The most common cause of enlarged salivary glands is a salivary mucocele. This is often caused by trauma to the salivary gland or duct from a wound, chewing on hard or sharp objects, using prong collars, etc. Other less common causes of enlarged salivary glands include sialadenosis (a neurological condition), infection, or inflammation. Enlarged lymph nodes, dental disease in the dog’s mouth, abscesses, and other types of masses may cause swelling around a dog’s neck.