Thyroid Bethesda reporting category, 'suspicious for papillary thyroid carcinoma', pitfalls and clues to optimize the use of this category.

OBJECTIVE

The Bethesda System of Reporting Thyroid Cytopathology classifies the indeterminate categories based on their differing risks of malignancy, as atypia of undetermined significance (AUS), follicular neoplasm/suspicious for follicular neoplasm (FLUS) and suspicious for malignancy. The vast majority of cases of the last category are suspicious for papillary thyroid carcinoma (PTC). The aim of the present study was to identify the pitfalls and clues to improve the usage of the suspicious category as well as improve its outcome of malignancy.

METHODS

We reviewed the cytological features on air dried Diff-Quik® and alcohol-fixed Papanicolaou smears from 54 thyroid fine needle aspirates (FNAs) with surgical follow-up that were originally diagnosed as suspicious. Procedure data/specimen adequacy was correlated and follow-up histology reports were reviewed after our cytological review was completed. Incidental PTC that was not the target of the FNA was excluded from the calculations for correlation.

RESULTS

In our cytological review, we retained a diagnosis of suspicious in 18 of the 54 cases and the remaining 36 were re-categorized as follows: 6 malignant, 10 neoplasm (which is used in our centre instead of FLUS) and 20 AUS. The reasons for overcall of suspicious cases included pseudopapillae, syncytial sheets, nuclear grooves and pinpoint nucleoli in chronic lymphocytic thyroiditis and Hürthle cell neoplasms, and intranuclear inclusions in parathyroid adenoma, hyalinizing trabecular adenoma and mesenchymal repair. The primary reasons for undercall of PTC as suspicious included cystic aspirates with minor features of PTC such as histiocytoid cells, bubblegum colloid, syncytial sheets and cellular swirls. Cases with cytoplasm similar to Hürthle cells were also noted to cause difficulty in accurate classification.

CONCLUSIONS

Recognition of these pitfalls and clues can help improve diagnosis, patient treatment and consequently reduce the number of unnecessary thyroidectomies.