EEG and the neuropathology in premature neonates with intraventricular hemorrhage

The American Clinical Neurophysiology Society Guideline on Indications for Continuous Electroencephalography Monitoring in Neonates

PURPOSE

Continuous EEG (cEEG) monitoring is increasingly used in the management of neonates with seizures. There remains debate on what clinically relevant information can be gained from cEEG in neonates with suspected seizures, at high risk for seizures, or with definite seizures, as well as the use of cEEG for prognosis in a variety of conditions. In this guideline, we address these questions using American Clinical Neurophysiology Society structured methodology for clinical guideline development.

METHODS

A working group was formed from American Clinical Neurophysiology Society membership with expertise in neonatal cEEG and a set of priority questions developed. We performed literature searches in PubMed and EMBASE to identify relevant studies. Evidence tables were compiled from extracted data and quality assessments performed. A modification of the GRADE process was used to evaluate the body of evidence and draft recommendations.

RESULTS

Our working group identified six priority questions to evaluate the accuracy of cEEG for neonatal seizure diagnosis and the formulation of prognosis. An initial literature search yielded 18,167 results, which were distilled to a set of 217 articles. Overall, the quality of evidence for most priority questions was rated as very low and we provided conditional recommendations based on published literature and expert consensus. For each priority question, we also considered the benefits and harms of cEEG, with relative harms considered to be far less than the potential benefits across recommendations.

CONCLUSIONS

We present evidence-based clinical guidelines regarding indications for cEEG monitoring in neonates. Considering resource utilization and feasibility, when cEEG monitoring results have a likelihood of altering clinical decision making, the authors felt the resource investment was justifiable.

Clinical value of cortical bursting in preterm infants with intraventricular haemorrhage

BACKGROUND

In healthy preterm infants, cortical burst rate and temporal dynamics predict important measures such as brain growth. We hypothesised that in preterm infants with germinal matrix-intraventricular haemorrhage (GM-IVH), cortical bursting could provide prognostic information.

AIMS

We determined how cortical bursting was influenced by the injury, and whether this was related to developmental outcome.

STUDY DESIGN

Single-centre retrospective cohort study at University College London Hospitals, UK.

SUBJECTS

33 infants with GM-IVH ≥ grade II (median gestational age: 25 weeks).

OUTCOME MEASURES

We identified 47 EEGs acquired between 24 and 40 weeks corrected gestational age as part of routine clinical care. In a subset of 33 EEGs from 25 infants with asymmetric injury, we used the least-affected hemisphere as an internal comparison. We tested whether cortical burst rate predicted survival without severe impairment (median 2 years follow-up).

RESULTS

In asymmetric injury, cortical burst rate was lower over the worst- than least-affected hemisphere, and bursts over the worst-affected hemisphere were less likely to immediately follow bursts over the least-affected hemisphere than vice versa. Overall, burst rate was lower in cases of GM-IVH with parenchymal involvement, relative to milder structural injury grades. Higher burst rate modestly predicted survival without severe language (AUC 0.673) or motor impairment (AUC 0.667), which was partly mediated by structural injury grade.

CONCLUSIONS

Cortical bursting can index the functional injury after GM-IVH: perturbed burst initiation (rate) and propagation (inter-hemispheric dynamics) likely reflect associated grey matter and white matter damage. Higher cortical burst rate is reassuring for a positive outcome.

