Abstract
Background : Atypical teratoid/rhabdoid tumor (AT/RT), a newly included entity in the latest WHO classification, is a rare brain tumor occurring in infants and children. We encountered 2 cases of AT/RT and report the cytologic and histologic findings.
Cases : Case 1 was a 11-month-old boy. Imprint cytology showed papillary growth of small atypical cells, some of which had eccentric nuclei, with thick cytoplasm. Histologically, the tumor had initially been diagnosed as a choroid plexus carcinoma, but re-examination revealed it to be an AT/RT because of the presence of rhabdoid cells and negative immunostaining for INI1. Case 2 was a 16-month-old girl. Imprint cytology exhibited scattering or gathering small atypical cells having the appearance of peculiar rhabdoid cells. The diagnosis of AT/RT was made histologically on the basis of the papillary epithelioid structure, primitive neuroectodermal tumor-like appearance, presence of rhabdoid cells, and the absence of INI1 expression.
Conclusion : Cytologic diagnosis of AT/RT is possible based on identification of the peculiar epithelioid clusters and rhabdoid cells, in combination with immunocyotological demonstration of the absence of INI1 expression.
