Instrument for an endoscope

An endoscope instrument comprising an insertion tube possessing a proximal portion for connection to an actuation support and a distal portion presenting an outlet section occupied, firstly, by a viewing zone and, secondly, by at least one outlet orifice of a passage for at least one appliance mounted inside the insertion tube by the proximal portion for occupying a retracted position inside the tube and a working position in which the appliance occupies at least a portion of the outlet section, the cross-section of the appliance being greater than the cross-section of the outlet orifice in the retracted position of the appliance, the instrument being characterized in that the distal portion of the insertion tube includes at least one radially deformable wall over only a portion of its length extending from the outlet section, and in that the insertion tube includes, in its distal portion, a guide system opening out into the passage for guiding the appliance in order to enable the deformable wall to be expanded radially during the movement of the appliance thereby enabling the surface of the outlet section of the distal portion of the tube to be increased on the appliance passing from its retracted position in which the appliance does not stress the deformable wall to its working position in which the deformable wall is stressed radially, the outlet section of the distal portion corresponding to the right cross-section of the insertion tube in the retracted position of the appliance.