Temporal lobe epilepsy: differential pattern of damage in temporopolar cortex and white matter

Abstract

Our purpose was to quantify structural changes of the temporopolar cortex (TPC) and its white matter (TPWM) in temporal lobe epilepsy (TLE) using MRI volumetry and texture analysis. We studied 23 patients with hippocampal atrophy, and 20 healthy controls. Gradient magnitude and entropy were calculated to model signal intensity blurring on T1-MRI. Two observers assessed signal changes and atrophy visually. Compared to controls, TLE patients had a decrease in TPC and TPWM volume ipsilateral to the seizure focus. The gradient magnitude and entropy were decreased ipsilateral to the focus only in TPWM, indicating blurring of this compartment. Eighty-seven percent of TLE patients had at least one volumetric or textural abnormality. Although sensitivity of visual and quantitative assessment of TPC atrophy was comparable (43 and 39%), specificity was higher for volumetry (54% vs. 95%). Compared to visual analysis of signal changes in TPWM on T1-MRI, texture metrics had higher sensitivity (65% vs. 17%) and specificity (100% vs. 69%). The proportion of patients with blurring of TPWM as determined by texture analysis was higher than that seen on visual inspection of T2 images (78% vs. 43%). We found no clear association between volumetric or textural changes of TPC and TPWM and outcome after surgery. Structural changes of the anatomically distinct TPC and TPWM are found ipsilateral to the seizure focus in the majority of TLE patients with hippocampal sclerosis. MRI post-processing allows dissociating different pathological tissue characteristics and shows that atrophy involves gray and white matter, whereas blurring is confined to white matter.

Figure 1

Anatomical boundaries of the temporopolar cortex (TPC) on coronal MRI in a healthy control subject. A: The rostral boundary of the TPC is the rostralmost coronal section in which the cortex of the temporal lobe becomes visible. B: The dorsolateral border is the lateral bank of the temporopolar sulcus (TPS), whereas the ventrolateral border is a line drawn perpendicularly downward from the medial tip of the temporopolar white matter (block arrow). C: MRI coronal slice at the same level than panel B showing the temporopolar white matter (TPWM) that occupies the white matter of the temporal lobe underlying the TPC. D: The caudal border of the TPC is considered to be the coronal slice immediately anterior to the slice where the collateral sulcus (CS) first appears. On panels B and C, ITS = inferior temporal sulcus.

Figure 2

Three‐dimensional rendering of the T1‐weighted MRI with superimposed label of the temporopolar cortex (TPC, in red) in a healthy subject. A mesio‐basal (left) and a fronto‐lateral (right) view are presented. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 3

Coronal MR images across the temporal lobe in a TLE patient. Cranial to caudal slices are shown from left to right. A: T2‐weighted images showing increase in signal intensity in the temporopolar white matter (TPWM) and its extent (arrows). B: T1‐weighted images reformatted to be at the same level and orientation than T2‐weighted images do not show obvious signal intensity changes. C: TPC (red) and TPWM (yellow) manual labels in the most anterior slice are presented. Texture analysis of T1‐weighetd MR images indicated the presence of ipsilateral blurring of the TPWM and showed z‐score values of −3.7 for the TPWM entropy and −6.3 for the TPWM gradient. Volumetry showed both TPC and TPWM atrophy ipsilateral to the seizure focus (TPC volume: −2.1 and TPWM TPWM: −2.3). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]