Ictal SPECT: Hyperperfusion at the Seizure Focus
CC BY-SA 3.0 · Dr Bruno Di Muzio / Radiopaedia / Wikimedia Commons · source file
Question
Brain SPECT is used in pre-surgical epilepsy evaluation. During an active seizure (ictal phase), the seizure focus shows which pattern on brain perfusion SPECT?
- ADecreased perfusion (hypoperfusion) at the seizure focus due to neurovascular uncoupling, where excessive glutamatergic excitation triggers compensatory vasoconstriction via pericyte-mediated capillary constriction
- BMarkedly INCREASED perfusion (hyperperfusion) at the seizure focus — seizure activity dramatically increases local cerebral blood flow
- CNo change from baseline perfusion, as SPECT tracer uptake reflects cerebral metabolic rate rather than blood flow, and transient ictal activity is below the detection threshold of hexamethylpropyleneamine oxime
- DDiffuse bilateral hypoperfusion secondary to ictal propagation through commissural pathways, resulting in bihemispheric inhibitory surround suppression that overwhelms focal hyperemic changes
Show the answer and explanation
B. Markedly INCREASED perfusion (hyperperfusion) at the seizure focus — seizure activity dramatically increases local cerebral blood flow
During an active seizure (ICTAL), the seizure focus shows dramatically INCREASED perfusion (hyperperfusion) on brain SPECT because neuronal hyperactivity drives a large increase in local cerebral metabolic demand and blood flow. The ictal scan is injected as close to seizure onset as possible (within 30–60 seconds) to capture this hyperperfusion. Between seizures (INTERICTAL), the seizure focus typically shows DECREASED perfusion (hypoperfusion). Ictal-interictal SPECT subtraction (SISCOM — subtraction ictal SPECT co-registered to MRI) dramatically improves localization of the seizure focus for pre-surgical planning.
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