Cerebral gray matter injuries in infants with intraventricular hemorrhage

While intraventricular hemorrhage (IVH) predominantly damages the periventricular white matter, it induces substantial injury to the cerebral gray matter. IVH destroys the germinal matrix, suppresses neurogenesis, and disrupts corticogenesis, thereby reducing the number of neurons in the upper cortical layer and volume of the cerebral gray matter. The pathogenesis of gray matter injury is attributed to IVH-induced oxidative stress, inflammation, and mass effect damaging the germinal matrix as well as to post-hemorrhagic ventricular dilation (PHVD). The IVH-induced cerebral gray matter injury and PHVD contribute to cognitive deficits and neurobehavioral disorders. Neuroimaging has enhanced our understanding of cerebral gray matter injury and is a valuable predictor of neurodevelopmental outcomes. Evidence from therapies tested in preclinical models and clinical trials suggests that strategies to promote neurogenesis, reduce cerebral inflammation and oxidative stress, and remove blood clots from the ventricles might enhance the outcome of these infants. This review offers an integrated view of new insights into the mechanisms underlying gray matter injury in premature infants with IVH and highlights the imminent therapies to restore neurodevelopmental dysfunction in IVH survivors.

Early Detection of Preterm Intraventricular Hemorrhage From Clinical Electroencephalography

OBJECTIVES

Intraventricular hemorrhage is a common neurologic complication of extremely preterm birth and leads to lifelong neurodevelopmental disabilities. Early bedside detection of intraventricular hemorrhage is crucial to enabling timely interventions. We sought to detect early markers of brain activity that preempt the occurrence of intraventricular hemorrhage in extremely preterm infants during the first postnatal days.

DESIGN

Cross-sectional study.

SETTING

Level III neonatal ICU.

PATIENTS

Twenty-five extremely preterm infants (22-28 wk gestational age).

MEASUREMENTS AND MAIN RESULTS

We quantitatively assessed electroencephalography in the first 72 hours of postnatal life, focusing on the electrical burst activity of the preterm. Cranial ultrasound was performed on day 1 (0-24 hr) and day 3 (48-72 hr). Outcomes were categorized into three classes: 1) no intraventricular hemorrhage (grade 0); 2) mild-moderate intraventricular hemorrhage (grades 1-2, i.e., germinal matrix hemorrhages or intraventricular hemorrhage without ventricular dilatation, respectively); and 3) severe intraventricular hemorrhage (grades 3-4, i.e., intraventricular hemorrhage with ventricular dilatation or intraparenchymal involvement). Quantitative assessment of electroencephalography burst shapes was used to preempt the occurrence and severity of intraventricular hemorrhage as detected by ultrasound. The shapes of electroencephalography bursts found in the intraventricular hemorrhage infants were significantly sharper (F = 13.78; p < 0.0001) and less symmetric (F = 6.91; p < 0.015) than in preterm infants without intraventricular hemorrhage. Diagnostic discrimination of intraventricular hemorrhage infants using measures of burst symmetry and sharpness yielded high true-positive rates (82% and 88%, respectively) and low false-positive rates (19% and 8%). Conventional electroencephalography measures of interburst intervals and burst counts were not significantly associated with intraventricular hemorrhage.

CONCLUSIONS

Detection of intraventricular hemorrhage during the first postnatal days is possible from bedside measures of brain activity prior to ultrasound confirmation of intraventricular hemorrhage. Significantly, our novel automated assessment of electroencephalography preempts the occurrence of intraventricular hemorrhage in the extremely preterm. Early bedside detection of intraventricular hemorrhage holds promise for advancing individual care, targeted therapeutic trials, and understanding mechanisms of brain injury in neonates.

The Neurological Outcome of Isolated PVL and Severe IVH in Preterm Infants: Is It Fair to Compare?

OBJECTIVE

We compared the neurological outcome of isolated periventricular leukomalacia and severe intraventricular hemorrhage in a cohort of very low birth weight infants born and managed at single tertiary-care center in Saudi Arabia.

METHODS

We undertook a descriptive retrospective chart review of the neurological status of very low birth weight infants who were born and managed over a 5-year period at King Abdulaziz Medical City, Riyadh. The neurological outcome of neonates with isolated periventricular leukomalacia and severe intraventricular hemorrhage (grades III and IV) was studied and compared in relation to developmental delay and cerebral palsy.

