Intracanalicular Acoustic Neuroma: Retromastoid Craniotomy
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This video reviews the techniques for resection of Intracanalicular Acoustic Neuroma, and also describes the tenants for Retromastoid Craniotomy. This is a 40 year old female, presented with decreased hearing on the right side, and was diagnosed with a small intracanalicular acoustic neuroma. The patient underwent the operation in the lateral position. The incurvinal incision was marked based on standard anatomical landmarks. You can see the location of the mastoid tip. And then, and the transfer Sigmoid junction. The myocutaneous flap was reflected inferiorly. Here's the mastoid groove. A bear hole was created at the prism junction of the transverse in sigmoid sinuses. A generous spare hole attempts to exposed more of the dura, rather than dural sinuses. Intra diploic veins are encountered and controlled. Here's the dura, curette is used to expand the pony opening kerrison rongeur are used to unroof, the edge of the dural venous sinuses. One of the Mastoid air cells is apparent. Gelfoam powder soaked and thrombin is used to seal the VNS bleeding. You can see the edge of the dural venous sinuses is apparent. In number III, penfield is used to mobilize the dura away from the inner aspect of the calvarial. A lumbar puncture was performed at the beginning of the operation and approximately 30 CC of CSF was removed. This maneuver led to decompression of intradural space. Here is additional bony removal, to expose the edge of the sigmoid sinus. That'd be one with a foot plate was used to carry on the craniotomy. First or the latter aspect of the craniotomy. And finally, over the posterior edge of the sigmoid sinus. The use of the foot plate directly on the sigmoid sinus, is not advised. As the sigmoid sinus can be quite adherent and embedded into the inner table of the skull bone. A drill is backed out, and a sick and bony cut is performed as described. Here's the elevation of the small bone flap. Which is somewhat adherent to the outer layer of the dura. Some of the bleeding from the Emissary vein is also controlled using gelfoam soaked and thrombin. Additional bone removal and unroofing of the sigmoid sinus is possible. And most likely safe. The bone is thinned out over the sigmoid sinus. And then the last shell of bone is removed using kerrison rongeurs. All the mastoid air cells are subsequently waxed. Unroofing of the sigmoid sinus, allows mobilization of this venous structure, laterally. An expansion of the operative corridor around the cerebellum. Here's the bone wax that is sealing the mastoid air cells. Obviously the bone wax should not interfere with our bony removal and mobilization of the sinus. Here's the final product. You can see the edge of the sigmoid sinus, the transverse sigmoid junction. Next the dura is incised. However, sometimes bony removal over the inferior aspect of their craniotomy may be necessary. Gelfoam powder soaked in thrombin, seals the epidural bleeding. And pulmonary irrigation is used to remove all the bony debris and the bone dust. As mentioned previously, the dura venous is incised parallel to the dural venous sinuses. This mode of dural opening lives, most of the Dura over the cerebellum. And may decrease the amount of dural shrinkage, caused by the intense heat of the microscope and its associated intense light. We continue to roll opening along the lateral border of the sigmoid sinus. The contours of the transverse sinus are also followed. The initial lumbar drain, leaves us with significant amount of brain relaxation, preventing, cerebellar herniation through the dural opening. Next, two or three dural retention stitches are placed, to mobilize the dura out of our working zone. You can see most of the dura is left over the cerebellum. A piece of rubber dam or cut piece of cloth, to the shape of a long Cottonwood, is used to slide around the cerebellum. Find the Petro tentorial junction. This landmark provides immediate anatomical orientation for the surgeon. Aggressive retraction of the cerebellum parallel to the route of their VII and VIII cranial nerves is avoided. Here is a meningeal branch, that can be safely coagulated and cut before it's avulsed. And the vessels that are closer to this VII and VIII complex are carefully protected. Only the meningeal branches actually, this connected. You can see it or to a branch that is entering the IAC. Obviously these branches are carefully protected. They are arachnoid bands over this VII and VIII cranial nerves are further dissected. Their lower cranial nerves are apparent. You can see the magnified view of the operative corridor through the retromastoid craniotomy after elevation of a sigmoid sinus. Here's the V cranial nerve superior petrosal sinus. The arachnoid bands again are generously opened. So mobilization of the cerebellum will not place the neurovascular structures at risk. A similar procedure is performed over the Laura cranial nerves. Here's the IX and X cranial nerves. Next, I divert my attention toward the surgical target. First, the arachnoid bands over the VIII cranial nerve are released. So, traction injury on their sensitive nerve is minimized. After this maneuver is complete. The tumor over the IAC is coagulated and reflected. In the manner illustrated and the bone over the fundus of the IAC is generously drilled until the tumor is encountered. Generous amount of irrigation is used to avoid any heat injury to the nerves within the canal. My ENT colleagues prefer the use of fixed retractors. The use of such retractors is very reasonable during bony and removal in this area. Here you can see, the continuation of our bony removal. All the way to the level of the nerves within the canal. A 270 degree skeletonization of the nerve is completed. Here you can see the dura over the IAC and the tumor, that is being widely exposed. Again, additional grooves are created just above and below the nerve so that the tumor can be manipulated with a significant traction on the neurovascular structures within the canal. So now the dura is sharply dissected and the tumor that is barely apparent here is exposed. The portion of the vestibular nerve that is involved with the tumor is selectively identified. Therefore, this operation is highly focused on removing only the part of the vestibular nerve. That is the source of the tumor. Here you can see the tumor and the nerve associated with it. You can see the other branches of the VII and VIII complex that are very apparent. You can see the VII nerve anteriorly. The tumor is carefully mobilized out of its canal. And gently delivered after it was disconnected from its corresponding vestibular branch. So essentially, the facial nerve that cochlear nerve and part of the vestibular nerve were all preserved at the end of this operation. It's important that all the air cells in the area of the IAC are covered and sealed off with bone wax or a piece of muscle to avoid operative CSF fistulas. Next dura is approximated in a watertight fashion. Before doing that, fibrin glue is used to keep the muscle in place over the area of the fundus of the IAC. And post operative MRI as expected demonstrates gross total removal of the tumor and this patient's hearing and facial function remained intact after the surgery. Thank you.
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