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Long-term morphologic changes may occur in the thyroid of patients who undergo external irradiation of the neck (usually as a therapy of malignancies) or administration of radioactive iodine (which is used to treat hyperthyroidism).
Cytologic diagnostic features
- sheets (macrofollicles)
- enlarged cells
- normal N/C ratio
- Hürthle cell change
- cytoplasmic vacuolization
- marked nuclear atypia:
- marked size variation (giant nuclei)
- hyperchromasia
- coarsely granular chromatin, prominent nucleoli
- grooves, pseudoinclusions
- bare nuclei
Follicular cells with radiation changes have to be differentiated from neoplastic cells, although external irradiation is associated with an increased risk of carcinoma. A microfollicolar architecture, like in follicular neoplasms, is usually not observed. The isolated cell pattern of anaplastic carcinoma is not present. Some of the features of papillary carcinoma may be occasionally observed (pseudoinclusions and grooves), but other findings are not typical, such as nuclear plemorphism and hyperchromasia.