Case No.: N-012

Diagnosis: Medulloblastoma

Organ: Cerebellum

Last Updated: 1/14/2010

Hematoxylin & eosin	Area 1: The tumor grow as a solid sheets composed of small blue cells. Although small islands of neuropils can be seen (delimited by the white arrows), genuine Homer Wright rosettes are not present. On high magniciation, you can the fine fibrillary cytoplasmic background can be well appreciated. They nuclei are hyperchromatic and the amount of cytoplasm is minimal. A small but inconspicuous nucleoli is present in some of the nuclei.
Hematoxylin & eosin	Area 2: In this area, there are many pink fibrovascular septa in between the tumor cells. When the leptomeninges are involved by the tumor cells, the entrapped fibrovascular component can give this histologic pattern.
Hematoxylin & eosin	Mitosis: Similar to other small blue cell tumors, mitotic figures are not uncommon in medulloblastoma (arrows). High mitotic rate is also a feature of the developing neuroepithelium.
Hematoxylin & eosin	Pyknotic nuclei: Many pyknotic nuclei (white arrow) are also present in medulloblasta. These pyknotic nuclei may represent apoptotic tumor cells and apoptosis is a characteristic of the developing neuroepithelium.

History: A 7 year-old girl with an enhancing mass in the midline of her posterior fossa and hydrocephalus.

Histologic Highlights of this Case:

Medulloblastoma is a neoplasm that resembles the embryonic stage of development of the brain and therefore it maintains several characteristics of the developing neuroepithelium. Therefore mitoses and pyknotic nuclei that may represent apoptosis are common findings.
It is essentially what we call a small blue cell tumor. The tumor is composed of solid sheets of small cells with hyperchromatic, small nucleoli without obvious nucleoli. Typically no definitive morphologic evidence of development into neuron or glial cells are present. The nuclei are often naked or at the most associated with a minimal amount of cytoplasm. Tumor cells in medulloblastoma often arrange into solid sheets without a pattern (Area 1). Although Homer Wright rosette may be present but the frequency of encountering them is far less than in neuroblastoma arising from the adrenal medulla or sympathetic chain.
Medulloblastoma also have a distinguished frequency to involve the leptomeninges and in these areas, the fibrous component can be trapped amoung the tumor (Area 2).

Original slide is contributed by Dr. Kar-Ming Fung, University of Oklahoma Health Sciences Center, Oklahoma, U.S.A.