It is characterised by bilateral swelling of the parotid glands, however other major salivary glands may also be affected in around 10% of cases. The swelling persists for about a week, along with low grade fever and general malaise. Recurrent parotitis of childhood is characterised by periods of pain and swelling in the parotid gland accompanied by a fever

Complications
Causes
Sialadenitis can be caused by cancer, autoimmune conditions, viral and bacterial infections, idiopathic causes or stones formed mainly from calculus. It was thought that morphological characteristics of the salivary ducts could also be a contributing factor, as stagnation of saliva due to these could perhaps cause an increased incidence of sialadenitis. However, one study found no statistically significant difference between the length of ducts or the angles they incorporate within them and the likelihood of developing sialadenitis, although this study only had a small sample size of 106. The study also confirmed that age, gender, side of face and degree of sialadenitis had no impact on the length of the ducts or the angles formed within the ducts.Viral pathogens more commonly cause sialadenitis in comparison to bacterial pathogens. Mumps is the most common virus that affects the parotid and submandibular glands, with the parotid gland affected most often out of these two. Other viruses that have been shown to cause sialadenitis in both these glands include HIV, coxsackie, and parainfluenza. Classically, HIV parotitis is either asymptomatic or a non-painful swelling, which is not characteristic of sialadenitis.
Minor criteria include phlebitis without obliteration of the lumen and increased numbers of eosinophils. There are two features relatively inconsistent with diagnosis of IgG4-related disease which are the presence of epithelioid cell granulomas and a prominent neutrophilic infiltrate.Sclerosing polycystic sialadenitis histologically resembles sclerosing adenosis/fibrocystic change of breast tissue. It composes of acini and ductal elements embedded in dense sclerotic stroma, and has a characteristic finding of large acinar cells present with abundant eosinophilic cytoplasmic granules. In addition, it may also present ductal epithelial proliferation which could range from hyperplasia, atypia to DCIS-like. Its stroma may show focal adipose tissue with myxoid change and variable radial scar. At present, there are immunohistochemical studies of limited value only. It is cytologically difficult to diagnose this type of sialadenitis due to the rarity of this condition and the presence of variable cell types in a cystic background.In autoimmune sialadenitis, activation of T and B cells that infiltrate the interstitium occurs due to a response to an unidentified antigen present in the salivary gland parenchyma. This response then results in acini destruction and the formation of epimyoepithelial islands. Autoimmune sialadenitis
Most histological appearance of autoimmune sialadenitis are similar to that of Myoepithelial sialadenitis. In general, a diffuse to multinodular expansion is observed in myoepithelial sialadenitis. A distinguishing feature is the presence of epithelial-myoepithelial islands infiltrated by lymphocytes. Germinal centers may form with the progression of lymphoid infiltrate resulting in acinar atrophy. Proliferation of ductal epithelium-myoepithelium arises causing the obliteration of ductal lumina causing the formation of the epithelial-myoepithelial islands.