Intracranial infections in children are relatively uncommon. When they do occur, they may be life threatening and result in permanent neurologic damage. Urgent medical attention or surgical intervention is required in most cases. Hence, imaging of the CNS plays a central role in diagnosis and efficient triaging of care. CT is usually the initial exam performed. This allows for identifying hydrocephalus, sulcal effacement, hypodense parenchymal edema, and extra-axial collections that may be present. Contrast-enhanced MR is the study of choice for characterizing intracranial infection and its complications. MR venography should also be performed if associated sinovenous thrombosis is suspected.

The brain is susceptible to infection in utero because both the CNS and the immune system are rapidly developing during fetal life. “TORCH” is a mnemonic for some of the more common congenital infections:

T: Toxoplasma gondii

O: Other (for instance, human immunodeficiency virus [HIV], syphilis)

R: Rubella

C: Cytomegalovirus (CMV)

H: Herpes simplex virus 2 (HSV-2)

Most infections are transmitted to the fetus from transplacental passage, though transvaginal transmission during delivery is also possible. As a general rule, infections acquired during the first two trimesters result in congenital brain malformations (please refer to Chapter 30). Those occurring during the third trimester tend to result in destructive brain lesions.¹

Cytomegalovirus is the most common TORCH infection, with up to 4,000 infants born annually in the United States with symptomatic congenital CMV infection. One percent of all live births show evidence of in utero CMV infection, but the majority of these are asymptomatic. Clinical manifestations of CMV infections include microcephaly, chorioretinitis, sensorineural hearing loss, skin rash, and hepatosplenomegaly. Cross-sectional imaging findings include parenchymal calcifications with a predominantly periventricular distribution, ventriculomegaly, prominent cerebral sulci, and periventricular and subcortical white matter density or signal changes (Fig. 33.1). Early CMV in utero infection is associated with neuronal migrational anomalies, for example, polymicrogyria, schizencephaly, and lissencephaly (Fig. 33.2). On cranial US, the basal ganglia and thalami may exhibit branching curvilinear hyperechogenicities called lenticulostriate vasculopathy (Fig. 33.3). This is a nonspecific sonographic finding that may be seen in other pathologies including toxic or ischemic insults, congenital heart disease, and trisomies 13 and 21.^{1, 2 and 3}

Congenital toxoplasmosis, or in utero infection with T. gondii, is the second most common TORCH infection. Domestic cats are the major source of toxoplasma infections in humans. Common clinical features are chorioretinitis, seizures, and hepatosplenomegaly. Imaging findings of toxoplasmosis include ventriculomegaly, encephalomalacia, and parenchymal calcifications (Figs. 33.4 and 33.5). The calcifications of toxoplasmosis are often more widespread—basal ganglia, periventricular, deep, and subcortical white matter—than are those in CMV, which tend to cluster around the ventricles.^{1, 2 and 3}