Although small, a 0.4cm stone in the common bile duct is basically impossible to drain out of the body.
In normal people, there is a structure called Sphincter of Oddi at the junction of the bile duct and the intestinal tract, which acts as a one-way valve for the flow of bile. If a stone travels down the bile stream to this area, due to the sphincter of Oddi, the stone is likely to become lodged in the bile duct, resulting in a blockage of bile flow to the intestinal tract and causing a severe cholangitis attack.
It is relatively safer for the bile duct stone to remain in place than to be expelled from the body, because if the stone becomes lodged in the bile duct, it will not only cause cholangitis, but may also cause biliary pancreatitis.
In summary, choledocholithiasis is basically not expelled from the body. If you find choledocholithiasis, you should consult a doctor in time, complete the relevant examinations, make a clear diagnosis, and then take the appropriate treatment program.