AN UNUSUAL VARIANT OF EPENDYMOMA WITH EXTENSIVE TUMOR-CELL VACUOLIZATION

We report a case of ependymoma with unusual vacuolar features arising in the left occipital lobe of a 2-year-old child. The tumor was compos ed of cells with single or multiple cytoplasmic vacuoles and clear cel ls. Some cells showed a signet ring-like configuration. Clear cells we re compactly arranged and showed an oligodendroglioma-like appearance. In addition, there were cellular ependymoma-like areas including peri vascular pseudorosettes. On immunohistochemistry, glial fibrillary aci dic protein and vimentin were mainly detected in cytoplasmic processes , and epithelial membrane antigen (EMA) staining showed granular and s mall vesicular reactivity. Ultrastructural investigation demonstrated intercellular microrosettes with or without cilia and long zonula adhe rens-type junctions that are typical of ependymoma. Furthermore, many intracytoplasmic lumina (ICL) were observed. Some ICL had microvilli a nd some did not. The latter varied in size, and may have fused with ea ch other to develop giant ICL which could correspond to the signet rin g-like configuration. Small ICL without microvilli had an appearance s imilar to that of distended endoplasmic reticula. Serial semithin and ultrathin sections revealed that EMA-positive structures were consiste nt with ICL containing microvilli and intercellular microrosettes. To determine the presence of unusual vacuolated ependymoma, electron micr oscopical examination was required. However, Light microscopy was usef ul for detecting EMA-positive microvesicular and granular structures.