Utility of cell block as an adjunct to liquid-based cytology for diagnosing papillary thyroid carcinoma

Background

Although liquid-based cytology (LBC) has gained popularity among clinical laboratories, it is unclear whether it is equivalent to conventional smears for making a definite diagnosis of papillary thyroid carcinoma (PTC). The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) suggests a definite diagnosis of PTC is preferred when there are at least one of three features (papillary architecture, psammomatous calcifications, and frequent pseudonuclear inclusions) plus other typical cytomorphological findings. This study evaluated whether an additional cell block (CB), prepared from the residual LBC material, could help improve the diagnosis of PTC.

Materials and Methods

A total of 62 cases with both ThinPrep LBC and CB preparations and histopathological follow-up of PTC were retrieved between November 2016 and March 2019. The ThinPrep LBC and CB slides were reviewed separately to identify any papillary architecture, psammomatous calcifications, or pseudonuclear inclusions for diagnosing PTC.

Results

Among the 51 cases with cytological diagnosis of PTC in the LBC+CB slides, the CB provided additional diagnostic information in 15 cases, which were initially diagnosed as suspicious for PTC based on the LBC slides alone. This information included papillary architecture (n=11), psammomatous calcification (n=1) and pseudonuclear inclusions (n=5). The number of specimens in the 51 cases containing at least one of the three features increased from 42 (LBC) to 51 (LBC+CB). The accuracy for diagnosing PTC increased from 58.1% for LBC alone to 82.3% for the LBC+CB examination.

Conclusion

An adjunctive CB preparation may improve the LBC technique for diagnosing PTC.

A diagnostic head and neck fine needle aspiration service can be provided using liquid-based cytology only

OBJECTIVE

Liquid-based cytology (LBC) has been used for non-gynaecological specimens since its introduction into routine use in cervical cytology in the mid-1990s. There are still relatively few large studies comparing performance in reporting the head and neck fine-needle aspirations (H&N FNA) processed by LBC only to conventional direct smears (CDS).

METHODS

This study compared 686 H&N FNAs processed by LBC only with 3719 CDS. All were taken under ultrasound (US) guidance by a small cohort of three consultant radiologists and reported by the author.

RESULTS

The (smaller) LBC sample was statistically representative of the larger CDS population at an alpha level of 0.05. There was no difference between CDS and LBC at a 95% confidence interval (CI) when comparing specificity and sensitivity (specificity: 94.8-96.5% versus 90.2-95.4%; sensitivity: 91.4-94.1% versus 86.8-93.4%). The inadequate rate between the two techniques was similar, 0.5-1.0% for CDS versus 0.7-2.5% for LBC. The significance difference was in the suspicious rate which was greater at 2.8-5.8% for LBC versus 1.7-2.6% for CDS. Consequently, there was a slight but non-significant difference between the two populations with respect to the overall accuracy: 93.5-95.1% for CDS versus 89.4-93.7% for LBC.

CONCLUSIONS

While there are morphological differences between LBC and CDS in H&N FNAs, once a degree of familiarity is achieved, the two techniques have equivalent sensitivity, specificity and inadequate rates.