English

Abstract

BACKGROUND: Follicular variant of papillary thyroid carcinoma is relatively common variant of papillary thyroid carcinoma. Fine needle aspiration cytology (FNAC) is an important investigation in preoperative diagnosis of thyroid lesions. The diagnosis of follicular variant of papillary thyroid carcinoma in FNAC is usually missed and is challenging compared to classic papillary thyroid carcinoma. OBJECTIVES: To assess the clinical and histopathological features of subtypes of follicular variant of papillary thyroid carcinoma and to document the features that would improve the sensitivity of FNAC in the preoperative diagnosis. METHODS: Retrospective study of histologically confirmed follicular variant of papillary thyroid carcinoma in our institution over 5 years from 2009 to 2013.RESULTS: Of 26 cases of FVPTC, 21 cases were encapsulated and 5 cases were non-encapsulated, with male: female ratio was 1:18. The median age was 33.5 years. The most frequent microscopic pattern on FNA was micro follicular (23 cases). The p value for monolayered sheets, papillary fronds, nuclear grooves, pseudo inclusions, nucleomegaly and irregular nuclear membrane were found to be significant. Non-encapsulated variant had significantly higher rate of intra tumoral fibrosis (80% vs. 14% compared to encapsulated variant), extra thyroidal extension (60% vs. 5% respectively), positive margins (60% vs. 5% respectively) and lymph node metastases (60% vs. 9% respectively). CONCLUSION: FVPTC appeared to be a heterogeneous disease composed of 2 distinct groups: an infiltrative/diffuse (non-encapsulated) subvariant, which resembles classic papillary carcinoma in its metastatic lymph node pattern and invasive growth, and an encapsulated form, which behaves more like FTA/FTC. The sensitivity of FNA in preoperative diagnosis of FVPTC can be increased by carefully looking for specific features like nuclear grooving and nuclear pseudo inclusions in suspected smears. Further studies with large sample size and long term follow up in required to document the prognosis of FVPTC.