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Updated: Jul 5, 2025
Use of a Wireless Video-EEG System to Monitor Epileptiform Discharges Following Lateral Fluid-Percussion Induced Traumatic Brain Injury
Published on: June 21, 2019
Brain abscess - A rare confounding factor for diagnosis of post-traumatic epilepsy after lateral fluid-percussion
Jenni Kyyriäinen1, Pedro Andrade1, Xavier Ekolle Ndode-Ekane1
1A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, FI-70211 Kuopio, Finland.
Objective:
To assess the prevalence of brain abscesses as a confounding factor for the diagnosis of post-traumatic epilepsy (PTE) in a rat model of lateral fluid-percussion-induced (FPI) traumatic brain injury (TBI).
Methods:
This retrospective study included 583 rats from 3 study cohorts collected over 2009-2022 in a single laboratory. The rats had undergone sham-operation or TBI using lateral FPI. Rats were implanted with epidural and/or intracerebral electrodes for electroencephalogram recordings. Brains were processed for histology to screen for abscess(es). In abscess cases, (a) unfolded cortical maps were constructed to assess the cortical location and area of the abscess, (b) the abscess tissue was Gram stained to determine the presence of gram-positive and gram-negative bacteria, and (c) immunostaining was performed to detect infiltrating neutrophils, T-lymphocytes, and glial cells as tissue biomarkers of inflammation. In vivo and/or ex vivo magnetic resonance images available from a subcohort of animals were reviewed to evaluate the presence of abscesses. Plasma samples available from a subcohort of rats were used for enzyme-linked immunosorbent assays to determine the levels of lipopolysaccharide (LPS) as a circulating biomarker for gram-negative bacteria.
Results:
Brain abscesses were detected in 2.6% (15/583) of the rats (6 sham, 9 TBI). In histology, brain abscesses were characterized as vascularized encapsulated lesions filled with neutrophils and surrounded by microglia/macrophages and astrocytes. The abscesses were mainly located under the screw electrodes, support screws, or craniectomy. Epilepsy was diagnosed in 60% (9/15) of rats with an abscess (4 sham, 5 TBI). Of these, 67% (6/9) had seizure clusters. The average seizure frequency in abscess cases was 0.436 ± 0.281 seizures/d. Plasma LPS levels were comparable between rats with and without abscesses (p > 0.05).
Significance:
Although rare, a brain abscess is a potential confounding factor for epilepsy diagnosis in animal models of structural epilepsies following brain surgery and electrode implantation, particularly if seizures occur in sham-operated experimental controls and/or in clusters.
Insights
Brain abscesses, though rare, can confound epilepsy diagnosis in animal models of traumatic brain injury (TBI). These infections, particularly in sham-operated rats, may mimic or exacerbate seizure activity, complicating research findings.
Area of Science:
- Neuroscience
- Pathology
- Animal Models
Background:
- Post-traumatic epilepsy (PTE) is a significant clinical concern following traumatic brain injury (TBI).
- Animal models are crucial for understanding PTE mechanisms, but confounding factors can impact results.
- Brain abscesses, a potential complication of neurosurgery and electrode implantation, may influence epilepsy development and diagnosis.
Purpose of the Study:
- To determine the prevalence of brain abscesses in a rat model of lateral fluid-percussion-induced (FPI) TBI.
- To assess the potential of brain abscesses to confound the diagnosis of post-traumatic epilepsy (PTE) in this model.
Main Methods:
- Retrospective analysis of 583 rats from three cohorts (2009-2022) subjected to sham-operation or lateral FPI-TBI.
- Histological examination of brains for abscesses, including Gram staining for bacteria and immunostaining for inflammatory markers.
- Review of available MRI scans and measurement of plasma lipopolysaccharide (LPS) levels.
Main Results:
- Brain abscesses were found in 2.6% (15/583) of rats, located primarily under implanted hardware.
- Epilepsy was diagnosed in 60% (9/15) of rats with abscesses, with 67% experiencing seizure clusters.
- Plasma LPS levels did not differ significantly between rats with and without abscesses.
Conclusions:
- Brain abscesses, while infrequent, represent a potential confounding factor in epilepsy diagnosis within experimental TBI models.
- The occurrence of seizures in sham-operated controls or in clusters should raise suspicion for underlying abscesses.
- Careful histological screening for abscesses is essential in neurotrauma research involving electrode implantation.
