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Large Pontine Cavernous Malformations: Telovelar Route

December 02, 2015

Transcript

The telovelar approach is quite versatile in accessing lesions along the floor of the fourth ventricle. This video describes cross section of a large pontine cavernous malformation along the posterior aspect of the pons reaching toward the floor of the fourth ventricle. This is a 32-year-old male who suffered from two pontine hemorrhages. The second one resulted in mild left facial weakness and some double vision. Repeat MRI examination demonstrated a large hemorrhagic lesion along the posterior aspect of the pons reaching the floor of the fourth ventricle with a large extracapsular component of hemorrhage from the cavernous malformation. This lesion can be approached through the floor of the fourth ventricle since it is coming essentially to the floor and is abiding the floor. Some of the colleagues have described the approach through the middle cerebellar peduncle if there's any functional neural tissue along the floor of the fourth ventricle, has the morbidity of going through the middle cerebellar peduncle is quite less than going through any neural tissue along the floor of the fourth ventricle. Let's go ahead and discuss the telovelar approach as well as pearls of technique for a section of this cavernous malformation. I like to place the patient in a lateral position for suboccipital craniotomy. This allows gravity drainage of the blood and the fluids within the operative field. And therefore the operative field is quite clear and clean and pristine during the procedure. In addition, this position allows me to sit during the microsurgical part of the operation, which is quite attractive to me for making the procedure much easier in terms of steady hands and decreasing fatigue on the hands of the surgeon. The shoulder of the patient obviously has been mobilized in fairly and anteriorly, a midline incision is used and the transfer sinus is marked with a small horizontal incision. For this operation, since we will map the floor of the fourth ventricle to determine the safe zone to enter the area of the lesion, the patient underwent electromyography for the face area. You can see again the mobilization of the shoulder out of the working zone of the surgeon. Here is the craniotomy. You can see the C1 lamina and the spinous process is at the tip of my arrow here. This is a relatively small suboccipital craniotomy. The transfer sinus and inion is somewhere up here and do not need to be unroofed. Here's the midline and here's the craniocervical junction and the dura over it. So relatively limited craniectomy actually because we're using the telovelar approach and the inferior to superior trajectory through the fourth ventricle and foramen of Magendie to reach the floor of the fourth ventricle. Now, this is a more de magnified view that can orient you in terms of location of the craniectomy and its breadth. Again, C1 in the spinous process, the dura of the cerebellum, the dura of the the craniocervical junction and the location of the dural venous sinuses more superiorly. I opened the dura in a curvilinear fashion for the telovelar approach. The closure is somewhat easier. The arachnoid between the tonsils are open generously and the inter tonsillar arachnoid dissection is extended until the telovelar membrane is exposed. I use gentle retraction, fixed retraction, here's the telovelar membrane that is being transected. So the floor of the fourth ventricle is identified. Fixed retraction allows exposure and gentle tension on the arachnoid membranes for their transection. Here using the monopolar stimulating probe to identify and map the facial colliculus. Is this stria terminalis? You can see the floor is rather full, the facial colliculus was mapped to a location here. Therefore, I may created my white matter dissection along the floor, more laterally and inferiorly. You can see the blood is being drained around the cavernous malformation. The edges of the incision within the brain stem can be problematic to manage, and it can get sucked into the suction device. I put a piece of cotton that adheres to these dissection walls and prevents the walls from being continuously and repeatedly sucked into the suction and cause their injury. Now that the hemorrhage has been evacuated, the second step is identification of the gliotic membranes and gentle devascularization of the cavernoma from the fine white matter feeders that you can appreciate here. So these white matter feeders are being carefully dissected and coagulated and cut the gliotic margin of the cavernoma is clearly apparent. This gliotic margin is not removed for resection of brainstem, cavernous malformations to prevent injury to the very vital and eloquent brain stem. Here you can see the feeders are being dissected. Now that the feeders are somewhat dissected, the cavernoma is being mobilized and the hemorrhage within the cavernous malformation is being evacuated so that the cavernous malformation proper is more manageable and dissectable. Here is the piecemeal removal of the cavernous malformation. The hemorrhage also removed for me to be able to go around the capsule of the cavernous malformation. Here is delivery of the larger portion of the malformation into our resection cavity. And here is the much larger piece that being evacuated piecemeal. After removal of the malformation, I identify the developmental venous abnormality that you can see here. Obviously, this DVA is protected and not injured. Some of the white matter feeders and the residual part of the cavernous malformation is removed. Their resection cavity is very carefully inspected as some of the residual malformation can look like gliotic perilesional tissue. Here's the final look of the resection cavity with the developmental venous anomaly, the gliotic margin of the brain stem without any obvious evidence of cavernous malformation. This is the final de magnified view of the operative field without any injury to the surrounding neural tissues. The post-operative MRI demonstrated gross total resection of cavernous malformation without any complicating features. These patient's preoperative deficits temporarily worsen after surgery, but within three months it was improved from his preoperative neurological status, thank you.

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