Cytologic artifacts and pitfalls of thyroid fine-needle aspiration using ThinPrep: a comparative retrospective review

The ThinPrep Processor has gained popularity as a collection and preparation technique for fine-needle aspiration biopsy (FNAB). Specific cytologic criteria to evaluate ThinPrep preparation (TP) may differ from those of conventional preparation (CP). The authors retrospectively reviewed the quality, cytologic features, and pitfalls of TP versus CP in thyroid FNABs and addressed the cytomorphologic criteria used to evaluate TP specimens.

Thyroid FNABs received between January 1996-July 1999 were identified from the computer files of the Department of Pathology, University of Michigan (Ann Arbor, MI). Histologic correlation and clinical follow-up were reviewed. The cytology slides were reevaluated for cellularity, cellular preservation, artifacts, background material, architectural integrity, cytoplasmic details, and nuclear details by two observers.

Of the 209 thyroid FNABs performed during the study period, TP and CP prepared 127 and 82 cases respectively. Histologic correlation was available in 68 (33%) cases (32 TP and 36 CP). Overall sensitivity was 80% and specificity was 98%. The sensitivity of CP versus TP was 87% and 70%, respectively. Thyroid FNABs prepared by TP, as compared with CP, were characterized by the following: The TP slide 1) allowed assessment of the overall specimen cellularity but not individual passes of an FNAB, 2) contained only "hard" colloid that appeared dense, markedly fragmented, or in droplets, 3) showed crowded, tight, tissue clusters with loss of cellular preservation, especially in the larger aggregates, 4) demonstrated more cell shrinkage, 5) showed increased disruption of the cytoplasm and numerous naked nuclei, 6) occasionally gave nucleoli a more prominent appearance, and 7) was less likely to show nuclear grooves and "pseudoinclusions" in papillary carcinoma.

This study concluded that cytologic features used to evaluate thyroid FNABs prepared by CP may need to be modified when using TP. Awareness of the above-described findings and further studies to evaluate TP are essential to avoid potential diagnostic pitfalls.