Objective To study the distributing pattern of bridging veins that drain into superior sagittal sinus in the parieto-occipital region, to compare the exposure range of all the interhemispheric approaches targeted at the trigone and to provide anatomical basis for designing and selecting approaches in clinical practice. Methods Craniotomies preserving the lambdoid suture were performed on 5 formalin-fixed and silicone-perfused cadaveric heads. In each specimen, the distance between the posterior fontanelle and torcular was measured, the number and location of bridging veins on either side of the midline were recorded, and the distance between the points where bridging veins joined the superior sagittal sinus and the posterior fontanelle was measured and recorded. With the help of navigation, different types of interhemispheric approaches were demonstrated in 5 formalin-fixed and silicone-perfused cadaveric head. The navigation bar was used to represent the visual line in surgical procedure. The maximum exposure of each interhemispheric approach was calculated and compared. Results The mean number of bridging veins joining the superior sagittal sinus before the posterior fontanelle and within the distance equal to that between the posterior fontanelle and torcular was 1.4+0.5 on the left, 1.6+0.5 on the right, and 3.0+0.6 on both sides. Compared with the homolateral approaches, the contralateral approaches provided a better lateral exposure. For the position of the cortical or callosal insision, those with a shorter distance to the border between the medial and lateral surface of the parietooccipital lobe had a better lateral exposure. All comparisons were of statistical significance. Conclusion The bridging veins in the parieto-occipital region tend to join the superior sagittal sinus before the posterior fontanelle, therefore it is safer to perform craniotomy behind the lambdoidal suture rather than behind the lambdoidal suture. Among the interhemispheric which approaches targeted at the trigone of the lateral ventricle, the contralateral approaches provide a better exposure in the lateral direction; those with a shorter distance to the border between the medial and lateral surface of the parietooccipital lobe provide a better lateral exposure.