Polymicrogyria refers to the abnormal development of the ridges and folds of the brain (gyri) during gestation. It is characterized by an excessive number (poly-) and small size (micro-) of the gyri in the cerebral cortex. Signs and symptoms of polymicrogyria depend on the extent of brain tissue affected, the regions of the brain affected, and whether it is unilateral or bilateral.
The signs and symptoms of polymicrogyria are variable; they depend on the degree and location of polymicrogyria. Infants with bilateral polymicrogyria have more severe symptoms compared to those that have unilateral involvement. Patients with generalized bilateral polymicrogyria present with various neurologic findings such as cognitive impairment, motor delay, refractory seizures, and/or quadriparesis    . Polymicrogyria has been associated with malformations such as schizencephaly, cerebellar hypoplasia , subcortical heterotopia , and periventricular nodular heterotopia .
While the symptoms of polymicrogyria vary, there are common clinical presentations based on the region of the brain affected. For example, patients with bilateral polymicrogyria of the frontal cortex often present with cognitive impairment, motor delay, epilepsy, and/or quadriparesis. Bilateral polymicrogyria of frontoparietal cortex results in significant cognitive impairment and motor delay, seizures, cerebellar problems, and/or dysconjugate gaze. Patients with bilateral perisylvian polymicrogyria present with cognitive impairment, epilepsy, pseudobulbar signs, arthrogryposis, and/or lower motor neuron disease. Bilateral polymicrogyria of the parasagittal parieto-occiptal region is associated with mental retardation and/or partial seizures.
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Work up for polymicrogyria consists of a physical exam, a thorough medical history (including maternal pregnancy history and family history), and imaging tests. Congenital infections have been associated with polymicrogyria; the toxoplasmosis, rubella, cytomegalovirus, herpes simplex, and a TORCH screen may be performed for detection of human immunodeficiency virus (HIV) if clinically indicated.
Genetic testing for mutations can be performed. For example, BICD2 has been associated with perisylvian polymicrogyria . Screening for syndromes commonly associated with polymicrogyria, can be useful for determining etiology. Polymicrogyria is often an isolated condition, however, it can occur as a part of genetic syndromes such as 22q11.2 deletion syndrome, Aicardi syndrome, Adams-Oliver syndrome, Chudley-McCullough syndrome, Zellweger spectrum disorder, Galloway-Mowat syndrome, and Joubert syndrome .
Magnetic resonance imaging (MRI) is used to diagnose polymicrogyria . MRI images will show abnormalities of the surface of the cortex and the gray-white matter junction . In patients with polymicrogyria, the cortical surface will show a thickened appearance due to the fused and infolded gyri. Other imaging modalities such as computed tomography (CT) do not have sufficient resolution or contrast to show the small gyri characteristic of polymicrogyria.
Brain tissue can be examined at the time of autopsy or during neurosurgery. Gross examination of the cerebral cortex shows an abnormal brain surface consisting of complex convolutions with miniature, fused, superimposed folds and the pia meningeal layer extending across multiple folds . Microscopic examination reveals an unusually thin cerebral cortex with abnormal lamination.
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