Atypical teratoid rhabdoid tumor (AT/RT) in adults: review of four cases.

Atypical teratoid/rhabdoid (AT/RT) tumor is a rare, highly malignant tumor of the central nervous system (CNS) most commonly found in children less than 5 years of age. Although the vast majority of cases are diagnosed in young children, there have been isolated case reports in adults. Since its histological appearance can be confused with other tumors, especially in adults, separating AT/RT from other neoplasms may be difficult. In many instances, a reliable diagnosis is not possible without demonstrating the lack of nuclear INI1 protein expression by immunohistochemical methods. The patients (three males and one female) ranged in age from 23 to 42 years (mean age, 32 years). Radiographically, two tumors were localized in the right fronto-parietal region, one was frontal and the other was found in the left temporal lobe. Varying degrees of hydrocephalus and heterogeneous enhancement were present on MRI. In all cases, diagnosis during intraoperative consultation and preliminary diagnosis was different from the final diagnosis after immunohistochemical analysis. Immunohistochemical staining showed that the tumor cells were positive for vimentin and reacted variably for keratin, epithelial membrane antigen (EMA), synaptophysin, neurofilament protein, CD34, and smooth muscle actin (SMA). All were negative for GFAP, S-100, desmin and CD99. Three of the four cases lacked nuclear expression of INI1. One patient is alive with no evidence of disease 17 years after the diagnosis. In adult examples of AT/RT, the diagnosis requires a high index of suspicion, with early tissue diagnosis and a low threshold for investigation with INI1 immunohistochemistry to differentiate this entity from other morphologically similar tumors. Although the prognosis is dismal in pediatric population, long term survival is possible in adult AT/RT cases after surgery and adjuvant radiotherapy and chemotherapy.