CABO SAN LUCAS, MEXICO — What looks like damage from hypoxic ischemic encephalopathy on neonatal brain imaging actually can be caused by intracranial infection, Robert A. Zimmerman, M.D., said at a conference on obstetrics, gynecology, perinatal medicine, neonatology, and the law.
Always correlate clinical findings and laboratory results with images of brain abnormalities to detect intracranial infections and to avoid attributing the infant's problems to hypoxic ischemic brain injury, said Dr. Zimmerman, chief of pediatric neuroradiology at Children's Hospital of Philadelphia.
He described several infections that could be confused with hypoxic ischemic encephalopathy:
▸ Acute cytomegalovirus infection, the most common intracranial infection that occurs in utero, causes fetal brain abnormalities in the second and third trimesters. Edema in the brain seen on imaging shortly after birth may simulate a toxic ischemic brain injury.
“The clinical work-up of the patient turns out to be critical” to differentiate the two, he said at the conference, sponsored by Boston University and the Center for Human Genetics.
▸ Neonatal meningitis may result from exposure to a pathogen in utero, at the time of delivery, or in the neonatal nursery.
Both gram-negative and gram-positive bacterial meningitis can be a problem, since neonates lack a functional immune system to resist CNS infection.
Severe brain swelling secondary to E. coli meningitis infection can look like severe brain swelling from hypoxic ischemic brain injury, Dr. Zimmerman said.
When infection damages areas of the brain rather than causing complete brain injury, this also can be confused with hypoxic ischemic injury. Cortical infarction from infection with streptococci or gram-negative rods, for example, may be confusing.
Areas of cortical hyperintensity on imaging due to these infections can simulate damage from a partial prolonged asphyxia.
Clinical findings become extremely important in differentiating the two, he said.
Infarction of the basal ganglia due to streptococcal infection may be confused with a profound asphyxial injury, but a gadolinium-enhanced MRI can highlight changes characteristic of meningitis to help make the diagnosis.
The most severe forms of infection with Citrobacter or Serratia cause diffuse brain swelling with supratentorial necrosis due to lack of perfusion, which can look like a severe hypoxic ischemic brain injury. The clinical findings and cerebral spinal fluid analysis look quite different between the two problems, however. Close to half of patients with meningitis due to Citrobacter or Serratia also will show brain abscesses on imaging.
▸ Herpes encephalitis can result from infection in utero or from infection acquired at birth. Symptoms from infection at birth typically present as seizures and fever days or weeks after birth. Herpes encephalitis can be a focal or diffuse disease. The diffuse form of herpes encephalitis causes cytotoxic edema that can mimic a hypoxic-ischemic type of injury on imaging. Herpes usually is easily recognizable on good-quality MRI scans with diffusion studies and using gadolinium enhancement.
In general, MRI is the best modality for imaging the neonatal central nervous system; CT scans can help you look for brain calcifications, Dr. Zimmerman commented.