How I do it: inside-out bony window design in the retrosigmoid suboccipital approach

The conventional retrosigmoid approach uses external landmarks like the asterion to locate the transverse-sigmoid sinus junction, but anatomical variability often makes these landmarks unreliable, risking inaccurate craniotomy and sinus injury.

We describe an individualized "inside-out" technique using preoperative 3D reconstruction to identify the transverse sinus, sigmoid sinus, and their junction on the inner skull table and project them onto the outer table, enabling precise burr hole placement and patient-specific bone flap design.

This inside-out approach offers a reliable, individualized method for safe and efficient retrosigmoid craniotomy, reducing sinus injury risk and optimizing surgical exposure.