* Imaging of intracranial infections is to be widely indicated in newborns and infants due to subtle clinical and biological signs.
It is essential for :
- The assessment of viral or bacterial encephalitis.
- Diagnosis and follow-up of suppurated collections (abscess and empyema..).
- Diagnosis of the cause of infection : petrous,
sinus..
* Transsutellar ultrasound is the first-line examination in neonate and infant before the closure of the anterior fontanel.
* CT is the most frequently realized.
It allows a good approach of particularly focal infectious lesions (abscess,
empyema,
tuberculoma..).
It also allows the follow-up.
* MRI,
with its high sensitivity and better resolution,
allows a better analysis and earlier detection of lesions especially in the viral infections.
1- Acquired infections :
a* Viral infections :
- Meningitis or meningoencephalitis.
- CT can show parenchymatous hypodensity with mass effect.
- MRI:
- FLAIR and diffusion sequences are very sensitive in the detection of restriction od water diffusion in the cerebral parenchyma.
- Restriction of DCA : predictive of constituted lesions.
- Enhancement : Absent or gyriform contrast enhancement.
- Specific lesions :
- Herpes type 1: temporal limbic involvement with tendency to bilateralisation.
- Varicella (cerebellitis) : post-infectious inflammatory origin.
MRI (if performed) show bilateral and symmetrical hyperintensity of the cerebellar hemispheres affecting the white and gray matter.
b* Bacterial meningitis :
- The most common form of central nervous system infections in children.
- Imaging (CT or MRI) if performed,
is normal or can show an intense enhancement of the meninges related to the vascular congestion of the meningeal spaces.
c* Pre-suppurative encephalitis and abscesses :
- Complications of meningitis or spread of haematogenous infection or extension of locoregional infection.
- Pre-suppurative encephalitis : inflammatory with edema without capsule.
- CT : hypodensity with mass effect.
- MRI: Hypo T1,
hyper T2 with diffusion restriction.
- Enhancement : absent or heterogeneous.
- Differential diagnosis: infiltrating tumor,
Ischemia.
- Abcess : progressive encapsulation with vascular proliferation around the area of necrosis.
- Peripheral enhancement.
- Restriction of DCA in the center of necrosis
- Increased DCA at the level of peri-lesional edema.
- Pic of lactate in spectroscopy at the center of necrosis.
d* Empyema :
- Complication of meningitis by necrosis of the arachnoid,
or secondary to an extension of local infection.
It can be sub or extra dural,
often bilateral.
- CT: hypodense or isodense collection,
peripheral enhancement.
- MRI: restriction of DCA within the collection.
e* Ventriculitis :
- Complication of bacterial meningitis.
it affect often newborn and infant.
- imaging : thickened ventricular walls,
enhanced after injection of contrast medium,
with sometimes intra-ventricular septa.
f* Tuberculosis :
- Meningitis: secondary to rupture of small parenchymal or leptomeningeal tuberculomes.
- Imaging : Hyperdensity or hyperintensity of basal cisterns with nodular meningeal enhancement.
Hydrocephalus is usually seen.
Tuberculomas : tuberculous abscess on white/gray matter junction
- Meningeal localization are possible
- Imaging:
- Nodular or annular enhanced lesions with or without peri-lesional edema.
- Calcifications are possible.
- MRI: central hypo T2 related to caseous necrosis.
g* Venous thrombophlebitis and arterial infarction : can complicate intracranial infections.
2- Congenital infections:
- Intrauterine contamination or during vaginal delivery
* Cytomegalovirus ++: microcephaly,
polymicrogyric often asymmetrical,
parenchymal calcifications,
cerebellar hypoplasia..
* Congenital toxoplasmosis: calcifications péri ventriculaires et corticales,
hydrocéphalie,
porencéphalie.
* HSV2 : diffuse and necrotizing eningo-encephalitis.
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