Background: The surgical approaches to lesions located in the pineal region, arising in the quadrigeminal
cistern or cerebellomesencephalic fissure, are challenging due to rich neurovascular
content of this region. The quadrigeminal cistern is situated posterior to the quadrigeminal
plate and communicates inferiorly into the cerebellomesencephalic fissure, which is
related to the roof of the fourth ventricle. The supracerebellar infratentorial (SCIT)
and interhemispheric transtentorial (IHTT) approaches are classic techniques used
to access this region. The objective of this study is to review the surgical anatomy
of such approaches and evaluate the differences in terms of exposure between them.
Methods: Surgical and microsurgical dissections were performed utilizing 4 formalin-fixed
and latex-injected adult cadaveric heads. Both approaches were completed to expose
the relevant anatomic structures and then demonstrate the advantages and limitations
of each technique. An “above” (IHTT) and “below” (SCIT) anatomical comparison is done
for the understanding of those different corridors to the pineal region.
Results: Both approaches are suitable to reach the structures in the quadrigeminal cistern
and cerebellomesencephalic fissure, which are: the posterior cerebral artery; the
superior cerebellar artery, along with the trochlear nerve, just below the inferior
colicullus; the medial posterior choroidal arteries; and the venous complex, composed
mainly by the internal cerebral vein, that exits the velum interpositum; the basal
vein of Rosenthal, that exits the ambiens cistern; the vein of Galen, which comes
into the straight sinus; the lateral mesencephalic vein; the internal occipital vein;
and the precentral cerebellar vein. In both approaches, we can reach the quadrigeminal
plate, the pineal body, the posterior part of the third ventricle, and the walls of
the cerebellomesencephalic fissure. The inner wall is composed by the lingula, the
superior and middle cerebellar peduncles, and the outer wall, by the culmen, the central
lobule and its wings.
The [Figs. 1 ] and [2 ] show this anatomy through the IHTT approach, which provide a superior to inferior
trajectory and is very useful to reach lesions in the most inferior portion of the
ipsilateral cerebellomesencephalic fissure, in the posterior aspect of the ambient
cistern, and lesions above the vein of Galen and its tributaries, displacing downward
these deep venous structures. Its limitations are associated with an inadequate visualization
of the contralateral quadrigeminal region and the ipsilateral cisternal pulvinar surface.
The [Figs. 3 ] and [4 ] show the same anatomy, but in a posterior to anterior trajectory, provided by the
SCIT approach, which is better to reach lesions in the pineal region below the vein
of Galen, and that displace the venous contents superiorly or anteriorly. The paramedian
variant can also provide access to the ipsilateral cerebellomesencephalic fissure.
On the other hand, the exposure of the pineal region below the level of the superior
colliculus is often limited when a pure midline SCIT approach is selected.
Conclusion: Good exposure of structures in the pineal region is provided by both approaches described,
but understanding how lesions in this space could modify the anatomy is paramount
for the selection of the most well-suited approach for each individual case.
