Page 404 - Concise Pathology for Exam Preparation ( PDFDrive )

14 The Oral Cavity and Gastrointestinal Tract 389

Lymphoid
tissue

Cystic spaces
lined by epithelial
and myoepithelial
cells

FIGURE 14.2. Section from Warthin tumour showing epithelial and myoepithelial cells in a
lymphoid stroma (H&E; 403).

Monomorphic Adenoma

• This tumour is similar to pleomorphic adenoma, except it does not contain a mesenchy-
mal stromal component.
• It is more common in minor salivary glands (eg, upper lip), is bilateral in about 10%
cases, and has a very rare malignant potential.
• Types include
• Basal-cell adenoma (most common)
• Canicular adenoma
• Myoepithelioma adenoma
• Clear-cell adenoma
• Membranous adenoma
• Glycogen-rich adenoma
Basal cell adenomas are well-encapsulated, smooth tumours on gross inspection, and
are divided into four subtypes based on their microscopic appearance—solid, trabecular,
tubular and membranous. The constituent tumour cells are monomorphic basaloid epithe-
lial cells that show peripheral nuclear palisading, and have hyperchromatic, round nuclei
and indistinct cytoplasm.

Mucoepidermoid Carcinoma (MEC)
• MEC is the most common malignant tumour of the parotid gland and the second most
common malignancy (adenoid cystic carcinoma is more common) of the submandibular
and minor salivary glands.
• On gross inspection, some MECs appear well circumscribed and may be partially
encapsulated. Others are poorly defined and infiltrative.
• The cut surface of the tumour may contain solid areas, cystic areas or both. The cystic
spaces contain viscous or mucoid material.
• Microscopically (Fig. 14.3); these tumours are characterized by presence of two popula-
tions of cells—the mucous cells and the epidermoid/squamous cells, the proportion of
which helps to define grade of the tumour. MEC may be low grade (well differentiated) or
high grade (poorly differentiated).
• Low-grade MEC has prominent cystic structures and proportionally more mucous cells,
which may form gland-like structures and fewer epidermoid cells.

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