Follicular adenoma is the most common benign thyroid tumor, seen more frequently in adult women. It is a benign neoplasm derived from the follicular epithelium that is usually solitary, encapsulated, and compressed surrounding thyroid parenchyma. While most are non-functional, a small proportion can produce thyroid hormones. The pathogenesis involves mutations in the TSH receptor signaling pathway or RAS gene. On microscopy, the tumor shows fibrous encapsulation and benign follicular epithelial cells lining follicles of varying size and patterns of growth.

1. FOLLICULAR
ADENOMA
By
MERIN JOSE
72/20

2. FOLLICULAR ADENOMA is the most common benign thyroid tumor.
• Seen more frequently in adult women.
• Benign neoplasm derived from the follicular epithelium.
• Solitary
• Majority are non functional while a small proportion produce thyroid
hormones(toxic adenomas)-thyrotoxiocosis.
PATHOGENESIS
• Mutation in the TSH receptor signaling pathway.
• Mutation in the RAS gene.

3. GROSS
• Characterised by four cardinal features:
Solitary nodule ,complete encapsulation
clearly distinct architecture inside and
outside the capsule and compressed
thyroid parenchyma outside the capsule.
• Usually small(up to 3 cm in diameter) and
spherical.
• On cut section,
The tumor is grey-white to red-brown,
and less colloidal than the surrounding
thyroid parenchyma.
• Secondary changes :- Fibrous scarring ,
focal calcification haemorrhages and cyst
formation.

4. MICROSCOPY
• The tumor shows fibrous encapsulation.
• The tumor cells are benign follicular epithelial cells lining the
follicles of varying size.
• Variety of patterns of growth may be seen, most commonly
being microfollicular (foetal) pattern characterized by small
follicles containing little or no colloid. Other patterns include
macrofollicular, hurthle cell type, trabecular and atypical.

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