Step 3. Identify the sigmoid sinus

3.3 Assess the shape of the area of exposed pneumatised cells. Start removing them with sweeps parallel to the sigmoid sinus and note that the area of the cells contracts early in the sinodural angle because the lateral surface of the sigmoid sinus is most superficial here. The trap is that the lateral wall may remain superficial as it passes inferiorly.

3.4 Clear the cells of the mastoid tip and display the medial wall of this space.