Atypical teratoid/rhabdoid tumors with multilayered rosettes in the pineal region.

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare, highly malignant tumor of the central nervous system (CNS) that typically occurs during infancy. These tumors exhibit morphologic heterogeneity and differentiate along multiple lineages, thus posing a diagnostic challenge. Here, we present two cases of AT/RT with a primitive neuroectodermal component and histological pattern resembling an embryonal tumor with multilayered rosettes (ETMR), a rare but distinctive embryonal entity with different therapeutic implications. Patient 1, a 23-month-old girl, presented with a history of gait unsteadiness and headache; cranial computed tomography (CT) identified a mass in the pineal and third ventricular regions. Patient 2, a 26-month-old girl, presented with headache and vomiting; CT revealed a mass in the posterior third ventricle. Both patients were treated via gross total tumor resection. Although histologically, AT/RT cases variably comprise primitive neuroectodermal, mesenchymal, and classic rhabdoid cells, the most striking feature of both cases was the presence of multilayered rosettes with a few Homer Wright rosettes and occasional primitive neuroepithelial tubes in focal primitive component areas. Immunohistochemistry revealed considerable heterogeneity within the tumors. We further present our findings in the context of the relevant literature.