Normal salivary gland

• Aspiration usually in microfragments of tissue.
• Acinar cells forming grape-like clusters display an eccentric small round nuclei with indistinct nucleoli and abundant vacuolated cytoplasm.
• Flat cohesive sheet of tubule of ductal cells display uniform, small cuboidal cells with round or oval nuclei and dense, sometimes squamoid, cytoplasm.
• Fibrovascular stroma holding acinar and ductal cells together.
• Adipose tissue can be seen.
• Scattered bared acinar cell nuclei may mimic lymphocytes derives from intraparotid or adjacent lymph nodes.

Acute Sialadenitis

• Aspirated material may be grossly purulent.
• Varying numbers of neutrophils seen.
• Small sheets of ductal cells admixed with fibrin, +/- background of necrotic debris.

Pleomorphic adenoma (PA)

• Epithelial cells ‘blend’ into stroma, becoming more spindled within the stroma.
• Myoepithelial cells can appear in several forms: epithelioid, plasmacytoid and spindle-shaped and are commonly found within the metachromatic fibrillary stroma which stained intensely red to purple with Romanowsky stains.
• Plasmacytoid cells may also be seen singly dispersed in the background.

Warthin Tumour

• Aspiration may yield cyst fluid.
• Flat cohesive monolayered sheets of oncocytes displaying round to oval, centrallu placed nuclei with bland chromatin and inconspicuous nucleoli and abundant densely granular cytoplasm which are orangeophilic.
• Mixed population of background lymphocytes, mainly mature lymphocytes.
• Amorphous and granular debris present in the background

Oncocytoma

• Cohesive, multilayered aggregates of oncocytes displaying round to oval, central placed nuclei with bland chromatin and inconspicuous nucleoli and abundant densely granular cytoplasm which is orangeophilic. Sometimes a nested architecture is discernible, unlike the flatter monolayered sheets seen in Warthin tumour.
• Scattered bare nuclei may be present.
• Absence of cyst debris and lymphocytes (both often present in Warthin tumour).
• Oncocytoma vs nodular oncocytosis is difficult to distinguish with radiologic correlation.

Acinic Cell Carcinoma

• Large branching tissue fragments with central vessels.
• Polygonal neoplastic cells forming vague acinar structures.
• The nuclei are usually round and fairly bland, sometimes with prominent nucleoli.
• Cytoplasm is abundant and granular or vacuolated.
• Bared round nuclei may be seen in the background.
• DDx: Normal salivary gland parenchyma – Tighter, well-formed grape-like clusters; some lobules may also feature ductal cells; may also have adipose stroma (which is not seen in Acinic cell carcinoma).

Adenoid Cystic Carcinoma

• Three variants: Tubular, cribriform and solid.
• May present in combination.
• Abundant acellular matrix which stains intensely metachromatic with Romanowsky stain while nearly invisible on Papanicolaou stain.
• Matrix/stroma is arranged in discrete, large globules with sharp borders and sometimes as cylinders.
• The cells are basaloid and uniform with oval to angulated, hyperchromatic nuclei and scant cytoplasm.
• Cells often surround balls of matrix.
• Sometimes bare oval nuclei are seen in the background.
• Rarely, nucleoli, mitoses and necrosis may be observed in high-grade tumours.

Mucoepidermoid Carcinoma

• Three cell types:
  • Mucin-secreting cells: Eccentric nuclear with vacuolated cytoplasm which can be mistaken as histiocytes.
  • Epidermoid cells: Polygonal and squamoid with dense cytoplasm.
  • Intermediate cells: May have an immature squamous metaplasia-like appearance; or may exhibit relatively high N/C ratios.
• Low-grade MECs are commonly cystic with abundant extracellular mucin and a predominance of mucin-secreting cells showing bland nuclear features.
  • Because of the hypocellular nature and bland nuclei, low-grade MEC may be categorised as AUS or suspicious for malignancy, if there are insufficient definitive features for malignancy.
  • DDx: Mucous retention cysts with squamous/mucinous metaplasia; Benign neoplasms with metaplastic changes.
• High-grade MECs have a predominance of epidermoid cells with marked cytologic atypia, and may not be recognised specifically as MEC.

Salivary Duct Carcinoma

• High grade malignant cells occurring in clusters and singly.
• The cells exhibit large nuclei and abundant cytoplasm.
• Necrosis in the background.