Paper II
Question
Morphology of Hashimoto thyroiditis
Answer
Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas, caused by autoimmune destruction of thyroid tissue.
Gross: Thyroid is diffusely, symmetrically enlarged (goitrous), with an intact capsule; cut surface is pale, grey-tan, firm, and somewhat nodular/lobulated.
Microscopy:
- Extensive infiltration of the parenchyma by a mononuclear inflammatory infiltrate — lymphocytes, plasma cells, and well-developed germinal centres.
- Thyroid follicles are atrophic and lined by Hürthle cells (oxyphil metaplasia) — enlarged epithelial cells with abundant eosinophilic, granular cytoplasm (due to mitochondrial accumulation).
- Variable interstitial fibrosis (may be extensive in the fibrosing variant).
- Colloid within remaining follicles is scant and pale.