RESULTS

A total of 20 patients with isolated periventricular leukomalacia and 26 with severe intraventricular hemorrhage (grades III and IV) were identified for this study. Of 20 patients with isolated periventricular leukomalacia, 9 (45%) had good developmental outcome and 11 (55%) had bad developmental outcome. Of 26 patients of severe intraventricular hemorrhage, 14 (54%) had good developmental outcome and 12 (46%) had bad developmental outcome (P = 0.55). Significant motor neurological deficit affecting function is distributed as follows: 11/20 (55%) in the isolated periventricular leukomalacia group and 7/26 (27%) in the severe intraventricular hemorrhage group (P = 0.05). Cerebral palsy was diplegic in 7/11 (64%) and quadriplegic in 4/11 (36%) in the isolated periventricular leukomalacia group, and hemiplegic 3/7 (43%), diplegic in 1/7 (14%), and quadriplegic in 3/7 (43%) in the severe intraventricular hemorrhage group (P = 0.03). Distribution of the neurological outcome according to periventricular leukomalacia grade was as follows: for periventricular leukomalacia grade I (n = 8), 6/8 (75%) had good neurological outcome and 2/8 (25%) had bad neurological outcome. In periventricular leukomalacia grade II (n = 4), good neurological outcome was seen in three patients (75%) and bad neurological outcome was seen in one patient (25%). All patients (n = 8) with periventricular leukomalacia grade III had bad outcome (P < 0.01).

CONCLUSION

About half of patients with isolated periventricular leukomalacia and severe intraventricular hemorrhage had a poor developmental outcome. However, the severity of cerebral palsy was greater in the isolated periventricular leukomalacia patients and correlates highly with periventricular leukomalacia grade. Symmetrical diplegic cerebral palsy is the most common motor deficit associated with isolated periventricular leukomalacia, whereas asymmetrical hemiplegic cerebral palsy is seen exclusively with severe intraventricular hemorrhage.

Early abnormal amplitude-integrated electroencephalography (aEEG) is associated with adverse short-term outcome in premature infants

BACKGROUND

In preterm infants with IVH the electrocortical background activity is affected and there is a correlation between the severity of cerebral injury to the degree of depression, however the usefulness of the early aEEG recordings has hardly been determined.

AIM

To identify early aEEG features that could be used as prognostic markers for severe brain injury in prematures.

METHODS

In 115 infants, 25-32 wk GA, aEEG recordings during the first 72 h of life were correlated with head ultrasound findings. Continuity (Co), sleep-wake cycling (Cy) and amplitude of the lower border (LB) of the aEEG were evaluated by semi-quantitative analysis.

RESULTS

The infants were divided into four groups based on head ultrasound findings: A (n=72, normal), B [n=16, grades 1-2 intraventricular hemorrhage (IVH)], C (n=21, grades 3-4 IVH) and D (n=6, periventricular leukomalacia). 18 infants (16 of group C and 2 of group D) died during hospitalization. Significantly lower values of all aEEG features were found in group C infants. The presence of pathological tracings (burst-suppression, continuous low-voltage, flat trace) or discontinuous low-voltage (DLV), the absence of Cy and LB<3 μV in the initial aEEG displayed a sensitivity of 88.9%, 63% and 51.9% respectively, for severe brain injury. Logistic regression of aEEG features and GA to the presence or absence of severe injury revealed that only Co was significantly correlated to outcome. Using this feature 83.19% of cases were correctly classified.

CONCLUSION

Pathological tracings or DLV in the initial aEEG is predictive for poor short-term outcome in premature neonates.

Intracranial hemorrhage in the preterm infant: understanding it, preventing it

New discoveries in neonatal imaging, cerebral monitoring, and hemodynamics, and greater understanding of inflammatory and genetic mechanisms involved in intracranial hemorrhage (ICH) in the preterm infant are creating opportunities for innovative early detection and prevention approaches. This article covers the spectrum of ICH in the preterm infant, including germinal matrix intraventricular hemorrhage, its complications, and associated phenomena, such as the emerging role of cerebellar hemorrhage. The overall aim of this article is to review the current knowledge of the mechanisms, diagnosis, outcome, and management of preterm ICH; to revisit the origins from which they develop; and to discuss future expectations.

