January 08, 2016
Let's review a resection of a petrotentorial meningioma, infiltrating the Meckel's cave. And also describe some of the techniques for managing bleeding from the sigmoid sinus during a retromastoid craniotomy. This is a 48 year old female who presented with right-sided trigeminal neuralgia and on MRI examination was known to harbor a petrotentorial meningioma in the area of the trigeminal nerve potentially infiltrating the Meckel's Cave, as you can see on the sagittal enhanced images. Her pain was refractory to medical therapy, therefore, a right-sided retromastoid craniotomy was deemed appropriate. You can see the location of the incision, the summit of which is located at the junction of a vertical line through the mastoid groove and the junction with the other line, which is from in here to the root of the zygoma. You also can see the location of the mastoid groove and the area of the mastoid tip. I performed a lumbar puncture at the beginning of the procedure, to achieve early brain decompression. Here is the retro mastoid craniotomy again, on the right side, this is the sigmoid sinus, transverse sinus will be located here. And as you can see, there was an initial massive amount of bleeding during performance of the craniotomy that required the use of the bone wax, indiscriminately to control the venous bleeding. It's important to avoid compaction of the gel foam or other hemostatic agents into the lumen of the sinus to avoid its permanent occlusion. I enter the operative field at this time, remove the bone wax. You can see part of the bone wax was occluding the sinus. I continue to remove the wax to measure the amount of injury to the sinus. You can see there is a sizable defect in the roof of the sinus. Gentle temper knot easily controls the bleeding. Next, I use a piece of wax to reconstruct the roof of the sinus without necessarily causing the compaction of the lumen of the sinus. Bone removal was continued toward the transverse sigmoid junction. Micro doppler ultrasonography confirmed flow within the sinus. This extent of injury to the roof of sinus is not amenable to primary closure. As you can see, the roof of the sinus was avulsed. The dural was incised along the dural sinuses, and here is the tentorium, the petrous bone, the junction of the two. This landmark is an important early landmark for identification of location of the trigeminal nerve. You can see the tumor, the nerve mobilized just anterior to its capsule. I continued to open the encasing arachnoid membranes, to be able to identify the dissection planes. Here is the tentorium and the interface of the tumor and its base along the tentorium. You can see, again, the tumor is based over petrotentorial junction. The first step is devascularization of the tumor along its petrous and tentorial connections. Some of that bleeding from the tentorial venus varices can be controlled using thrombin soak gel foam. This bleeding can be especially problematic at the entry point of the superior petrosal sinus. I continued dissection of the base of the tumor along the tentorium. You can see the fifth cranial nerve located more caudally, the fourth cranial nerve at the area of the incisure has to be carefully protected after tumor is somewhat devascularized and slightly debulked. I'm going to do some dissection to be able to again, find the margins of the tumor and protect the fifth cranial nerve from the coagulation injury. Here is the tumor being mobilized away from the fifth nerve. Next, the tumor has shrunken to stay away from the nerve. The tumor is quite vascular. I could not completely dissect the base of the tumor since I was unable to find the exact location of the fourth cranial nerve, and I did not want to inadvertently injured the nerve. So I continued to dissect at the more safer zones away from the fourth nerve, here it is along the petrotentorial junction. Now that I can see the margins of the tumor better after I've dissected it along its anterior capsule, I can come more superiorly and identify the fourth cranial nerve at the level of the incisura. You can see the nerve here and now under direct vision and monitoring of the nerve, be able to dissect the residual tumor. I then follow the tumor into the Meckel's cave. As you can see here, this is the part of the tumor moving along the tentorium that's being dissected. Here's that portion of the tumor that is being disconnected and delivered. Next, I inspect the part of the tumor infiltrating the Meckel's cave along the superior aspect of the nerve, and pull as much of the tumor as possible out of the Meckel's cave using pituitary rongeurs. The nerve is quite decompressed. I can see there's no further compression on the nerve through the Meckel's cave. Various dissectors are used to remove the tumor along the posterior aspect of the cave. Following gross total removal of the mass, the dura was closed in a watertight fashion. Cranioplasty was completed. Postoperative MRI demonstrated gross total resection of the mass without any complicating feature, and you can see the portion of the tumor infiltrating through the Meckel's cave was removed by widening the opening into the Meckel's cave through the posterior fossa operative corridor. This patient's pain resolved after surgery without any evidence of new numbness. Thank you.
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