Clinical use of ictal SPECT in secondarily generalized tonic–clonic seizures

Abstract

Partial seizures produce increased cerebral blood flow in the region of seizure onset. These regional cerebral blood flow increases can be detected by single photon emission computed tomography (ictal SPECT), providing a useful clinical tool for seizure localization. However, when partial seizures secondarily generalize, there are often questions of interpretation since propagation of seizures could produce ambiguous results. Ictal SPECT from secondarily generalized seizures has not been thoroughly investigated. We analysed ictal SPECT from 59 secondarily generalized tonic-clonic seizures obtained during epilepsy surgery evaluation in 53 patients. Ictal versus baseline interictal SPECT difference analysis was performed using ISAS (http://spect.yale.edu). SPECT injection times were classified based on video/EEG review as either pre-generalization, during generalization or in the immediate post-ictal period. We found that in the pre-generalization and generalization phases, ictal SPECT showed significantly more regions of cerebral blood flow increases than in partial seizures without secondary generalization. This made identification of a single unambiguous region of seizure onset impossible 50% of the time with ictal SPECT in secondarily generalized seizures. However, cerebral blood flow increases on ictal SPECT correctly identified the hemisphere (left versus right) of seizure onset in 84% of cases. In addition, when a single unambiguous region of cerebral blood flow increase was seen on ictal SPECT, this was the correct localization 80% of the time. In agreement with findings from partial seizures without secondary generalization, cerebral blood flow increases in the post-ictal period and cerebral blood flow decreases during or following seizures were not useful for localizing seizure onset. Interestingly, however, cerebral blood flow hypoperfusion during the generalization phase (but not pre-generalization) was greater on the side opposite to seizure onset in 90% of patients. These findings suggest that, with appropriate cautious interpretation, ictal SPECT in secondarily generalized seizures can help localize the region of seizure onset.

The Default Mode Network and Altered Consciousness in Epilepsy

“…Similar increases have been captured in humans as well. SPECT studies have revealed that the earliest increases are often in the temporal lobe, where tonic-clonic seizures most commonly originate [14,68]. Additionally, large CBF increases during the generalization phase have been observed in the bilateral medial and lateral parietal cortex [9,21] as well as in the thalamus, basal ganglia, and superior medial cerebellum [9,14,21].…”

“…For example, in absence seizures, it has been proposed that the variable impairments observed are likely the result of focal disruptions of specific brain networks [12,38]. This view has been supported by mounting evidence that even so-called "generalized" seizures, such as absence and tonic-clonic seizures, are of focal origin and likely do not affect the whole brain homogeneously [4,20,68]. Thus, networks affected by generalized seizures may in some ways resemble those involved in partial seizures [10].…”

Regional differences in cerebral perfusion associated with the α-2A-adrenergic receptor genotypes in attention deficit hyperactivity disorder

“…Voxel-level inference was performed at a height threshold of p < 0.0005 (uncorrected for multiple comparisons) and cluster-level inference at p < 0.05 (corrected for multiple comparisons, extent threshold = 125 voxels, which has been reported to be an appropriate spatial resolution for SPECT in tissue). 22 We converted the Montreal Neurological Institute (MNI) coordinates to the Talairach space (http://imaging.mrc-cbu. cam.…”

Right parietal source in Mahjong‐induced seizure: a system epilepsy of focal origin

“…Another important factor to modify the sensitivity and specificity of ictal SPECT is the timing of tracer injection. Whether CBF change is identified in the cases of partial seizure depends on the generalization and the timing of tracer injection, namely, either (i) pregeneralization period (during the partial seizure phase prior to generalization), (ii) during the generalization period, or (iii) postictal period 10, 11. In the partial seizure without generalization, CBF often decreases postictally both within and around the seizure focus 10.…”

“…Whether CBF change is identified in the cases of partial seizure depends on the generalization and the timing of tracer injection, namely, either (i) pregeneralization period (during the partial seizure phase prior to generalization), (ii) during the generalization period, or (iii) postictal period 10, 11. In the partial seizure without generalization, CBF often decreases postictally both within and around the seizure focus 10. In contrast, in the secondary generalized partial seizure, CBF tends to increase in multiple lobes ipsilateral to the seizure focus with relatively decreased CBF in the contralateral hemisphere 11.…”