1. Diagnostic Challenge Pathology for Neurosurgery & Neurology Residents Department of Pathology University of Oklahoma Health Sciences Center, Oklahoma City, OK, U.S.A. Case 20 History: A 13 year-old boy with a pineal mass and hydrocephalus. Contributor: Kar-Ming Fung, M.D., Ph.D., karming-fung@ouhsc.edu Last updated: 3/5/2009karming-fung@ouhsc.edu

2. Paraffin Section AB

3. Cytologic preparationParaffin Section BC

4. Ki67 Synaptophysin Neurofilament Immunohistochemistry D E F

5. What is your diagnosis?

6. Diagnosis: Pineoblastoma, WHO grade IV. Discussion: The histopathology shows many features of a malignant neoplasm. The tumor is a densely cellular small blue cell tumor with no specific pattern of cellular arrangement. There are small islands of necrosis (white arrows). The cells have pleomorphic nuclei and a minute amount of cytoplasm. Mitoses are readily seen (black arrow). The pleomorphic cytologic features are best visualized in the cytologic preparation (panel on the most right). The tumor are positive for synaptophysin and neurofilament but not glial fibrillary acidic protein. The Ki67 labeling index is very high. In essence, pineoblastomas share histologic features as well as the peak age of incidence with medulloblastomas.