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Brainstem Pilocytic Astrocytoma:  Paramedian Supracerebellar Route

January 20, 2016


This is another video in the series of the videos for the use of the Paramedian Supracerebellar Approach for Resection of Lesions Within the Dorsolateral Aspect of the Mesencephalon. And in this case, a pilocytic astrocytoma. This is a 28-year-old female who presented with an incidental lesion found during the workup for headaches. On MRI evaluation, a lesion along the dorsolateral aspect of the mesencephalon was identified. This lesion was noted to be heterogeneous on T2 weighted images and minimally enhancing. You can see the lesion extend somewhat inferiorly toward the roof of the fourth ventricle. The inferior extent of the tumor would make the use of a midline super Servo approach quite challenging. Therefore, a paramedian approach was selected so that the more inferior slope over the lateral aspect of the cerebellum can be used to reach the tumor. A lumbar drain was installed. The patient was placed in a lateral position. Obviously a left sided paramedian approach was selected. Incision is a third above and two third-below the transverse sinus. You can see the extent of the craniotomy, you can see the transverse sinus. The exposure of the poster fossa dura. The midline is located here. The torcular would be here. The dura is opened in a curvilinear fashion based over the sinus. Lumbar drain facilitates brain relaxation. Any bleeding from the dural edges is controlled. In this case, there was some venous bleeding close to the transverse sinus. Next, the supracerebellar corridor is developed by elevation of the transverse sinus using two sutures along the posterior aspect of the tentorium. These retention sutures are quite effective for mobilizing the transverse sinus. Aggressive elevation of the sinus should be avoided so that the lumen of the sinus is not affected. Here's the second suture. Here's the configuration of the exposure. The super cerebellar quarter is relatively unobstructed because of these two retention sutures. A micro Doppler probe using ultrasonography ensures flow within the transverse sinus and excludes it's obstruction. The arachnoid bands over the poster lateral aspect of mesencephalon are widely dissected and a fourth cranial nerve is identified. Here are the branches of the superior cerebellar artery. Dynamic retraction is used. Here is the fourth nerve. An infratrochlear window is used to expose the tumor through a small incision within the dorsal lateral aspect of the mesencephalon. You can see the use of ultrasonic aspirator until the pre-tumoral areas are identified. Here you can see the discoloration of the tumor versus relatively glistening normal pre-tumoral areas. The duro is approximated primarily. In this case, the postoperative MRI reveals subtotal resection of the tumor. The pathology was consistent with a pilocytic astrocytoma, and I felt that the safest approach would be not to transgress the more mid-position of the brainstem as you can see here. However, more than 70% of the tumor was removed via this approach. The posteriolateral approach to the mesencephalon is quite flexible. And the paramedian super servo route provides a very reasonable operative corridor to this area. Thank you.

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