Infectious Inflammations (Sialadenitis)
Based on etiology and clinical course, sialadenitis is classified into bacterial and viral, as well as acute and chronic forms. Primary forms (arising independently) and secondary forms (developing as complications) are recognized, with the latter being diagnosed much more frequently. Infection can reach the gland via three routes: stomatogenic (ascending along the ducts), lymphogenous, and hematogenous.
Acute purulent sialadenitis most commonly affects the parotid gland, causing acute purulent parotitis. The main causative agents are Staphylococcus aureus and group A streptococci, which ascend through the excretory duct. The primary predisposing factor is a decrease or complete cessation of saliva flow. This occurs due to fluid imbalance (resulting from high fever, diuretics, or fasting) or following abdominal surgery.
Chronic sialadenitis is predominantly localized in the submandibular gland. Its development is associated with ductal obstruction by stones or strictures, which increases tissue susceptibility to retrograde bacterial infection. During exacerbations, the disease transitions into purulent inflammation.
Complications of purulent forms include phlegmon and abscesses of surrounding soft tissues with fistula formation opening onto the skin or into the oral cavity. The ultimate outcome is gland sclerosis or cirrhosis. Clinically, cirrhosis may mimic a neoplasm, a condition known as Küttner tumor.
Viral and Specific Infections
Specific types of sialadenitis are caused by specialized flora and classified into actinomycotic, tuberculous, and syphilitic.
Viral infections are triggered by Coxsackie viruses, Epstein-Barr virus, influenza viruses, and others, but mumps virus and cytomegalovirus hold the greatest clinical significance. In cytomegalovirus parotitis, lymphomacrophage infiltration is observed in the stroma and parenchyma. Individual epithelial cells of the ducts and acini undergo marked enlargement (cytomegaly). Large purple intranuclear and small basophilic cytoplasmic inclusions appear within them. A pathognomonic feature is a clear halo of cytoplasm surrounding the nucleus, giving the affected cell the characteristic "owl-eye" appearance.
Radiation-induced (iatrogenic) injuries occur separately following therapy for head and neck malignancies. The serous acini of the parotid gland exhibit the highest radiation sensitivity. An acute inflammatory reaction eventually transitions into chronic sclerosing sialadenitis.
Obstructive Disorders
Obstructions develop due to ductal stones, external compression, ligation, or duct kinking. Major nosologies include:
- Sialolithiasis (Salivary stone disease) — a chronic disease characterized by the formation of calcium salts. Desquamated cells and mucin serve as the stone matrix. Three main pathogenetic factors include secretory stasis, shift of saliva pH toward the alkaline side (7.1–7.4) with increased viscosity, and infection. The disease is accompanied by glandular swelling and "salivary colic"—pain during meals. Disease progression leads to parenchymal atrophy, squamous or oncocytic metaplasia, and cyst formation.
- Mucocele — a mucous cyst up to 1 cm in size, arising from trauma to the minor salivary gland ducts. Large mucoceles of the floor of the mouth are termed ranulas.
- Retention cyst — a cystic dilation of the duct resulting from its obstruction or compression.
Autoimmune and Tumor-Like Processes
Autoimmune pathologies include Sjögren syndrome (keratoconjunctivitis sicca, xerostomia, and systemic disease) and Sjögren disease (isolated involvement with antibodies directed against ductal epithelium).
Tumor-like lesions include:
- Sialadenosis (sialosis) — non-inflammatory bilateral enlargement of the parotid glands associated with endocrine disorders, leading to lipomatosis.
- Oncocytosis — cellular transformation, most frequently in the parotid gland.
- Necrotizing sialometaplasia — acinar necrosis with squamous metaplasia in minor glands, regressing within 6–10 weeks.
- Benign lymphoepithelial lesion (Mikulicz disease) — replacement of glandular parenchyma by a lymphoid infiltrate carrying a high risk of progression to lymphoma or carcinoma.
- Lymphoepithelial cysts of the parotid glands, frequently associated with HIV infection.
Salivary Gland Tumors
Salivary gland tumors account for up to 4% of all human neoplasms. The parotid gland is most frequently affected (64–80%), with peak incidence in the 6th–7th decades of life. More than half of all tumors are benign.
The most common benign tumor is pleomorphic adenoma. It presents as a painless nodule ranging from 1 to 10 cm, surrounded by a fibrous capsule. On cross-section, the tissue is whitish-yellow with small cysts and dense cartilage-like areas.
The tumor frequently recurs (especially when a myxoid component is present) because its thin capsule is easily damaged during surgery. An additional challenge for the surgeon is the risk of injuring the facial nerve, which courses through the parotid gland. Recurrent adenomas frequently acquire a solid structure and demonstrate a marked tendency toward malignant transformation.