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Midline Suboccipital Craniotomy: Resection of Posterior 3rd Ventricular Tumors

December 02, 2015

Transcript

The midline suboccipital craniotomy and supracerebellar approach is the work horse approach among posterior fossa corridors. Although this approach is most commonly used in practice these days, I have essentially abandoned the midline approach in favor of the paramedian supracerebellar approach because the tentorial surface of the cerebellum through the paramedian approach provides a more inferior trajectory toward the midline tectal area without significant retraction on the coalmine or the midline of the cerebellum. However, since the middle approach is very popular, I'm going to use this video to describe its use for resection of the posterior third ventricular tumor. This is a 30 year old female with progressive history of headaches. Wonder what an MRI examination which demonstrated a mild amount of hydrocephalus associated with obstructive lesion along the area of the posterior third ventricle. Again, this tumor comes just to the area of the tectal area and therefore is an appropriate candidate for this supracerebellar approach. Importantly, the lesions, the posterior third ventricle can be approached via this route and do not necessarily require a transcallosal approach, which is much more invasive in terms of reaching that tumor. So the supracerebellar route does have a good indication for accessing posterior third ventricular tumors, as long as the anatomy of the veins including Galen and the basal veins of Rosenthal are favorable. And that lesion reaches the area of the tectum. And there is space between the tectum and the veins to access the posterior capsule of the tumor. This patient underwent surgery in the sitting position, as I've said, I have abandoned the sitting position in favor of the paramedian approach since they lower slope of the tentorial surface of the cerebellum, obvious the need for significant retraction of the cerebellum, which would be decreased by the use of sitting position. However, for the colleagues who like the sitting position after appropriate measures for detection and managing venous air embolism is instituted, the patient is placed in a sitting position. as you can see here in a skull clamp, the transesophageal echo and a central venous catheter is placed. The incision is pretty much midline and goes over or superior to the inion so that torcula and medial portions of the transverse sinus are exposed, so they can be mobilized superiorly to expand the supracerebellar corridor. Since this patient did have hydrocephalus, the incision was prepared in case a ventriculostomy catheter was necessary. The patient's head was slightly bent. However, over flection of the neck should be avoided to prevent any risk of compromising the cranial venous drainage. Following completion of the midline incision, you can see the inion is apparent here. The superior nuchal line is exposed and C1 is not necessarily exposed since most of our approach in this case would be supracerebellar. Two burr holes are placed over the transverse sinuses. One burr hole would expose the entire width of the sinus. As you will see momentarily. I like to use the M3 rather than a perforator because I have more control over the drill and the risk of penetrated dura and injuring the sinus is less. The burr hole is generous. You can see the sinus is barely apparent through the burr hole. The details of the supracerebellar craniotomy are being reviewed, as you can see here. Here's the left transverse sinus. The dura just below it is exposed. The number three Penfield is used to mobilize the dura of the sinus and a torcula generously from the inner surface of the calvarium. Small amount of bleeding is most likely from the intradiploic veins that connect the dura. Gelfoam powder soaked in thrombin can be used for hemostasis in this case. After the two burr holes are created over the sinus, I complete a... craniotomy. I do not go all the way to the foramen magnum unless the tumor is midline vermin. The keel of the suboccipital bone can prevent further progress and it'd be one without a foot plate. It is used to thin the keel. Obviously the last craniotomy cut is over the sinus so that if there's evidence of venous bleeding, the bone flap can be timely elevated to control bleeding. In this case, the midline was very thick and I did not force the drill over the torcula and used the B1 without a footplate to protect the torcula. Anytime that drill is facing resistance, it's best to step back and use the B1 without a foot plate to thin the bone. After elevation of the bone flap, the bone over the sinus is bevelled toward the superior surface so that the dura can be tacked up superiorly without any obstruction from the edges of the bone. You can see the entire width of the sinus. On both sides is exposed here is the torcula. This additional bone removal over the venous sinuses is imperative so that the supracerebellar operative corridor is expanded through reflection of the dura. Again, removal of the bone over the foramen magnum is not necessary. The midline suboccipital sinus can be generous at times into control venous bleeding. It's best to open through on both sides of the sinus and subsequently place with clips or sutures. Following opening of the dura, I place a suture just beyond the transverse sinus or the posterior aspect of the tentorium, so that both sinuses and the torcula can be reflected superiorly. Aggressive elevation of the sinus should be avoided so that the sinus is not occluded, which can lead to its thrombosis. A micro-Doppler ultrasound device may be used to check the flow within the sinus upon placement of the sutures before the intadural operation is started. Here is our two retraction sutures along the posterior aspect of the tentorium. You can see a bridging midline vein where at least two of them that have to be sacrificed. This is another disadvantage of the midline approach. If I had used the paramedian approach in this case, these veins could have been protected. Sacrificing too many veins in this area can lead to congestion of the cerebellum and compromise the supracerebellar space due to cerebellar swelling. Upon disconnection of these veins, you'll see that the cerebellum will gently fall down due to the sitting position. And now I can reach the thick interior arachnoid membranes. This is an important neurons that I'd like to emphasize here. If I follow the contours of the tentorium, I'll actually end up facing the vein of Galen in the posterior aspect of the splenium. This is important to realize so the surgeon does not blindly end up injuring the vein or the splenium. If one follows the contours it's best to change the trajectory of the viewing angle of the microscope more inferiorly, so the tumor in this area can be exposed as you get close to the surgical target. I'll go ahead and show again the anatomy in this case, just for our viewers to be aware of this operative. This orientation can be dangerous. Here is the splenium. Here's the vein of Galen just under the suction, you can appreciate the anatomy there. I'll go ahead and now reposition my view here, and you can see the tumor. The Coleman had to be retracted here again, and here's the poster capsule of the tumor with a vessel over it. I'm going to retract the tectum gently in this case, open the capsule of the tumor, And keep off the tumor first using ring curettes before the capsule of the tumor is mobilized away from the posterior walls of the ventricle. A pituitary rongeur is used to decompress the tumor, ring curette are quite effective in this case. You can see the superior wall of the third ventricle and the internal cerebral veins on both sides. And these are the walls of the ventricle. This is choroid plexus over the area foramen of Monroe. This is anterior third ventricle and I'm using the ring curette to remove this tumor. Here's the operative trajectory again, without using the retractors the postoperative MRI in this case demonstrates posterior resection of the mass without any significant complicating features. However, there is some evidence of edema related to retraction injury of the Coleman that can be avoided through a paramedian approach. This patient subsequently underwent placement of the ventricle peritoneal shunt despite the resection of the tumor, which ultimately turned out to be pineal parenchymal tumor of intermediate differentiation. Thank you.

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