoid bands over the basilar artery, nice view of the ventral lateral brain stem. Continue to remove the tumor more posteriorly hiding behind the petrous apex. The arachnoid bands again generously opened and dissected, the tumor capsule is mobilized. Pituitary rongeurs are used to remove tumor fragments because of previous history of surgery there's some scarring specially more posteriorly. Continue to open the dura in the posterior direction, over around the arcuate eminence. Again, their fourth nerve is mobilized superiorly and the tumor is pulled out of the posterior fossa. Here again another look in the basilar artery, no additional tumor is present, except a more smaller one anteriorly. You can see the use of the endoscope to inspect via the superior posterior fossa. Here you can see via the posterior fossa in the previous area there was section cavity using a 45 degrees angle of the endoscope. Small fix of tumor had to be left behind if they were very adherent to the surrounding neurovascular structures. Here's a view of the operative cavity and the fifth cranial nerve entering the posterior aspect of the cavernous sinus. Large pieces of bone wax in the form of thin sheets are used to seal the air cells that were open during drilling of the petrous apex. Post-operative MRI demonstrates reasonable resection of the tumor and this patient recovered from her surgery without any untoward effect. Thank you.

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