December 12, 2015
Let's discuss resection of cerebellopontine angle epidermoid tumors. This is a 32 year old male who presented with slight gait imbalance and harbored intact hearing. MRI evaluation demonstrated a cerebellopontine angle epidermal tumor extending all the way to the level of the medulla. Most likely involving the lower cranial nerves. A relatively pathognomonic finding on diffusion weighted images is the hyperintensity of the epidermoid tumor relative to the CSF. Interestingly, this epidermal tumor was somewhat hypointense compared to the surrounding CSF. Brainstem auditory evoked responses were monitored during this operation. The patient was placed in the lateral position, as you can see here. A curvilinear incision such as the one used for retromastoid operations for microvascular decompression surgery was used. The location of transfer sinus is marked with a line connecting the inion to the root of the zygoma, another vertical line parallel to the mastoid groove marks the poster edge of the sigmoid sinus. The junction of these two lines, most likely defines the approximate location or the transfer sigmoid junction, and this is the summit of the incision. A lumbar drain was also used during the operation to achieve early decompression of the cisterns that were filled with tumor. Following a standard left sided retromastoid operation, dura was open along the dural venous sinuses. As you can see here, one suture was used along the transfer sinus, another one at the junction and the last one along the inferus aspect of the sigmoid sinus. The mastoid air cells were generously waxed. You can see the decompression achieved early on using the lumbar drain. Gentle mobilization of the cerebellum exposes the tumor through the arachnoids of the CP angle. Here's the lower aspect of our dissection. The fifth cranial nerve is most likely pushed anteriorly. Here are the lower cranial nerves that been pushed inferiorly. I attempt to define all the cerebrovascular structures early on. Here's the seventh and eighth cranial nerves. Again the fifth cranial nerve is mobilized anteriorly. Now that I have some idea of the location of the cranial nerves, to protect them during the operation, I continue to debulk the tumor using pituitary rongeurs. After the tumor's somewhat debulked, the arachnoid membranes along the anterior aspect of the tumor are debulked. That was the sixth cranial nerve that was in view a moment ago. The arachnoid layers between the tumor and neurovascular structures are exploited to mobilize the tumor and achieve a relatively thorough decompression. Here's the tumor that's adhering to the seventh and eighth cranial nerves. The tumor is being mobilized when safe, some of the capsule may be left on the cranial nerves to avoid their injury. Here you can see the tumor intimately related to the middle cerebellar peduncle. This is most likely where the tumor originated early on when the epidermal elements at the level of the skin did not disconnect from the neural elements at the embryonic stage. Here's the seventh and eighth cranial nerves. Here's the fifth cranial nerve, can see the sixth cranial nerve, really a beautiful panoramic anatomy of the poster fossa. You can see that a piece of a cotton soaked in the paverin was used to cover the seventh and eighth as well as the other cranial nerves momentarily. So the vasospasm on their associated vessels are relieved as much as possible. Ample amount of irrigation is used to remove the epidermoid flakes that could be hiding within the arachnoid bands and corners. The irrigation can dislodge them and allow their removal. Furthermore, this aggressive irrigation could decrease the risk of postoperative aseptic meningitis, 'specially the delayed form of it about a week after surgery that can lead to cranial nerve dysfunction. You can see that I investigate these corners, 'specially the medial corners along the middle cerebellar peduncle where the tumor can be hiding. Additional tumor fragments were identified and removed. Here's a more panoramic view, seventh and eighth cranial nerve, sixth cranial nerve. Vascular structures are protected. Branch of PICA, the lower cranial nerves. The fine piece of tumor are also removed when possible, without placing the seventh and eighth cranial nerves at risk. Further inspection reveals no evidence of obvious residual tumor. Here's the fifth cranial nerve, seventh and eighth. Really a panoramic view of the poster fossa. Here are the lower cranial nerves. The dura was closed in watertight fashion as much as possible as resection of epidermal tumors can be associated with increased CSF pressure postoperatively and the risk of CSF leak. The mastoid air cells were thoroughly waxed. The postoperative MRI demonstrates no residual tumor. More specifically the diffusion images do not reveal any residual tumor at the resection bed. This patient recovered from his surgery without any complication. Thank you.
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