Electrosurgical apparatus and method of tissue ablation

An electrosurgical apparatus for treating a biological growth that contains a fluid-filled sac, the apparatus comprising:

• an electrosurgical instrument for delivering microwave energy into biological tissue, the electrosurgical instrument comprising:
• a coaxial cable for conveying microwave energy;
• and
• a radiating tip portion disposed at a distal end of the coaxial cable to receive microwave energy from the coaxial cable;
• and
• a fluid delivery mechanism for transporting fluid to and from a treatment zone located around the radiating tip portion,
• wherein the fluid delivery mechanism comprises:
• a flexible fluid conveying conduit that extends along the coaxial cable, and
• a rigid insertion element in fluid communication with a distal end of the fluid conveying conduit and arranged to extend into the treatment zone,
• wherein the fluid delivery mechanism is arranged:
• to aspirate fluid from the treatment zone, and
• to inject a substance into the treatment zone to replace the aspirated fluid, and
• wherein the substance has dielectric properties selected to facilitate uniform delivery of treatment energy to biological tissue in the treatment zone, and
• wherein the coaxial cable comprises an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and outer conductor, and wherein the inner conductor is hollow to provide a passageway for the fluid delivery mechanism.