Images - Department of Radiology & Biomedical Imaging ...

Figure 3 Side-by-side comparison (T1 ((MPRAGE) TR/TE/TI = 2300/3/950 ms, 7° flip angle, 1.0 × 1.0 × 1.0 mm 3 resolution,
acquisition time 5.17 min) with high resolution image) of the four atrophy types of MST seen in TLE.
pus provides an excellent estimate of the thickness of the
hippocampal cortex at this point. This permits identification
of circumscribed regions of hippocampal atrophy, particularly
if they are combined with patchy hypointensities.
This hypointense line, along with external hippocampal
landmarks, can also be used to subdivide the hippocampus
into subsections. These subsections correspond to the histological
subfields (Figure 2), so the volumes obtained by
this procedure can be used as surrogate subfield volumes.
Clinical Applications of Hippocampal
High-Resolution Imaging
In some diseases the hippocampal volume losses are so
characteristic that their regional selectivity is easily detected
on visual inspection. A typical example is temporal lobe
epilepsy (TLE) with mesial temporal sclerosis (TLE-MTS).
In TLE-MTS the seizures arise from the hippocampus and
neighboring mesial temporal structures, e.g., parahippocampus.
Mesial temporal sclerosis (MTS), a specific form
of hippocampal atrophy, is the hallmark of TLE-MTS. Large
histopathological studies of surgical specimens have shown
that MTS is not homogenous, but has four major subtypes:
isolated DG atrophy, isolated CA1 atrophy, CA1 and DG
atrophy with sparing of CA2, and global atrophy. CA1 and
DG is the most common and is often referred to as “classical
type” MTS.
Figure 3 shows a side-by-side comparison of the hippocampus
in a standard 4T T1 whole brain image and a
dedicated high-resolution image. While all four atrophy
types are easily identifiable by visual inspection in the highresolution
image, this is difficult to do on the conventional
T1 image, despite the fact that the hippocampal atrophy is
obvious to the experienced reader. A quantitative assessment
using statistical thresholds to distinguish atrophied
subfields from those in the normal range confirmed the
existence of atrophy patterns in a larger population of TLE-
MTS patients.
The ability to distinguish among different MTS patterns
on a MRI is not solely of academic interest. Large
histopathological series have shown that the different atrophy
patterns may represent different clinicopathological
TLE subtypes and may even have predictive value for the
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