A method for accessing a target location (61) relative to an anatomical region (41) involves a navigation of a distal end (11) of an endoscope (10) to a cannula insertion location (60) that defines a position and an orientation of the distal end (11) of the endoscope (10) relative to the anatomical region (41). The method further involves an insertion of a nested cannula (20) through an instrument channel (12) of the endoscope (10) to the target location (61) with the nested cannula (20) including a plurality of telescoping tubes (21-24) configured to reach the target location (61) relative to the cannula insertion location (60).