How are ictal patterns identified in the visual analysis of neonatal electroencephalogram (EEG)?

Updated: Nov 08, 2018
  • Author: Samuel Koszer, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Ictal patterns

  • A generally accepted definition of what constitutes an ictal discharge has not been established. Some authors classify a discharge as ictal if it lasts at least 10 seconds, while other authors require a duration of at least 20 seconds. However, documented clinical and electrical seizures long have been described as lasting only a few seconds. With increasing age, electrical seizure activity becomes more frequent and longer in duration. Some have proposed that any rhythmic discharge accompanied by clinical changes be considered an ictal event, while rhythmic discharges lasting 10 seconds or longer be considered electroencephalographic events, regardless of whether behavioral changes occur.

  • Electrographic seizure discharges typically consist of rhythmic theta, alpha, delta, or beta waves or sharp waves or spikes that are focal or multifocal and vary in frequency and amplitude as the seizure progresses. The electroencephalographer must be aware that a variety of artifacts may resemble electroencephalographic seizures. Changing location, waveform morphology, or frequency suggests that the rhythmic activity is cerebral. The cerebral hemispheres in the neonate function relatively autonomously, so that, even when seizures spread, they may not spread to the other hemisphere. In cases when seizures do spread to the opposite hemisphere, the discharges often alternate from side to side. See the images below.

    Alternating seizure 1. An infant of 32 weeks' gest Alternating seizure 1. An infant of 32 weeks' gestational age at 40 weeks' conception with serratia meningoencephalitis. Surgery for drainage and dural repair was performed. This seizure begins at 00:36:12 in the right posterior quadrant with sharply contoured rhythmic delta at 1.5-2 Hz. Note the compressed nature of the time base, with each gradation representing 1 second. By 00:36:50, the spread to the left posterior quadrant is evident. The seizure continues in the next figure.
    Alternating seizure 2. In the first 10 seconds of Alternating seizure 2. In the first 10 seconds of the page, the electrographic seizure pattern in the right posterior quadrant attenuates, leaving behind the ongoing left posterior quadrant discharge. By 00:37:32, spread to T3 is evident. Seizures in neonates often alternate or "ping pong" from one side to the other.
    Electrographic seizure, surface positive. An infan Electrographic seizure, surface positive. An infant of 40 weeks' postconceptional age with partial seizures and hypocalcemia. An asymptomatic surface-positive electrographic seizure occurs at C4 with rhythmic spikes at 4 Hz.
    Electrographic seizure, focal 1. An infant of 40 w Electrographic seizure, focal 1. An infant of 40 weeks' postconceptional age with meningitis. This page contains 2 minutes of compressed EEG to demonstrate the entire extent of the seizure. At 00:37:32, repetitive T4 spikes begin, and, over the next 10 seconds, they become rhythmic spikes. This spreads centrally, and, by 00:39:05, the discharge begins to end with slow spike discharges at T4 and then completely attenuates.
    Electrographic seizure focal 2. Expanded time base Electrographic seizure focal 2. Expanded time base of seizure onset from the previous image. In the 2nd second, a clear rhythmic spike onset is seen in the right temporal region.
  • Focal spikes or sharp wave discharges consist of trains of rhythmic spikes or sharp waves that erupt focally out of the background activity, usually abruptly. While initially the amplitude may be low, it often increases as frequency decreases. Frequency of discharge varies most commonly in the delta to alpha bands (from 4-10 Hz), with the most frequent location in the rolandic areas. Discharge may spread to the adjacent cortex, but usually at a much slower pace in neonates than in older patients. The discharge may appear in homotopic areas of the other hemisphere. In general, these types of focal patterns correlate well with the clinical manifestations of seizures that are usually clonic.

  • Ictal focal EEG discharges do not necessarily indicate an underlying lesion because they often occur in the context of transient metabolic disorders following a mild hypoxic-ischemic event or a subarachnoid hemorrhage. In these situations, the background activities and state organizations usually are normal, and prognosis is good. Similar focal ictal discharges also may occur in the presence of acquired or congenital brain lesions. In these infants, the EEG often exhibits abnormalities of background, such as interhemispheric amplitude asymmetry and focal attenuation.

  • Pseudo-delta, -theta, -alpha, and -beta activity consists of runs of rhythmic monomorphic waves ranging from 0.5-15 Hz, therefore resembling normal background activities. Their amplitude varies from a low of 20-30 µV to a high of 200 µV, generally being higher for the slower frequencies. They may occur with a generalized distribution or a focal distribution. They can appear in all states, but, because they often occur in severely compromised neonates, state organization may be disrupted and background activities may be undifferentiated. These discharges can be seen (1) after severe hypoxic-ischemic insults, (2) after intraventricular hemorrhages, (3) in neonates with inborn metabolic defects, or (4) in infants with various chromosomal and dysgenetic brain abnormalities. See the image below.

    Pseudo theta. An infant of 35 weeks' gestational a Pseudo theta. An infant of 35 weeks' gestational age at age 3 days. Patient is having alternating jerking movements of all 4 extremities. Focal monorhythmic theta at 7 Hz is seen in the right temporal and left central regions, independently.

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