Described are novel medical delivery devices that can be used to effectively distribute a medical agent to multiple sites within a tissue volume without requiring the device to be repositioned, including for example to distribute the medical agent within the nucleus pulposus tissue of a spinal disc. Also described are medical delivery devices configured to simultaneously remove fluid from the tissue volume into which a medical agent is being delivered, thus avoiding or otherwise decreasing any pressure build-up and facilitating an effective, uniform delivery of the therapeutic agent.