Immunohistochemical study of intracranial cysts.

Immunohistochemical characterization of 14 cases of intracranial cysts was performed. Among these 14 cases, five different types of cysts were represented; Rathke's cleft cyst (4 cases), neurenteric cyst (2 cases), colloid cyst (1 case), choroidal epithelial cyst (2 cases) and arachnoid cyst (5 cases). Immunohistochemical evaluation utilized antibodies to glial fibrillary acidic protein (GFAP), S-100 protein, prealbumin, carcinoembryonic antigen (CEA), and epithelial membrane antigen (EMA). GFAP-positive cells were detected in 1 Rathke's cleft cyst and in 1 choroidal epithelial cyst. S-100-positive cells were detected in 2 Rathke's cleft cysts, in 2 neurenteric cysts, in 1 colloid cyst, and in 2 choroidal epithelial cysts. Prealbumin-positive cells were detected only in the 2 choroidal epithelial cysts. CEA-positive cells were detected in 1 Rathke's cleft cyst and in 2 neurenteric cysts. EMA-positive cells were detected in all cases. Immunohistochemical study of prealbumin and S-100 protein is useful for correct diagnosis of choroidal epithelial cyst and study of CEA is useful for diagnosis of neurenteric cyst. The arachnoid cyst is negative for immunoreactivity to GFAP, S-100, prealbumin, and CEA; this can be helpful in distinguishing this type of cyst from single epithelial cysts, a task that is sometimes difficult with only light microscopy.