About Polymicrogyria

	About Polymicrogyria (PMG)
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Bilateral Perisylvian PMG : Bilateral Frontoparietal PMG : Bilateral Posterior Parietal PMG : Other types of PMG

What is Polymicrogyria?

The name Polymicrogyria broken down describes its characteristics...

Poly - many, micro - small, gyri - folds on the surface of the brain.

The brains surface normally has gyri which give it a wiggly appearance, but in PMG there are many small wiggles that can be difficult to see on an MRI or CT scan, even for an experienced radiologist. The diagnosis of PMG is merely descriptive and is not a disease in itself nor does it describe the underlying aetiology or cause of the brain malformation. There are frequent associations with other brain malformations, including abnormalities of the corpus callosum, white matter and cerebellum.

PMG is not lissencephaly, but is often included because of the similarity in brain scan appearance on poorer quality scans and because many of the symptoms are similar.

Most children with polymicrogyria, but not all, have some degree of global developmental disabilities or delays, seizures, feeding difficulties, respiratory problems, motor dysfunction and mental retardation. It is difficult to make a predictable prognosis for children with the diagnosis of PMG because each child is very unique in their presentation of this disorder.

PMG results from several different causes that are both genetic and non-genetic in nature as follows:

a genetic disorder (sometimes inherited, but mainly sporadic);
viral infections of the baby during the 2nd trimester (i.e. cytomegalovirus infection);
insufficient blood supply to the baby's brain during the 2nd trimester (i.e. umbilical cord entanglement) including twin-to-twin transfusion syndrome;
other causes which have not yet been identified.

Research is ongoing into PMG, both in identifying the different types and in the understanding of the underlying causes.

Click here for some general information about PMG, here and here.

What are the different types of PMG?

PMG is generally seen with different areas of the brain affected. These types are described below:

Bilateral Perisylvian PMG (BPP)

The sylvian fissure is a feature found on either side of a normal brain. In BPP there are areas of polymicrogyria around these fissures. Of all the PMG conditions, this type appears most commonly.

Individuals with BPP may have learning difficulties, cerebral palsy, and seizures. What is more distinctive about this condition is that individuals often have problems using the muscles of the face, throat, jaws and tongue – when this is mild it may lead to just a speech impediment or a tendency to drool but if more severe it can lead to difficulties with feeding as a baby.

Consistent familial recurrence has been reported for BPP, but is sporadic in the great majority of patients. It has been reported in children born from identical twin pregnancies which were complicated by twin-twin transfusion syndrome.

For more information on BPP click here.

BPP is also known as Congenital Bilateral Perisylvian Syndrome (CBPS) and more recently it has been found that Worster-Drought Syndrome (WDS) is also the same condition.

Bilateral Frontoparietal PMG (BFPP)

MRI shows symmetric polymicrogyria affecting the frontoparietal regions most severely, as well as ventriculomegaly, bilateral white matter signal changes, and small brainstem and cerebellar structures.

The syndrome is characterized by global developmental delay of at least moderate severity, seizures, dysconjugate gaze (the eyes do not align), and bilateral pyramidal and cerebellar signs.

BFPP shows an autosomal recessive inheritance pattern that has been mapped to a locus on chromosome 16q12-21. It appears to be more common than previously recognized and may be frequently misdiagnosed.

For more information on BFPP click here

Bilateral Posterior Parietal PMG (BPPP)

This may be a mild form of BPP. Click here for more information.

Other types of PMG

Bilateral mesial occipital polymicrogyria
Bilateral diffuse polymicrogyria
Bilateral parieto-occipital polymicrogyria
Bilateral parasagittal parietooccipital polymicrogyria,
Bilateral frontal polymicrogyria
Unilateral perisylvian or multilobar polymicrogyria.

Disclaimer: Always consult your doctor for the most up-to-date information on your child's condition. The information on this page may have been superseded as the understanding of these conditions improve.

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This page last updated: 21/02/04