Atypia in Follicular Neoplasm: Making a Case for Follicular Variant of Papillary Thyroid Carcinoma
Berrin Ustun, Constantine Theoharis, David Chhieng, Adebowale J Adeniran. Yale School of Medicine, New Haven, CT
Background: The Bethesda thyroid classification describes follicular neoplasm (FN) as a cellular lesion showing microfollicular architecture with scant or absent colloid. Fine-needle aspiration (FNA) diagnosis of FN is a screening test that does not differentiate between a benign and malignant tumor. The majority of thyroid nodules (up to 80%) diagnosed as FN are benign upon histologic examination. This study is designed to determine the predictive value of cytologic diagnosis in a subset of FN and offer a practical guide for thyroid physicians by identifying significant risk factors for malignancy based on cytologic atypia.
Design: Based on a retrospective review of cytologic diagnosis between January 2008 and December 2011, all thyroid FNA cases with the diagnosis of FN were reviewed. A subset with cytologic atypia – some features suggestive but not diagnostic for Papillary thyroid carcinoma follicular variant (FVPTC) – was identified. The PPV of the cytologic interpretation of FN with atypia for neoplasia (including adenoma and carcinoma) and that for malignancy were calculated.
Results: A total of 38 cases of thyroid FNA (29 females and 9 males) with the cytologic diagnosis of FN with atypia (and with surgical follow-up) were identified (representing 12% of the total number of cases diagnosed as FN with surgical follow-up over this time period). All patients had undergone either lobectomy with completion thyroidectomy or total thyroidectomy. The 38 FNA samples resulted in the following distribution of final histological diagnosis: Neoplastic – 30/38 (out of which 26 were malignant), Benign – 8/38. The positive predictive values for neoplasia and malignancy were 78% and 68% respectively. The malignant cases were predominantly FVPTC (19/26). Others included classic PTC (5/26) and follicular carcinoma (2/26).
Conclusions: The reported incidence of malignancy in FN is 10%-30%. FN with subtle atypical features has a much higher rate of malignancy (68%). The main diagnostic challenge is to differentiate FVPTC from other follicular lesions. Subclassifying FN based on presence of atypia has implications for management. This subset of patients will benefit from a more aggressive follow-up including immediate referral for lobectomy.
Tuesday, March 5, 2013 1:00 PM
Poster Session IV # 86, Tuesday Afternoon