Steerable medical puncture instrument

The invention is directed to a steerable mandrel comprising a stationary part and a movable part. The stationary part comprises a tubular sleeve having a mantle wall with a longitudinal semi-circumferential opening or weakening, which divides the stationary part into a proximal portion located on a proximal side of the longitudinal semi-circumferential opening or weakening and a distal portion located on distal side of the longitudinal semi-circumferential opening or weakening. The movable part comprises a rod-like member, which is slidable within the proximal portion of the stationary part. The movable part is attached to distal portion of the stationary part, such that relative movement of the movable part in relation to the stationary part causes a bending of the mandrel.