That snake died, the infection was found post-mortem. The only outward signs was rapid shedding and the snake's eyes actually swelled from the pressure. The vet's theory was that the infection entered via a scratch in the snake's throat.
The savu I lost a few weeks ago had an irregular neck swelling that turned out to be cancer.
The OP only thinks his snake's swelling is from a piece of substrate lodged in the snake's throat. Until a vet looks at it he doesn't know what is really wrong.