Neuroimaging of PTCD patients. MRI and DTI at 1.5 T of patient 1 (A, D, G), patient 2 (B, E) and patient 3 (C, F, H). In all the patients, sagittal T1-weighted images (A, B, C) show the typical "cap" (arrows) in the pontine tegmentum protruding into the fourth ventricle, diagnostic for the malformation. Note also the flat ventral pons and dysplastic cerebellar vermis. T2-weighted images (D, E, F) at the level of the isthmus reveal a "molar tooth-like" appearance, with laterally displaced superior cerebellar peduncles. Colour-coded fractional anisotropy maps of patient 1 (G) and patient 3 (H) are shown with standard DTI conventions (blue for superior↔inferior direction perpendicular to plane of section, red for right↔left direction, green for anterior↔posterior direction). The tegmental "cap" (arrowhead) is a bundle of transversely oriented fibres, possibly representing "ectopic" pontine transverse fibres, normally located in the midpons (double arrowheads in "control").