Current concepts of polymicrogyria

Abstract

Polymicrogyria is one of the most common malformations of cortical development. It has been known for many years and its clinical and MRI manifestations are well described. Recent advances in imaging, however, have revealed that polymicrogyria has many different appearances on MR imaging, suggesting that is may be a more heterogeneous malformation than previously suspected. The clinical and imaging heterogeneity of polymicrogyria is explored in this review.

Fig. 1

Parasagittal (a) and axial (b) T1-weighted images show the delicate appearance of PMG (black arrows) in the right sylvian and suprasylvian cortex. Note the continuity of the posterior sylvian fissure on the parasagittal image (a); this is diagnostic of perisylvian PMG

Fig. 2

Thick and irregularly bumpy, “coarse” appearance of PMG. Parasagittal (a) and axial (b) images show coarse PMG in the parieto-occipital (small black arrows) and perisylvian (large black arrows) regions

Fig. 3

Axial FSE T2 weighted image shows right frontal PMG (white arrows) with fusion of the molecular layer of cortex resulting in paradoxically smooth cortical surface

Fig. 4

Axial T1-weighted image shows diffuse coarse PMG with an appearance of “palisades” of cortex

Fig. 5

Surface rendering of PMG from volumetric acquisition of data. a Image shows a parasagittal image of extensive perisylvian coarse PMG (arrows). The surface rendering (b) shows the absence of normal sulci and the bumpy cortical surface in the affected area (arrows)

Fig. 6

Grade 1 perisylvian PMG. Parasagittal (a) and axial (b) T1-weighted images show coarse polymicrogyria extending from the frontal pole to the occipital pole

Fig. 7

Grade 2 perisylvian PMG. Parasagittal (a) and axial (b) images show coarse perisylvian polymicrogyria sparing the anterior frontal lobes and the occipital lobes

Fig. 8

Grade 3 perisylvian PMG. Parasagittal T1-weighted images (a) and axial T2-weighted images (b) show polymicrogyria limited to the insulae and operculae

Fig. 9

Bilateral frontoparietal polymicrogyria. Axial (a) and coronal (b) T2-weighted images show a different appearance to the cortex, that of multiple radially oriented neuronal components separated by fibro-glial stroma. Note the prominent cerebellar fissures and the subcortical cerebellar cysts (arrows)

Fig. 10

Bilateral frontal polymicrogyria. Axial T2-weighted image shows delicate PMG in both frontal lobes. The lateral ventricles are somewhat dilated

Fig. 11

Bilateral parasagittal parieto-occipital polymicrogyria. Parasagittal (a) and axial (b) T1-weighted images show coarse parasagittal infoldings (arrows) of polymicrogyria