DEFINITION:

• A neoplastic growth of epithelial cells showing serous acinar differentiation

CLINICAL FEATURES:

• Occurs most commonly in parotid gland
• Occurs unilaterally. May occur bilaterally.
• Occurs more frequently in women than men (3:2)
• Occurs in young and old individuals
• Slowly growing, mobile or fixed mass of various durations
• Asympotatic
• Pain or tenderness
• Facial muscle weakness

GROSS FEATURES:

• Single, well circumscribed to multinodular and ill-defined
• Firm to cystic
• 0.5-13 cm
• Lobular, red to tan cut surface

MICROSCOPIC FEATURES:

• Patterns
• Sheets
• Cysts, some with papillary growth
• Microcystic
• Acini
• Ducts
• Glands
• Follicles (similar to thyroid)
• Epithelium
• Large polygonal
• Lightly basophilic cytoplasm
• Uniform to variable eccentic nuclei

MICROSCOPIC FEATURES:

• Acinar epithelium
• Large polygonal
• Lightly basophilic cytoplasm (blue dot tumors)
• Protuberance of luminal membrane producing a tombstone appearance
• Uniform to variable eccentic nuclei
• Cytoplasmic granules (PAS positive-diastase resistant; mucicarcmine positive)
• Hemosiderin
• Duct epithelium
• Eosinophilic cytoplasm
• Variable cell size
• Central lumen of various size

MICROSCOPIC FEATURES:

• Vacuolated cells
• Eosinophilic to amphophilic cytoplasm
• Clear vacuoles
• PAS and mucicarmine negative
• Clear cells
• Lack of glycogen
• Glandular cells
• Round to polgonal
• Eosinophilic to amphophilic cytoplasm
• Lack of cytoplasmic granules or PAS positivity
• Nuclear pleomorphism

MICROSCOPIC FEATURES:

• Vacuolated cells
• Eosinophilic to amphophilic cytoplasm
• Clear vacuoles
• PAS and mucicarmine negative
• Clear cells
• Lack of glycogen
• Glandular cells
• Round to polgonal
• Eosinophilic to amphophilic cytoplasm
• Lack of cytoplasmic granules or PAS positivity
• Nuclear pleomorphism

MICROSCOPIC FEATURES:

• Stroma
• Delicate fibrovascular tissue
• Collagenous tissue
• Lymphoid infiltration (in some cases)
• Hemorrhage
• Hemosiderin
• Psammoma bodies

ULTRASTRUCTUAL FEATURES:

• Main epithelial cells
• Multiple round, membrane bound, electron dense cytoplasmic granules
• Vacuoles
• Lumina
• Apical junctional complexes
• Few microvilli
• Clear cells
• Dilated ER
• Lipid inclusions
• Intracytoplasmic pseudolumina
• Myoepithelial cells
• Elongated
• Microfilaments
• Dense bodies
  
  IMMUNOHSITOCHEMICAL FEATURES:
  
• Cytokeratin(present)
• CEA (present)
• alpha 1 antitrypsin (present)
• alpha 1 antichymotrypsin (present)
• Leu-M1 (present)
• Amylase (present)
• Transferrin (present)
• Lactoferrin (present)
• Vasocactive intestinal polypeptide (present)
• S-100 (some)
• GFAP (some)

DIFFERENTIAL DIAGNOSIS:

• Papillary-cystic and follicular type
• Cystadenocarcinoma (lack of microcycstic and vacuolated cells)
• Mucoepidermoid carcinoma (presence of mucous cells)
• Metastatic thyroid carcinoma (presence of thyroglobulin)
• Polmorphous low-grade adencarcinoma (perineural invasion, homogeneous cell population, single cell infiltration at the periphery)