Benign Neoplasms (Adenomas)
The morphological picture of benign lesions features a diverse cellular composition and stromal architecture. They are most frequently localized in the parotid gland.
- Pleomorphic Adenoma: Characterized by a complex structure. Epithelial cells form trabeculae and duct-like structures with cysts, embedded in a myxoid (mucus-like) matrix. A hallmark feature is the presence of chondroid (cartilage-like) areas and numerous myoepithelial cells forming networks.
- Myoepithelial Adenoma: Found predominantly in women aged 40–80 years. Appears as a dense, whitish nodule. It consists of spindle-shaped, polygonal, plasmacytoid, or clear cells forming cords within a myxoid or hyalinized background. Three morphological variants are recognized: solid, reticular, and mixed.
- Basal Cell Adenoma: Accounts for 80% of cases in the parotid gland. It is an encapsulated nodule composed of basaloid cells forming solid, trabecular, tubular, or membranous structures within a sparsely developed fibrous stroma.
- Warthin Tumor (Papillary Cystadenoma Lymphomatosum): A relatively common benign tumor (~6% of all salivary gland tumors) affecting predominantly men over 40 years old. Cross-section reveals cysts with serous fluid and papillary projections. The epithelium is bilayered (inner layer of columnar cells with apical hyperchromatic nuclei and eosinophilic, oncocytic cytoplasm). The stroma is heavily infiltrated by lymphocytes forming lymphoid follicles with germinal centers.
- Oncocytoma: A very rare adenoma composed of differentiated oncocytic epithelial cells derived from striated ducts.
Malignant Epithelial Tumors (Carcinomas)
Malignant forms make up a significant proportion of salivary gland pathologies (up to 46%). The most common among them is mucoepidermoid carcinoma. It occurs predominantly in women in their 5th and 6th decades of life.
The grade of mucoepidermoid carcinoma directly determines prognosis (along with surgical margins and depth of invasion):
- Low-grade: Dense, relatively fixed nodules. Cellular pleomorphism, rare mitotic figures, marked stromal hyalinization. Mucus-secreting cells are abundant.
- Intermediate-grade: Composed of epidermoid, intermediate, and mucous cells. Microfoci of necrosis and focal hyalinization may be present.
- High-grade: Marked cellular pleomorphism and necrosis. Predominance of solid epidermoid elements with scant mucous cells.
Adenoid Cystic Carcinoma (Cylindroma) is the second most frequent malignant tumor (1.2–10%). A favored site is the minor salivary glands of the palate. The tumor grows slowly but aggressively, characterized by early perineural invasion. The cribriform (sieve-like) pattern contains PAS-positive basement membrane-like material in pseudocysts, while the solid variant (if comprising more than 30% of the tumor) indicates a very poor prognosis.
Other notable forms include:
- Acinic Cell Carcinoma: A slow-growing, encapsulated tumor characterized by cells with basophilic granular cytoplasm resembling normal serous acinar cells. Prognosis depends on invasion; unpredictable hematogenous metastasis to the lungs can occur.
- Carcinoma Ex Pleomorphic Adenoma: Accounts for 15–20% of all malignant salivary gland neoplasms. Regardless of the specific carcinoma type (most commonly adenoid cystic or mucoepidermoid carcinoma), it is characterized by necrosis, hemorrhage, and stromal hyalinization.