A medical introducer for use in locating an energy delivery probe, such as an RF ablation probe, at a target location in tissue includes a proximal hub and an elongate cannula having a distal end and a proximal end, the proximal end connected to the hub. An elongate opening extends proximally from the distal end along a longitudinal axis of the cannula, the elongate opening defined by a long side of the cannula that extends to the distal end and an opposite open side. The elongate opening has a shape such that an active distal tip region of a probe inserted into the cannula is exposed longitudinally along the elongate opening and is covered by the long side along an opposite side of the distal tip region. A resulting lesion formed by use of the introducer with the probe is non-spherical and includes an enlarged lobe oriented along the elongate opening.
