Polymicrogyria : MRI Teaching Case

Case – 35 yrs male with history of seizures presents for MRI showing – Right posterior frontal - temporo-occipital- parietal cortical pattern suggests gross asymmetric thickness & gyral pattern with subtle asymmetric CSF cleft in the sylvian fissure region with polymicrogyric appearance with normal septum pellucidum & temporal horns – suggesting disorder of cortical malformation of late intrauterine onset ( >20wks ) - Polymicrogyria. Case submitted by  Dr MGK Murthy, Dr GA Prasad

Discussion -

Polymicrogyria is one of the most common malformations of cortical development

in which the process of normal cerebral cortical development is disturbed late in the stage of neuronal migration or early in the stage of cortical organization, thus considered a disorder of neuronal organization.

1. Causes - Congenital infection (particularly cytomegalovirus infection).

               - Localized or diffuse in utero ischemia.

               - Mutations.

2. Clinical profile - ranging from hemiparesis or partial epilepsy to developmental delay, quadriparesis, medically refractory, intractable epilepsy.

3. Associations – can be isolated malformation or it may be associated with other brain malformations like corpus callosum agenesis and hypogenesis, cerebellar hypoplasia, periventricular nodular heterotopias and subcortical heterotopias.

4. The imaging appearance of polymicrogyria is variable which can be due to

-     imaging factors (amount of gray matter–white matter  contrast, thickness of the slices).

-     the stage of maturity/  myelination of the brain at the time of the imaging study.

-     the type of PMG.

4a. Types of polymicrogyria -

- Multiple small delicate gyri.

- Thick and irregularly bumpy or be paradoxically smooth because the outer cortical (molecular) layer fuses over the microsulci.

- Thick and coarse gyri with an appearance of “palisades” of cortex.

4b. Polymicrogyria may be unilateral (40%) or bilateral (60%). The cortex surrounding the sylvian fissures is involved in 80% of cases, with the frontal lobe being most  commonly involved (70%), followed by parietal (63%),temporal (38%), and occipital (7%) lobes.

4c. Polymicrogyria can be superficial, with the cortex appearing flat and congruent to the arc of normal cortex, or may course radially inward, as if it were buckled or folded toward the ventricle. Anomalous venous drainage is common in areas of dysplastic cortex, seen in up to 51% of patients with polymicrogyria with large vessels common in regions where there is a large infolding of thickened cortex. Such large vessels should not be mistaken for vascular malformations.

5. Several syndromes of bilateral symmetrical polymicrogyria  have been described,  few are

-     Bilateral perisylvian polymicrogyria (also called congenital  bilateral perisylvian syndrome.

-     Bilateral frontoparietal polymicrogyria.

-     Bilateral symmetrical frontal polymicrogyria.

-     Bilateral parasagittal parieto-occipital polymicrogyria.

6. Few of the specific syndromes associated with cerebral  polymicrogyria are

-     Aicardi syndrome.

-     Delleman syndrome (oculo-cerebral-cutaneous syndrome).

-     DiGeorge syndrome.

-     Warburg Micro syndrome.

-     D-bifunctional protein deficiency