A 4-month-old female infant presents with clusters of brief flexor spasms beginning 3 weeks ago. Neuroimaging reveals agenesis of the corpus callosum and pathognomonic chorioretinal lacunae around the optic disc. The EEG shows the pattern marked **A** in the diagram. Which of the following best explains the electrophysiological finding marked **A**?
A. Bilateral occipital spikes that attenuate with eye opening, indicating photosensitive occipital lobe dysfunction
B. Generalized 3 Hz spike-wave discharges with normal background activity reflecting primary generalized epilepsy
C. Absence of the corpus callosum prevents interhemispheric synchronization, resulting in independent asynchronous bursts from each hemisphere
D. Symmetric, synchronous chaotic high-voltage polyspike activity arising from both hemispheres simultaneously due to cortical immaturity
Explanation
Why option 1 is right
The dissociated burst-suppression pattern (split-brain hypsarrhythmia) marked A is the pathognomonic EEG hallmark of Aicardi syndrome. Because the corpus callosum is absent or severely hypoplastic, the two cerebral hemispheres cannot communicate or synchronize their electrical activity. This results in independent, asynchronous, asymmetric bursts of high-voltage polyspike-and-slow-wave activity arising from each hemisphere separately, with intervening periods of relative voltage attenuation. This is the direct consequence of the anatomical disconnection between hemispheres (Aicardi J., Neuropediatrics; OMIM 304050).
Why each distractor is wrong
Option 2: This describes classic hypsarrhythmia seen in West syndrome (infantile spasms from other causes). Classic hypsarrhythmia is symmetric, synchronous, and chaotic—the opposite of the dissociated pattern in Aicardi syndrome. The key difference is the presence of an intact corpus callosum in West syndrome, allowing synchronization.
Option 3: Generalized 3 Hz spike-wave activity is characteristic of absence seizures and primary generalized epilepsy, not Aicardi syndrome. This pattern has a normal background and lacks the high-voltage polyspike bursts and suppression periods seen in split-brain hypsarrhythmia.
Option 4: Bilateral occipital spikes attenuating with eye opening suggest photosensitive occipital lobe epilepsy or a focal occipital process. While Aicardi syndrome may have occipital colobomas and heterotopias, the EEG pattern marked A is not primarily an occipital phenomenon and does not attenuate with eye opening.
High-YieldNEET PG
Dissociated burst-suppression (split-brain hypsarrhythmia) = absent corpus callosum in Aicardi syndrome; asynchronous hemispheric bursts cannot occur if the corpus callosum is intact.
Aicardi J., Neuropediatrics; OMIM 304050
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