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.

Update on the cytologic features of papillary thyroid carcinoma variants

“…The known cytologic diagnoses that were given for the reported MFV cases were: PTC ( n = 13), benign ( n = 10), AUS/FLUS ( n = 7), and FN/SFN ( n = 5) . The cytologic features of MFV, which have rarely been described, are neither sensitive nor specific . At low magnification, MFV can be easily overlooked as a benign nodule due to the often abundant thin and focally thick colloid (75% of cases) and sheet‐like arrangement of follicular cells (76% of cases) with subtle and patchy nuclear atypia (Fig.…”

“…At low magnification, MFV can be easily overlooked as a benign nodule due to the often abundant thin and focally thick colloid (75% of cases) and sheet‐like arrangement of follicular cells (76% of cases) with subtle and patchy nuclear atypia (Fig. ) . At higher magnification, the neoplastic cells usually have round to ovoid nuclei, small eccentric to conspicuous nucleoli, chromatin pallor, nuclear overlapping and nuclear grooves .…”

“…The macrofollicular variant (MFV) of PTC is an extremely rare morphological variant of PTC/FVPTC with <80 cases reported in the literature. [98][99][100][101][102][103] MFV is arbitrarily defined by the predominance of macrofollicules (>200 mm). [98][99][100][101][102][103] Most cases (85%) are encapsulated and the prognosis appears to be similar to FVPTC, although there are a few case reports with systemic metastases and death.…”

“…[98][99][100][101][102][103] MFV is arbitrarily defined by the predominance of macrofollicules (>200 mm). [98][99][100][101][102][103] Most cases (85%) are encapsulated and the prognosis appears to be similar to FVPTC, although there are a few case reports with systemic metastases and death. 98,99 In addition, although their incidence is usually low (26%), 99 cervical lymph node metastases in MFV may be extensive and/or bulky, and may occur even in non invasive encapsulated cases.…”

“…101,103 At higher magnification, the neoplastic cells usually have round to ovoid nuclei, small eccentric to conspicuous nucleoli, chromatin pallor, nuclear overlapping and nuclear grooves. [101][102][103] However, only 45% of cases show the presence of nuclear pseudoinclusions, which range from rare to few. 101 Furthermore, psammoma bodies or papillary structures have not been reported in MFV.…”