The wall of the sac consists of inflammatory granulation tissue with inflammatory cells. It does not secrete saliva, so the term "cyst" is not an accurate description to use.
In dogs they almost always arise from the sublingual salivary glands.
Cats are rarely affected.
If the sialocele has been drained by passing a needle into it under un-sterile conditions it can become infected and form an abscess.
Sialography is useful in some cases to confirm the diagnosis.
Long term problems