Macrofollicular variant of papillary carcinoma: a potential thyroid FNA pitfall

Macrofollicular variant of papillary carcinoma (MFPC) is a rare variant of papillary carcinoma in which over 50% of the follicles are represented by macrofollicles. The cytologic features from 7 cases of histologically confirmed MFPC were evaluated. The cytology specimens were evaluated for the following criteria: cellularity, cluster arrangement (micro and macrofollicular), chromatin pattern, nuclear grooves, pseudonuclear inclusions, nuclear shape, nuclear overlap, nucleoli, presence of lymphocytes, macrophages and Hurthle cell, amount and characteristics of background colloid. Most cases were moderately to highly cellular with presence of both microfollicles as well as macrofollicles, but nuclear features of papillary thyroid carcinoma were absent or focal in all cases. MFPC is a variant of papillary carcinoma that can be extremely difficult to diagnose cytologically. The presence of abundant colloid, macrophages, macrofollicular follicular cell arrangement and/or absence of widespread cytologic features associated with papillary carcinoma can lead to an erroneous diagnosis of goiter.