Aneurysm treatment apparatus includes a steerable catheter assembly (10) having a catheter (12) with a steerable distal end (14). A pouch (40) is disposed over the distal end (14) of the catheter (12) so as to be in co-axial overlying relationship therewith. A constraining sheath (60) is disposed over a major portion of the pouch (40) and has a proximal sheath portion (64) which is bonded to the catheter (12). The sheath (60) terminates short of the distal end (26) of the catheter (12), so as to leave a distal end of the pouch (40) exposed. The steerable catheter can be steered into an aneurysm sac (80) and filler material fed through the catheter (12) in order to fill chamber (50) of the pouch (40). The pouch (40) will expand from its distal end (44) with filler material and gradually slide off the sheath (12) as it fills the aneurysm sac (80). The sheath (60) prevents the pouch (40) from expanding proximally, and potentially adversely affecting the filling process.
