Posterior Pontine Pilocytic Astrocytoma
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This video describes the technique for paramedian super cerebellar approach for resection of inferiorly located midbrain and pontine lesions. In this case, Posterial Pontin Pilocytic Astrocytoma. This is a 46 year old male who presented with six months history of brainstem dysfunction, which was progressive, including left side of spasticity, dysarthria, and swallowing difficulty. An MRI evaluation revealed this cystic lesion relatively in the midline on the enhanced XL MRI. You can see the cyst is entered to the enhancing nodule. Here's the area of the tectum, what is very important about this lesion is that it is not in the tectum area, it is actually in the lower midbrain and maybe the opera pontine area. And there will be a long reach around the colon or the midline of the cerebellum to be able to reach this lesion. Therefore, a paramedian super cerebellar approach was deemed more appropriate because the lateral wing of the cerebellum provide a more lower inferior trajectory to reach the postural lateral mesencephalon and the opera ponds. So the important finding in summary is that, the slope of the cerebellum over the lateral aspect of its tentorial surface allows a more inferior trajectory unilaterally toward the midbrain and the opera pontine area. However again, this approach is unilateral, but provides ample amount of space to remove a midline lesion. Let's therefore review the techniques for such a Paramedian super cerebellar approach. The patient is placed in a lateral position and Lamar during is placed for poster fossa decompression. You can see that the transfer sinus is marked using neuronavigation. Our paramedian linear incision is used, which is halfway between the mastoid and the area of the midline marked by the Indian here. one-third of incision is above the transfer sinus and two-third is below. Further details of positioning are as follows. The patient's head is somewhat tilted away from the shoulder. As you can see here, this angle has been expanded to provide a working space for the surgeon around the area of the suboccipital area. Furthermore, a lumbar drain is placed to provide early decompression of the posterior fossa without the need to open the bone over there for him in magnum to reach the cisterna magna. The exposure here is worth further discussion. I bear hole was placed over the transfer sinus, which is located here. This is the transfer sequin which junction a craniotomy was subsequently elevated, before which some CSF was withdrawn to decompress the dural and aloe mobilization of the venous sinus, from the inner aspect of the calvarial before the footplate of the trill passed over the venous sinus. Here, you can see again, the outline of the transfer sinus joining the sigmoid sinus at burr hole was placed just above over the sinus and it craniotomy was elevated. Importantly, some of the Douro above the transfer sinus was exposed. So the transfer sinus can be mobilized superiorly and improve the working space within the superior cerebellar corridor. The doodle was opened in a curvilinear fashion. You can see the bone over the lore suboccipital area is not removed. This is another important nuance. You can see that two sutures are placed across the poster aspect of the tentorium so that the transfer sinus is mobilized superiorly. I use a piece of club or Robert dam to go around the superior aspect of the cerebellum and glide over the cerebellum with a cotton Lloyd. You can see that effect of the suture in terms of elevating the transfer sinus. The dissection starts with sliding over the cerebellum and finding the posterolateral aspect of the mesencephalon, where the arachnoid membrane is, or the trochlear nerve are opened. And again, you can see the breadth of this approach all the way to the trigeminal nerve and its anterior extent. You can see the superior cerebellar artery there. In this view, you can appreciate the trochlear nerve as it originates from the posterolateral aspect of the mesencephalon the perforating vessels over the lateral aspect of the mesencephalon or mobilized away from the area where we are planning to make a incision, to reach the nodule and assisted component of the tumor. Fix retractors or avoid it. You can see that dynamic through attraction over the lateral Surface of the cerebellum bromides and plant a space to work and achieve an inferior trajectory toward the tumor. Also, you can see using narrative navigation that I'm able to reach almost to the mid or lower portion of the lesion by just going over the lateral aspect of the cerebellum, the Coleman, which is the highest point of the cerebellum can be quite obstructive. If you want to reach the lower portion of this tumor to provide a gross total resection of the mass for the patient. Now ideal, we have an idea how far further mobilization of the cerebellum may be necessary. We can start by creating an incision, which I already have done and removing their nodule of the tumor. The tumor subsequently was diagnosed as a pilot city astrocytoma. You can see this cystic wall has been drained and the ultrasonic aspirate is used to remove this discolored tumor, which is relatively dense. And here is the lure extent of the tumor and evidence of clear margins confirming the gross total resection of the mass. Here's an magnified view of our operative corridor. As you can see over the cerebellum, the Coleman is here. The lateral interoral service of the cerebellum is demonstrated here. We went over the cerebellum and we were able to remove the tumor using retraction sutures to elevate the transfer sinus. This is a post operative MRI, which demonstrates gross total resection of the mass without any complicating features. This patient's preoperative symptoms slightly improved within the six months period after surgery and has since remained stable without any further worsening of his preoperative symptoms. Thank you.
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