409 OBJECTIVE: To study the occurrence and significance of Charcot-Leyden crystals (CLC) in routinely processed, eosinophil-rich smears. STUDY DESIGN: Fine needle aspiration (FNA) smears of 258 cases of cysticercosis, 35 of lymphatic filariasis and 19 of nonparasitic lesions with significant eosinophils were screened for the presence of CLC and correlated with the cytomorphology of the underlying disease. RESULTS: Charcot-Leyden crystals were seen in lym- phatic filariasis (4), eosino- philic granuloma (1), chronic myelogenous leukemia (1) and pyogenic abscess (1). CLC were conspicuous by their absence in smears of cysticercosis, although cho- lesterol crystals were frequently observed. CLC were present in both May-Grünwald-Giemsa– and Papanicolaou-stained smears. Necrosis was a prominent cytologic feature in all cases with CLC. CONCLUSION: CLC encountered in routinely pro- cessed aspirates containing eosinophils, albeit infre- quently, indicate in vivo formation. Necrosis probably provides a milieu for suspension of eosinophils, facilitat- ing the formation of CLC. Absence of CLC in cysticerco- sis could be attributed to the high lipid content of these le- sions, as indicated by the frequent occurrence of cholesterol crystals. (Acta Cytol 1997;41:409–412) Keywords: crystallization, aspiration biopsy, Charcot-Leyden crystals. Charcot and Robin 6 observed distinctive micro- scopic crystals in the spleen of a patient with chron- ic leukemia; subsequently, Leyden 16 described similar crystals in the sputum of individuals with bronchial asthma. These crystals, Charcot- Leyden crystals (CLC), have been observed in a variety of conditions as- sociated with eosinophilia and have been detected in tissues, 15,22 body flu- ids, 9,20,21 urine 13 and stool. 7 The in vitro crystal formation can be readily induced in eosinophilic pleural effusions by refrig- eration of fluid for 24 hours. 20 Seven cases subject- ed to fine needle aspiration (FNA) are described in which CLC were identified in routinely processed material. M aterials and M ethods All parasitic infestations diagnosed on FNA cytol- ogy in our hospital over a 10-year period from Jan- uary 1986 through February 1995 and nonparasitic lesions with prominent eosinophils constitute the material used for this study. A total of 312 cases, From the Cytology Section, Department of Pathology, University College of Medical Sciences and Guru Tegh Bahadur Hospital, Delhi, India. Drs. Arora and Singh are Readers. Dr. Bhatia is Professor, Department of Pathology. Address reprint requests to: Vinod K. Arora, M.D., Cytology Section, Department of Pathology, University College of Medical Sciences and Guru Tegh Bahadur Hospital, Delhi 110 095, India. Received for publication September 20, 1995. Accepted for publication January 25, 1996. Charcot-Leyden Crystals in Fine Needle Aspiration Cytology Vinod K. Arora, M.D., Navjeevan Singh, M.D., and Arati Bhatia, M.D. Acta Cytologica 0001-5547/97/4102-0409/$02.00/0 © The International Academy of Cytology Acta Cytologica While the presence of CLC in FNA signifies activated tissue eosinophils, the exact role of CLC protein and its crystallization in vivo needs to be further investigated. DO NOT DUPLICATE © Copyrighted Material