7.2 Neonatal & Pediatric EEG Patterns
Key Takeaways
- Neonatal EEG is interpreted by conceptional (postmenstrual) age (CA) - gestational age plus weeks since birth - because normal patterns change week to week as the brain matures.
- Background continuity matures with age: the very premature EEG is highly discontinuous (trace discontinu), the term newborn shows trace alternant in quiet sleep, and continuity increases toward continuous slow-wave sleep by term-plus.
- Neonatal graphoelements include delta brushes (most prominent ~28-34 weeks CA), encoches frontales (frontal sharp transients), and temporal/occipital sharp waves; excessive or persistently focal sharp activity is abnormal.
- Neonatal seizures are often subtle and focal with minimal motor signs, so an electrographic-only seizure on EEG can be the only sign - making neonatal recording an EEG-dependent diagnosis.
- Pediatric normal variants such as hypnagogic hypersynchrony, posterior slow waves of youth, and a posterior dominant rhythm that matures from ~4 Hz (4 months) to the adult 9-10 Hz (by ~8 years) must not be over-read as abnormal.
Why Neonatal and Pediatric Patterns Get Their Own Section
The ABRET content outline lists 'waveform analysis, pediatric and neonatal EEG pattern identification/description (normal/abnormal/normal variant)' as a knowledge area distinct from adult waveform analysis. The reason is physiologic: the neonatal and infant brain matures so rapidly that a pattern that is perfectly normal at 30 weeks is abnormal at 40 weeks. A technologist who applies adult norms to a neonate will mislabel normal immaturity as pathology, and miss subtle neonatal seizures that have almost no clinical signs.
Conceptional Age Is the Anchor
Conceptional age (CA), also called postmenstrual age, equals gestational age at birth plus the chronologic weeks since birth. Every neonatal pattern is judged against CA, not days since birth.
- A baby born at 28 weeks who is now 4 weeks old has a CA of 32 weeks, and the EEG should look like a 32-week brain.
- The technologist documents CA, birth history, medications, and behavioral state because normal features are both age- and state-dependent.
Background Continuity and State
The single most testable neonatal concept is continuity - how much of the record is active versus interburst quiescence.
| Conceptional Age | Expected Background |
|---|---|
| < 30 weeks | Highly discontinuous (trace discontinu) - high-voltage bursts separated by long, very low-voltage interburst periods |
| 30-34 weeks | More continuous when awake; delta brushes most prominent |
| 34-37 weeks | Increasing continuity; clearer state differentiation |
| Term (~40 weeks) | Trace alternant in quiet sleep (alternating higher- and lower-voltage segments); continuous activity in active sleep and wakefulness |
| Term + weeks | Continuous slow-wave sleep replaces trace alternant |
Neonates are scored by behavioral state - active (REM-like) sleep, quiet (non-REM) sleep, and wakefulness - using added physiologic channels (respiration, electrocardiogram, eye movements, chin electromyogram). A modified, reduced electrode array is used because the head is small.
Neonatal Graphoelements (Normal Age-Specific Transients)
The premature and term EEG contains transients that look 'sharp' but are normal for age. Recognizing them prevents over-reading.
| Graphoelement | Peak Age (CA) | Description | Significance |
|---|---|---|---|
| Delta brush (brush) | ~28-34 weeks | Slow delta wave with superimposed fast (8-20 Hz) activity riding on it | Normal hallmark of prematurity; persistence at term is abnormal |
| Encoches frontales | ~34-week to term | Frontal sharp transients, often bilateral and synchronous | Normal frontal graphoelement |
| Temporal/occipital sharp waves | Premature to term | Sporadic regional sharp transients | Normal in low numbers; frequent/persistently focal is abnormal |
| Trace alternant | Term, quiet sleep | Alternating higher- and lower-voltage segments | Normal quiet-sleep pattern of the term newborn |
The exam trap is calling delta brushes, encoches frontales, or occasional temporal sharp waves 'epileptiform.' They are normal maturational features. Abnormal neonatal findings include persistent or excessive discontinuity for age, lack of state differentiation, marked asymmetry/asynchrony, persistently focal sharp activity, and electrographic seizures.
Neonatal Seizures: An EEG-Dependent Diagnosis
Neonatal seizures are frequently subtle - eye deviation, lip-smacking, pedaling, apnea, or autonomic changes - and many are electrographic-only (visible on EEG with little or no clinical sign). This is why the EEG is often the only way to detect them. Neonatal electrographic seizures appear as evolving rhythmic discharges (changing in frequency, amplitude, and location) lasting at least ~10 seconds, usually focal or multifocal rather than the generalized synchronous discharges seen in older children, because the immature brain cannot sustain bilateral synchrony.
The technologist's role is to capture and clearly annotate these events and to escalate per critical-value protocol.
Pediatric Normal Patterns and Maturation
Once past the neonatal period, the child's EEG continues to mature. The posterior dominant rhythm (PDR) frequency is the most testable progression.
| Age | Expected Posterior Dominant Rhythm |
|---|---|
| 3-4 months | ~3.5-4 Hz reactive posterior rhythm appears |
| 6 months | ~5 Hz |
| 12 months | ~6 Hz |
| 3 years | ~8 Hz (reaches adult lower limit) |
| ~8 years and older | ~9-10 Hz (adult range) |
Pediatric normal variants that must not be over-read:
- Hypnagogic hypersynchrony: high-amplitude, rhythmic 3-5 Hz bursts at drowsiness onset in children ~3 months to ~12 years. It is not a spike-wave burst - it lacks spikes and resolves with deeper sleep.
- Posterior slow waves of youth: delta intermixed with the PDR posteriorly in children/adolescents; suppresses with eye opening, which proves it is benign.
- Sleep spindles appear by ~2-3 months and may be asynchronous between hemispheres until ~2 years (normal asynchrony), then become synchronous.
- Sharply contoured vertex waves are common and prominent in young children and are normal.
Practical Recording Adaptations
Pediatric recordings demand behavioral flexibility: allow caregiver presence, distract the child, prioritize sleep capture (often the highest-yield state), and lower the sensitivity number's effect appropriately because pediatric amplitudes are typically higher than adults (so a setting like 10 uV/mm may be needed to keep high-amplitude activity on scale). Always preserve 10-20 measurement accuracy on the small head and document state, CA (for neonates), and any deviation. The unifying principle: interpret by age and state, and never apply adult norms to a developing brain.
An infant was born at 30 weeks gestation and is now 3 weeks old. At what conceptional age should the technologist interpret this EEG?
A 31-week conceptional-age neonate shows slow delta waves with superimposed fast 10-18 Hz activity riding on them. How should the technologist regard this finding?
Why is EEG often the only way to detect seizures in a neonate?
A drowsy 5-year-old shows high-amplitude rhythmic 3-5 Hz bursts at sleep onset that resolve with deeper sleep and contain no spikes. The correct interpretation is: