Approach Considerations
Delayed diagnosis of neonatal meningitis is a potentially critical pitfall. Failure to perform a lumbar puncture and detect infection in a neonate with mild fever and minimal, nonspecific clinical findings is problematic; all neonates in whom meningitis might be the cause of symptoms should undergo CSF examination. Delay in treatment because of equivocal laboratory screening tests or because findings are altered by prior partial treatment may cause significant harm.
In a 2001 survey of pediatricians, “meningitis or other infectious disease” and “newborn conditions other than congenital vision/hearing loss” were the 2 most frequent bases reported for malpractice suits. [28] In this survey, “the most prevalent condition for which claims were filed against pediatricians was neurological impairment of an infant. Thirty percent of claims paid were for this condition alone. However, the second most prevalent condition, meningitis, resulted in a higher percentage of paid claims (46%) and a higher total and average indemnity.”
Laboratory Studies
Suspected bacterial infection is often, but not uniformly, confirmed by positive results from cultures of cerebrospinal fluid (CSF) or blood. CSF cultures should be obtained in all symptomatic infants; despite the close relationship between bacterial sepsis and meningitis, it has been estimated that 15-30% of infants with CSF-proven meningitis will have negative blood cultures. [29]
A study from Duke emphasized that with the exception of CSF culture, no single CSF value can be relied upon to exclude neonatal meningitis. [30] The onus is on the clinician to justify initiation of antimicrobial and antiviral therapy, regardless of the CSF values.
Polymerase chain reaction (PCR) assay is a powerful diagnostic tool with excellent sensitivity and specificity. It permits identification of group B streptococcal (GBS) antigen in urine or CSF, and it is the standard for identification of herpes simplex virus (HSV) and enterovirus in CSF. In neonates, PCR is 71-100% sensitive for HSV but 98-99% specific. [16] If initial HSV PCR is negative and HSV meningitis is suspected, a repeat lumbar puncture 5-7 days later may be useful. Blood in the CSF can also lead to false-negative results.
As PCR becomes more widely available, recognition of enteroviral infections has increased. [12] Additionally, PCR for human parechovirus-3 is becoming more widely available.
Rapid screening is available with latex particle agglutination (LGA) testing of urine, which can be performed for GBS, E coli, and Streptococcus pneumoniae. Unfortunately, the presence of GBS antigen does not prove invasive disease.
If vesicles are present on the skin, evaluation for HSV infection should include cultures of fluid from these vesicles. Swabs of the nasopharynx, conjunctiva, and rectum have also been used to identify viral agents. DNA from HSV or enteroviruses can be identified from either vesicles or CSF by using PCR.
It should be kept in mind that interpretation of CSF findings is more difficult in neonates than in older children, especially in premature infants whose more permeable blood-brain barrier causes higher levels of glucose and protein.
The classic finding of decreased CSF glucose, elevated CSF protein, and pleocytosis is seen more with gram-negative meningitis and with late gram-positive meningitis; this combination also is suggestive of viral meningitis, especially HSV. Only if all 3 parameters are normal does the lumbar puncture provide evidence against infection; no single CSF parameter exists that can reliably exclude the presence of meningitis in a neonate. [30]
The number of white blood cells (WBCs) found in the CSF in healthy neonates varies according to gestational age. Many authors use a cutoff value of 20-30/µL. Bacterial meningitis commonly causes CSF pleocytosis greater than 100/µL, with predominantly polymorphonuclear leukocytes (PMNs) gradually evolving to lymphocytes. In neonates with viral meningitis, the picture may be similar but with a less dramatic pleocytosis. HSV meningitis may be particularly associated with a large number of red blood cells (RBCs) in the CSF.
If the mother is symptomatic, maternal investigation may be warranted; bacterial or viral cultures can provide valuable adjunctive information.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is the neuroimaging modality of choice for identifying focal areas of infection, infarction, secondary hemorrhage, cerebral edema, hydrocephalus, or, rarely, abscess formation. It should be considered in the context of focal neurological abnormalities, persistent infection, or clinical deterioration. Sinovenous occlusions, ventriculitis, and subdural collections are best diagnosed with MRI.
Follow-up MRI scans are useful for following the resolution of the infection, as well as for contributing to prognostication. If available, magnetic resonance spectroscopy can add important information on the metabolic function of the neonatal brain.
