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Neonatal Meningoencephalitis


Postnatal Meningoencephalitis


Meningoencephalitis in infants often has a worse outcome than in older patients. Infectious diseases of the brain often lead to the death of the patient or to severe complications.


In more than one half of the patients, meningoencephalitis is complicated by

1.               postmeningitic hydrocephalus

2.               subdural effusions

3.               cerebral infarction

4.               ventriculitis

5.               brain abscess

6.               cerebral vasculopathy .

Prenatal and neonatal infections are complicated by postmeningitic hydrocephalus in more than 2/3 of the cases.

Infectious diseases with gram-negative bacteria often lead to prognostic unfavourable ventriculitis. Rare complications in this age group are subdural effusions, porencephalic cysts and brain abscesses . Beyond the neonatal period complications occur much rarer. Meningoencephalitis in later infancy is complicated in only one third of the cases by postmeningitic hydrocephalus and postinfectious subdural effusions in 20 % of the cases .


1.               Meningoencephalitis is characterised by :

2.               Arachnoiditis

3.               Ventriculitis

4.               Vasculitis

5.               Brain oedema pathologically .

 Especially in the acute phase of the disease, vasculitis and the developing brain oedema may influence blood flow. Later on, brain perfusion may be influenced by progressive ventricular dilatation as well as by subdural effusions .

In the acute phase the disease is complicated by vasculitis and brain oedema which may influence the flow in the intracranial arteries. Vasculitis is nearly always found in bacterial meningitis . Pathologically phlebitis can be differentiated from arteritis. Infectious infiltrates of the adventitia of the arteries may lead to obstruction of the vessels. Complete arterial occlusion however is very rare. Infectious infiltrates within the veins can be found more frequently. Phlebitis is often complicated by thrombosis or complete occlusion. Vasculitis can already be found in the first days of the disease. It is however most prominent in the 2nd or 3rd week of the disease .


2D Image

2D images have to distinguish between acute and chronic changes. In the acute phase, signs of bacterial infection, such as pus or brain oedema, have to be ruled out. Later images show postinfectious hydrocephalus, subdural effusions, ventriculitis and abscess formation.


2D Images in the Acute Phase

Besides vasculitis a more or less severe brain oedema may be found in association with meningoencephalitis.

Oedema may be so severe that the ventricular system is slit-like or can no longer be shown in the individual case. Oedema is caused by increased permeability of the vessels caused by vasculitis (vascular oedema) and by cell  death (cytotoxic oedema) caused by bacterial toxins .

2D images show

1.               Increased echogenicity of the brain tissue and the subdural space . Increased echogenicity of the brain can best be shown on midline sections .

2.               Focal increased echogenicity: can be found within the brain tissue . It may be caused by focal brain oedema, brain abscesses or vascular occlusion. The various Doppler techniques can help by the differential diagnosis .



2D in Chronic Changes

Postinfectious alterations are :

1.               postmeningitic hydrocephalus

2.               subdural effusions

3.               porencephalic cysts

4.               abscess formation

5.               ventriculitis.

They usually occur with a delay of several days to some weeks. Therefore, serial sonographic investigations have to be performed .

postmeningitic hydrocephalus

As mentioned earlier postmeningitic hydrocephalus occurs very often in neonatal meningitis . The shape of the ventricular dilatation does not differ from posthaemorrhagic hydrocephalus.  


postmeningitic subdural effusion

The second complication is postmeningitic subdural effusion. Imaging techniques are not different from other dilatations of the subdural or subarachnoid space. Subdural empyema is characterized by hyperechoic fluid collections over the convexity of the brain, hyperechoic fibrinous strands and thick, hyperechoic inner  membranes in most patients .



is characterized by increased echogenicity within the dilated ventricles . The inner surface of the dilated ventricles appears echogenic due to ependymitis. Additionally fibrin fibres may transverse the ventricular space .

Unfortunately postmeningitic hydrocephalus often develops which has to be treated by a ventriculoperitoneal shunt. A severe complication after ventriculitis is the development of a compartment hydrocephalus.


Compartment hydrocephalus

 are characterized by missing communication of the different parts of the ventricular system with each other. The cerebrospinal fluid is produced by the choroid plexus of the lateral ventricles, the third and the fourth ventricles. If the different parts of the ventricular system do not communicate with each other, a single ventricular catheter will not be able to drain the complete ventricular system. A ventricular catheter, placed in one dilated lateral ventricle, will not be able to drain the whole ventricular system if the foramina of Monro or the cerebral aqueduct are obstructed. Therefore, different draining catheters have to be placed within the not communicating parts of the ventricular system . Another possibility is endoscopic creation of new communications between the different ventricles (e.g. third ventriculostomy or septostomy).


