Synchronous subcutaneous and calvarial Rosai–Dorfman disease diagnosed on fine needle aspiration cytology

cellular central core composed of basement membrane material. Rosettes in a carcinoid tumour are composed of cytoplasm and not the matrix material. Moreover, carcinoid cells lack nuclear grooves and show more cytoplasm than AGCT cells. Ovarian aspirates from younger women undergoing fertility treatment may mimic an AGCT as a result of heightened stimulation of the follicular cells. The younger age of a patient and a clinical history of treatment can avoid misdiagnosis in such situations. Moreover, an FNA is unlikely to be attempted in such cases. Identification of AGCT on fluid cytology is more challenging, as it is difficult to appreciate nuclear grooves owing to tight clustering of AGCT cells in fluids. Failure to recognize them in peritoneal fluids may lead to under-staging of the tumour. However, Call-Exner bodies, if present, allow an easy diagnosis. Both AGCT and mesothelial cells are immunopositive for calretinin, so its use may be misleading when the need for distinction between the two arises. GCTs are usually indolent and more than 80% of cases present at stage 1. Rare cases are aggressive with early or late recurrence and metastasis. Increased mitotic activity, fewer Call-Exner bodies and nuclear atypia (pleomorphism, hyperchromasia and prominent nucleoli) indicate aggressiveness in AGCT. A pathologist’s comment on these features conveys the aggressive behaviour and chance of recurrence to the clinicians.