Histological correlates of hippocampal magnetization transfer images in drug-resistant temporal lobe epilepsy patients

Abstract

Highlights Hippocampal MTR in TLE does not add to volume or T2 signal regarding lateralization. Extracellular CSPG are the most relevant correlate to MTR in hippocampal sclerosis. Increased CSPG counterbalances neuron loss over the reduction in hippocampal MTR.

A controversial question: Can morphometry and clinical history be enough to diagnose hippocampal dysplasia?

“…FCDII cases often present daily seizures, in contrast with HS, and have frequent interictal discharges. 8,9 As the frequency of interictal spikes, besides other interictal EEG abnormalities, are directly associated with the density of dysmorphic neurons in the seizure onset zone, 9 the low number of dysmorphic cells in our patient may account for the lower frequency of spikes detected in scalp EEG.…”

“…19 Regardless of the induction mechanism (i.e., mutation of FCDII or inflammation in encephalitis), mTOR pathway dysregulation may be the cause for these dysmorphic neurons in HS, as it is known that chronic inflammation can be seen in HS. 8 However, why only some HS patients present with dysmorphic-like neurons remain unknown.…”

Improving surgical outcome with electric source imaging and high field magnetic resonance imaging

“…On visual inspection, while in most patients HS is seen as reduced hippocampal volume and increased T2 signal on MRI [24][25][26], FCDs can be seen as cortical thinning (FCD I) or cortical thickening (FCD II), blurred grey -white matter transition, increased T2 signal sometimes as a characteristic transmantle sign, and water diffusion changes [22,[27][28][29][30]. LEATs present a wide range of MRI changes, such as the well-defined "bubbly" appearance of DNETs or the less defined lesion with perilesional T2 hypersignal, contrast enhancement, and calcifications that characterize the gangliogliomas [23,31].…”

“…However, some hippocampal sclerosis cases have no significant volume loss [46,52]. In these HS cases with normal volume, other tissue changes can influence the hippocampal volume and help hide neuron loss in some cases [46], and measurement of T2 relaxation often reveals the epileptogenic hippocampus [25,53]. A study with MRI-negative FCDs showed that volume-based morphometry identified atrophy in seven cases [54].…”

“…Increased T2 signal is a hallmark of HS, and even cases with normal hippocampal volume can present increased T2 relaxation (Fig. 1), helping the correct lateralization of the epileptogenic zone in more than 80 % of the patients [25,45,53,57]. T2/FLAIR signal intensity analysis by subfield in presurgical images can be crucial in differentiating mesial temporal lobe epilepsy cases without HS from HS type 3.…”