Pleomorphic adenoma

Pleomorphic adenoma, abbreviated PA, is a very common benign salivary gland tumour.

General

Features:

• Very common - approx. 60% of parotid gland tumours.
• May transform into a malignant tumour.
  • Other benign salivary gland tumours do not do this.
• Only benign childhood salivary gland tumour of significance.

Weinreb's dictums

1. Most common salivary tumour in all age groups.
2. Seen in all sites (unlike other benign tumours).
3. Recurrence and malignancy risk (unlike other benign salivary gland tumours).
4. Any part of a tumour that looks like PA makes it a PA.

Gross

• May be cartilaginous appearing.

Image:

• PA in situ (iarc.fr).

Microscopic

Features:

• Proliferation of myoepithelium and epithelium (ductal cells) in mesenchymal stroma.
  • Cells in ducts = epithelial.
  • Cells not in ducts = myoepithelial.
• Mesenchymal stroma - important feature.
  • May be any of following: myxoid, mucochondroid, hyalinized, osseous, fatty.
    • Chondroid = specific for PA; can diagnose PA without an epithelial (ductal) component if chondroid is present.
    • Myxoid = not specific for PA.

Notes:

• Mesenchymal stroma not required for diagnosis -- if >5% ducts.
  • No chondroid stroma and <5% ductal cells = myoepithelioma.
• Complete excision is often elusive; stating "completely excised" on a surgical pathology report is unwise.
• Look for, i.e. rule-out, poorly differentiated carcinoma: carcinoma ex pleomorphic adenoma.

Memory device: MEC = myoepithelium, epithelium, chondromyxoid stroma.

DDx:

• Myoepithelioma.
• Carcinoma ex pleomorphic adenoma.
• Epithelial-myoepithelial carcinoma.

Images

• 

  PA. (WC)

• 

  PA. (WC)

• 

  PA. (WC)

• 

  PA. (WC)

www:

• PA - myxoid stroma (webpathology.com).

IHC

• S-100 +ve, SMA +ve, GFAP +ve.

See also

• Salivary glands.