Table 1.

Main characteristics of the studies retrieved through a systematic review of the literature

Reference	Journal	Year	Period of enrollment	Country	Study type	Cytology reporting systema)	FNA category	Nodules with histologic follow-up
Park et al. [15]	Head Neck	2011	Feb 2005-Jun 2009	Korea	Pro	Not detailed	Indeterminate	53
Na et al. [16]	Thyroid	2012	Feb 2009-Jan 2010	Korea	Pro	Bethesda	AUS/FLUS	104
Nasrollah et al. [17]	Endocrine	2013	Dec 2011-May 2012	Italy	Retro	SIAPEC-IAP	TIR 3	40
Choi et al. [18]	Thyroid	2015	Jan 2011-Dec 2012	Korea	Retro	Bethesda	AUS/FLUS	159
Na et al. [19]	Eur Thyroid J	2015	Feb 2010-Jun 2013	Korea	Retro	Bethesda	AUS/FLUS	91
Trimboli et al. [20]	Endocrine	2016	Jun 2012-Dec 2013	Italy	Retro	SIAPEC-IAP	TIR 3	74
Han et al. [21]	Eur J Neuroradiol	2016	Apr 2006-Dec 2010	Korea	Retro	Bethesda	Indeterminate	61

This table does not include the five excluded studies: four studies were excluded due to unclear data [27-30], while the study of Choi et al. [26] was excluded due to potential overlap of the period of enrollment (from October 2008 to July 2011) with that of another series [22].

FNA, fine-needle aspiration; Pro, prospective; AUS/FLUS, atypia of undetermined significance/follicular lesion of undetermined significance; Retro, retrospective; SIAPECIAP, Societá Italiana di Anatomia Patologica e Citologia diagnostica - Divisione Italiana della International Academy of Pathology (the Italian consensus for thyroid cytology classification); TIR 3, category 3 in the five-tiered system for FNA cytology.

^a)System adopted to classify thyroid nodules on initial cytology.