Tyrosine crystals in benign parotid gland cysts: report of two cases diagnosed by fine-needle aspiration biopsy with ultrastructural and histochemical evaluation.

Two cases were encountered in which tyrosine crystals were identified by fine-needle aspiration biopsy in nonneoplastic, retention cysts of the parotid. Tyrosine crystals occasionally have been described in parotid neoplasms, but have not been reported in benign retention cysts. To study the frequency and significance of tyrosine crystals in parotid gland cysts, the authors reviewed parotid cytology specimens collected at Loyola University Medical Center from 1985-1993. Among 97 patients, 8.2% (n = 8) had benign retention cysts. No other patients had tyrosine crystals. The presence of tyrosine crystals in benign retention cysts is largely enigmatic. However, because tyrosine crystals previously have been associated with parotid gland neoplasms, awareness of the fact that these unusual structures may be found in benign retention cysts is useful to avoid the erroneous interpretation of tyrosine crystals as an indication of neoplasia, particularly in aspirated material.