December 08, 2015
Large, acoustic tumors that are cystic, or lead to edema within the brain stem, can be quite challenging to resect due to their adherence to the surrounding structures, including the pia of the brain stem. This is a 55 year-old female, who presented with hearing loss and imbalance. And on MRI evaluation, was diagnosed with a large acoustic neuroma, with small cystic portions. In addition, there was evidence of edema within the brain stem and middle cerebellar peduncle, and also a larger medial cyst, associated with a tumor. She subsequently underwent a right-sided retromastoid craniotomy. You can see my traditional curvilinear incision. The sigmoid sinus was unroofed. The posterior capsule of the tumor was exposed. The lower cranial nerves are evident early, so they can be protected. The posterior capsule of the tumor is mapped to roll out the presence of the facial nerve. The inferior pole of the tumor is also generously and carefully mapped. Here's the superior pole of the tumor. Next, the tumor is aggressively debulked, to allow the mobilization of its capsule. Here's another portion of the capsule is being opened for further decompression. Here is a cystic portion of the tumor around the petrotentorial junction. The capsule has been dissected, just underneath the tentorium. Additional cysts within the tumor are being drained, so that the trigeminal nerve can be identified along the superior pole of the tumor. Next, the tumor is being generously debulked. Aggressive debulking is a key maneuver for efficient removal of acoustic tumors. I continue to debulk the tumor as much as possible, without violating the capsule. Here's now, mobilization of the lower pole of the tumor and it's mapping. The lower cranial nerves are being released. Additional arachnoid bands along the lower pole of the tumor, are also dissected. A nerve is apparent along the lower pole of the tumor. I continue to debulk the mass as much possible. It's a relatively large mass, therefore extensive debulking is necessary for its removal. Here's another cyst within the medial part of the tumor that was in close proximity of the brain stem. Now the capsule of the tumor is being rolled laterally. Here, a retractor had to be used because of cerebellar edema caused by the tumor. Here, you can see violation of the pia and the brainstem. To avoid any further injury to the parenchyma of the middle cerebellar peduncle, I use a piece of cottonoid, and gently wipe the middle cerebellar peduncle away from the capsule of the tumor, while the capsule is being mobilized and rolled laterally. This is an important maneuver to protect as much of the middle cerebellar peduncle, and the brain stem, as possible. This part of the capsule is more mobilizable. I continue to exploit those planes that are a mobilizable, to continue and move toward those planes that are a little less recognizable, in order to preserve the pial membranes as much as possible. There are veins over the brain stem, can easily rupture. Aggressive coagulation should be minimized as much as possible, and gentle tamponade, using thrombin-soaked cotton can often be quite effective. Also, a piece of cotton may be placed under a retractor blade, to control the venous bleeding. Here again, is the very adherent capsule of the tumor to the pial surfaces of the middle cerebellar peduncle, and the brain stem. I continue to shrink the tumor as much as possible, in order to advance my dissection planes more anteriorly. You can see the mobilization of the capsule, and dissection of the pial surfaces of the brain stem. Obviously when the tumor is so adherent, I continue to carefully map the adhering surfaces of the brainstem, to assure preservation of the facial nerve. Especially if the pial membranes are violated due to edema within the brainstem. Preservation of the root exits on of the nerve can be difficult, and the pial surfaces should be reconstituted, and found as one continuous dissection. More anteriorly here, you can see reconstitution and identification of the pial surfaces along the brainstem. All of the arachnoid membranes over the nerve are carefully protected. Here's the route of the facial nerve, just along the more inferior-anterior aspect of the tumor capsule. Due to significant adherence of the tumor, I planned on a radical near-gross total removal of the mass, while leaving small piece of the tumor over the cisternal route of the facial nerve. Here's continuation of our dissection, and the trigeminal nerve along the superior pole of the tumor. I continue to debulk the tumor as much as possible, when it's safely doable. Here is again, additional debulking of the mass toward the area of the porus. Tumor has been removed piecemeal, and only a very thin sheet of tumor is left over the route of the facial nerve, to maintain normal facial function after surgery. The nerve, still, is stimulated at 0.05 milliamps, which corresponds to very functional and near normal status of the facial nerve after surgery. Here is again, further dissection of the tumor along the brain stem. So you can see the very thin sheet of the tumor that was left over the facial nerve. In this case, more than 95% of the tumor was removed, with preservation of function. And the postoperative MRI only demonstrates a very small amount of the tumor over the facial nerve and into the porus. And this patient recovered from the surgery with normal facial function. This small piece of the tumor that has remained, underwent surveillance imaging, and has not grown in size for about five years in follow-up. And if there is any evidence of small growth, radiosurgery can be quite effective for long-term control of the residual tumor. Thank you.
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