Brainstem Tumors

The brainstem is the evolutionarily oldest and most fundamental structure in the brain. It is located at the base of the skull and connects the brain proper with the spinal cord. It controls such basic functions as breathing, heartbeat, and other critical circadian functions. Tumors that develop in this area of the brain are especially difficult to treat, since any intervention in the area can cause devastating neurological damage.

The brainstem has three distinct parts:

• The midbrain, which is the upper part of the brainstem;
• The medulla oblongata, the lower part, which connects to the spinal cord; and
• The pons, which sits between the medulla oblongata and the midbrain.

Most of the tumors that arise in the brainstem are gliomas, meaning a tumor that arises from glial cells — the cells in the brain that support and protect the brain’s neurons. Gliomas can develop in many different locations in the brain, but brainstem gliomas are very challenging, especially because they occur primarily during childhood and adolescence.  Brainstem gliomas, which are rare in adults, account for approximately 15 percent of childhood brain tumors. Gliomas can be characterized based on their morphology, cellular characteristics, and location.

Approximately 80 percent of brainstem tumors are diffuse intrinsic pontine glioma (DIPG), which has a very poor prognosis. It is an infiltrative tumor, meaning it does not have defined borders. DIPG, also commonly known as a pontine glioma (located in the pons part of the brainstem), or infiltrative brainstem glioma, is not surgically accessible and is typically treated with radiation therapy.  Some symptoms of DIPG (e.g. hydrocephalus, due to fluid accumulation) can, however, be treated surgically if necessary.  (More about DIPG.)

The other 20 percent of brainstem tumors may be candidates for surgical intervention and have better prognoses. Focal gliomas of the brainstem are better defined, and in a smaller area, than the more diffuse pontine gliomas. They more commonly develop in the midbrain or medulla, not the pons, and are usually low grade (i.e., slow growing). These include dorsal brainstem tumors, which develop on the back of the brainstem; tectal gliomas, which arise in the roof of the brainstem, called the tectum; and medullary brainstem tumors, which develop on the medulla. Focal brainstem tumors are usually low-grade, slow-growing tumors more amenable to surgical intervention.

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