MR volumetry of the entorhinal, perirhinal, and temporopolar cortices in drug-refractory temporal lobe epilepsy

Abstract

Background and purpose: The occurrence of damage in the entorhinal, perirhinal, and temporopolar cortices in unilateral drug-refractory temporal lobe epilepsy (TLE) was investigated with quantitative MR imaging.

Methods: Volumes of the entorhinal, perirhinal, and temporopolar cortices were measured in 27 patients with unilateral drug-refractory TLE, 10 patients with extratemporal partial epilepsy, and 20 healthy control subjects. All patients with TLE were evaluated for epilepsy surgery and underwent operations.

Results: In left TLE, the mean volume of the ipsilateral entorhinal cortex was reduced by 17% (P <.001 compared with control subjects) and that of the ipsilateral temporopolar cortex by 17% (P <.05). In right TLE, the mean ipsilateral entorhinal volume was reduced by 13% (P < or =.01), but only in patients with hippocampal atrophy. Asymmetry ratios also indicated ipsilateral cortical atrophy. When each patient was analyzed individually, the volume of the ipsilateral hippocampus was reduced (> or = 2 SD from the mean of controls) in 63% and that of the entorhinal cortex in 52% of patients with TLE. Furthermore, ipsilateral entorhinal (left: r = 0.625, P <.001; right: r = 0.524, P < or =.01), perirhinal (left: r = 0.471, P <.05), and temporopolar (right: r = 0.556, P <.01) volumes correlated with ipsilateral hippocampal volumes. There was no association, however, with clinically or pathologically identified causes of epilepsy, duration of epilepsy, or age at onset of epilepsy. Mean cortical volumes were unaffected in extratemporal partial epilepsy.

Conclusion: Subpopulations of patients with unilateral TLE have ipsilateral damage in the entorhinal and temporopolar cortices. The damage is associated with hippocampal damage.

fig 1.

Coronal MR images from a control subject demonstrate the boundaries of the temporopolar, entorhinal, and perirhinal cortices (white outlines). Six rostrocaudal levels are shown (A, most rostral; F, most caudal). A, The temporopolar cortex is the area between the lateral edge of the superior temporal sulcus and the medial bank of the inferior temporal sulcus. B, The appearance of the collateral sulcus marks the beginning of the perirhinal cortex. C, The boundaries of the perirhinal cortex at the level of the limen insula. The collateral sulcus is shallow (depth, < 1 cm), and therefore, the lateral border of the perirhinal cortex is located at the midpoint of the occipitotemporal gyrus . D, The boundaries of the entorhinal and perirhinal cortices at the level of the amygdala. The collateral sulcus is shallow, and therefore, the border between the entorhinal and perirhinal cortices is located at the fundus of the collateral sulcus (arrowhead). The lateral border of the perirhinal cortex is located at the midpoint of the occipitotemporal gyrus. E, The boundaries of the entorhinal and perirhinal cortices at the level of the hippocampus. The borders of the entorhinal and perirhinal cortices are identical to those in D. F, The caudal limit of the perirhinal cortex is located two sections behind the end of the uncus. A indicates amygdala; CS, collateral sulcus; EC, entorhinal cortex; HC, hippocampus; LI, limen insula; PRh, perirhinal cortex; TP, temporopolar cortex. Scale bar, 10 mm.

fig 2.

Scatterplots show the intraobserver variability of repeated measurements in different cortical areas of 10 control subjects. A, Temporopolar cortex; B, entorhinal cortex; and C, perirhinal cortex. The limits of agreement between the first and the second measurements are expressed as the mean difference in volume: [volume in the first measurement minus volume in the second measurement (mm³)] ± 2 SD. Inserts in the lower left corner show the association between the first (y-axis) and second (x-axis) measurements. Mean indicates mean difference in volume; +2 SD, mean difference in volume plus 2 SD; -2 SD, mean difference in volume minus 2 SD

fig 3.

Percentage of TLE patients with damage to the hippocampus (A), entorhinal cortex (B), temporopolar cortex (C), or perirhinal cortex (D). Contra indicates the side contralateral to the seizure focus; Dam+, a volume reduction of at least 2 SD from the control mean; Dam-, a volume reduction of less than 2 SD from the control mean; EC, entorhinal cortex; Focus, side of the seizure focus; HC, hippocampus; n, number of patients; PRh, perirhinal cortex; TP, temporopolar cortex

fig 4.

Scatterplots show the correlation between the volumes of the left (A–C) or right (D–F) hippocampus and the volumes of the entorhinal, temporopolar, and total perirhinal (ie, combined perirhinal and temporopolar volumes) cortices on that side in patients with TLE. Closed circles refer to patients with right TLE and open circles to patients with left TLE. Mean indicates mean volume in control subjects; -1SD, mean volume in control subjects minus 1 SD; -2 SD, mean volume in control subjects minus 2 SD; n, number of patients; r, Pearson's correlation coefficient

fig 5.

Coronal MR images of a 32-year-old man with cryptogenic right TLE. The duration of epilepsy at the time of imaging was 29 years, and the seizure frequency was 36 complex partial seizures per year. The patient subsequently underwent surgery and is currently seizure-free (Engel's class IA). A, Ipsilaterally, the volume of the entorhinal cortex is 81% of that (mean volume) in control subjects and 78% of that on the contralateral side. B, MR image taken from a more caudal level shows the volume reduction in the ipsilateral hippocampus (volume 41% of that in control subjects and 50% of that on the contralateral side). The volume of right perirhinal cortex is 2597 mm³; left, 2924 mm³ (both within normal range). A indicates amygdala; EC, entorhinal cortex; HC, hippocampus; L, left; PRh, perirhinal cortex; R, right. Scale bar, 10 mm.