Fourth Ventricular Ependymoma
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Let's review resection of a caudal fourth ventricular ependymoma and demonstrate how far we can push the limits of gross total removal of the tumor adherent to the post lateral floor of the fourth ventricle. This is a 21 year old male who presented with an incident or lesion in the caudal aspect of the fourth ventricle, herniating through the foramen of Magendie. You can see the appearance of the mass on an axial T2 MRI, closely related to the posterior aspect of the brainstem and floor of the fourth ventricle. There is an area of calcification along the more inferior aspect of the tumor. And again, tumor is primarily herniating through the foramen of Magendie, affecting the floor of the fourth ventricle and the posterior aspect of the caudal brainstem. This is one of my older videos. I used to use the prone position for a midline suboccipital craniotomy. Within the past five to six years, I've consistently used the lateral position as I'm able to sit and conduct the microsurgical part of the procedure under the microscope. Obviously a standard midline incision was utilized. Here you can see the tumor clearly evident. The dura was open in a midline. You can see the inferior vermis and both tonsils. A very important maneuver in resection of these tumors is to carefully isolate only the perforating vessels from the PICA to the tumor, and then coagulate them and sharply cut them. Inadvertent abrasion of these perforating vessels to the tumor from the PICA can place PICA at a significant risk. I continue circumferential disconnection of the tumor. Here is disconnection of the tumor from the inferior aspect of the vermis. Sharp dissection is used as much as possible. This part of the tumor appears not very adherent to the PICA and it's readily immobilizable. Again, careful coagulation of the feeding vessels that are clearly going to the tumor. Some of the in passage vessels are carefully immobilized. The arachnoid bands are used as the section planes so the peeled surfaces of the cerebellum are protected. Here, you can see a branch of PICA. The tumor is reduced through debulking or coagulation. Very important maneuver is early identification of the floor of the fourth ventricle and the peeled surfaces of the posterior brain stem, so the surgeon is well oriented regarding the depth of the section without injuring the brainstem. Here you can see in the branches of PICA the surface of the brain stem, and more specifically the posture lateral aspect of the brain stem. You can see the midline is not affected by the tumor. Here's the foramen of Margendie. The finding that the midline is spared by tumor adherence is a common finding in these tumors. However, the posterior lateral aspect of the brain stem typically is quite adherent to the interface of the tumor, and the surgeon has to make an important decision about how aggressive he or she should be to achieve gross total removal of the mass without placing the patient at risk. Here's some adherence apparent. I continued to persist on removal of the tumor and staying on the capsule. Again, this area of the adherence is not at the level of the floor of the fourth ventricle and therefore I feel there is some small margin of error where I can coagulate the small surface of the posterior lateral brainstem affected by the tumor. The tumor is further reduced, so I can more effectively immobilize the tumor without placing any traction injury on the brain stem. Tumor is rolled to both sides so I can maintain my planes of the section and further tumor decompression is achieved. You can see now the floor of the fourth ventricle is apparent along the superior pole of the tumor. Now I continue to follow the capsule of the tumor, understanding that again, the lateral anterior face of the mass is somewhat adhering to the posterior lateral aspect of the brain stem, however, these areas of adherence are relatively minor. If the tumor was adherent along the significant length of the brain stem, a thin sheet of tumor should be left behind to avoid any injury to the posterior lateral brain stem. Staying on the peeled surface of the brain stem. You can see the attachment of the tumor at this area. Now the tumor is delivered. You can see gross total removal of the mass and minor amount of invasion to the posterior lateral aspect of the pia. The post-operative MRI revealed gross total removal of the mass without any complicating features, and this patient made an excellent recovery. Thank you.
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