Benign Neonatal Variants

Benign Neonatal Variants

John Giang, MD

Why it matters

Sharp transients are common in normal neonatal EEGs. Before you call one abnormal, check PMA, state, morphology, field and how often it recurs. Sporadic sharp waves appear in all preterm and term recordings.

Key points

• Monomorphic (monorhythmic) occipital delta: synchronous occipital delta waves in the very preterm infant. Expected from about 24–34 weeks (AES atlas, Table 3), or until about 30–32 weeks.
• Temporal sawtooth theta: the very preterm form of rhythmic temporal theta, seen as sharply contoured bitemporal theta bursts. Expected from about 24 to 30–32 weeks.
• Encoches frontales: bifrontal, symmetric, synchronous sharp transients, most prominent in quiet sleep. Seen from about 34–44 weeks (AES atlas), or up to 46 weeks.

• Anterior dysrhythmia: bifrontal semi-rhythmic delta, often seen with encoches. Seen from about 35–44 weeks.

• Location: frontal and centrotemporal sharps are usually benign. Midline and occipital sharps are more often abnormal.
• Temporal alpha bursts are normal preterm graphoelements that can be seen independently in left and right midtemporal regions that evolve directly from preceding temporal theta bursts and is maximally seen around 33 weeks and fades by 34 weeks.
• Temporal theta and delta brushes are normal preterm graphoelements. Temporal theta (maximal around 29-31 weeks) fades by 34 weeks. Delta brushes should be gone by 40–42 weeks.

• Multifocal sharps: a few per hour is normal in the first month. They should fade by about 49 weeks. How many is too excessive depends on the patient’s gestational age:
  • For a term baby (≥37 weeks or greater), having more than 11 multifocal sharp transients per hour can be interpreted as excessive and abnormal.
  • For a preterm baby (<37 weeks), having more than 13 multifocal sharp transients per hour can be interpreted as excessive and abnormal.
• Occipital sharp transients in healthy term infants: occasional independent bioccipital sharps can be normal, for example at 39 weeks. They become concerning if they are frequent, persistent, or lateralized.
• Red flags:
  • Negative polarity
  • A true field
  • An after-going slow wave that disrupts the background
  • Excessive/repetitive focal location, rhythmicity, or asymmetry

Common pitfalls

• Overcalling sparse, shifting multifocal sharps.
• Assuming frontal or centrotemporal sharps are always benign, even when they are excessive or persistently focal.
• Mistaking single-electrode artifact for a sharp wave.