The invention relates to a portal and/or obturator assembly comprising a fixing device. The fixing device comprises a tubular element to be fitted in a passage surrounded by vascular wall tissue. The tubular element is provided with a bottom flange and a top flange, the bottom and top flanges extending in the peripheral direction of the tubular element, and the bottom and top flanges having a first position in which they extend outwards from the tubular element in order to be able to accommodate said wall tissue between them for fixing the fixing device. The bottom flange is bent, or bendeable, reversibly, against a resilient force, from the first position into a second position in which the projection of the bottom flange on a radial transverse surface of the tubular element is located essentially on and/or within the periphery of the tubular element. The bottom flange is fixed, or fixeable, in said second position in such a way that the fixing can be released in order to bend back the bottom flange towards the first position under the influence of said resilient force.
