The patient had had a biopsy at the time of the third ventriculostomy.
Histology
Sections show several small fragments comprised of tumour cells with uniform round nuclei and occasional rosette formations. There are no mitotic figures, necrotic areas, or significant nuclear pleomorphism seen. Immunohistochemistry reveals that the tumour cells are strongly positive for synaptophysin and neuron-specific enolase, including the rosette formations. Processes, particularly within the rosettes, are identified with the phosphorylated and non-phosphorylated neurofilaments. Reticulin stain confirms the absence of lobular architecture of a normal pineal gland. The tumour cells are negative for chromogranin and LCA. The MIB-1 index is very low.
FINAL DIAGNOSIS: pineocytoma