Large Acoustic Neuroma: Principles of Preserving Function
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Let's re-review the principles for resection of a large acoustic neuroma. This is a 52 year old female who presented with progressive gait imbalance. She also noted hearing loss in the left side. A typical acoustic tumor, a medial acoustic tumor is noted. There is small amount edema within the middle cerebellar peduncle. Left-sided retromastoid craniotomy was completed. Sigmoid sinus was unroofed. Gentle mobilization of the cerebellum allowed me to reach the inferior cerebellopontine angle cisterns. So, CSF is drained and cerebellar decompression is attained. Despite drainage of CSF, the cerebellum was quite under tension. Therefore, a very small part of lateral cerebellum was resected for this large tumor. To avoid undue sebum retraction during the entire procedure. Here's the poster capsule of the tumor. After the capsule was stimulated at 0.1 milliamps and presence of the facial nerve excluded. The capsule was opened and aggressive decompression of its internal contents accomplished. I like to use pituitary rongeurs to remove as much of the tumor as possible. Again the internal decompression, a very aggressive decompression is a key factor for removal of these tumors. Here's the inferior pole of the tumor. The lower cranial nerves are gently dissected away from the capsule. You can see, I use the arachnoid bands as the handle to mobilize the cranial nerves. I do not directly manipulate these nerves. Piece of cotton is used to maintain the dissection planes between the lower cranial nerves and the capsule of the tumor. Circumferential mapping of the mass continues. As the capsular incision is extended more superiorly and an ultrasonic aspirator is utilized for tumor debulking. Here is further exposure of the superior pole of the mass. Stimulation continues to exclude presence of the facial nerve along the superior pole of the tumor. I look for the trigeminal nerve. Since I don't see it there, I continue to extend my capsular incision. Some more tubal debulking can be pursued. Enough debulking continues until mobilization of the capsule is readily possible. Venous bleeding is controlled. Indiscriminate coagulation is minimized and a piece of carotenoid that may be quite effective to control the venous bleeding that is not clearly visualizable regarding its source. Piece of cotton is used to protect the pier of the middle cerebellar peduncle. The tumor capsule is reduced using bipolar coagulation. I continue to roll the tumor capsule laterally into my resection cavity. The arachnoid bands over the pier of the middle cerebellar peduncle are used to mobilize the neural structures away from the capsule of the tumor. One has to always look for any structure that can look like a nerve. Stimulation mapping is quite important to protect neurovascular structures. Here are the lower cranial nerves draping along the inferior pole of their tumor Here's mapping on the superior pole of the tumor. Identification of the trigeminal nerve. The suction device is used to keep the tumor away from the neural structures. While aggressive tumor debulking via ultrasonic aspirator continues. Piece of cotton and patties again used to cover the trigeminal nerve and keep it out of harm's way. There's the mapping of the superior and inferior poles of the tumor as decompression continues. Again, using the arachnoid bands as a handle. To mobilize the increasing cranial nerves. Now, the inferior pole of tumor is well mobilized. Additional portions of the tumor can be removed. Again, one has to always look out for any structure that can look like a nerve. Even if it's just the surface of the brainstem. I continue to roll the tumor capsule, followed by its removal. Now I'm close to the surface of the brainstem. I continue to look for the root access on the facial nerve. Hemostasis is paramount so that the dissection planes are recognizable. Here's the root entry zone of the trigeminal nerve around the superior pole of the capsule. Here's the inferior pole of the tumor. Here's the facial nerve at the level of the brainstem, quite attenuated being stimulated at 0.05 milliamps. Here's the nerve again. Appears to be quite antero to the capsule at the level of the porous. I believe in neuro removal of the tumor while preserving function. I do not aggressively dissect the tumor where it's quite here into the facial nerve. Again, you can see the use of this important technique. In terms of using the arachnoid bands of the facial nerve as a handle to mobilize the nerve away from the tumor while avoiding direct manipulation of the nerve. Now, I have a better idea about the route of the nerve and continue to debulk the tumor in areas that are away from the nerve. Again is the trigeminal nerve and its rootlets. The superior pole of the tumor is mobilized and radically reduced. Here's the brainstem again at the area of the root and through zone of. the trigeminal nerve. Mapping continues further debulking is accomplished. You can use the facial nerve. Which is about at the area of the porous. Here's the area of the porous, a very small piece of tumors left behind. And here's the nerve very adherent and attenuated to the tumor at this juncture. The tumor is reduced as much as possible until I reach the point where the nerve is quite adherent to the tumor capsule. Here's the small piece of the tumor that was left behind for preservation of normal facial function after surgery. Three months MRI evaluation reveals only small piece of the tumor over the nerve. This patient had normal facial function after surgery. This small residual piece of the tumor was observed yearly with MRI scans. If there's any evidence of small growth patient would undergo radiosurgical treatment. Thank you.
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