Changes in thyroid fine needle aspiration practice during the COVID‐19 pandemic

Abstract Purpose To investigate the diagnostic accuracy of a different sample preparation protocol for fine needle aspiration cytology (FNAC) of thyroid nodules established during the COVID‐19 pandemic. Methods From April 2020, conventional smears during FNAC were ceased according to World Health Organization recommendations due to the increased infection risk for operators, and a new protocol using only liquid‐based cytology (LBC) was adopted. FNACs performed between April and July 2020 (COVID‐19 group) were retrospectively compared with those from December 2019 through March 2020 (Pre‐COVID‐19 group). The distribution of diagnoses based on SIAPEC‐IAP categories and the concordance between cytological and histological results were compared using the chi‐squared test. Results Categories based on FNAC for 90 and 82 thyroid nodules in the Pre‐COVID‐19 and COVID‐19 groups showed no significant difference in distribution (P = .081), with the following respective cases (and percentages): TIR1, 7 (8%) and 8 (10%); TIR1C, 0 (0%) and 6 (7%); TIR2, 59 (66%) and 55 (67%); TIR3A, 8 (9%) and 5 (6%); TIR3B, 1 (1%) and 2 (3%); TIR4, 5 (6%) and 1 (1%); and TIR5, 10 (12%) and 5 (7%). Among patients with potentially malignant lesions, surgery was performed for 12/16 (75%) nodules in the Pre‐COVID‐19 and 7/8 (88%) nodules in the COVID‐19 groups, with no significant differences between cytological and histological diagnoses (P = .931). Conclusion The new LBC‐only protocol provided similar diagnostic accuracy in comparison with conventional smears, and can be effectively applied during a viral pandemic improving operator safety.


| INTRODUC TI ON
Thyroid nodules are very common in the general population (being detected at rates of up to 65%), especially in women, 1 and thyroid cancer is the most common neoplasm of the endocrine system, accounting for about 90% of cases.
Most thyroid lesions are benign and the malignant ones account for less than 10%, 2 being usually well-differentiated neoplasms with a slow growth and excellent outcomes. Papillary carcinoma is the most common form of well-differentiated thyroid cancer. 3,4 The initial evaluation of a patient with thyroid nodules includes a full laboratory workup and ultrasound (US) evaluation with or without fine needle aspiration cytology (FNAC).
FNAC is a cost-effective and useful method for assessing the nature of thyroid nodular lesions 5 characterised by high sensitivity and many advantages such as ready-to-use equipment for a high-quality product, a low rate of complications, and good patient tolerability. 6 In most centres, the standard protocol for FNAC slide production consists of preparing thin smears that are rapidly air-dried and/or fixed in 95% ethanol solution. 7 Liquid-based methods for cytology (LBC) have been reported to provide good diagnostic accuracy and are becoming routinely used, either alone or in combination with standard cytological preparation, especially to standardise the preanalytical procedures that are needed to perform immunocytochemistry (ICC) or molecular tests. [8][9][10][11] Even if there is still some debate regarding the routine application of LBC in thyroid FNAC, it should be noted that this method carries the not negligible advantage of also reducing the risk of aerosol diffusion of potentially infected material, which could be of particular value during a pandemic.
By April 2020, the coronavirus disease 2019 (COVID-19) 12 which was firstly reported in Wuhan, China, 13 in December 2019, had dramatically spread in northern Italy. By then, stricter measures to address its specific biological risk in laboratories were being recommended. 14 Due to the potential presence of the virus in histological and cytological specimens, the World Health Organization (WHO) advised that specimen processing should occur in accordance to biosafety level 2 guidelines. 15,16 Only tissue samples completely fixed in formalin (after 24 hours at room temperature) or in ethanol 95° were to be considered not a microbiological risk. 14,17,[18][19] virus was identified mainly in samples of lung and oral origin, rarely in other biomaterials such as blood 19 and faecal material. 20  Moreover, transmission of coronaviruses from contaminated inert surfaces was postulated, including self-inoculation of mucous membranes of the nose, eyes, or mouth. 22 According to a recent review article, the Severe Acute Respiratory Syndrome Coronavirus-2 virus (SARS-CoV-2) can last on different surfaces between hours and a few days, though a rapid virus inactivation is possible using commonly available chemicals and biocides on dry surfaces. 23 However, at our institution, from April 2020 a change in the FNAC protocol was decided, avoiding both air-dried and alcohol-fixed slides. To avert potentially infectious aerosol formation, all biological material must be fixed in an alcohol-based fixative solution. The adoption of LBC with a ThinPrep ® automated system was decided according to our security criteria.
The aim of this work is to report the diagnostic accuracy of this new sample preparation protocol for FNAC of thyroid nodules established during the COVID-19 pandemic and to compare it with the diagnostic accuracy of the previously established standard protocol.

| ME THODS
Approval for this retrospective study was obtained from our institution's Ethics Committee and patients' informed consent was waived.
All thyroid US-guided FNACs for suspicious lesions performed between December 2019 and July 2020 at our institution were retrospectively analysed. Surgery was performed when high-risk or malignant lesions (TIR3B, TIR4, TIR5) were detected. The final diagnosis on histopathological reports was recorded when surgery was carried out at our institution.
All FNAC procedures were US-guided. Following identification of the lesion by ultrasonography and skin disinfection with alcohol, a 25-gauge needle was inserted into the desired nodule with the no-aspiration technique, according to which the needle was moved in different directions for a few seconds allowing material to enter it by capillary action. In the Pre-COVID-19 period, the needle content was expelled onto previously labelled slides and the smear was simply prepared by touching the second slide to the surface and separating them again. One set of slides was placed in the holder containing 95% alcohol solution while another set was left to air-dry.
Another tissue sample was then performed on the desired nodule

| Data analysis
The distribution of the diagnostic categories between the Pre-COVID-19 and COVID-19 group was evaluated. When considering high-risk or malignant lesions, we also evaluated the accuracy and reliability of the Pre-COVID-19 and COVID-19 protocols using subsequent diagnosis on surgical specimens as reference when available.

Continuous data are reported as median values and ranges.
Categorical data are reported as counts and percentages. Pearson's chi-squared test was used to assess the distribution of the diagnostic categories between the two groups and to evaluate the agreement of cytological and histological diagnoses of potentially malignant lesions between the two methods. P values less than .05 were considered statistically significant. All data were collected and analysed on a Microsoft Excel spreadsheet.  Table 1). Among the high-risk patients (TIR3, TIR4, TIR5), 12/16 (75%) in the Pre-COVID group and 7/8 (88%) in the COVID group underwent surgery at our institution, and no statistically significant difference was found between the two groups in terms of agreement between cytological and histological diagnoses of potentially malignant lesions (P = .931) ( Table 2).

| D ISCUSS I ON
US-guided FNAC has an essential role in the diagnostic pathway of thyroid nodules especially for its availability, rapidity, costeffectiveness, and low level of associated procedural risks. In the future, another approach, based on cytology combined with molecular testing on an LBC method, could improve the diagnosis of indeterminate FNAs, still avoiding the use of CSs. [30][31][32] Our study has some limitations, mainly its retrospective nature and the fact that from a pathologist's perspective, common Papanicolaou and Romanowsky stains on CSs are still used in a complementary fashion and currently represent the mainstay in the approach to the FNAC diagnosis. 8 However, our approach, developed in a case of extreme emergency, suggests the reliability of an LBC method in terms of diagnosis and safety for healthcare workers.

I N FO R M ED CO N S ENT
Informed consent was obtained from all individual participants included in the study.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author.