Most common malignant tumour of thyroid:

Ans: a (Papillary) Ref: Schwartz, 8th ed, p. 1417; Harrison, 16th ed, p. 2122TYPE OF THYROID CARCINOMAAPPROXIMATE PREVALENCEPapillary CA80-90 %Follicular CA5-10%Medullary CA10%Anaplastic CARareLymphoma1-2%Histological features of Papillary CA1. Papillary projections - PTC contains branching papillae of cuboidal epithelial cells.2. Orphan annie nulei - Nucleus of PTC contain finely dispersed chromatin which imparts an optically clear or empty appearance giving rise to term ground glass or orphan annie nuclei. In addition invagination of cytoplasm in cross sections give the appearance of intranuclear inclusions or grooves - Diagnosis of papillary Ca is is based on these nuclear characteristics.3. Psammoma bodies - These are concentrically calcified structures.