Calcium oxalate crystals in thyroid fine needle aspiration cytology

OBJECTIVE: To determine the occurrence, distribution and location of calcium oxalate crystals (COCs) in thyroid fine needle cytology specimens. STUDY DESIGN: Thyroid tissues from 60 fine needle aspiration cytology specimens (31 benign and 29 malignant lesions) were reviewed. These lesions were also histologically examined, and their pathologic diagnosis was confirmed. The cytologic slides were examined by normal and polarized light microscopy to determine their size, shape, occurrence, distribution and location. RESULTS: The size and shape of COCs varied from case to case. The total incidence was 45% (benign diseases, 68%; malignant lesions, 21%). No significant relationship between age and occurrence of COCs was found. Benign diseases showed more multifocal than focal distribution of COCs, unlike malignant diseases. Twenty-three (85%) of 27 cases with COCs revealed background location of COCs, especially within thyroid colloid. CONCLUSION: The occurrence of COCs in thyroid fine needle cytology was lower than that in histologic specimens reported in the literature, and COCs were more often identified in benign than malignant lesions. The presence of COCs may be a clue to benign lesions if their distribution is taken into consideration.