Macrofollicular variant of papillary carcinoma, a potential diagnostic pitfall: A report of two cases including a review of literature

Abstract

Macrofollicular variant of papillary thyroid carcinoma (MFVPTC) is one of the rarest histologic types of papillary carcinoma. This tumor may mimic an adenomatoid/colloid nodule or follicular neoplasm (macrofollicular type) both on histology and cytology. There are very few articles describing the cytologic features of MFVPTC. We report the cytologic findings of two surgically confirmed MFVPTC. The first case showed abundant thin colloid with moderate amount of follicular cells arranged in a honeycombed and syncytial pattern. Some but not all the follicular cells showed enlarged round to ovoid nuclei, overlapping nuclei, few nuclear grooves and rare intranuclear inclusions. The second case showed abundant thin colloid and predominantly benign appearing follicular cells with few overlapping nuclei, enlarged round to ovoid nuclei and rare nuclear grooves. No intranuclear inclusions were identified. A review of the literature was done and the cytologic findings of MFVPTC including our two cases were tabulated. The cytologic findings showed moderate to abundant thin with focally thick colloid in 75% of cases and sheet like arrangement of follicular cells in 76%. Although nuclear features such as chromatin clearing, overlapping and grooves were present in majority of cases, the quantity varied from rare to focal. Small to prominent nucleoli were present in all of the evaluable cases. Intranuclear inclusions were seen only in 45% of patients. Hence, the cytologic features of macrofollicular variant of papillary carcinoma though present can be subtle and intranuclear inclusions may not be present always.

Keywords: Fine needle aspiration; macrofollicular variant; papillary carcinoma; thyroid.

Figure 1

Case 1. Abundant thin colloid and follicular cells arranged in honeycombed and syncytial pattern (Diff-Quik, ×200)

Figure 2

Case 1. Follicular cells with enlarged round to ovoid nuclei, focally overlapping nuclei, and nuclear grooves (Diff-Quik, ×600)

Figure 3

Case 1. Follicular cells with occasional intranuclear inclusions (Diff-Quik, ×600)

Figure 4

Case 1. Follicular cells with fine nuclear chromatin pattern and small eccentrically located nucleoli (Papanicolaou, ×600)

Figure 5

Case 2. Follicular cells with enlarged round to ovoid overlapping nuclei and occasional nuclear grooves (Diff-Quik, ×400)

Figure 6

Case 2. Follicular cells with focally enlarged round to ovoid nuclei and small nucleoli (Papanicolaou, ×400)