Table 2. Cytological classification and corresponding recommendations according to the guidelines of the European Thyroid Association (6).

Cytological classification		Recommendation
I	Non-diagnostic	Repeat FNA within a short time frame*, except for simple cysts
II	No tumor cells detected	Clinical and ultrasound follow-ups to exclude progressive growth, repeat FNA if nodule increases in size or according to the evaluation of the clinician/pathologist
III	Follicular neoplasia of undetermined significance	Typically surgery; in individual cases, monitoring based on an interdisciplinary decision
IV	Presence of tumor cells suspected	Surgery; exemption: repeat FNA, if more sample material is required
V	Tumor cells detected	Surgery for well-differentiated carcinomas; further diagnostic work-up for anaplastic carcinomas, lymphomas, and metastatic lesions

^*A repeat FNA should be performed either directly after receipt of the results or after 3 months, because otherwise the desmoplastic changes caused by the needle trauma could make it more difficult for the pathologist to interpret the findings