|ECR 2018 / C-0751|
|Step by step in the brain US in children with meningitis|
Findings and procedure details
SONOGRAPHIC FINDINGS IN MENINGITIS:
Ultrasound abnormalities are present in approximately 65% of infants with acute bacterial meningitis. However, the frequency of imaging abnormalities in patients with a clinical presentation complicated by persistent seizures, abnormal neurological findings and a deterioration of CSF examination within the first 48 hours can be as high as 100%.
Because the major advantage of sonography is its ability to be safely repeated, a second study should be performed if any clinical deterioration occurs, such as increasing head circumference, occurrence of new neurological findings and/or lack of response to therapy.
We divide the main ultrasound findings that we shoud look for in meningitis suspicion into 3 main groups, as follows: Fig. 2
1). EXTRA-AXIAL AND MENINGEAL FINDINGS: Fig. 3
- Echogenic widening of brain sulci, or meningeal thickening, is the most common and earliest sonographic sign of meningitis, seen in 26–83% of affected patients.
In healthy individuals, the pia-arachnoidal membrane is seen as an echogenic line on the surface of the brain. Normal thickness of the membrane measured from the surface of a frontal gyrus (single layer) and within a sulcus (double layer) should not exceed 1.3 mm and 2 mm, respectively.
This can be accompanied by prominent cortical vessels within the arachnoid on color Doppler sonography. These findings reflect the intense inflammatory exudate that accumulates in the depths of the fissures and sulci, especially around the pial and subarachnoid vessel.
- Accumulation of extra-axial fluid might be present in 8– 33% of infants with bacterial meningitis. Most commonly, these represent sterile, reactive subdural effusions that have no prognostic significance.
- On sonography, they appear as hypoechoic concave fluid spaces and sometimes may contain mobile echogenic debris.
- Color Doppler sonography can be very helpful in differentiating benign enlargement of subarachnoid spaces from subdural effusions. When subarachnoid fluid is present cortical vessels on the brain surface are surrounded by fluid, whereas fluid in the subdural space compresses the cortical vessels along the surface of the brain.
- Venous thrombosis. If meningeal inflammation extends to the walls of bridging and cortical veins it can lead to thrombophlebitis and sagital venous thrombosis.
2). PARENCHYMAL FINDINGS: Fig. 4
- Areas of abnormal brain echogenicity have been reported in 12% to 65% of infants with bacterial meningitis.
Lesions can be focal or diffuse and can represent parenchymal involvement by cerebritis, infarction, secondary hemorrhage or early abscess. The presence and size of parenchymal lesions are associated with significant neurological sequelae and are indicators of a poor prognosis.
- During the initial stage of cerebritis, sonography might only show a poorly marginated area of increased echogenicity with increased vascularity using color or power Doppler.
- In the acute stage of meningitis, both intra- and extracellular edema can occur. On sonography, there might be a diffuse or heterogeneous increase in the echogenicity of the brain with effacement of the sulci and gyri.
- Elevated resistive index (RI) on pulsed Doppler sonography due to increased intracranial pressure, which is associated with increased pulsatility of arterial flow.
Other causes of elevated pulsatility of flow include venous thrombosis, which may also show reversal of flow during the entire diastolic phase in duplex Doppler waveform of the anterior cerebral artery.
- Diffuse cerebral atrophy, multicystic encephalopathy, and porencephaly might be seen as the end-stage of complications of bacterial meningitis.
3). VENTRICULAR FINDINGS:
- Irregular and echogenic ependyma, and
- Intraventricular debris and stranding Fig. 5 , often associated with ventricular dilatation, are the most common sonographic signs of ventriculitis. Debris in the ventricles can be caused by any infecting organism; however, it is most frequently seen with E. Coli meningitis.
- Hydrocephalus (ventricular dilatation) Fig. 6 is present in 14–65% of infants with bacterial meningitis and can occur in either the acute or the chronic phase of the disease.
- The level of obstruction to CSF flow is usually outside the ventricular system but can occur within the narrowest portions of the ventricles as a result of ependymitis and secondary adhesion.
- Pulsed Doppler of the anterior cerebral artery before and after compression of the anterior fontanel can be a useful adjunct in the serial monitoring of infants with postinfectious hydrocephalus.
- Increasing response to fontanel compression as manifested by increasing changes in arterial RI can be an indication for shunt placement in infants with rapidly progressive hydrocephalus.
Thematically related posters
ECR 2018 / C-2086
A Guide to the Sonography of the Eye and its Role in Ophthalmological Emergencies.