Medial temporal lobe atrophy in patients with refractory temporal lobe epilepsy
The objective of this study was to assess the volumes of medial temporal lobe structures using high resolution magnetic resonance images from patients with chronic refractory medial temporal lobe epilepsy (MTLE). We studied 30 healthy subjects, and 25 patients with drug refractory MTLE and unilateral hippocampal atrophy (HA). We used T1 magnetic resonance images with 1 mm isotropic voxels, and applied a field non-homogeneity correction and a linear stereotaxic transformation into a standard space. The structures of interest are the entorhinal cortex, perirhinal cortex, parahippocampal cortex, temporopolar cortex, hippocampus, and amygdala. Structures were identified by visual examination of the coronal, sagittal, and axial planes. The threshold of statistical significance was set to p<0.05. Patients with right and left MTLE showed a reduction in volume of the entorhinal (p<0.001) and perirhinal (p<0.01) cortices ipsilateral to the HA, compared with normal controls. Patients with right MTLE exhibited a significant asymmetry of all studied structures; the right hemisphere structures had smaller volume than their left side counterparts. We did not observe linear correlations between the volumes of different structures of the medial temporal lobe in patients with MTLE. Patients with refractory MTLE have damage in the temporal lobe that extends beyond the hippocampus, and affects the regions with close anatomical and functional connections to the hippocampus.
Medial temporal lobe atrophy in patients with refractory
temporal lobe epilepsy
L Bonilha, E Kobayashi, C Rorden, F Cendes, L M Li
See end of article for
Dr L M Li, Department of
University of Campinas,
Campinas, SP, Brazil;
Received 4 April 2003
In revised form 4 June 2003
Accepted 9 June 2003
See Editorial Commentary, p 1606–7 J Neurol Neurosurg Psychiatry 2003;74:1627–1630
Objective: The objective of this study was to assess the volumes of medial temporal lobe structures using
high resolution magnetic resonance images from patients with chronic refractory medial temporal lobe
Methods: We studied 30 healthy subjects, and 25 patients with drug refractory MTLE and unilateral
hippocampal atrophy (HA). We used T1 magnetic resonance images with 1 mm isotropic voxels, and
applied a field non-homogeneity correction and a linear stereotaxic transformation into a standard space.
The structures of interest are the entorhinal cortex, perirhinal cortex, parahippocampal cortex,
temporopolar cortex, hippocampus, and amygdala. Structures were identified by visual examination of
the coronal, sagittal, and axial planes. The threshold of statistical significance was set to p,0.05.
Results: Patients with right and left MTLE showed a reduction in volume of the entorhinal (p,0.001) and
perirhinal (p,0.01) cortices ipsilateral to the HA, compared with normal controls. Patients with right MTLE
exhibited a significant asymmetry of all studied structures; the right hemisphere structures had smaller
volume than their left side counterparts. We did not observe linear correlations between the volumes of
different structures of the medial temporal lobe in patients with MTLE.
Conclusion: Patients with refractory MTLE have damage in the temporal lobe that extends beyond the
hippocampus, and affects the regions with close anatomical and functional connections to the
he entorhinal cortex is considered to be the starting
point of the basic circuitry involving the hippocampal
formation because the information that reaches the
hippocampus is tunnelled through it.
The perirhinal, para-
hippocampal, and temporopolar cortices, in turn, provide the
incoming connections to the entorhinal cortex, conveying
information from polymodal and unimodal cortices.
Damage to the medial temporal lobe region in patients
with medial temporal lobe epilepsy (MTLE), as described by
neuropathological studies, is not confined to the hippo-
but extends to the parahippocampal region.
Quantitative magnetic resonance imaging (MRI) studies
have demonstrated that patients with MTLE show a
significant reduction in the volume of the parahippocampal
region ipsilateral to the side of hippocampal atrophy (HA).
Nevertheless, it is not clear whether there is a uniform
gradient of atrophy among patients with drug refractory
MTLE, with regions closer to the hippocampus showing more
degeneration. Moreover, there are conflicting data regarding
which structures do present volume reduction in lateralised
The tight spatial arrangement of the medial temporal lobe
structures poses a challenge for anatomical differentiation of
cortical and subcortical structures based solely on gross
surface landmarks. In this region of the brain, there is no
straightforward correspondence between landmarks such as
sulci or gyri and the boundaries defined by histology.
particularly important because manual delineation of distinct
regions with MR images relies mostly on anatomical land-
marks. As each one of the relevant structures is generally
composed of no more than a few cubic centimetres, minor
imperfections in delineation may yield gross discrepancies
and erroneous interpretation of important conclusions. With
high resolution MRI imagery, this limitation can be mini-
mised by using three dimensional visualisation
relevant anatomical structures.
