Atypical teratoid/rhabdoid tumor of the brain: Cytopathologic characteristics and differential diagnosis

BACKGROUND. Atypical teratoid/rhabdoid tumor (AT/RT) is a highly aggressive neoplasm with a unique cytogenetic profile. Although the clinicopathologic and radiologic features of AT/RT have been described previously, to the authors' knowledge the cytomorphologic profile of this tumor has not been studied well. METHODS. Nine samples of AT/RT from 8 patients were analyzed from the pathology files of 2 large institutions in a 10-year period (1993-2002). Material consisted of slides made from scraping and smearing (SS) or squash preparation (SP) of the tissue cores (six slides), fine-needle aspiration (FNA) (two slides), and cerebrospinal fluid (one slide). Smears were stained with Diff-Quik, Papanicolaou, and hematoxylin and eosin stains. RESULTS. There were 4 males and 4 females who ranged in age from 1-16 years (mean age, 7.1 years). Cytomorphologic features consisted of hypercellularity (eight of eight tumors); predominantly large tissue fragments with tumor cells surrounding proliferating capillaries depicting a "papillary-like" appearance (five of eight tumors); large, round, "plasmacytoid" cells and characteristic "rhabdoid" cells (i.e., intermediate-sized cells with granular to fibrillary, brightly eosinophilic cytoplasm with or without globoid "inclusions"; large, eccentrically located, round-to-reniform nuclei with single prominent nucleoli; eight of eight tumors); small, round, primitive "neuronal-appearing" cells with a high nuclear to cytoplasmic ratio (five of eight patients); and bizarre, multinucleated giant cells (two of eight tumors). Also seen were numerous apoptotic bodies, mitoses, and significant necrosis (seven of eight tumors), and prominent dystrophic calcification (four of eight tumors). CONCLUSIONS. AT/RT is extremely rare. Cytologic examination by SS, SP, or FNA offers a useful alternative to frozen section during intraoperative consultation. Cytomorphologic features are unique and lead to an accurate diagnosis in the right clinicoradiologic context. The differential diagnosis includes medulloblastoma (in cerebellar tumors), primitive neuroectodermal tumor (in suprasellar tumors), choroid plexus carcinoma, and malignant glioma.