Typically, these tumours are discrete and non encapsulated and are made up of polygonal, round, or spindle-shaped cells arranged in sheets, nests or trabeculae, with prominent intervening collagenous stroma (Fig. 16.12). Amyloid is present in varying amounts, both within cell masses and in the stroma. The individual tumour cells show little variation in morphology, with stippled nuclei of regular shape and size and finely granulated cytoplasm. Surviving non-neoplastic thyroid follicles are incorporated into the periphery of the tumour. Occasionally, other patterns are seen, including glands and even mucin secretions.
