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Petrous Apex Meningioma: Transtentorial Approach

April 29, 2016


Petrous apex meningiomas can reach a large size and can be quite challenging regarding their resection. This is a 42 year old male who presented with progressive gait imbalance and dysarthria. MRI valuation revealed a large dumbbell mass centered over the tentorium, with a large posterior fossa component, as well as a subtemporal component. You can see the morphology of the mass in the coronal image. There is evidence of significant brainstem compression, specially at the level of the midbrain. Although a posterior petrous approach can be quite effective in removing this mass, I believe a less disruptive route would be an extended retromastoid craniotomy, with an adjunct transtentorial route. T2 MRI evaluation revealed the hyper vascularity of this lesion based on numerous T2 flow-void appearance. CT scan revealed no evidence of hyperostosis associated with this mass. Again, the majority of vascularity of this lesion arises from the level of the tentorium, and therefore, this part of the mass has to be tackled first. Patient was placed in a lateral position. A horseshoe incision was marked, just in case, a subtemporal approach would be necessary, in addition to the retromastoid approach. However, only the vertical limb of the incision was employed initially, and only a retromastoid craniotomy was utilized. Following, completion of the left retromastoid craniotomy. You can see the arachnoid bands over the several pontine angles. The hyper vascularity of the petrotentorial junction is apparent. The superpetrosal sinus was coagulated and cut. Here, you can see the base of the tumor over the petrous apex. Therefore, I started by devascularizing the tumor along the tentorium and the petrotentorial junction. Bleeding can be quite problematic in this area. Therefore, one has to remain patient and methodically devascularize the base, layer by layer. As the tumor was hypervascular and therefore devascularized at the tentorium. Next, the tumor was mobilized away from the fifth cranial nerve so that additional devascularization can be completed without placing the nerves at risk. Here's the fourth cranial nerve entering the tentorium. This nerve is certainly at risk during resection of this mass, and one has to always look out for it. Next, the arachnoid bands over the tumor were dissected. Certainly, debulking of the mass is necessary. Here's the fourth cranial nerve that was preserved during mobilization of the mass. Only the arachnoid bands encasing the nerve were manipulated. Here's the entire route of the nerve along the posture lateral mesencephalon. The tumor is now being debulked and then mobilized away from the brain stem. Appears quite adherent here and there. Here's the surface of the brainstem mobilization of the tumor after its further decompression. Now the posterior fossa or the symptomatic component of the tumor has been removed. Next, I focus my attention on the expansion of the retro mass storage, super cerebella route with the use of a trans transtentorial corridor. Therefore a window is created, just lateral to the petrous apex located here. Again, this cut is lateral to the base of the tumor that is based over the posterior temporal lobe. The fourth nerve has to be protected. Here's the inferior surface of the occipital lobe. Bleeding from the edge of the tentorium is controlled using gel from powder and bipolar cautery. Here's the base of the tumor super tentorially. Gel from pads soaked in thrombin can be quite effective in sealing the venous lakes in the tentorium. Here now is the tumor that has descended into our resection cavity after cutting a window in the tentorium. Here's a petrous apex and the tumor is being disconnected along the lateral border of the petrous apex. Here's the posterior basal temporal lobe. Obviously there is going to be a small residual tumor just along the petrous apex. Here's the super tentorial component of the tumor that was removed. And the postoperative MRI revealed adequate removal of the mass. The brainstem was thoroughly decompressed. There was only very minimal minor residual tumor, where expected just along the anterior aspect of the petrous apex. This patient made an excellent recovery and subsequently underwent radiosurgery for the small residual tumor. Thank you.

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