Curved reformat of the paediatric brain MRI into a 'flat-earth map' - standardised method for demonstrating cortical surface atrophy resulting from hypoxic-ischaemic encephalopathy

Abstract

Hypoxic-ischaemic encephalopathy is optimally imaged with brain MRI in the neonatal period. However neuroimaging is often also performed later in childhood (e.g., when parents seek compensation in cases of alleged birth asphyxia). We describe a standardised technique for creating two curved reconstructions of the cortical surface to show the characteristic surface changes of hypoxic-ischaemic encephalopathy in children imaged after the neonatal period. The technique was applied for 10 cases of hypoxic-ischaemic encephalopathy and also for age-matched healthy children to assess the visibility of characteristic features of hypoxic-ischaemic encephalopathy. In the abnormal brains, fissural or sulcal widening was seen in all cases and ulegyria was identifiable in 7/10. These images could be used as a visual aid for communicating MRI findings to clinicians and other interested parties.

Keywords: Children; Cortex; Curved reformat; Hypoxic–ischaemic encephalopathy; Magnetic resonance imaging; Watershed.

Fig. 1

T1-weighted 3-D turbo spin-echo brain MRI in a 7-year-old boy in the control group is used to show deposited cursors for generating flat-earth maps. a The landmark coronally reconstructed image for generating a Mercator map is the one demonstrating the foramina of Monro. The pathway for generating the curved reconstructions is plotted 1-cm deep to the surface of the brain by depositing cursors at the following 6 landmarks in a clockwise direction on both sides of the midline (a total of 12 points): lateral hippocampus, inferior temporal gyrus, gyrus inferior to Sylvian fissure, gyrus superior to Sylvian fissure, gyrus midway from the previous to the final point, gyrus abutting the midline/falx. b The landmark midline sagittal reconstructed image demonstrating the aqueduct of Sylvius is selected for generating a scroll map. The pathway for generating the curved reconstructions is plotted 1-cm deep to the cortical surface by depositing cursors at 8 points starting anteriorly and ending posteriorly: posterior aspect of the straight gyri (1 cm anterior to the optic chiasm), the anterior aspect of the straight gyri, anterior frontal lobes along a horizontal line extending through the genu and splenium of the corpus callosum, halfway between the previous and next points, posterior frontal lobes along a vertical line extending from the upper cervical cord and brainstem, halfway between the previous and next points, occipital lobes along a horizontal line extending through the genu and splenium of the corpus callosum, posterior occipital lobe 1 cm superior and anterior to the torcula. The resultant image derived from sagittal images is likened to unrolling a scroll

Fig. 2

Mercator and scroll maps generated from the T1-weighted 3-D turbo spin-echo brain MRI in a 7-year-old boy in the control group demonstrate sulcal and fissural anatomy for the purposes of defining the watershed and perirolandic regions involved in hypoxic–ischaemic encephalopathy. a Mercator map reconstructed from coronal images demonstrates the inferior frontal sulcus–precentral sulcus sign (IFS-PCS), superior frontal sulcus–precentral sulcus sign (SFS-PCS), central sulcus (CS), Sylvian fissure (SF), pars bracket (PB) and postcentral sulcus (post-CS). In addition, the watershed region (WZ) and perirolandic/perisylvian continuum is indicated in shaded blocks, based on the identified anatomy. b Scroll map reconstructed from sagittal images demonstrates the superior frontal sulcus joining the precentral sulcus (SFS-PCS), central sulcus (CS), pars bracket (PB), postcentral sulcus (post-CS), parieto-occipital sulcus (POS), intraparietal sulcus (IPS) and calcarine sulcus (Cal–S). In addition, the watershed zone and perirolandic regions are indicated in shaded blocks based on the identified anatomy

Fig. 3

Comparison of normal and abnormal T1-weighted 3-D turbo spin-echo brain MRI using the suggested post-processing technique. a, b Images in a 7-year-old boy from the control group. a Mercator map reconstructed from the coronal images in the control child demonstrates the parallel hemispheres, which are abutting at the midline, and also demonstrates the close proximity of the frontal and temporal lobes to each other at the Sylvian fissures. b Scroll map reconstructed from the sagittal images in the control child demonstrates the normal gyral anatomy with parallel hemispheres in close proximity to each other at the midline. c–f Images in a 7-year-old boy who sustained hypoxic–ischaemic injury at term delivery. c Mercator map demonstrates bilateral parafalcine atrophy separating the hemispheres from the midline in a bi-convex or lentiform manner (straight arrows) as well as perisylvian atrophy with visible ulegyria (curved arrows). The ulegyria is manifest as gyri with preferential thinning at the base as opposed to the apex, resulting in a mushroom-shape or drumstick appearance. d Scroll map demonstrates bilateral parafalcine atrophy separating the hemispheres from the midline in a bi-convex or lentiform manner (arrows). e Standard axial slice demonstrates parafalcine atrophy in the frontal lobes (arrow), which correlates well with the Mercator and scroll projections. f Standard axial slice demonstrates the perisylvian atrophy (straight arrows) and ulegyria (curved arrows), in both the perisylvian inter-vascular watershed regions

Fig. 4

Comparison of normal and abnormal T1-weighted 3-D turbo spin-echo brain MRI using the suggested post-processing technique. a, b Images in a 3-year-old male from the control group. a Mercator map reconstructed from the coronal images in the control child demonstrates the parallel hemispheres, which are abutting at the midline, and also demonstrates the close proximity of the frontal and temporal lobes to each other at the Sylvian fissures. b Scroll map reconstructed from the sagittal images in the control child demonstrates the normal gyral anatomy with parallel hemispheres in close proximity to each other at the midline. c–f Corresponding images from a 3-year-old female who sustained hypoxic–ischaemic injury at term delivery. c Mercator map demonstrates parafalcine atrophy, separating the hemispheres from the midline in a lentiform manner (thick arrow). This map shows widening of the Sylvian fissures (straight dotted arrows) and marked atrophy of the post-central gyrus (thin arrow). There is evidence of posterior inter-vascular watershed damage with cystic change (curved arrow), but the extent is not as well demonstrated as with the scroll map. d Scroll map demonstrates parafalcine atrophy, separating the hemispheres from the midline in a lentiform manner (thick arrow). This map shows marked atrophy of the post-central gyrus (thin arrow) and of the posterior inter-vascular watershed regions (curved arrows). There are ulegyria and cystic changes in this region, which is shown to better effect than on the Mercator map. e Standard axial image through the vertex demonstrates the parafalcine atrophy causing lentiform separation of the hemispheres (thick arrow) and the perirolandic atrophy (thin arrow), which correlate well with the appearances on the Mercator and scroll maps. f Axial slice at the level of the lateral ventricles demonstrates extensive posterior watershed distribution atrophy, which correlates with the scroll map (d) and to a lesser extent with the Mercator map (c). There is visible ulegyria in the occipital lobes (curved arrow) while tear-drop-shape sulci are confirmatory features of ulegyria in the left temporal lobe (arrowhead). Widening of the Sylvian fissure is noted (straight arrows) and correlates well with the appearances on the Mercator map