Papillary thyroid carcinoma (PTC) is the most common type of malignant thyroid tumor constituting more than 70% of thyroid malignancies [1
]. There has been an increasing incidence of PTC worldwide for the past few decades. There are significant geographic variations, but sampling techniques also contribute to this wide variability.
The etiology of PTC is related to environmental, genetic and hormonal factors [1
]. Radiation as a genotoxic factor for PTC has been well documented [1
]. The widespread use of X-irradiation in the 1950s for treating conditions such as enlarged thymuses and acne have contributed to the increased incidence of PTC [2
]. The Chernobyl nuclear accident in 1986 led to a marked increase in the incidence of PTC in Belarus and other areas of the former Soviet Union close to the accident [2
]. The most striking increase in the incidence was in children, since the growth of the thyroid is most rapid in childhood and falls to low levels in adults [2
Patients with PTC usually present with a cold nodule on radioactive iodine scan [1
]. A few patients may present with cervical lymphadenopathy. Involvement of the Delphian lymph node is an adverse prognostic sign in PTC, since this may indicate advanced disease with a need to examine the central and lateral lymph node compartments more carefully [4
Patients with PTC usually present with a palpable nodule in the thyroid. Non-palpable nodules of PTC may be discovered incidentally after CT and MRI examination. Small nodules of PTC or microcarcinomas (less than 1 cm in size) are usually of no clinical significance especially in young patients (less than 40 years), since such individuals have a 20-year survival of greater than 98% even with palpable tumors.
Fine needle aspiration biopsy (FNAB) is the most common method of examining solitary thyroid nodules today. FNAB of enlarged cervical lymph nodes may also reveal a PTC, since patients may present with a palpable cervical LN even when the primary tumor is small or non-palpable.
The gross appearance of PTC can be quite variable. Most tumors are firm solid and gray-white, but a significant percentage of tumors may be cystic. It is not uncommon to have a solid primary tumor with a cystic metastasis to a lymph node. PTC may have an infiltrative growth pattern in the thyroid or may show direct extension beyond the thyroid to adjacent tissues.
The conventional PTC shows a papillary architecture with branching [1
]. The papillae are covered by cells with eosinophilic cytoplasm and enlarged nuclei (Fig. a). The polarity of the cells may be abnormal or lost in some tumors. Squamous metaplasia may be present. Psamomma bodies with concentric lamellae composed partly of thyroglobulin are more common in some variants of PTC. Some tumors may also contain multinucleated giant cells.
Fig. 1 Conventional papillary thyroid carcinoma and papillary thyroid carcinoma variants. a Conventional papillary thyroid carcinoma. The carcinoma has papillae with fibrovascular cores and enlarged nuclei with nuclear clearing. b Follicular variant of papillary (more ...)
Cytologic features are very helpful in making the diagnosis in some variants of PTC. These consist of enlarged irregular nuclei that are often oval shaped and overlapping because of the nuclear enlargement. The nuclei often show clearing or have a ground glass appearance with prominent nuclear grooves and pink cytoplasmic invaginations [1