A 3-week-old term-born infant is undergoing routine EEG screening. The recording shows bilateral synchronous diphasic sharp waves with initial negative deflection followed by a larger positive component, maximal over the frontal polar regions (Fp1, Fp2), with amplitude 80 µV and duration 0.8 seconds. These transients appear predominantly during quiet sleep. The pattern marked **A** in the diagram is observed. What is the most appropriate clinical interpretation of this finding?

Explanation

## Why option 1 is correct Frontal sharp transients (encoches frontales) are a **normal developmental EEG graphoelement** of the neonatal period. The clinical presentation in this case—bilateral synchronous diphasic sharp waves, maximal over frontal polar regions (Fp1, Fp2), amplitude 50–150 µV, duration 0.5–1.5 seconds, occurring during quiet sleep in a 3-week-old term infant—matches all defining characteristics of normal encoches frontales. These waves first appear at 34–35 weeks conceptional age, peak around 36–38 weeks, and persist normally through the first 4–6 weeks postterm. Their presence reflects normal maturation of bifrontal cortical-thalamic circuitry and requires no intervention (Mizrahi & Kellaway Atlas of Neonatal Electroencephalography, 3rd ed.; Volpe Neurology of the Newborn, 6th ed., Ch. 9). ## Why each distractor is wrong - **Option 2 (perinatal stroke)**: Unilateral focal sharp waves over central or other regions (as marked **B** in the diagram) are suggestive of perinatal stroke. The pattern in this case is **bilateral synchronous and symmetric**, which excludes stroke as a diagnosis. - **Option 3 (severe HIE with burst-suppression)**: Burst-suppression pattern (marked **C**) is characterized by long inter-burst intervals (>10 seconds), severe background suppression, and poor prognosis. The infant's EEG shows continuous background activity with normal sleep-wake cycling, not burst-suppression. - **Option 4 (West syndrome with hypsarrhythmia)**: Hypsarrhythmia (marked **D**) is a chaotic, high-amplitude, disorganized pattern seen in West syndrome, typically presenting after 3–6 months of age. The organized, bilateral synchronous, sleep-related pattern here is incompatible with hypsarrhythmia. **High-Yield:** Encoches frontales = bilateral synchronous frontal sharp waves in quiet sleep during the first 4–6 weeks postterm = **normal**; persistence beyond 6 weeks or marked asymmetry = abnormal. [cite:Mizrahi & Kellaway Atlas of Neonatal Electroencephalography, 3rd ed.; Volpe Neurology of the Newborn, 6th ed., Ch. 9]