Several studies have documented periventricular white matter abnormalities on MRI in infants with neonatal meningitis. [31] Newer MRI technologies, including diffusion-weighted and diffusion tensor imaging, have allowed this association to be evaluated in more detail, and such evaluation may prove to have prognostic implications. [32]
Other Imaging Modalities
Although computed tomography (CT) carries the risk of exposing the neonatal brain to radiation, the rapidity and ease with which it can be obtained (in comparison with MRI) makes it useful in decision-making for potential neurosurgical interventions, such as ventriculostomy for hydrocephalus or surgical drainage of empyema or abscess. It may be particularly appropriate for a critically ill neonate being considered for neurosurgery.
Cranial ultrasonography provides an alternative imaging modality for critically ill neonates, but it does not provide optimal detail in all circumstances. However, it is a low-risk and thus is useful in monitoring ventricular size for hydrocephalus during the acute phase of meningitis.
Chest radiography provides important information about the lung parenchyma and the cardiac silhouette. Meningitis or sepsis may occur with pneumonia but may be indistinguishable from surfactant deficiency, pulmonary hypertension, and obstructive cardiac disease.
Electroencephalography
Electroencephalography (EEG) is not an essential part of the initial diagnostic process. However, in neonates who are unresponsive or have seizures presenting as episodes of apnea, bradycardia, or rhythmic focal movements, EEG monitoring provides useful information to guide treatment with anticonvulsant drugs.
EEG also has some prognostic utility. In a study by Klinger et al, infants with normal or mildly abnormal EEGs had better outcomes, whereas those with moderately-to-markedly abnormal EEGs were more likely to die or to suffer adverse outcomes. [33] In a study by Poblano et al, EEG was predictive of microcephaly and spasticity at 9-month follow-up. [34]
Lumbar Puncture
Lumbar puncture is indicated for evaluation of the CSF in all neonates suspected of having sepsis or meningitis, even in the absence of neurological signs.
Many clinicians are reluctant to perform this procedure on a critically ill infant. Although the theoretical complications of lumbar puncture include trauma, brain-stem herniation, introduction of infection, and hypoxic stress, none of these complications were reported in a meta-analysis of more than 10,000 infants who underwent lumbar puncture. [29]
Meningitis, however, increases the risk of death in neonates. Stoll et al reported a mortality of 23% in babies with CSF-proven meningitis, compared with a mortality of 9% in neonates whose lumbar puncture results were not consistent with meningitis. [35] Additionally, many infants who had negative blood cultures had positive CSF cultures, suggesting that cases of meningitis may be missed.
In cases of bacterial meningitis, repeat lumbar puncture should be performed 24-48 hours after initiation of therapy to ensure sterilization of the CSF. After a full course of therapy for PCR-proven HSV, repeat lumbar puncture should be undertaken to rule out incompletely treated infections.
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Acute bacterial meningitis (same patient as in the other two images). This axial nonenhanced CT scan shows mild ventriculomegaly and sulcal effacement.
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Acute bacterial meningitis (same patient as in the other two images). This axial T2-weighted MRI shows only mild ventriculomegaly
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Acute bacterial meningitis (same patient as in the other two images). This contrast-enhanced, axial T1-weighted MRI shows leptomeningeal enhancement (arrows).
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Meninges of the central nervous parts
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Neisseria meningitidis
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Neonate with a lumbar myelomeningocele with an L5 neurologic level. Note the diaphanous sac filled with cerebrospinal fluid and containing fragile vessels in its membrane. Also, note the neural placode plastered to the dorsal surface of the sac. This patient underwent closure of his back and an untethering of his neural placode. The neural placode was circumnavigated and placed in the neural canal. A dural sleeve was fashioned in such a way to reconstruct the neural tube geometry.
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This anteroposterior skull radiograph demonstrates the craniolacunia or Luckenschadel seen in patients with myelomeningocele and hydrocephalus. Mesodermal dysplastic changes cause defects in the bone. The thin ovoid areas of calvaria are often surrounded by dense bone deposits. They are most likely the result of defective membranous bone formation typical of neural tube defects and not increased intracranial pressure as once thought. These characteristic honeycomb changes are seen in about 80% of the skulls in children with myelomeningocele and hydrocephalus
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Sagittal T1-weighted MRI image of a child after closure of his myelomeningocele. Child is aged 7 years. Note the spinal cord ends in the sacral region far below the normal level of T12-L1. It is tethered at the point in which the neural placode was attached to the skin defect during gestation. The MRI showed dorsal tethering, and the child complained of back pain and had a new foot deformity on examination. By definition, all children with a myelomeningocele have a tethered cord on MRI, but only about 20% of children require an operation to untether the spinal cord during their first decade of life, during their rapid growth spurts. Thus, the MRI must be placed in context of a history and examination consistent with mechanical tethering and a resultant neurologic deterioration.