We assessed the degree of damage to the medial temporal
lobe in consecutive patients with drug refractory MTLE
through manual delineation of the cortical and subcortical
structures of the medial portion of the temporal lobe in high
resolution three dimensional MR images.
We studied 30 healthy adult subjects (19 women) without
previous medical history of epilepsy. All subjects were
contacted in the local community and were volunteers for
this study. We also studied 25 consecutive patients with
chronic refractory MTLE. All patients were referred from the
outpatient epilepsy clinic of our institution, where they were
diagnosed by a detailed neurological evaluation. The nature
of the epileptic syndrome was determined based on ILAE
Seizures were lateralised according to the medical
history, a comprehensive neurological examination, interictal
EEG, and prolonged video EEG monitoring of seizure onset.
Visual inspection of the MRI scans following a standard
revealed unilateral HA in all the patients. Each
patient was diagnosed with drug refractory MTLE,
unilateral seizure onset. The ethics committee of our
institution approved the study.
MR image acquisition
We acquired diagnostic MRI using a standardised protocol.
T1 weighted images with 1 mm isotropic voxels were
acquired on a 2 Tesla Elscint Prestige scanner (Haifa,
Israel) using a spoiled gradient echo sequence (TR = 22 ms,
Abbreviations: Amy, amygdala; Hip, hippocampus; ERC, entorhinal
cortex; PHC, parahippocampal cortex; PRC, perirhinal cortex; ROI,
regions of interest; TPC, temporopolar cortex
TE = 9 ms, flip angle = 35
, matrix = 2566220, field of
view = 25622 cm, 1 mm thick sagittal slices).
We transferred the volumetric images to a Silicon Graphics
O2 workstation (Mountain View, CA, USA). The raw images
were initially converted into MINC format, corrected for field
non-homogeneity using N3,
and transformed into a
standard space by linear stereotaxic transformation.
We performed manual segmentation using the interactive
software package Display (David McDonald) developed at the
Brain Imaging Centre of the Montreal Neurological Institute.
This software enables precise and fully scalable image
analysis by simultaneously displaying coronal, sagittal, and
axial planes. It also makes it possible to draw regions of
interest (ROI), and delineation of anatomical boundaries is
facilitated by contrast adjustment and the possibility for
navigation through isotropic voxels of 1 mm in different
orientations with the same resolution. The software auto-
matically calculates the volumes of the labelled structures.
The structures were manually delineated by a single
observer (L B), according to previously published compre-
hensive reviews of the MRI anatomical boundaries of medial
temporal lobe structures.
We evaluated the volumes of the temporopolar cortex
(TPC), perirhinal cortex (PRC), entorhinal cortex (ERC),
parahippocampal cortex (PHC), amygdala (Amy), and
Data was evaluated using Systat (9.0) software for Windows.
Group differences for age were evaluated using one way
analysis of variance, and gender distribution was evaluated
using the x
test. Differences of volumes among control
subjects were evaluated with multivariate analysis of
variance with two intra-subject factors (side (left or right)
and structure (TPC, PRC, ERC, PHC, Amy, Hip)). The value of
each individual’s volume measurement was standardised
according to the volumes of th mean observed in the controls
group. For each individual, asymmetry of volumes was
calculated according to the symmetrical index (L2R)/
[(L+R)/2]. Group differences of volume were evaluated with
multivariate analysis of variance with one inter-subject
grouping factor (controls, left MTLE, right MTLE) and one
intra-subject control group through Z score transformation—
that is, the number of standard deviations (SD) away from
that grouping factor (structures: right TPC, left TPC, right
PRC, left PRC, right ERC, left ERC, right PHC, left PHC, right
Amy, left Amy, right Hip, left Hip). The multivariate analysis
of variance was followed by Tukey HSD post hoc comparisons
to evaluate the structures that would exhibit significant
volume reduction in patients with MTLE compared with
The degree of atrophy across the different structures was
performed using a one way analysis of variance to compare
the Z scores of each medial temporal lobe structure. Group
differences for asymmetry were evaluated with multivariate
analysis of variance with one inter-subject grouping factor
(controls, left MTLE, right MTLE) and one intra-subject
grouping factor (TPC, PRC, ERC, PHC, Amy, Hip). We used
correlation and simple regression to assess the inter-
dependent variability of the volumes measured. The thresh-
old for statistical significance was set at p,0.05. We
considered the volume of the structure to be abnormally
reduced when its Z score was below 2 SD.
