Subependymoma is a rare type of ependymoma that develops from the glial cells that line the ventricles of the brain and the spinal cord. It is classified as a grade I tumor, which indicates that subependymomas are slow-growing and generally have a favorable prognosis. The tumor can occur in children and adults. Eight percent of all diagnosed ependymomas are classified as subependymoma. In general, subependymomas occur more in males, individuals over 40 years old, and in Caucasians. People with subependymomas often do not have symptoms at the time of diagnosis but common symptoms can arise depending on where the tumor is located. Patients with symptoms experience a buildup of fluid in the brain, known as hydrocephalus.  Other symptoms can include headache, change in vision, weakness on one side of the body (paresis), numbness or tingling (dysesthesia), loss of bladder control, seizures, memory loss, dizziness and tremors. Subependymomas can be treated with surgery and radiation therapy. In many cases, complete removal with surgery will be curative.  When the tumor removal is not complete, radiation treatment can provide a long period of control. Overall, subependymomas have a high survival rate.

What does subependymoma look like on an MRI?

Like other central nervous system tumors, an MRI of the brain or spine is a test done that leads to a diagnosis.  Subependymomas usually appear slow-growing and on MRI appear as a well-defined mass that does not light up when contrast is given during the MRI scan. They are characteristically small lesions (often less than two centimeters (an inch) in diameter). However, subependymomas can also grow to be larger, causing severe symptoms in some people at the time of diagnosis. These tumors may also show presence of calcifications, which may represent that the tumor has been slow growing over time. 

What does the pathologist report?

When the pathologist looks under the microscope, the lesion is discrete/well circumscribed with low cellularity and a lobulated appearance. The nuclei appear small, uniform and clustered together. These cells are contained in a fibrillary or hair-like background with microcysts (tiny cysts). The microcysts found in subependymomas contain myxoid material (mucous like substance). This tumor does not have high grade features such as how fast the tumor cells are growing (mitoses), growth of tumor blood vessels (vascularity), and tendency for tumor cells to outgrow their blood supply (necrosis). The pathologist often uses stains to identify common markers in subependymoma to help in determining the diagnosis. GFAP stain is usually positive in tumor cells, and the neurofilament stain will appear negative in tumor cells and highlight the well circumscribed nature of the lesion. EMA, a common marker in other ependymoma tumors, is often negative in subependymomas. The pathologist may perform a Ki-67 on the tumor, which is a marker of tumor growth, by highlighting cells that are proliferating. In subependymoma the Ki-67 is low.