January 24, 2016
My strategies for resection of large acoustic neuromas have evolved. Over time I have come to learn that radical subtotal removal of the tumor at the expense of a normal facial function after surgery is very worthwhile. Let's go ahead and review the techniques for resection of acoustic neuromas. One of the most important principles for improving the efficiency and safety of the operation is aggressive tumor debulking, so that the tumor capsule can be mobilized without placing the surrounding neurovascular structures at risk. Let's illustrate these important points. This is a 62-year-old female who presented with progressive hearing loss and imbalance and was diagnosed with this acoustic neuroma, which was relatively heterogeneously enhancing. Here is the positioning for a retromastoid craniotomy. You can see the curvilinear incision. The inion, the root of the zygoma, a line joining them defines the approximate location of the transverse sinus. And this line defines the location of the mastoid groove and a vertical line going through it. Their junction, or the junction of these two lines, should be a summit of the incision, which is approximately around the area of the junction of the dural venous sinuses. Following elevation of the craniotomy, the bone over the sigmoid sinus is removed. Also part of the bone over the transverse sinus is removed and the dura is mobilized and the sigmoid sinus is gently elevated. You can see that this kind of craniotomy and these maneuvers allow adequate exposure of the cerebellum without it's significant retraction. Please note that a lumbar puncture was performed at the beginning of the procedure, and approximately 40 cc of CSF was removed to achieve this very desirable cerebellar decompression. Here is more demagnified view of the operative corridor. I use a piece of glove or rubber dam to go around the cerebellum or slide around the cerebellum without injuring the cerebellum. You can see the poster pole of the tumor. Monopolar stimulation was used to exclude surprise locations of the facial nerve. The inferior pole of the tumor was also stimulated. You saw the location of the lower cranial nerves. The superior petrosal vein was coagulated and sacrificed. The arachnoid bands were opened. You can see the posterior pole of the tumor has been generously exposed. This is an important maneuver, the decompression of the core of the tumor using pituitary rongeurs and the ultrasonic aspirator. Next, the superior pole of the tumor is being mobilized, the arachnoid bands are dissected, and the trigeminal nerve is exposed. Obviously the location of the facial nerve is excluded at this area. Next, the tumor capsule is mobilized from medial to lateral direction. Sharp dissection is utilized to protect the pial surfaces of the brainstem. You can see that aggressive decompression of the tumor leads to efficient mobilization of the tumor capsule. The arachnoid bands are used as handles to mobilize the capsular tumor. While the, again, the pia on the surface of the brainstem is protected. A demagnified view illustrates, again, the importance of aggressive decompression. Here are the lower cranial nerves that are being mobilized from the lower pole of the tumor. Any vessels in this area are sharply and microsurgically dissected. I can readily find again the surface of the brainstem here. Use of sharp dissection. The operative field is kept clean for adequate visualization. The monopolar stimulator is used to localize the location of the facial nerve and its exit point at the level of the brainstem. You can see arachnoid bands are used to mobilize the pia of the brainstem away from the tumor capsule. This is an important maneuver. Here you can see aggressive decompression leads to early mobilization of the tumor. Additional debulking is now necessary. The tumor capsule is shrunken using bipolar forceps, and the dissection is continued. I search for the root exits on all the facial nerve that is apparent here. It's overlying arachnoid band is left intact. The inferior pole of the tumor is again removed. You can see the root exits of the facial nerve at the level of the brainstem. This area of the tumor is quite adherent to the anterior capsule of the tumor. Now I unroof the portion of the tumor within the IAC, and the intracanalicular part of the tumor is removed. Further tumor debulking at the level of the is accomplished. Here you can see the facial nerve. In the canal this part of the tumor was very adherent to the nerve and was left behind. Here you can see the nerve and how adherent the tumor is to the nerve at this location. Further tumor debulking is accomplished. Very small piece of the tumor that is essentially devascularized was left behind. Postoperative MRI demonstrates essentially gross total removal of the tumor. There is no abnormal enhancement. Although, obviously we know that there is a small part of the tumor that is left behind. This patient enjoyed a normal facial function after surgery, which I do believe is very important to these patients. I have, therefore, evolved my strategies from aggressive resection of the tumor in a gross total fashion to a radical subtotal strategy with preservation of function. Thank you.
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