False positive cases in thyroid cytopathology – the experience of a single laboratory and a systematic review

Abstract

Introduction Fine needle aspiration (FNA) is fundamental in the pre‐operative assessment of thyroid nodules. However, the shining success of thyroid FNA is occasionally eclipsed by false positive (FP) cytological diagnoses. We describe our experience regarding FP cytological diagnoses and present a literature review concerning FP rates. Materials and methods We retrospectively analyzed 2031 consecutive cytology reports. FP was defined as a case with “suspicious for malignancy” or “malignant” cytology, whose surgical follow‐up failed to confirm the initial diagnosis of malignancy. We used the PubMed database for the literature review using specific search terms (“thyroid”, “cytology”, “false positive”). Results Out of 2031 FNA reports, 93 cases with “suspicious for malignancy” or “malignant” cytology underwent surgical excision. Histopathology did not confirm malignancy in 10 cases (0.6% FP rate). Nodules with FP cytology were significantly larger (P = 0.0024) than those with with TP (true positive) cytology. A review of 25 publications shows comparable results to ours with some slight differences. The majority of studies achieve a FP rate below 3%. Most FP cytological diagnoses turn out to be non‐neoplastic lesions (nodular hyperplasia, adenomatous nodule, lymphocytic thyroiditis), which combined account for 80.5% of all histological diagnoses. Conclusions Thyroid nodules with FP cytology were larger than nodules with TP cytology. Most studies manage to adhere to the recommended FP rates, or values close to them, with some outliers. Nevertheless, the mean FP rate values are very close to the value recommended by The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). The FP rate value depends on how one defines true negative cases, which can be either histologically proven benign cases, via a benign clinical course, or by assuming that cytologically benign cases remain as such.

Diagnostic Value and Challenges of BRAF V600E Molecular Testing and Thyroid Fine-Needle Aspiration Cytology: A Retrospective Study from a Tertiary Institution in Southern Hunan Province, China

“…Although cost-effective and rapid, this conventional preparation and staining method has limitations seldom discussed in the literature [30]. For instance, although thyroid category VI lesions were finally confirmed as PTC in our study, some benign diseases, mostly nodular goiters, were initially recognized as categories III to V. Evidence suggests 3 plausible reasons why FNA cytology may mistakenly assign nodular goiters into categories higher than category II [30–32]. First, hyperplastic and adenomatous components are the most common pitfall in thyroid FNA cytology since some follicular cells may also demonstrate nuclear atypia, involving nuclear grooves, overlapping, oval shape, and chromatin clearing [30].…”

Diagnostic Accuracy of the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC): An Institution Experience

“…Based on the 2017 TBSRTC, the risk of malignancy (ROM) was presented as a range where the lower limit in each respective category is the number of malignant nodules/total number of nodules and the upper limit in each respective category is the number of malignant nodules/number of surgically excised nodules, where "malignant nodules" refers to confrmed malignancy upon surgical excision. Due to this range, it is believed that the true ROM lies between the two risk values [8,15]. In addition, nodules found to be "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) were considered benign in this study.…”

Cytomorphological analysis of histologically confirmed cases of medullary thyroid carcinoma

“…A citológiai képben domináltak a diszkohezív és mikrofollicularis sejtcsoportok; szövettani diagnózis: göbös golyva reak-tív és degeneratív elváltozásokkal. Ezen különös esetet bemutattuk egy másik publikációban [15]. Medullaris pajzsmirigyrák esetek MTC-vel diagnosztizált betegek átlagéletkora 53±13 év (medián 53, legfiatalabb 37, legidősebb 75 éves), amelyből 9 nő (77%, átlagéletkor 51±14 év, medián 51) és 3 férfi (23%, átlagéletkor 61±6 év, medián 58) volt.…”