Hippocampal and Thalamic Diffusion Abnormalities in Children with Temporal Lobe Epilepsy

Abstract

Summary:Purpose: Previous studies using diffusion MRI in patients with temporal lobe epilepsy have shown abnormal water diffusion in the hippocampus. Because thalamus and lentiform nuclei are considered important for the regulation of cortical excitability and seizure propagation, we analyzed diffusion tensor imaging (DTI) abnormalities in these subcortical structures and in hippocampus of children with partial epilepsy with and without secondary generalization.Methods: Fourteen children with partial epilepsy involving the temporal lobe underwent MRI including a DTI sequence. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were obtained in the hippocampus, thalamus, and lentiform nucleus, and compared with DTI data of 14 control children with no epilepsy, as well as glucose positron emission tomography (PET) findings.Results: Decreased FA (p < 0.001) and increased ADC (p = 0.003) values were found in the hippocampi ipsilateral to the seizure focus. Significant FA decreases (p = 0.002) also were seen in the contralateral hippocampi, despite unilateral seizure onset and excellent surgical outcome in patients who underwent surgery. ADC values showed a trend for increase in the thalami ipsilateral to the epileptic focus in the seven children with secondarily generalized seizures (p = 0.09). No group differences of ADC or FA were found in the lentiform nuclei. The DTI variables did not correlate with regional glucose metabolism in any of the structures analyzed.Conclusions: Increased ADC values in hippocampus can assist in lateralizing the seizure focus, but decreased FA in the contralateral hippocampus suggests that it too may be dysfunctional despite unilateral seizure onset. Less-robust thalamic abnormalities of water diffusion in patients with secondarily generalized seizures suggest secondary involvement of the thalamus, perhaps due to recruitment of this structure into the epileptic network; however, this must be confirmed in a larger population. DTI appears to be a sensitive method for detection abnormalities in children with partial epilepsy, even in structures without apparent changes on conventional MRI. Key Words: EpilepsyHippocampus-Thalamus-MRI-Diffusion tensor imagingAnisotropy.Alterations in temporal and subcortical structures in patients with temporal lobe epilepsy (TLE) have been demonstrated by using various imaging methods, including positron emission tomography (PET) of glucose metabolism (1-4) and flumazenil binding (1,3,5), volumetric MRI (3,6-8), proton MR spectroscopy (9-11), and single-photon emission computed tomography (SPECT) of cerebral blood flow (12)(13)(14). Diffusion tensor imaging (DTI) of the human brain is a relatively new MRI method that allows noninvasive modeling of the diffusive transport of water molecules by means of a diffusion tensor (15)(16)(17). Of the several indices used to characterize the diffusion tensor, those most commonly used include the Accepted July 27, 2005. Address correspondence and reprint requests to Dr. H.T. Chugani at Pediatric...

Thalamic atrophy and cognition in unilateral temporal lobe epilepsy

“…Second, both the hippocampus and thalamus play significant roles in seizure initiation, modulation, and propagation (Bertram et al, 2001;Guye et al, 2006;Norden & Blumenfeld, 2002). Third, neuroimaging studies have confirmed that the thalamus is affected in patients with unilateral TLE (Bonilha et al, 2005;Dreifuss et al, 2001;Juhasz et al, 1999;Kimiwada et al, 2006;Natsume et al, 2003). Finally, the thalamus is posited to play an important role in both memory and nonmemory cognitive domains (Crosson, 1992;Johnson & Ojemann, 2000).…”

“…Recent neuroimaging studies have confirmed that the thalamus is affected in patients with unilateral TLE. Cerebral and metabolic hypoperfusion on positron emission tomography, abnormalities on diffusion tensor imaging and magnetic resonance (MR) spectroscopy, and quantitative MR brain volume and voxelbased morphometry (VBM) abnormalities of the thalamus have been reported (Bonilha et al, 2005;DeCarli et al, 1998;Juhasz et al, 1999;Kimiwada et al, 2006;Sperling et al, 1990). However, findings are mixed about the extent of brain volume loss in the thalamus (ipsilateral or bilateral) relative to other neural structures, and its association with clinical seizure characteristics also remains unclear (Dreifuss et al, 2001;Natsume et al, 2003).…”

White matter development in children with benign childhood epilepsy with centro-temporal spikes

“…This is particularly relevant for BCECTS where the occurrence of seizures is very rare, from one to six over the entire duration of the disease in 70% of cases (Rosser, 2007). Interictal DTI studies in children with epilepsy have mostly been performed in temporal lobe epilepsy, showing reduction of fractional anisotropy in the hippocampus (Kimiwada et al, 2006) and in the white matter tracts ipsilateral to left temporal foci (Govindan et al, 2008), or increased mean-, axial-and radial diffusivity in the temporal and cingulate white matter (Lee et al, 2004;Nilsson et al, 2008). Similarly, the coefficient of diffusion (ACD), which is often used interchangeably with mean diffusivity, increased interictally in the epileptogenic hippocampus of adult patients with temporal lobe epilepsy (Kantarci et al, 2002;Duzel et al, 2004).…”

Water diffusion reveals networks that modulate multiregional morphological plasticity after repetitive brain stimulation

“…Water diffusion is altered by the structures of gray matter (12). DWI can be used to evaluate morphological changes in cortical microstructures (13)(14)(15)(16)(17)(18)(19) and can function as a probe to estimate immediate and transient changes in water diffusion that are associated with ischemia (17) or neuronal firing (13,16,19) and delayed and persistent changes that are associated with long-term plasticity in experimental settings (20) or pathological conditions (15,18,21). Here, using DWI techniques, we examined whether subthreshold, low-frequency (<1 Hz) rTMS to the left primary motor cortex (M1), a protocol that induces LTD-like plasticity (22, 23), increased water diffusion in the left M1 and other regions after the end of rTMS.…”