Portosystemic shunts (liver shunts- LS) usually always require surgery to close them. There are other diseases like microvascular dysplasia (MVD) which can mimic LS and do not require surgery but do require life long management.
The first thing you need to do is have a Bile Acid Test done on your dog- the vet will take blood from your dog, feed him a fatty food, wait two hours and then take another blood test. If the second number (post meal) is over 100, it is usually considered a shunt, under 100 but elevated is considered MVD.
If LS is suspected your pup will need further testing to determine whether there is actually a shunt and whether it can be successfully closed. If MVD is suspected, a liver biopsy is needed to confirm and the vet will usually wait until the pup is altered. Some people choose not to biopsy if everything but MVD has been ruled out and the vet will just treat MVD.
If a shunt is closed- the liver is usually biopsied at that time because MVD can still be present as a secondary condition. MVD is small internal shunting throughout the liver. The treatment for this condition is a low protein, low fat food for life- consisting of easily digestible proteins such as chicken, cod, and egg protein. Some vets will recommend denamarin as a daily supplement- if this does not agree with your dog- some people just use a milk thistle supplement. Personally, I use this supplement
http://www.homevet.com/osc/product_info.php?products_id=74&osCsid=986806cfed6167aacb80759dfcf0a926
Many vets have not dealt with LS and MVD in their practice- if you are going to have your regular vet do the Bile Acid Test they can contact Dr. Centers at Cornell and she will explain the procedure to them. If the Bile Acids are elevated- the best thing you can do is find a board certified specialist to take it from there.
This is not a condition to wait on- Bile Acid Tests should be done as soon as possible.
What breed of dog do you have? Just wondering because it is much more likely in certain breeds.
Also- I dont know where you got your puppy- but LS and MVD are congenital defects that will usually trigger a health guarantee if you have one from the breeder.
Please feel free to PM me with any questions- I have been researching both LS and MVD for years now.
On a more positive note, I have seen and read stories of many dogs who have come through LS surgery with flying colors and are doing well... as well, I am successfully managing two MVD dogs (one confirmed, one suspected) and know many others as well.
Good Luck.