Jerome Harrison UPDATE: Brain tumor was an ependymoma

These were the details I was looking for!

An update by ESPN shed more light on the nature of Jerome Harrison's brain tumor. To summarize (and elaborate):

• Harrison had surgery and the neurosurgeons believed they were able to remove all of the tumor. The tumor was located in the fourth ventricle of the brain (see diagram to the right for the anatomic location). It's actually located lower down in the brain just in front of the cerebellum and is one of the spaces (i.e. ventricles) that contain cerebrospinal fluid (CSF). The function of the CSF is to act as a buffer between the brain and the skull. The brain literally "floats" in the fluid.
• The tumor was identified, presumably via histology, as an ependymoma. I'll talk about ependymomas below.
• Apparently Harrison also had an arteriovenous malformation which may have contributed to the tumor. I posted about arteriovenous malformations earlier when Eagles DT Mike Patterson had a seizure in training camp presumably as a result of one. I didn't actually know AVMs were a risk factor for tumors. You learn something new every day I guess.

Now, about ependymomas...

Ependymomas are a rather rare form of neurological tumor. They can actually occur almost anywhere in the spinal cord, not just the brain, although most commonly in the fourth ventricle like in this case. They only account for about 10% of all central nervous system tumors and 25% of all spinal cord tumors. These tumors arise from tissue called ependyma which are cells that normall produce CSF. 

They are definitively diagnosed through histology and with molecular genetics although when they are seen on MRI or CT there are certain visual characteristics that may make an ependymoma vs. other type of brain tumors more likely. 

Treatment, as stated before, involves surgery to remove as much of the tumor as possible. With ependymomas, some patients receive radiation therapy after surgery.

Prognosis: A number of factors affect chances of recurrent disease. These factors include... 

1. how much of the original mass was resected in surgery (the more removed, the better obviously), 

2. Grade (cell appearance) - patients with high histological grade tumors (i.e. cells that do not resemble the original tissue) tend to have higher tumor recurrence rates

One study cited disease-free rates at 5 and 10 years at 84.8 and 76.5%, respectively.