Early amplitude-integrated EEG correlates with cord TNF-alpha and brain injury in very preterm infants

AIM

To investigate if the early electroencephalogram (EEG) and amplitude-integrated EEG (aEEG) in very preterm infants is affected by perinatal inflammation and brain injury, and correlates with long-term outcome.

METHODS

Sixteen infants born at 24-28 gestational weeks (median 25.5) had continuous EEG/aEEG during the first 72 h of life. Minimum and maximum EEG interburst intervals (IBI), and aEEG amplitudes were semi-automatically quantified and averaged over the recording period. Neonatal brain injury was diagnosed with repeated cranial ultrasound investigations. Nine cytokines from four time-points were analyzed during the first 72 h (umbilical cord blood, 6, 24 and 72 h), and outcome was assessed at 2 years of corrected age.

RESULTS

Infants with neonatal brain injury (n=9) had prolonged IBI, 11.8 (9.6-23.2) sec versus 8.2 (7.1-11.6) sec in infants (n=7) without brain damage (p=0.005). Handicap at 2 years (n=8, including two infants without neonatally diagnosed brain injury) was associated with prolonged neonatal IBI and lower aEEG amplitudes. Also aEEG amplitudes were decreased in infants with neonatal brain injury. There was a significant positive correlation between the averaged IBI and cord blood TNF-alpha (rs=0.595, p=0.025).

CONCLUSION

Early EEG depression is associated with increased cord blood TNF-alpha, neonatal brain damage and handicap at 2 years.

Background patterns and sleep-wake cycles on amplitude-integrated electroencephalography in preterms younger than 30 weeks gestational age with peri-/intraventricular haemorrhage

AIM

The objective of this prospective study was to evaluate the influence of peri-/intraventricular haemorrhage (PIVH) grades I-IV on amplitude-integrated electroencephalographic (aEEG) activity in preterm infants<30 weeks gestational age (GA).

METHODS

The aEEG tracings of the first 2 weeks of life of 56 preterm infants younger than 30 weeks GA (2 groups: group A=23-26 weeks GA, group B=27-29 weeks GA) born during a 4-year period with PIVH grades I-IV were assessed for the relative duration of four background aEEG activity patterns (continuous pattern, discontinuous high-voltage pattern, discontinuous low-voltage pattern and nearly isoelectric pattern), the presence of seizure activity and the appearance of sleep-wake cycles and compared to the tracings of 75 neurologically healthy preterms without PIVH.

RESULTS

Analysis of aEEG background activity showed a decrease of continuous activity whereas discontinuous activity increased in both groups with larger haemorrhages (grades III and IV) and when compared to controls. Suspected seizure activity was more common with increasing degree of bleeding in group A (50% with PIVH I or II, 75% with PIVH III or IV) and when compared to controls and was the same with increasing degree of bleeding in group B (47% with PIVH I or II, 45% with PIVH III or IV). Sleep-wake cycles were less common with larger haemorrhages in both groups (group A: 41% with PIVH I or II, 25% with PIVH III or IV; group B: 52% with PIVH I or II, 9% with PIVH III or IV) and when compared to controls.

CONCLUSIONS

The aEEG characteristics of severe PIVH consist in a combination of a more discontinuous background pattern, a lack of sleep-wake cycles and a higher likelihood of seizure activity when compared to age-matched controls.

Continuous electroencephalography monitoring of the preterm infant

Continuous electroencephalography (EEG) monitoring provides clinically relevant information in preterm infants. Acute changes during development of intraventricular hemorrhage and white matter injury are associated with EEG and amplitude-integrated EEG (aEEG) deterioration. The early EEG background is also correlated with outcome in preterm infants, although other problems associated with prematurity may influence the long-term prognosis. The limitations of EEG monitoring should be well-understood by users and the continuous EEG monitor should be used as a complement to the standard EEG.

