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Modified Peri-Insular Hemispherotomy: Hemimegalencephaly

December 16, 2015


This is another surgical video describing the procedure of Modified Peri-Insular hemispherotomy for Hemimegalencephaly. This is a 16 month-old boy with generalized seizures up to 30 per day, and progressive left-sided hemiparesis. MRI evaluation reveals evidence of malformation of the right hemisphere, specially in the areas of the right parietal occipital region. The right hemisphere appears larger than the left one. Because of presence of hemiparesis and arrest in his development, he underwent a right-sided peri-insular hemispherotomy. Here's patient positioning. A generous curvilinear incision was used, pediatric pins for their skull clamp were utilized. Following completion of the craniotomy and dural opening, a temporal lobectomy was completed. Here's the Sylvian fissure on the right side, sphenoid wing. The lateral temporal neocortical resection extends from the temporal tip up to 8-9 cm more posteriorly. The neocortical resection is performed using standard microsurgical techniques until the floor of the middle fossa is found. More importantly, here I entered the temporal horn of the lateral ventricle. And the edge of their hippocampus was exposed. Here's the area of the uncus anterior hippocampus anterior cortical point, or in this case, an inferior cortical point, as some refer to it. I stay just lateral to the cortical fissure and disconnect the hippocampus. After removal of the hippocampus, I unroof the area of the atrium of the lateral ventricle, the calcar avis is exposed. Here was the area of the temporal lobectomy. So, I'm moving all the way more posteriorly and following the contours of the lateral ventricle, essentially unroofing the ventricle through a C-shaped gyrectomy. I covered the choroid plexus with a piece of cottonoid. Here's this splenium of the Corpus callosum. Although some of the bridging arteries are disconnected, I attempt to save as many of them as possible. Here's the exposure of the body of the lateral ventricle. I continue to follow the roof of the ventricle until the genu of the Corpus callosum is exposed. Here's the area of the insula. One has to remain very vigilant of blood loss in such young children. Next, I started the genu callosotomy while finding the distal ACA branches. So purely using these ACA branches as landmarks to conduct a callosotomy. One has to avoid any injury to the contralateral normal hemisphere. Fibers are disconnected layer by layer to avoid any inadvertent injury to the ACA branches. Genu callosotomy continues up to the level of the foramen of Monro. You can see the angle of disconnection, relatively oblique, is one of the ACA branches through its corresponding PL membrane. As I dissect more posteriorly, I use the edge of the folks as a landmark, since the very distal pericallosal arteries are very thin in caliber, and may not remain a very viable surgical landmark. So here is the edge of the folks moving posteriorly to complete a splenium callosotomy. Suboptimal disconnection at any point can lead to postoperative seizures. Now, I come back to the area of the temporal lobectomy, find the edge of the tentorium, and follow the tentorium contours until I reach the falcotentorial junction. The tentorium provides another operative landmark for complete disconnection of the white matter, the area of the calcar avis. I continued disconnection over the tentorium until the falcotentorial junction is reached, and then further pursue the disconnection toward the area of the Folks where the initial disconnection of the Corpus callosum was left off. Here you can see the callosotomy where I started more anteriorly from the area of the genu. Here's the disconnection starting from the area of the temporal lobectomy in the atrium. This final piece of connection is also disconnected. Here's the next step in the disconnection procedure. I follow the route of the sphenoid wing, starting laterally and moving more medially. The funnel fiber tracts are disconnected. I continue the disconnection toward the area where the genu callosotomy was completed. I complete the sup funnel disconnection, just short of the anterior clinoid process. And this part of the procedure completes the funnel tractotomy. Here's the edge of the sphenoid wing moving with two of the clinoid process. The appeal surface over the hypothalamus and septal region are left intact to minimize any injury to these structures. Here's the extension of the tractotomy toward the previous area of genu callosotomy. Here's the more de-magnified view of the operative corridor. Next, I remove the cortices of the insula in a sub peel fashion while preserving as many of the MCA branches as possible. Here's the final product, and pulmonary irrigation is used to clear the ventricles. All the disconnections are reexamined to assure their completion. Thank you.

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