A glioma is any tumor that originates from the glial (connective/supporting) cells of the brain. Since glial cells are present throughout the central nervous system, gliomas can occur in various places in the brain or spinal cord. A thalamic glioma, as its name implies, is a glial tumor characterized by a primary growth center within or very near the thalamus. These tumors are very rare and account for a small minority of brain tumors in children and young adults.
The thalamus, a paired structure that is positioned just above the brainstem, is a major processing and relaying center for sensory information traveling between the body and the cerebral cortex (the brain surface). It also plays a role in movement, and in regulating sleep states, consciousness, and awareness. The thalamus sits in close proximity to the lateral and third ventricles (chambers in which cerebrospinal fluid, or CSF, flows). The two thalami are interconnected through fibers that travel across the brain’s midline. It is through these connections that thalamic gliomas can frequently cross over to involve both sides of the brain (bilateral thalamic glioma).
While any glial cell (astrocyte, oligodendrocyte, or gangliocyte) can give rise to a thalamic glioma, the overwhelming majority are derived from astrocytes and are referred to as astrocytomas. Astrocytomas are further subdivided based degree of aggressiveness.
Grade I tumors, also referred to as juvenile pilocytic astrocytomas (JPA), are benign and have the best prognoses. They are focal, meaning they have well-defined borders.
Grade II tumors are also considered benign but are more infiltrative or diffuse. Even though Grade I and II tumors are referred to as low-grade tumors, Grade II tumors are expected to eventually transition into Grade III astrocytomas.
Grades III (anaplastic astrocytoma) and IV (glioblastoma multiforme) tumors are more aggressive and are grouped together as malignant tumors.
Treatment options and prognosis depends on the grade, so tissue diagnosis is crucial.
Since thalamic gliomas are complicated tumors in a delicate area, they are best diagnosed and treated at a major medical center. Many doctors have never seen a thalamic glioma — at the Weill Cornell Brain and Spine Center we see some of the most challenging brain tumors from around the country and around the world. (Find out more about the Weill Cornell Brain and Spine Center.)
Reviewed by Mark M. Souweidane, M.D.
Last reviewed/last updated: July 2015
Illustration by Thom Graves, CMI