Electroencephalography and brain damage in preterm infants

Electroencephalography (EEG) is a sensitive method for detection of brain injury in preterm infants. Although the acute and chronic EEG changes are mainly non-specific regarding type of damage, they correlate with later neurological and cognitive function. In infants developing brain white matter damage, acute EEG findings include depression of background activity and presence of epileptic seizure activity. The chronic EEG changes associated with white matter injury and abnormal neurological development include delayed maturation, and presence of abundant Rolandic sharp waves. Cognitive limitations in preterm infants have been associated with changes in various sleep measures in EEG's recorded at full term. Continuous EEG-monitoring during neonatal intensive care shows that cerebral electrical activity during this vulnerable period can be affected by several extracerebral factors, e.g. cerebral blood flow, acidosis and some commonly used medications. For diagnosis of brain damage in preterm infants with neurophysiological methods, a combination of early continuous EEG monitoring during the initial intensive care period and full EEG, performed at later stages, is probably optimal.

Electronic medical devices: a primer for pathologists

CONTEXT

Electronic medical devices (EMDs) with downloadable memories, such as implantable cardiac pacemakers, defibrillators, drug pumps, insulin pumps, and glucose monitors, are now an integral part of routine medical practice in the United States, and functional organ replacements, such as the artificial heart, pancreas, and retina, will most likely become commonplace in the near future. Often, EMDs end up in the hands of the pathologist as a surgical specimen or at autopsy. No established guidelines for systematic examination and reporting or comprehensive reviews of EMDs currently exist for the pathologist.

OBJECTIVE

To provide pathologists with a general overview of EMDs, including a brief history; epidemiology; essential technical aspects, indications, contraindications, and complications of selected devices; potential applications in pathology; relevant government regulations; and suggested examination and reporting guidelines.

DATA SOURCES

Articles indexed on PubMed of the National Library of Medicine, various medical and history of medicine textbooks, US Food and Drug Administration publications and product information, and specifications provided by device manufacturers.

STUDY SELECTION

Studies were selected on the basis of relevance to the study objectives.

DATA EXTRACTION

Descriptive data were selected by the author.

DATA SYNTHESIS

Suggested examination and reporting guidelines for EMDs received as surgical specimens and retrieved at autopsy.

CONCLUSIONS

Electronic medical devices received as surgical specimens and retrieved at autopsy are increasing in number and level of sophistication. They should be systematically examined and reported, should have electronic memories downloaded when indicated, will help pathologists answer more questions with greater certainty, and should become an integral part of the formal knowledge base, research focus, training, and practice of pathology.

Lowered electroencephalographic spectral edge frequency predicts the presence of cerebral white matter injury in premature infants

OBJECTIVE

Current methods for early identification of cerebral white matter injury in the premature infant at the bedside are inadequate. This study investigated the utility of advanced spectral analysis of the neonatal electroencephalogram (EEG) in the early diagnosis of white matter injury in the premature infant. The critical measurement used, suggested largely by previous studies in animal models, was the spectral edge frequency (SEF), calculated here as the frequency below which 90% of the power in the EEG exists.

METHODS

Fifty-nine very low birth weight infants (87% of eligible infants) had electrodes placed over the central and parietal regions (C3, P3, C4, and P4 sites according to the 10-20 international system) for the collection of EEG amplitude, intensity, and SEF. All averaged signals were analyzed off-line using software (Chart Analyzer; BrainZ Instruments, Auckland, NZ). All infants had a magnetic resonance imaging scan at term to identify the presence and severity of white matter injury.

RESULTS

There was no significant difference between conventional EEG amplitude and intensity for infants with or without evidence of white matter injury. However, premature infants with increasingly severe white matter injury had progressively lower SEFs compared with infants who did not exhibit white matter injury.

