Thyroid and Parathyroid Pathology

The thyroid gland is a bilobate structure, typically weighing between 15 g and 25 g. Thyroiditis can be autoimmune or non-autoimmune. Nodules in a multinodular goiter are designated hyperplastic nodules and are comprised of numerous follicles, often with a growth pattern similar to that in the adjacent gland. Follicular adenoma classically occurs as a solitary, encapsulated tumour that shows follicular epithelial differentiation with no evidence of capsular/vascular invasion and no features of papillary thyroid carcinoma. Follicular thyroid carcinoma is a malignant tumour showing follicular differentiation, with no features of papillary thyroid carcinoma. Poorly differentiated thyroid carcinoma shows limited evidence of follicular differentiation, with biological behaviour intermediate between differentiated thyroid carcinoma and undifferentiated/anaplastic carcinoma.