Brainstem 4th Ventricular Pilocytic Astrocytoma
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Here's another video describing resection of a brainstem or fourth ventricular pilocytic astrocytoma. This is a 32 year female who presented with imbalance, hoarseness and headaches. MRI evaluation revealed partially cystic mass associated with an enhancing nodule into the posterior aspect of the medulla. You can see the masses filling the fourth ventricle more on the left side, the location of the mass is well delineated in the sagittal view. There was also associated hydrocephalus. A telovelar approach is very reasonable for this tumor to preserve as much of the Varmus as possible. Obviously the floor of the fourth ventricle will not be violated and the medulla would be carefully preserved. This is a lateral position for the patient. Tonsils exposed through a suboccipital craniotomy Full amount of is entered. The tumor is easily exposed. Dissection continues just underneath the Varmus dissecting the telovelar membranes. So the posterior capsule of the tumor is identified. Sharp dissection continues. Posterior cerebral arteries are in this area and should be carefully protected. Often these arteries have tributaries to the tumor. These tributaries should be carefully coagulated and cut. And not avulsed. Here, you can see one of the PICAs, the right PICA at the tip of my arrow, just underneath the suction. It's important to expose as much of the capsule as possible before any significant manipulation or decompression of the tumor is performed. I like to identify as much or as many as the important cerebrovascular structures early on. So they can be protected during the next stages of dissection. Tumor is being debulked, so we can create more mass to remove the rest of the tumor. As mentioned earlier, as much of the floor of the fourth ventricle is protected. As the tumor is being removed Here, you can see the capsule of the tumor coming into view on the right side. This tumor is expected to infiltrate the posterior brainstem and therefore one has to keep in mind the plane of the tumor against the posterior brainstem as dissection continues. Superior pole of the tumor is also being mobilized Coagulating the tumor capsule then shrinking it inferiorly a fixed retractor is positioned just to hold the cerebellum in place while the rest of the tumor is being debulked. I continue until floor of CSF is encountered from the superior pole of the tumor as you can see here. Now floor of the fourth ventricle is evident. That gives me a very useful landmark in terms of what is tumor and where the tumor ends at the floor of the ventricle. Now I can easily go around the capsule. As I know where the floor of the fourth ventricle is located. This knowledge significantly improves the efficiency of the operation Here, I dissect the tumor from there tonsil. Okay you can see the floor of the fourth ventricle. Some of the feeding arteries to the tumor is also evident. I try to dissect as many of the arteries from the capsule. So I can clearly identify what is a tumor vessel versus an emphasized vessel. Superior pole of the tumor is being decompressed Tumor debulking is specially important so that the capsule can be readily dissected away from their normal structures without placing the normal structures under significant traction. Here, you can see the floor along the posterior brainstem, obviously connecting the floor of the fourth ventricle, to posterior medulla. What define the most anterior plane of dissection. An ultrasonic aspirator is specially useful in debulking the tumor and shaving off the tumor all the way to the floor of the fourth ventricle and posterior aspect of the medulla. Polarizing part of the tumor on the right side into the resection cavity. Obviously this is an important operative blind spot and the tumor capsule should be pursued and delivered into the resection cavity. The capsule should be preserved, so that a small piece of tumor is not left underneath the cerebellum in this area inadvertently. Here, you can see the capsule being carefully preserved using the suction device to mobilize the capsule without its inadvertent avulsion and enter into the tumor bulk. You can see how the suction holds the tumor away from the cerebellum. Here, you can see the midline, floor of the fourth ventricle, a small residual tumor entering into the medulla. You can see a clear plane between the tumor in this area and the medulla is not evident. The cyst is entering into the medulla. Obviously the wall of the cyst is not resectable Again, you can see how useful the ultrasonic aspirator is in shaving off tumor all the way to the level of the floor of the fourth ventricle. Significant traction on the tumor in this areas is avoided, so no force is placed on the brainstem. Here, you can see the cyst that's being drained enters into the medulla. Here is a large opening into the cyst to allow it's future drainage. In one more time, how useful the ultrasonic aspirator is in shaving off the tumor all the way to the level of the brain stem and pier. Some of the tumor is also coagulated to hopefully decrease the chance of its future growth. Looking around for any evidence of tumor that can be easily removed without violating the pier of fit medulla. Piers that all the safely resectable tumor has been removed. Here is an operative view of the final product piece of allograft dura was used to close the dura in a water-tight fashion. Three month post-op MRI revealed gross total resection of the enhancing lesion that was readily available outside of the medulla oblongata. There is a small nodule that was embedded in the cyst on the floor of the fourth ventricle that was not deemed safe to remove. And this patient made an excellent recovery after surgery. Thank you.
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