CONCLUSIONS

These data suggest that SEF-based measures are useful for defining the presence and severity of white matter injury at the bedside.

Occipital sawtooth: a physiological EEG pattern in very premature infants

OBJECTIVE

To evaluate EEG maturational features in preterm infants below 27 weeks postmenstrual age.

METHODS

EEGs recorded from 5 preterm infants (postmenstrual age 24-26 weeks) were examined and selected maturational features were scored and quantified. The five infants also had serial cranial ultrasound scans (US) and magnetic resonance images of the brain within the first weeks after birth.

RESULTS

Background activity was markedly discontinuous in all patients and very variable. Temporal sawtooths occurred but less frequently than in older preterm infants. All 5 infants also showed a particular novel feature, characterized by rhythmic, regularly shaped, medium-high amplitude 4-7 Hz activities, lasting 0.5-3 s and located in the occipital regions. This pattern was symmetrical but sometimes asynchronous.

CONCLUSIONS

Occipital sawtooth, so called because it shares shape and frequency with temporal sawtooth but has an occipital localisation, constitutes a physiological EEG pattern characteristic of premature infants between 24 and 26 weeks of postmenstrual age.

Electroencephalography in infants with periventricular leukomalacia: prognostic features at preterm and term age

Cystic periventricular leukomalacia represents the most severe white-matter lesion in preterm infants and its occurrence accounts for most cases of neurologic impairment in these subjects. Electroencephalographic (EEG) findings and their prognostic value in relation to motor and cognitive outcome were investigated in a group of preterm infants affected by different degrees of cystic periventricular leukomalacia. EEG recordings were carried out in the early postnatal period (first 2 weeks of life) on 24 infants and at term age on 29. In the early postnatal period, background EEG abnormalities ("dysmaturity") were significantly more apparent in affected infants than in a control group, and, among infants with cystic periventricular leukomalacia, this parameter related to the occurrence of cerebral palsy; moreover, at the same age, the incidence of abnormal EEG transients seemed to show a correlation with cognitive outcome. At term age, these latter abnormalities were significantly more apparent in neonates with cystic periventricular leukomalacia than in control subjects, but they did not show any prognostic value. In conclusion, these data indicate that, during the early postnatal period, the EEG is a useful diagnostic and prognostic tool for preterm infants with white-matter lesions, whereas at term age, the role of EEG tracings appears secondary.

Neonatal EEG: a powerful tool in the assessment of brain damage in preterm infants

Serial EEG recordings beginning immediately after birth are not only of great diagnostic and prognostic value but also useful to elucidate the timing and the mode of brain injuries in the preterm newborn. It is extremely useful to distinguish between acute stage and chronic stage EEG abnormalities. The former is characterized by findings of acute depression such as increased discontinuity, decreased faster frequency activities, and lowered amplitudes. The latter mainly includes dysmature patterns and disorganized patterns. The timing of brain insult can be assessed by considering EEG findings in relation to the time of birth. Different modes of brain injury are associated with different types of EEG abnormalities and different types of neurological outcome. Sudden strong brain insults are usually associated with findings of severe depression followed by disorganized pattern and later cerebral palsy, while persistent mild insults are usually associated with prolonged mild depression followed by dysmature pattern and later mental retardation. Routine serial EEG studies in preterm infants demonstrated that one fourth of cerebral palsies in these infants were of antenatal origin, two thirds of perinatal origin and postnatal injuries played the least role. Periventricular leucomalacia (PVL) manifesting itself on the ultrasound in the late neonatal period and suggesting postnatal origin was often found to be of antenatal origin with an EEG soon after birth. PVL without apparent causes was often associated with abnormal fetal heart rate patterns and early neonatal EEG abnormalities, and considered to have originated in the antepartum period.

