A surgical instrument assembly for use in snare cauterization operations comprises a tubular sheath member, a metallic cauterization loop, and a metal wire operatively connected to the loop, the wire passing longitudinally through the sheath. An electrical supply is operatively connectable to the wire for feeding an electrical current to the loop via the wire, while a manually actuatable shifter is operatively connected to the wire for longitudinally sliding the wire along the sheath in alternately opposite directions. A flexible web member is connected to the loop to form a capture pocket, the loop defining a mouth opening of the pocket. During use of the snare cauterization instrument, the loop is at least partially expanded from a collapsed configuration and passed over the selected internal body tissues to be removed, so that the web member substantially surrounds the selected internal body tissues. The loop is then at least partially closed to engage the selected internal body tissues around a base region thereof and an electrical current is subsequently conducted through the loop to burn through the selected internal body tissues at the base region thereof, thereby severing the selected internal body tissues at the base region. Upon a completed burning of the loop through the base region of the selected internal body tissues, the loop is at least partially closed, whereby the severed internal body tissues are automatically captured by the web member.