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Anteromedial Temporal Lobectomy and Selective Amygdalohippocampectomy

November 03, 2015

Transcript

Let's talk about Anteromedial Temporal Lobectomy and Selective Amygdalohippocampectomy, and more specifically for Hippocampal Cortical Dysplasia. This is an 19 year old male with intractable partial seizures. MRI evaluation revealed an abnormality along the lateral midsection of the hippocampus suspicious for cortical dysplasia versus low grade glioma, versus DNET. The contralateral hippocampus appeared normal. Due to intractable nature of his seizures, he underwent an anteromedial temporal lobectomy and amygdala hippocampectomy. Here's the head positioning for this procedure. I usually extend the neck more than usual to bring the axis of the hippocampus more in the horizontal position, therefore facilitating resection of the tail of the hippocampus. You can also see the extension of the neck in the coronal plane, making their malar eminence the highest point on the operative field. The incision goes all the way to the root of zygoma so that the temporal lobe can be adequately exposed. Let's go ahead and review the details of the craniotomy. You can see their scalp flap reflected anteriorly. A generous craniotomy is elevated exposing primarily the temporal lobe and minimal amount of frontal lobe. Here is the area of the Sylvian fissure. and the pterion. Again, this surgery is primarily a temporal lobe surgery and not a frontal lobe surgery. Let's briefly review the extent of neocortical resection. For the non-dominant hemisphere, three and a half to four centimeter can be relatively safe if only the inferior and middle temporal gyri are removed. The superior temporal gyri obviously can be removed in the non-dominant hemisphere. However, in the dominant hemisphere, I avoid removal of the superior temporal gyrus to minimize the risk to the language. Let's go ahead and open the dura. Again measuring the extent of resection using a number three Penfield. After I have determined the location of the corticotomies, for the non-dominant hemisphere, I try to save most of the superior temporal gyrus as well. And the horizontal corticotomies placed at the level of the crown of the superior temple gyrus. At the floor of the middle fossa there is this boney protuberance that is a very effective landmark for guiding the lateral neocortical resection. The vertical corticotomy is performed standard fashion. The horizontal one is performed at the level of the crown of the superior temporal gyrus and these two planes are deepened into the white matter and white matter transection is guided toward the apex of this protuberance. In other words, there's one plain of dissection here, and another plane of dissection, both planes join another plane leading to this protuberance. This use of landmark avoids early entry into the temporal horn during transection of the lateral temporal neocortex. Here's the pial transection more inferiorly. Now it's time to get into the temporal horn of the lateral ventricle. Just at the level of the middle temporal gyrus, I remove some more white matter and I'm readily able to get into the temporal horn of the lateral ventricle. Entry into the temporal horn is very important as it is the most important landmark for resection of the medial structures. Here's a lateral contour of the hippocampus. I continue a transection of the occipital temporal fasciculus as you can see here. So most of the hippocampus is exposed. Here is pes hippocampus, the anterior part of the hippocampus. Here is the amygdala. The amygdala is removed subpially. Here's the inferior choroidal point, which is the most anterior aspect of the choroidal fissure. That's one important landmark. The second important landmark is exposure of the MCA through its corresponding arachnoid bands. Connecting the MCA to the inferior choroidal point defines the most superior border of the amygdala. I place a piece of Cottonoid to maintain surgical orientation regarding the anterior aspect of the choroid plexus. Next, I remove a little bit of brain to identify the MCA as you can see here through its arachnoid bands of the Sylvian fissure. Again connecting the MCA to the inferior choroidal point defines no superior aspect of the amygdala against the stratum. A selective amygdalectomy can now be completed since the superior border of the amygdala has been defined. Here's removal of the amygdala. Here's the medial edge of the tentorium and the third nerve through the arachnoid bands. You can see the subpial removal of the amygdala and preservation of all the medial pial planes overlying the third nerve and the brain stem. Now that the amygdalectomy has been completed, let's go ahead and continue with selective hippocampectomy. Here's the intralimbic gyrus. Choroidal fissure is readily apparent. First I undermine the hippocampus and disconnect it from the parahippocampal gyrus. The anterior aspect of the hippocampus or pes hippocampus is removed first. Some of the perforators from the PCA are carefully found, coagulated and cut. Next the hippocampus is disconnected medially. Again, you can see a perforator from the PCA. Here is selective resection of the hippocampus. Now I continue removal of the tail of the hippocampus. I may now remove the tail and block or rather use the suction device to evacuate the tail. I extend my hippocampal resection very posteriorly, as you can see all the way to the level of the atrium or the lateral ventricle, here's the edge of the tentorium. Any aggressive coagulation should be avoided to minimize the risks of fourth nerve palsy. Here's the choroid plexus. You can see the parahippocampus has been aggressively resected. Some of the perforators from the PCA to the hippocampus are also identified. They were coagulated and cut sharply. Post operative MRI demonstrated gross total resection of the mass which was consistent with cortical dysplasia. You can see aggressive removal of the medial epileptogenic structures so that the chance of postoperative seizure freedom is maximized. Again, it's important to me to remove all the amygdala, all the hippocampus to the level of the choroidal fissure and as far posteriorly as where the tail of the hippocampus curves around the brain stem. This patient made an excellent recovery after surgery and has remained seizure free since his operation. Thank you.

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