When a definite diagnosis of papillary carcinoma has been made on FNA, the surgeon may proceed to total thyroidectomy with or without lymph node dissection. In cases with a suspi cious FNA, preoperative core biopsy or intraoperative frozen section may be used to confirm the diagnosis.
Grossly, the tumor may range in size from less than 1 mm to several centimeters. Most are irregular in shape and infiltrate the gland. They are often associated with scarring. Some are encapsulated and others show cystic change. The diagnosis depends to a great extent on the characteristic nuclear features (Figure 9.5). These are nuclear enlargement and irregularity, nuclear clearing (or ground glass appearance), prominence of the nuclear membrane, grooves, and pseudoinclusions. There is heaping up of nuclei, with what has been described as a "basket of eggs" appearance. Most show a mixture of papillary and follicular structures and trabecular and solid areas may be found. Some show squamous metaplasia. This has no implications for tumor behavior. It is important not to confuse it with squamous carcinoma, which has an aggressive course. Psammoma bodies are often found. Indeed, they may be the only intrathyroidal evidence of tumor in some patients who present with nodal metastases and in whom the primary tumor has regressed. Multicentric tumors are common. Some of these may represent intrathyroidal lymphatic spread, but there is also evidence to suggest that some may be multiple primary tumors in that individual tumors within a gland showed different RET/PTC translocations .
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