Thirteen patients had left HA and left MTLE and twelve
patients had right HA and right MTLE. There was no
significant difference in age or sex distribution between
controls and patients with MTLE.
The volumes of the different structures in of the control
subjects are shown in table 1. There was no significant side to
side difference in any of the structures analysed
= 0.57, p = 0.45; TPC l
= 0.29, p = 0.59;
= 0.59, p = 0.44; PHC l
= 0.84, p = 0.36;
= 1, p = 0.32; Hip l
= 0.04, p = 0.84.
Patients with MTLE
The volumes of the studied structures in patients with MTLE
are shown in table 1. Multivariate analysis of variance with
Tukey post hoc comparison between patients and controls
showed a significant reduction in the volumes of the left PRC,
left ERC, and left Hip in patients with left MTLE, and
significant reduction in the volumes of the right PRC and
right ERC in patients with right MTLE (fig 1). Patients with
left MTLE exhibited a larger right amygdala compared to
controls and patients with right MTLE: l
= 4.6, p,0.05.
Group differences on asymmetry were significant for all
structures analysed, as follows: PRC l
= 36.5, p,0.001
Tukey’s: left MTLE,control,right MTLE; TPC l
p,0.001, left MTLE = control,right MTLE; ERC l
106.9, p,0.001, left MTLE,control,right MTLE; PHC
= 22.3, p,0.001, left MTLE = control,right MTLE;
= 8.5, p,0.01, left MTLE = control,right MTLE;
= 274.1, p,0.001, left MTLE,control,right
The analysis of the Z score revealed that the degree of atrophy
was significantly different among the medial temporal lobe
structures in patients with left MTLE F
p,0.001 and in patients with right MTLE F
p,0.001 (fig 2). Tukey post hoc comparison did not show
difference between the Z scores of the ERC and the PRC in
patients with left and patients with right MTLE.
Correlation and simple regression
Linear correlation and simple regression analysis were
performed with the data from similar structures ipsilateral
to HA—that is, left perirhinal cortex in patients with left
MTLE and right perirhinal cortex in patients with right
MTLE, grouped together. All structures were analysed
simultaneously in the search for significant inter-structure
correlation. There was no significant linear correlation
between the volumes of structures analysed—that is, there
was no inter-dependent variability between the volumes of
the different structures of the medial temporal lobe.
Simple regression analysis revealed R
= 0.3 for the
comparison between the entorhinal and perirhinal cortices.
All other comparisons revealed smaller values of R
Volumetric analysis of the amygdala and hippocampus has
been successfully used to determine tissue damage in
patients with temporal lobe epilepsy.
Currently, few studies
have examined the other temporal lobe structures, particu-
larly the cortical structures of the medial temporal lobe, as
reviewed below. As there is a large and intricate network of
connections involving all structures in the medial temporal
lobe, it is possible that damage to the medial temporal lobe
1628 Bonilha, Kobayashi, Rorden, et al
may extend beyond the amygdala and the hippocampus,
which may contribute to the symptoms of temporal lobe
It is not yet established to what extent damage to the
medial temporal lobe involves the cortical structures. Jutila
examined patients with unilateral MTLE and reported
that patients with right HA have ipsilateral damage in the
entorhinal and temporopolar cortices, whereas patients with
left HA have ipsilateral damage only in the entorhinal cortex.
Salmenpera et al
observed that in patients with MTLE the
mean volumes of the entorhinal cortex ipsilateral to the side
of seizure onset did not differ from controls. However, they
found that the entorhinal volume correlated with hippocam-
pal volume and that patients with right MTLE with HA had a
19% volume reduction of the ipsilateral entorhinal cortex. In
their study, the volume of the entorhinal cortex correlated
with the duration of MTLE. They also found that none of the
patients showed additional atrophy in the hippocampus,
amygdala, or the entorhinal and perirhinal cortices at a
1 year follow up.
However, Bernasconi et al
volume reduction of the entorhinal cortex ipsilateral to the
seizure focus in all MTLE patients studied, reduction of the
perirhinal cortex in 33% of the patients, and contralateral
reduction of the entorhinal cortex in 50% of the patients. The
same group also found bilateral reduction of the entorhinal
cortex volume in patients with MTLE, the atrophy being
greater ipsilateral to the epileptic focus,
and observed that it
was possible to lateralise the seizure focus in patients with
MTLE and normal hippocampal volumes based on the
entorhinal cortex volume.
Recently, they examined a group
of 25 patients with drug refractory MTLE and observed that
the entorhinal and the perirhinal cortices ipsilateral to the HA
were significantly smaller than in normal controls. They also
observed that the entorhinal cortex was more severely
reduced than the perirhinal cortex.
