External References to Access the Ventricular Atrium. A, Illustration showing the external references to access the ventricular atrium (VA). Yellow dot marks the intraparietal sulcus (IPS) to make one of the lateral transulcal-transcortical approaches. Red dot marks the isthmus of the cingulum at the access point to perform a contralateral interhemispheric transfalcine approach to the VA. B, In this dissection, the base of the occipital and temporal lobes are shown after the removal of the cerebellum to understand the supracerebellar transtentorial transcollateral sulcus approach to the VA. Blue dot marks the most posterior region of the collateral sulcus. Access zone to approach the atrium. (Images courtesy of E de Oliveira)