Paucicellular variant of anaplastic thyroid carcinoma: A diagnostic pitfall in thyroid pathology

Paucicellular variant is a rare variant of anaplastic carcinoma. Anaplastic thyroid carcinomas usually creates no problems in histologic diagnosis because of the obvious invasive growth, high cellularity, and marked degree of anaplasia, but paucicellular variant of anaplastic carcinoma is problematic in diagnosis because of its histologic mimicry to benign lesions, e.g. Riedel disease and fibrous variant of Hashimoto thyroiditis, i.e. prominent fibrosis and low cellularity. It is important to distinguish it from these two lesions because both are reactive conditions with favorable prognosis while anaplastic carcinoma is a malignant condition with poor prognosis. We present a case of 45-year-old female presented with a history of thyroid swelling for 10 years. The cytological diagnosis was given as colloid goiter while histopathological examination turned out to be paucicellular variant of anaplastic carcinoma thyroid. To conclude paucicellular variant is the entity to which all pathologists should be familiar and should know differential diagnosis while dealing with any fibrosed lesion of the thyroid.