ABSTRACT
<p><b>OBJECTIVE</b>To study the clinicopathologic features, immunohistochemical findings, diagnosis and differential diagnosis of atypical teratoid/rhabdoid tumors (AT/RT) of central nervous system in childhood.</p><p><b>METHODS</b>The clinicopathologic data, morphologic features and immunophenotypes were reviewed in 6 cases of AT/RT. EnVision method was applied. Antibodies include cytokeratin (CK), epithelial membrane antigen (EMA), vimentin, smooth muscle actin (SMA), muscle specific actin (MSA), glial fibrinary acid protein (GFAP), desmin, placental alkaline phosphatase (PLAP) and INI1.</p><p><b>RESULTS</b>Five of the six cases of AT/RT occurred in infancy and early childhood. Histologically, the predominant component was rhabdoid cells. Cytoplasmic inclusions were present in all cases. Primitive neuroectodermal tumor (PNET) component was also identified in 5 of the 6 cases studied. Immunohistochemically, the tumor cells were positive for cytokeratin, epithelial membrane antigen and vimentin. The staining for INI1, desmin and PLAP was negative. Smooth muscle actin was expressed in 2 cases and glial fibrillary acidic protein in 5 cases. The proliferative index as demonstrated by Ki-67 staining was high.</p><p><b>CONCLUSIONS</b>AT/RT is not a particularly uncommon malignancy in childhood. The histologic hallmark is the presence of rhabdoid cells with cytoplasmic inclusions. The tumor cells are positive for cytokeratin, epithelial membrane antigen and vimentin, and negative for INI1. Differential diagnosis includes PNET, medulloblastoma and medullomyoblastoma.</p>