PEDIATRIC DIFFUSE MIDLINE GLIOMA (DMG)
NAME & LOCATION
What is diffuse midline glioma? Let's break it down.
Diffuse
This refers to the growth pattern of the tumor. Diffuse tumors do not have defined margins. Rather than growing as a contained mass that displaces the surrounding tissue, they infiltrate the surrounding tissue.
Midline
This refers to the location of the tumor. DMG typically forms in a structure of the brainstem called the "pons". For this reason, the disease was previously called DIPG (diffuse intrinsic pontine glioma). However, these tumors can form in any of the midline structures of the brain including the medulla, cerebellum, thalamus, and spinal cord.
Glioma
This refers to the type of cell the tumor arises from. Gliomas arise from glial cells, which are the cells that support the neurons of the brain. Some examples of glial cells are astrocytes, oligodendrocytes, and ependymal cells. DMG arises from astrocytes, which get their name from their star-like shape.
PONS
CEREBELLUM
THALAMUS
MRI SCAN OF DMG IN THE PONS
SYMPTOMS
DMG typically forms in the pons. In Latin, "pons" means bridge. This name reflects its vital function as a connection between the cerebrum and the cerebellum. This “bridge” transmits signals that help control many critical processes including breathing, the sleep-wake cycle, balance, and the sensation of pain. When a tumor disturbs this area, it causes a variety of symptoms including:
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headaches
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nausea & vomiting
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fatigue
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strabismus (misaligned eye)
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slurred speech
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facial paralysis
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trouble swallowing
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balance disturbances
Strabismus (pictured above) and blurred vision are often some of the first symptoms of DMG parents notice.
STATISTICS
Why can't it be removed with surgery?
Because DMG grows in a diffuse pattern, it becomes intertwined with the healthy surrounding tissue. This makes it impossible to remove surgically, as doing so would entail removing a portion of the brainstem. The brainstem is a delicate structure that regulates life-sustaining functions; a patient could not survive having part of it removed.
TREATMENT
Why doesn't chemotherapy work?
The brain is protected by the "blood-brain-barrier" (BBB). The BBB is a specialized system of cells that shields the brain from toxic substances in the blood and filters harmful compounds from the brain. This is a vital protection mechanism, but it has a downside; chemotherapy drugs can't penetrate the BBB and/or are filtered out too quickly to have a therapeutic effect.
What treatment(s) do kids receive?
The standard treatment for DMG is a 6-week course of radiation therapy and high dose steroids. This is NOT a cure. It provides only a transient improvement in symptoms and likely prolongs survival by just a few weeks.
0 PERCENT
survival rate
5 - 9 YEARS
average age @ diagnosis
9 MONTHS
median survival time after diagnosis
DMG, like almost all pediatric cancers, is not preventable. Scientists have not pinpointed what causes DMG. No environmental or infectious causes have been associated with its development. However, through research, we've learned what these tumors have in common. In more than 80% of DMG cases, the tumor has an epigenetic mutation called H3K27M. Epigenetic mutations alter gene expression, not gene sequence. In H3K27M, the amino acid methionine (M) is substituted for lysine (K) at position 27 on histone 3 (H3).
CAUSES
References: World Health Organization, Mayo Clinic, Radiopaedia
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