Transchoroidal Approach to Tumors of the Posterior Third Ventricle

Dissection of the Choroidal Fissure

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This video segment shows the most important and difficult part of the surgical approach: identification, dissection and opening of the choroidal fissure, with exposition of the upper pole of the tumor.

Keywords

  • Choroid plexus
  • Foramen of Monro
  • Fornix
  • Thalamostriate vein
  • Choroidal fissure
  • Internal cerebral vein
  • Thela chorioidea
  • Taenia Fornicis
  • Third ventricle
  • Tumor

About this video

Author(s)
Giuseppe Cinalli
Nicola Onorini
First online
07 February 2019
DOI
https://doi.org/10.1007/978-3-030-13673-4_4
Online ISBN
978-3-030-13673-4
Publisher
Springer, Cham
Copyright information
© The Author(s) 2019

Video Transcript

After adequate opening of the septum pellucidum, we proceed to identification of the right foramen of Monro. The choroid plexus allows easy identification of the right foramen of Monro that gives access to the third ventricle. We proceed to a slow and careful coagulation of the choroid plexus in order to expose the attachment of the plexus to the taenia fornicis and expose the attachment of the thela choroidea. We coagulate a small afferent to the thela choroidea, and we proceed with coagulation of the choroid plexus posteriorly. And these maneuvers allow exposure of the attachment of the taenia fornicis at the level of the thalamostriate veins. We can coagulate this very, very small bleeding that can be induced by the detachment of the choroid plexus.

And at this time, we can identify very well and very clearly the choroidal fissure that is identified by the attachment of the taenia fornicis these white ependymal structures that is attached to the thela choroidea. At this point, we have clearly in view the taenia fornicis, the choroidal fissure, the right choroid plexus, and the right thalamostriate vein.

We continue the dissection of the taenia fornicis posteriorly, and it is very evident the point of the reflection of the taenia fornicis and its attachment on the ependyma of the right thalamus. We continue to dissect the taenia from the choroidal fissure at this level and going deeper and deeper into the choroidal fissure exposing completely the choroidal fissure and the thela choroidea in the most anterior part of the choroidal fissure and separating the taenia fornicis from the thalamostriate vein. Then we continue to dissect posteriorly the taenia fornicis from the ependyma of the right thalamus, and a smooth hook can be extremely effective in identifying the plane of separation between the taenia fornicis and the ependyma of the thalamus. And we can dissect even further posteriorly the choroidal fissure, a very, very careful dissection and very, very careful movement in order to avoid lesion to the thalamostriate vein.

Then after a clear identification of the choroidal fissure, we proceed to coagulation of the most anterior part of the thela choroidea. Here we can see that the only structure visible are choroid plexus and the thela choroidea that can be completely coagulated and separated in order to start the dissection and the wide opening of the choroidal fissure from the most anterior part. We can see the tumor in the depth of the third ventricle, and after opening of the most anterior part, we continue our posterior dissection of the choroidal fissure until the point of reflection of the thalamostriate vein that becomes right internal cerebral vein. And at this point, we know that we have gone far enough in the choroidal fissure because we have identified the internal cerebral vein.

And we continue our dissection and opening of the thela choroidea in order to expose the tumor that is well visible below the thela choroidea. We have to coagulate very minor vessels that can bleed during this phase of dissection, but normally, after the careful separation of the taenia fornicis, the opening of the thela choroidea is relatively easy. We should identify at the given moment the right internal cerebral vein from the left internal cerebral vein. This can occur even very posteriorly if the two veins are not very close to each other. But as you can see, the thela choroidea can be opened very widely and very easily with a very, very nice plane of separation between the thela choroidea itself and the tumor that is very well exposed until here. And at this point, posteriorly, we arrive to identify the posterior pole of the tumor, and we can identify and separate it from and dissect it from the right internal cerebral vein in order to gain access to the whole volume of the tumor during this approach through the choroidal fissure.

The dissection of the choroidal fissure has to be very careful. Direct suction should not be applied on the veins to avoid any risk of injury of the larger vein, internal cerebral vein. But with slow and progressive advancement of the dissection maneuvers, the posterior pole of the tumor can be identified and dissected by the right and the left internal cerebral vein. At this point, after exposition of the tumor, we can reposition our self-retaining retractors, and we can perform a biopsy of the tumor.