An electrosurgical apparatus for treating tissue comprises an elongate shaft including a proximal region, a distal region having an electrically conductive region and one or more lumens through the shaft. A stylet is located within one of the lumens for obturating at least a portion of an opening defined by a distal end of the elongated shaft. The stylet distal end has a sensor and may include an occluding component substantially surrounding and affixed to it. The elongated shaft and the stylet can possibly be configured to allow passage of fluid through the lumen while the stylet is located within the lumen. Related stylet configurations are also disclosed.