An aneurysm treatment apparatus includes a catheter assembly (10, Fig 1) comprising a catheter 12 which preferably has a steerable distal end (14, Fig 1). A pouch 40 is further disposed over the distal end of the catheter 12 so as to be in co-axial overlying relationship therewith. A constraining sheath 60 is further attached to the catheter 12 and extends over at least a part of the pouch 40. In a preferred arrangement the sheath 60 is bonded to the catheter 12 at its proximal end and a distal end thereof extends over a major portion of the pouch 40 but terminates short of the distal end 26 of the catheter 12, so as to leave a distal end of the pouch 40 exposed. In use the catheter can be steered into an aneurysm sac (102, Fig 11) and filler material fed through the catheter 12 in order to fill the pouch 40. The pouch 40 will expand with filler material from its distal end 44 and gradually slide off the sheath 12 as it fills the aneurysm sac 102. The sheath 60 prevents the pouch 40 from expanding proximally, and potentially adversely affecting the filling process.