Postmeningitic abscesses

may occur after infections with staphylococci and gram-negative bacteria and after fungal infections. They appear as areas of increased echogenicity . After several days they may develop a liquid centre . If multiple small echogenic foci scattered all over the brain are found, fungal infection is very probable .


Doppler Sonography

Colour Doppler

If colour or power Doppler sonograms are performed, increased vascularity can be found. The increased vascularity is typical for meningoencephalitis . Sometimes focal increased echogenicity can be found on 2D images . With the help of colour or power Doppler, differentiation between arterial or venous occlusion and infectious infiltrates can be performed . Infectious infiltrates show increased vascularity, whereas arterial occlusion or venous thrombosis is free of vessels .


Spectral Doppler

Doppler sonographic flow measurements in intracranial arteries of patients with meningoencephalitis showed an increase of all flow velocities. The mean flow velocities in patients with bacterial meningitis were significantly increased . The mean cerebral flow velocities were significantly higher in patients with neurological sequelae .

As peak systolic, end-systolic and end-diastolic flow velocities are simultaneously increased, the resistive index does not significantly differ from a control collective of healthy infants . The increase of the flow velocities is probably caused by the narrowing of the arteries caused by associated brain oedema and vasculitis.

According to the continuity equation of Bernoulli, inflow in narrow vessels equals outflow. Within physiologic limits a decrease of the vessel diameter leads to an increase of the flow velocities. A further decrease of the diameter of the arteries may theoretically lead to a decrease of the diastolic flow velocities while systolic flow is still increased. A retrograde diastolic flow would be typical for a marked increase of the intracranial pressure over the diastolic blood pressure. Retrograde diastolic flow could never be found in our patients with meningoencephalitis. If flow measurements are performed simultaneously in the extracerebral and intracerebral section of the internal carotid artery, the flow velocities increase in the intracranial part of the artery due to brain oedema . According to our experience, this is the first and most sensitive sign of increasing intracranial pressure.


If colour Doppler shows flow of the cerebrospinal fluid within the sylviduct and the foramina of Monro, this is a sensitive sign of associated ventriculitis. In these cases small particles within the cerebrospinal fluid reflect the ultrasound beam. These reflecting particles are leucocytes indicative of associated ventriculitis. In these cases

cerebrospinal fluid flow can be shown by colour Doppler and spectral Doppler within the physiologic constrictions of the ventricular system.

The flow is either :

1.               ventriculopedal (e.g. from the fourth to the third ventricle)

2.               ventriculofugal (e.g. from the third to the fourth ventricle) .

Colour Doppler shows ventriculofugal flow blue and ventriculopedal flow red . Pulsed Doppler reveals ventriculofugal flow beneath the baseline, whereas ventriculopedal flow is displayed above the baseline . Ventriculopedal flow is caused by respiratory movements and by moderate compression of the abdominal wall.


meningitis complicated by ventriculitis

Doppler sonography can be used for the diagnosis of meningitis complicated by ventriculitis. In the case of postmeningitic hydrocephalus associated with ventriculitis, colour Doppler can show if the aqueduct is open or if stenosis or occlusion has occurred.


Prenatal Infections of the Brain

Prenatal infections that may affect the developing brain are described by the TORCH infections (toxoplasmosis, syphilis, HIV, rubella, cytomegalovirus and herpes simplex). Depending on the time of infection, they may cause :

·         Microcephaly

·         disturbances in neuronal migration

·         cerebellar hypoplasia

·         haemorrhagic or leucomalacic lesions

·         periventricular and/or cortical calcifications

·         subependymal cysts

·         vasculopathy of the lenticulostriatic vessels

Sonographically vasculopathies appear as linear or punctate echodensities within the basal ganglia that often are candlestick shaped . Colour Doppler confirms the vascular nature of the echodense stripes . Within the walls of the lenticulostriatic arteries and veins, basophilic material as well as mineralisation and hypercellularity was found .

Vasculopathy of the lenticulostriatic arteries

 is not specific for a specific prenatal infection (e.g. cytomegalovirus). Other prenatal infections of the brain such as HIV, rubella, syphilis infections, etc. may cause vasculopathy of the basal ganglia too . However, vasculopathy of the basal ganglia is also not specific for prenatal infections of the

brain . It can additionally be found in chromosome anomalies (e.g. trisomy 13 and 18), dysmorphic syndromes, lysosomal disorders (sialidosis), inborn errors of metabolism (glutaracidemia type 1), asphyxia and other

diseases . In any patient with stripe-like or punctate echogenicities of the basal ganglia, prenatal infections, caused by TORCH infections, and inborn errors of metabolism have to be ruled out.

If these infants do not look syndromic and have no signs of inborn errors of metabolism and TORCH infections have been excluded, possibly no serious disease is present.

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