In summary, we analysed medial temporal lobe structures
in consecutive patients with unilateral chronic refractory
MTLE defined and documented by video EEG, along with
unilateral HA. Our findings demonstrated that patients with
MTLE have significant reduction of the volume of the cortical
structures closer to the hippocampus—that is, the entorhinal
and perirhinal cortices. Other structures, such as the
Figure 1 Box and whiskers plot
showing the distribution of the volumes
of the structures significantly atrophied
in MTLE: the entorhinal cortex (ERC), the
perirhinal cortex (PRC) and the
hippocampus (Hip). (A) Distribution
between groups (control, right MTLE
(Rtle) and left MTLE (Ltle)) of the volumes
of the ERC, PRC and Hip on the right
side; and (B) distribution between
groups of the left sided structures.
Table 1 Volumes of mesial temporal structures of normal subjects and patients with MTLE
PRC TPC ERC PHC Amy Hip
LRLRLRLRL R LR
R MTLE Mean 2140 1709 3337 2954 1159 856 1642 1331 1454 1335 3031 1764
SD 363 315 541 522 126 127 297 229 140 285 290 328
Max 2670 2247 4118 3924 1550 1066 2087 1786 1741 2065 3558 2305
Min 1527 1259 2492 1836 982 669 1201 1026 1239 987 2590 1137
L MTLE Mean 1701 2083 2990 3314 802 1139 1522 1580 1479 1616 1823 3051
SD 290 350 524 584 119 153 259 206 240 178 293 312
Max 2182 2712 4032 4308 959 1363 2100 1857 1873 1871 2291 3520
Min 1225 1671 2189 2550 627 828 1185 1246 1090 1281 1385 2561
Controls Mean 2266 2187 3244 3173 1187 1226 1661 1573 1539 1479 3279 3260
SD 386 418 454 547 182 197 366 371 233 222 374 352
Max 3063 2922 4032 4282 1660 1897 2590 2572 1946 2175 3949 3999
Min 1315 1395 1987 1981 819 827 1227 1146 1046 1010 2458 2369
R, right; L, left; PRC, perirhinal cortex; TPC, temporopolar cortex; ERC, entorhinal cortex; PHC, parahippocampal cortex; Hip, hippocampus; Amy, amygdala;
Max, maximum; Min, minimum
Medial temporal lobe atrophy in MTLE 1629
parahippocampal and temporopolar cortices, are less affected.
For all medial temporal lobe structures, there was a
significant difference in the asymmetry index between
patients with right MTLE and controls, while patients with
left TLE exhibited significant difference of the asymmetry
indexes of the Hip, PRC, and ERC. This information can be
used as additional information for lateralisation of seizures.
We did not observe significant correlations between the
volumes of any of the structures analysed, nor did we observe
significant difference between the degree of damage to the
entorhinal and perirhinal cortex. These null results may
reflect both the relatively small number of patients examined
in this study and the variability found when studying an
unselected set of consecutive patients rather than a more
homogenous group matched for other factors. Nevertheless,
as there is a large neural network involved in the generation
and propagation of seizures in MTLE,
it is also possible that
MTLE reflects a heterogeneous population composed of
different patterns of atrophy beyond the hippocampus
according to the different sub-pattern of network most
In conclusion, our work extends the understanding of the
extent of atrophy of the medial temporal lobe in patients with
MTLE. Some issues related to the pattern of medial temporal
lobe volumetric alterations require further studies. For
instance, it is not currently possible to define the role of the
cortical structures in the symptom presentation of medial
MTLE, neither is it possible to predict which clinical factors
may influence the presence and extent of medial temporal
lobe damage. However, the observation and quantification of
damage extending beyond the hippocampus may be helpful
for understanding the lateralisation of seizures in patients
with MTLE and may provide clues to further investigation of
the role of temporal lobe cortical structures in the patho-
physiology of medial temporal lobe epilepsy.
L Bonilha, E Kobayashi, F Cendes, L M Li, Neuroimaging Laboratory,
Department of Neurology, State University of Campinas, Brazil
C Rorden, School of Psychology, University of Nottingham, UK
Competing interest: none declared
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Figure 2 Box and whiskers plot
showing the distribution of the Z scores
of all structures analysed. (A) Z score of
structures ipsilateral to the hippocampal
atrophy; (B) Z score of structures
contralateral to the hippocampal
atrophy. R, right; L, left; PRC, perirhinal
cortex; TPC, temporopolar cortex; ERC,
entorhinal cortex; PHC,
parahippocampal cortex; Amy,
amygdala; Hip, hippocampus.
1630 Bonilha, Kobayashi, Rorden, et al