A CED treatment, i.e. a convection-enhanced delivery treatment, is a neurosurgical application in which a catheter is introduced into solid brain tissue, in order to dispense an active agent and/or drug in said brain tissue over a longer period of time and in very small amounts. In order to enable such a catheter to be placed along a planned trajectory, a stylet is needed which provides the necessary stability for the catheter during placement, in order to be able to penetrate all the surfaces in the tissue. After the placing process, the stylet is removed and the catheter which remains in the tissue is then soft and/or flexible in accordance with its material, such that traumas are prevented.
A hollow stylet for an infusion catheter system is known from US 2004/0215143 A1, wherein the hollow stylet is filled with a drug while the catheter is placed together with the stylet. When the stylet, which has been accommodated in the fluid-guiding catheter line for placing, is removed, the drug inserted in the hollow stylet is supposed to remain in the catheter line, thus minimizing the formation of air bubbles in the catheter line after the stylet is removed.
A backflow catheter comprising a hollow stylet is known from U.S. Pat. No. 5,098,411, and U.S. Pat. No. 4,046,144 describes a catheter placement assembly comprising a rigid needle and a special connection system.
Catheter placing systems comprising stylets which are not hollow have, to an even greater extent, the problem that air remains in the fluid-guiding catheter line when the stylet is removed, wherein such air bubbles are extremely problematic, especially in the field of CED applications. The air penetrates into the administering region first, where it takes up space. This leads to a longer backflow region and an unpredictable distribution of the drug in the tissue, which in turn calls the treatment outcome into question. Air mainly penetrates into the catheter for two reasons. One reason is removing the stylet arranged in the fluid-guiding catheter line, as already described above. Another reason is the connecting process to the drug supply unit. Air is likewise introduced into the infusion line during this connecting process, because the air is pushed into the line in the accommodating part of the Luer adaptor by the penetrating part of the Luer adaptor.