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Sagittal T1 MRI image of a child with a myelomeningocele and associated Chiari II malformation. Note the cerebellar vermis and part of the brainstem has herniated below the foramen magnum and into the cervical canal (arrow). This patient had multiple brainstem symptoms and findings to include stridor and cranial nerve paresis (cranial nerves III, VI, IX, X) despite having a well-functioning ventricular-peritoneal shunt. He required a posterior fossa decompression of his hindbrain in order to relieve the symptoms of hindbrain herniation and brainstem compression. A minority of myelomeningocele patients require a Chiari II decompression. Those that do usually present in their first year of life with similar symptoms, stridor and cranial nerve paresis. A functioning shunt is imperative prior to exploring the posterior fossa in these children. Often times, especially in older children, a shunt revision may alleviate some of the symptoms of hindbrain compression. Tube Defects in the Neonatal Period
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Neonate with a large occipital encephalocele lying in the prone position prior to surgical intervention. Note the large skin-covered sac that represents a closed neural tube defect. Often called cranium bifidum, it is a more serious condition that represents a failure of the anterior neuropore to close. In this patient, a defect in the skull base (basicranium) was associated with this large sac filled with cerebrospinal fluid and a small, disorganized remnant of brain. The patient fared satisfactorily after the surgery in which the encephalocele was excised. However, the patient needed placement of a ventricular-peritoneal shunt to treat the resultant hydrocephalus, which is not uncommon. At age 5 years, the child was doing well and had only moderate developmental delay.
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Autopsy specimen on a child with anencephaly. This is one of the most common CNS malformations in the West. The neonate, like almost all with such a severe forms of neural tube defects, did not survive more than a few hours or days. This malformation represents a failure of the anterior neuropore to close. This photograph also reveals an absence of the calvaria and posterior bone elements of the cervical canal, as well as the deficiency in the prosencephalon. Photo courtesy of Professor Ron Lemire.
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Ventral view of a child with anencephaly that, like the previous picture, shows the loss of cranium and enclosed nervous tissue. In addition to the primary defect in development, a secondary destruction of nervous tissue occurs. Direct exposure to the caustic amniotic fluid causes progressive destruction of the remaining neural structures and secondary proliferation of a thin covering of vascular and glial tissue. Photo courtesy of Professor Ron Lemire.
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These 2 photographs depict the lumbar regions on 2 different children with closed neural tube defects. Both children have lipomyelomeningocele. The child in the left has a dorsal lipoma that is pedunculated. The child on the right has a more common-appearing lipomatous mass that is heaped up beneath the skin. Both lipomas lead from the subcutaneous tissue, through the dura and into the intradural space, where they are attached to the spinal cord. Photos courtesy of Professor J.D. Loeser.
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Photograph of a child undergoing a neurosurgical procedure in which the spinal cord is being detached (untethered) from the intradural and extradural lipomatous mass that fixes it to the subcutaneous tissue. The white arrow shows the laser char on the lipoma that has been shaved off the spinal cord and was connected to the extradural mass. The black arrow shows the extradural lipoma, which crept through the dura and attached to the spinal cord, thereby firmly fixing the spinal cord at too low and too dorsal a location in the sagittal plane.
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The lumbar region of a newborn baby with myelomeningocele. The skin is intact, and the placode-containing remnants of nervous tissue can be observed in the center of the lesion, which is filled with cerebrospinal fluid (CSF).
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Axial T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. Considerable ventricular dilatation is shown on the lateral and third ventricles. Periventricular lucency is observed around the frontal horns, indicating raised intraventricular pressure.
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Sagittal T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. The third and lateral ventricles are dilated, whereas the fourth ventricle is of normal size. Aqueductal stenosis is shown. The appearance is typical of this condition.
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Phase-contrast MRI scan of an 8-week-old girl who presented with enlarging head circumference, obtained 3 months after endoscopic third ventriculostomy. A large signal void is shown in the prepontine region, corresponding to the flow through the stoma in the floor of the third ventricle, indicating that the ventriculostomy is functioning well.
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Axial T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. She was treated with a ventriculoperitoneal shunt. The ventricular system has a characteristic shape, with small frontal and large occipital horns, which are typical in patients with spina bifida. The shunt tube is shown in the right parietal region.
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Sagittal T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. Significant hindbrain hernia and low-lying fourth ventricle are shown in the context of the Arnold-Chiari II syndrome. Damaged shunt valve removed during shunt revision from a 22-year-old woman with hydrocephalus and spina bifida. The material of the valve has dramatically disintegrated.
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Damaged shunt valve removed during shunt revision from a 22-year-old woman with hydrocephalus and spina bifida. The material of the valve has dramatically disintegrated.
