Calcium oxalate crystals in thyroid fine needle aspiration cytology

OBJECTIVE: To determine the occurrence, distribution and location of calciu m oxalate crystals (COCs) in thyroid fine needle cytology specimens. STUDY DESIGN: Thyroid tissues from 60 fine needle aspiration cytology speci mens (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 Microsco py to determine their size, shape, occurrence, distribution and location. RESULTS: The size and shape of COCs varied from case to case. The total inc idence was 45% (benign diseases, 68%; malignant lesions, 21%). No significa nt relation ship between age and occurrence of COCs was found. Benign disea ses showed more multifocal than focal distribution of COCs, unlike malignan t diseases. Twenty-three (85%) of 27 cases with COCs revealed background lo cation of COCs, especially within thyroid colloid. CONCLUSION: The occurrence of COCs in thyroid fine needle cytology was lowe r than that in histologic specimens reported in the literature, and COCs we re 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 co nsideration.