The Pre-Cuneal, Interhemispheric, Trans-Tentorial Corridor to the Pineal Region: A Step-By-Step Dissection and Two Case Reports

Introduction: The pineal region and dorsal midbrain are among the most challenging surgical targets as several eloquent neurovascular structures traverse, or reside in, this space. While several approaches exist to this region, namely the supracerebellar variants and the occipital transtentorial, they do not afford great visualization from the splenium down to the inferior most portion of the cerebello-mesencephalic fissure. Here we present an anatomical study of the pre-cuneal, interhemispheric, trans-tentorial approach along with two cases of its utilization.

Methods: To study the safety and anatomical considerations for this approach, cortical venous anatomy was studied on seven right hemispheres and six left hemispheres. The distance from the top of the transverse sinus in the midline to the most posterior cortical vein was measured. The distance from the calcarine sulcus to the most posterior cortical vein was also measured. Further, a step-by-step dissection of the pre-cuneal, interhemispheric, trans-tentorial approach was completed in a formalin-fixed and latex-injected specimen. This was done under microscopic and endoscopic magnification to highlight important steps and identify the anatomical limitations of this approach. The anatomical study was also supplemented by two operative cases.

Results: The median distance from the transverse sinus to the most posterior cortical vein was 5.6 cm on the right and 6.25 cm on the left. The median distance from the calcarine sulcus to the most posterior cortical vein was 5.2 cm on the right and 5.1 cm on the left. Key steps of the dissection are as follows: a horseshoe flap based on the transverse sinus; a rectangular craniotomy with one burr hole placed on the inion to expose the torcula, and one burr hole placed 7 cm above the previous burr hole on the superior sagittal sinus; a cruciate durotomy under the microscope to afford protection of the transverse and sagittal sinus by inferior and medial reflection of dural leaflets respectively; dissection of the interhemispheric fissure; and a linear incision of the tentorium that extends anteriorly to the incisura, followed by lateral reflection of the tentorium with sutures, obviating the need to section a window in the tentorium. This technique affords excellent access to the falcotentorial junction, splenium, pineal region, quadrigeminal cistern, and dorsal pons once the cerebello-mesencephalic fissure has been dissected. Additionally, this approach was used for two brainstem cavernous malformations that were completely resected using an infratrochlear entry point and resulted in neurologically intact patients.

Conclusion: Our dissection elucidates that the pre-cuneal, interhemispheric, trans-tentorial approach provides excellent access to the splenium down to the cerebello-mesencephalic fissure. We also demonstrated the efficacy and safety of this approach with the uncomplicated resection of two cavernous malformations of the dorsal pons. Surgical considerations prior to the utilization of this approach include a careful study of the cortical venous anatomy to assure a wide enough operative corridor without the need to sacrifice potentially eloquent bridging veins ([Figs. 1]–[3]).

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Artikel online veröffentlicht:
15. Februar 2022