Periventricular Nodular Heterotopia: Detection of Abnormal Microanatomic Fiber Structures with Whole-Brain Diffusion MR Imaging Tractography

Abstract

Advances in knowledge:1. Whole-brain Constrained Spherical Deconvolution (CSD) based fibre tractography and superresolution Track Density Imaging (TDI) mapping revealed abnormal fibre projections in nodular tissue suggestive of abnormal organization of white matter (with abnormal fibres both within nodules and projecting to the surrounding white matter) in patients with bilateral periventricular nodular heterotopia (PVNH).2. The detection of abnormal fibre structures by all four readers in all fourteen patients studied (Fleiss Kappa (κ ) = 1.0 SE = 0.0, 95% CI = 1.0 to 1), indicates that these architectural abnormalities are particularly prevalent in patients with bilateral PVNH. Implications for patient care:Whole-brain tractography mapping techniques provide an opportunity to non-invasively detect in vivo abnormal structures potentially involved in ictal networks; such maps could be used to aid the identification of appropriate surgical targets for individuals undergoing evaluation for epilepsy surgery. Results: Abnormal fibre tracks emanating from one or more regions of heterotopia were reported by all four readers in all 14 patients with PVNH studied (Fleiss Kappa (κ) = 1). These abnormal structures were not visible in the tractography data of any of the control subjects, and not discernable on the conventional T1 weighted images of the PVNH patients. Conclusion:Whole-brain CSD-based fibre tractography and super-resolution TDI mapping reveals abnormal fibre projections in nodular tissue suggestive of abnormal organization of white matter (with abnormal fibres both within nodules and projecting to the surrounding white matter) in patients with bilateral PVNH.

Epileptogenic networks in nodular heterotopia: A stereoelectroencephalography study

“…Furthermore, in animals with experimentally induced PNH, it has been demonstrated that heterotopic neurons can form aberrant connections with the hippocampus, thereby giving rise to a complex epileptogenic network, data confirmed by a human case study . Tractography studies using diffusion‐weighted imaging in human subjects confirm aberrant projections suggestive of abnormal white matter organization . However, few human data are available using direct intracerebral EEG recording within distributed networks of NH, in terms of both resting state activity (interictal period) and seizure activity (ictal period).…”

“…31 The EI is a normalized quantity ranging from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). This quantity may be estimated using a twostage procedure: (1) within a sliding window (5 s duration), the signal energy ratio (ER) is computed, between high (beta [12][13][14][15][16][17][18][19][20][21][22][23][24], gamma ) and low (theta [4-7.4 Hz] and alpha [7.4-12 Hz]) frequency bands of the EEG obtained from the signal spectral density C(w) (squared modulus of Fourier transform) (2) change-points in the ER[n] quantity, which is sensitive to frequency changes in the signal, are detected. An optimal algorithm ("cumulative sum algorithm" or "CUSUM") is used to automatically determine the time instant when ER[n] increases, that is, when theta alpha activity (predominant in background SEEG signals) changes into higher frequency activity (predominant during the rapid discharge).…”

“…20 Tractography studies using diffusion-weighted imaging in human subjects confirm aberrant projections suggestive of abnormal white matter organization. 21 However, few human data are available using direct intracerebral EEG recording within distributed networks of NH, in terms of both resting state activity (interictal period) and seizure activity (ictal period).…”

Similarities and differences in neuroplasticity mechanisms between brain gliomas and nonlesional epilepsy

“…For instance, fiber projections from periventricular heterotopias to distant neocortical areas are obviously sustained by nonanatomic pathways, even if they may cross them. 77 Moreover, patterns of increased connectivity related to the epileptogenic zone, coupled with decreased connectivity in widespread distal networks have been found, and are correlated to the severity and the duration of the disease. 78 Those pathologic networks may provide a benefit in terms of seizure-spreading limitation, but may also impair physiologic networks of the connectome and have a negative impact on function.…”

“…These pathologic organizations are described at a local level, as well as on long‐distance tracks, and are constituted of abnormal fiber tracts, distinct from the normal white matter anatomy. For instance, fiber projections from periventricular heterotopias to distant neocortical areas are obviously sustained by nonanatomic pathways, even if they may cross them . Moreover, patterns of increased connectivity related to the epileptogenic zone, coupled with decreased connectivity in widespread distal networks have been found, and are correlated to the severity and the duration of the disease .…”