[Emergency electroencephalography during perinatal cerebral intensive care: indications and results]

The main contribution of EEG during intensive care in infants with hypoxic-ischemic encephalopathy is i) to help determine whether infants with subtle clinical manifestations present with epileptic seizures, ii) to determine whether paralyzed or heavily sedated infants present with convulsive phenomena, iii) to assess the therapeutical response to anticonvulsants, 4) to contribute, in combination with ultrasound scanning, to diagnostic evaluation of the severity of lesions, and to provide valuable prognostic informations via the analysis of the background activity, as normal EEG is highly predictive of normal outcome, whereas various abnormal EEG features are constantly associated with subsequent major neurological abnormalities or death. These EEG features are readily available from a very early stage and may both precede and be prognostically more sensitive than information obtained from ultrasound. Recording of neonatal electroencephalogram requires awareness of the normal development of electroencephalographic features in the newborn, skilled technicians, and experienced readers of EEG tracings.

Prognostic value of neonatal electroencephalography in premature newborns less than 33 weeks of gestational age

In a prospective study of 417 premature neonates born before 33 weeks' gestational age, neonatal tracings were reviewed to evaluate the use of EEG in prognosis of neurological injuries. The population was divided into two groups: Group 1, infants who died before the age of 1, and Group 2, survivors in which two categories of motor development were considered. Category A, were abnormal, and Category B, were always normal. Positive rolandic sharp waves (PRSW), which reflect white matter injury, occurred equally in both groups, indicating a similar incidence of white matter damage in Groups 1 and 2. In Group 2, there was a significant correlation of PRSW with developmental motor sequelae (Category A). A frequency of PRSW above 2/min (suggesting more severe periventricular white matter injury) and seizures were significantly more prevalent in Group 1 than in Group 2 and in Category A of Group 2 than in Category B. Background abnormalities occurred equally in both subgroups of extremely premature infants (< or = 28 weeks' gestation) they were significantly more numerous in the subgroup of very premature infants (between 28 and 33 weeks' gestation) who died, than in the subgroup of very premature infants who survived. This study shows the potential utility of using neonatal EEG in association with transfontanellar ultrasonography in anticipating the neurological development of very (> 28 weeks' gestation) and extremely (< or = 28 weeks' gestation) premature newborns.

Prognostic value of abnormal EEG transients in preterm and full-term neonates

The prognostic value of abnormal EEG transients was investigated in 362 subjects submitted to EEG recording during the neonatal age and followed-up at least until the 12th month of corrected age. The incidence of negative and positive spikes and sharp waves, of rhythmic sharp theta and delta activities and of alpha discharges were evaluated by means of a quantitative score. These abnormal EEG transients appeared to be generally rare and even absent in a large number of subjects. In infants with normal outcome their incidence tends to increase from low postmenstrual ages towards term period. Full-term newborns with abnormal neurological outcome presented a significantly higher incidence of these transients. Preterm infants with unfavourable evolution showed a higher incidence only when submitted to EEG recording at around term age. However, no difference between subjects with normal and abnormal outcome was detected in preterm infants when evaluated at low postmenstrual ages. The hypothesis that at low postmenstrual ages brain damage might, on the one hand, give rise to abnormal transients and, on the other, alter the "capability' of manifesting them (together with other EEG maturational aspects), might explain these results.

Neonatal encephalopathies as classified by EEG-sleep criteria: severity and timing based on clinical/pathologic correlations

Neonatal encephalopathies can be characterized in functional terms using electroencephalography. Severity of an encephalopathic state can also be estimated by electrographic interpretation independent of the time of disease process onset. Moderately or markedly abnormal electroencephalographic patterns on serial studies are highly correlated with neurologic sequelae in survivors. Electroencephalography is rarely pathognomonic or specific in determining when a condition initially occurred. However, electroencephalographic abnormalities are associated with different clinical situations, and brain lesions documented on neuroimaging or with postmortem neuropathologic examination are observed in infants with certain abnormal electrographic patterns. When interpreted in the context of history, clinical findings, and other laboratory information, the neurophysiologic studies augment the understanding of both the severity and timing of an encephalopathic state.