Abstract: Surgical instruments providing access to delicate tissue, such as brain tissue, through a transcutaneous channel. A surgical access assembly has a pin component removably fastened to a cannula component such that rotational forces are translated between the pin component and the cannula component. The pin component is adapted to receive and secure a guide-pin component from a navigation system to assist in the proper initial placement of the surgical access assembly. The cannula component has features on the outer surface configured to facilitate insertion and retention of the surgical access assembly in the target delicate tissue. When desired, pin component can be removed from cannula component to reveal an inner cavity configured to provide access to the target delicate tissue and a working channel for the particular procedure to be performed.