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Current concepts of polymicrogyria.

Barkovich AJ - Neuroradiology (2010)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Neuroradiology, University of California at San Francisco, San Francisco, CA 94143-0628, USA. Jim.Barkovich@radiology.ucsf.edu

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.

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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
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Fig3: 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

Mentions: The imaging appearance of polymicrogyria is variable. This variability is most likely a result of three factors: 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; and, in all likelihood, the type of PMG. In a previous analysis of PMG, I noted that it can have a coarse appearance or a delicate appearance and that the appearance seen in the so-called cobblestone malformations differs from that seen in most bilateral polymicrogyria syndromes [40]. The precise reasons for these differing appearances are not known, but the development of the cerebral cortex is so complex that it is not surprising that disruptions of the processes of late cortical migration and cortical organization at different stages might result in slightly different malformations. The cortical surface can have multiple small, delicate gyri (Fig. 1) or appear thick and irregularly bumpy (Fig. 2) or be paradoxically smooth (Fig. 3) because the outer cortical (molecular) layer fuses over the microsulci. Sometimes the cortex appears thick and coarse (with an appearance of “palisades” of cortex [40], (Fig. 4)), while other times the microgyri appear fine and delicate (Fig. 1), even when the brains are similarly myelinated. However, these variations in appearance may not be detectable on routine, 5-mm thick images. Therefore, images with thin sections and optimal gray matter–white matter contrast [we acquire volume 3DFT spoiled gradient acquisition (T1 weighted) and volume 3DFT fast spin echo (T2 weighted) images, both in the sagittal plane with ≤1.5 mm partition size] should always be acquired. Evaluation in three planes is often necessary to detect irregularities of the gray matter–white matter junction, which are often the most convincing evidence of dysplastic brain (Fig. 3) [41]; this is most easily accomplished via volumetric acquisition with display in all three orthogonal planes (sagittal, axial, and coronal). The volume acquisitions can be displayed as three-dimensional surface images (Fig. 5) and can be utilized for stereotactic localization, aiding in surgical therapy, if appropriate. The degree of myelination affects the appearance. In unmyelinated regions, the inner surface of the polymicrogyric cortex looks thin [2–3 mm] and bumpy, while in myelinated areas it looks thicker (5–8 mm) and relatively smooth [42]. The reason proposed for this is that a 4–5 mm layer of gliotic white matter runs through the polymicrogyric cortex, blending in with white matter in the unmyelinated brain and blending in with cortex after myelination [42]. Finally, as stated earlier, polymicrogyria is almost certainly a heterogeneous malformation that can have many different appearances: thick and coarse, fine and delicate, with shallow or deep sulci. Whatever the reason, it is important to realize that a spectrum of cortical appearances, all having some sort of small gyri, can be seen in patients with polymicrogyria.Fig. 1


Current concepts of polymicrogyria.

Barkovich AJ - Neuroradiology (2010)

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
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2872023&req=5

Fig3: 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
Mentions: The imaging appearance of polymicrogyria is variable. This variability is most likely a result of three factors: 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; and, in all likelihood, the type of PMG. In a previous analysis of PMG, I noted that it can have a coarse appearance or a delicate appearance and that the appearance seen in the so-called cobblestone malformations differs from that seen in most bilateral polymicrogyria syndromes [40]. The precise reasons for these differing appearances are not known, but the development of the cerebral cortex is so complex that it is not surprising that disruptions of the processes of late cortical migration and cortical organization at different stages might result in slightly different malformations. The cortical surface can have multiple small, delicate gyri (Fig. 1) or appear thick and irregularly bumpy (Fig. 2) or be paradoxically smooth (Fig. 3) because the outer cortical (molecular) layer fuses over the microsulci. Sometimes the cortex appears thick and coarse (with an appearance of “palisades” of cortex [40], (Fig. 4)), while other times the microgyri appear fine and delicate (Fig. 1), even when the brains are similarly myelinated. However, these variations in appearance may not be detectable on routine, 5-mm thick images. Therefore, images with thin sections and optimal gray matter–white matter contrast [we acquire volume 3DFT spoiled gradient acquisition (T1 weighted) and volume 3DFT fast spin echo (T2 weighted) images, both in the sagittal plane with ≤1.5 mm partition size] should always be acquired. Evaluation in three planes is often necessary to detect irregularities of the gray matter–white matter junction, which are often the most convincing evidence of dysplastic brain (Fig. 3) [41]; this is most easily accomplished via volumetric acquisition with display in all three orthogonal planes (sagittal, axial, and coronal). The volume acquisitions can be displayed as three-dimensional surface images (Fig. 5) and can be utilized for stereotactic localization, aiding in surgical therapy, if appropriate. The degree of myelination affects the appearance. In unmyelinated regions, the inner surface of the polymicrogyric cortex looks thin [2–3 mm] and bumpy, while in myelinated areas it looks thicker (5–8 mm) and relatively smooth [42]. The reason proposed for this is that a 4–5 mm layer of gliotic white matter runs through the polymicrogyric cortex, blending in with white matter in the unmyelinated brain and blending in with cortex after myelination [42]. Finally, as stated earlier, polymicrogyria is almost certainly a heterogeneous malformation that can have many different appearances: thick and coarse, fine and delicate, with shallow or deep sulci. Whatever the reason, it is important to realize that a spectrum of cortical appearances, all having some sort of small gyri, can be seen in patients with polymicrogyria.Fig. 1

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Neuroradiology, University of California at San Francisco, San Francisco, CA 94143-0628, USA. Jim.Barkovich@radiology.ucsf.edu

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.

Show MeSH
Related in: MedlinePlus