Normal histology	Histopathology	Pathological basis of disease	Clinical findings	
Tissue architecture:
•	The thyroid gland is enveloped by an outer capsule of loose supporting tissue & an inner capsule of fibro-elastic tissue.
•	From the inner capsule, fine collagenous septa extend into the gland dividing the gland into lobules & conveying a rich blood supply together with lymphatics & nerves.

Cellular characteristics:
•	Thyroid follicles are lined by a simple cuboidal epithelium responsible for the synthesis of thyroid hormones.
	Abnormal histology:
•	A well-demarcated, solitary lesion, occasionally accompanied by fibrosis, hemorrhage, or calcification.
•	Sharply demarcated from adjacent parenchyma by a well-defined fibrous capsule.
•	Tumor compresses the surrounding gland.
•	Follicles are lined by cuboidal & columnar cells.
•	Closely apposed nests & trabeculae to well-developed follicles containing abundant colloid.
•	Hurthle cell adenomas: granular, eosinophilic cells containing abundant mitochondria. 	•	Somatic mutations in some components of the TSH receptor signaling system cause chronic stimulation of cAMP pathway, generating cell that acquire a growth advantage.
•	This results in clonal expansion of specific epithelial cells leading to formation of autonomous monoclonal thyroid adenomas.	•	Typically presents as a painless mass.
•	Most adenomas take up less radioactive iodine than does normal thyroid parenchyma.
•	Fine-needle aspiration biopsy is frequently used to evaluate suspected adenomas before surgical excision.