A device for use as a portal in percutaneous minimally invasive surgery performed within a patient's body cavity includes a first elongated hollow tube having a length adjusted with a self-contained mechanism. The first elongated tube includes an inner hollow tube and an outer hollow tube and the inner tube is adapted to slide within the outer tube thereby providing the self-contained length adjusting mechanism. This length-adjustment feature is advantageous for percutaneous access surgery in any body cavity. Two or more elongated tubes with adjustable lengths can be placed into two or more adjacent body cavities, respectively. Paths are opened within the tissue areas between the two or more body cavities, and are used to transfer devices and tools between the adjacent body cavities. This system of two or more elongated tubes with adjustable lengths is particularly advantageous in percutaneous minimally invasive spinal surgeries, and provides the benefits of minimizing long incisions, recovery time and post-operative complications.