Coronal and Axial T1-Weighted MRI Scan Showing Right Hippocampal Sclerosis (Arrow)


http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=epi&part=ch3&rendertype=figure&id=ch3.f1

Left hippocampal sclerosis (3.0 T MRI). (A) Inversion recovery prepared (IRprep) T1 weighted acquisition showing an atrophic hippocampus (on right of image: arrow). (B) T2 weighted fluid attenuated inversion recovery (FLAIR) image demonstrating increased T2 weighted signal within the sclerotic hippocampus. (C) Early echo image from dual echo data (TE 30 ms). (D) Later echo image from the same dual echo data (TE 120 ms). Hippocampal T2 relaxation times may be obtained using the data from the dual echo sequence. (Click here to magnify the figure)

http://yassermetwally.files.wordpress.com/2008/03/epi1.jpg

Hippocampal sclerosis is characterised by neuronal cell loss and gliosis in CA1, CA3, and dentate hilus subfields of the hippocampus, and can be reliably identified with MRI. The hippocampus is best visualised by acquiring thin slices (1–3 mm) orthogonal to its long axis. The primary MRI features of HS are hippocampal atrophy, demonstrated with coronal T1 weighted images, and increased signal intensity within the hippocampus on T2 weighted images . Additionally, decreased T1 weighted signal intensity and disruption of the internal structure of the hippocampus may be present. Other MRI abnormalities associated with hippocampal damage include atrophy of temporal lobe white matter and cortex, dilatation of the temporal horn, and a blurring of the grey-white border in the temporal neocortex. Atrophy of the amygdala and entorhinal cortex variably accompany hippocampal damage but may also occur in patients with TLE and normal hippocampi. FLAIR images provide an increased contrast between grey and white matter and facilitate differentiation of the amygdala from the hippocampus.


http://yassermetwally.wordpress.com/epilepsy-and-seizure-disorders/neuroimaging-of-seizure-disorders/

MRI technique for epilepsy diagnosis:
The sensitivity of MRI for detecting abnormalities depends on the pathological substrate, the MRI techniques applied, and the experience of the interpreting physician. A routine optimal MRI protocol should include T1 and T2 weighted, proton density and fluid attenuated inversion recovery (FLAIR) sequences. These contrasts need to be acquired in at least two orthogonal planes covering the whole brain, using the minimum slice thickness possible. An oblique coronal plane, orientated perpendicular to the long axis of the hippocampus, gives the best definition of medial temporal lobe structures. In general, T1 weighted images give the best definition of the anatomy and differentiate grey and white matter, while T2 weighted images provide high sensitivity for detecting pathology in the brain. A three dimensional T1 weighted volume sequence with a partition size of 1.5 mm or less should be included as these images may be reformatted in any orientation and used for post-acquisition processing such as measuring hippocampal volumes. FLAIR imaging produces heavy T2 weighting and suppresses signal from cerebrospinal fluid (CSF). This provides high lesion contrast in areas close to CSF and enables anatomical detail to be seen with greater conspicuity than with conventional T2 weighted sequences. Gadolinium does not improve the sensitivity of MRI in patients with epilepsy, but may be useful to characterise intracerebral lesions associated with breakdown of the blood–brain barrier.