Objective: Atypical teratoid rhabdoid tumor is a rare neoplasm with a distinct cytogenetic profile that predominates in infancy. Many cases show predominance of small cells with scanty rhabdoid cells, making recognition of this tumor difficult. We aim at describing our experience with atypical teratoid rhabdoid tumor cases diagnosed over a 6-year period.

Material and Method: Clinicopathologic features and immunohistochemical staining of atypical teratoid rhabdoid tumor cases diagnosed between 2006 and 2011 are presented.

Results: Fifteen cases were identified including 9 males with a median age of 26 months. The most common presenting symptom was recurrent vomiting with a mean duration of 6 weeks. Nine cases (60%) were infratentorial and cerebrospinal fluid was positive in 2 cases (13.3%) at time of diagnosis. The median overall survival of the group was 9.5 months. All cases except one showed admixture of rhabdoid and/or small round blue cells in variable proportions. Only 5 out of fourteen referred cases (35.7%) were correctly diagnosed. Three cases showed unusual growth patterns. In 2 cases, nodular medulloblastoma-like growth pattern predominated, with loss of INI-1/BAF47 staining both within the nodules and the inter-nodular areas. The third case contained scattered individual and small groups of large cells with abundant acidophilic cytoplasm and eccentric nuclei, reminiscent of rhabdomyoblasts that were positive for GFAP and desmin, and retained nuclear staining for INI-1/BAF47, consistent with reactive gemistocytes.

Conclusion: Pathologists should be aware of the various, and unusual histopathologic patterns of atypical teratoid rhabdoid tumor. INI-1/ BAF47 immunostain should be performed on all central nervous system embryonal tumors, especially in infants and young children.