What are the CNS findings in neuroimaging (head ultrasound, brain CT scan, and/or brain MRI) for a fetus or newborn with suspected congenital infections such as cytomegalovirus (CMV), toxoplasmosis, syphilis, herpes simplex virus (HSV), rubella, and Zika virus?

CNS Neuroimaging Findings in Congenital Infections

Each congenital infection produces distinct neuroimaging patterns that can guide diagnosis when combined with clinical history and laboratory confirmation, though findings overlap significantly and are not pathognomonic.

Cytomegalovirus (CMV)

Head Ultrasound Findings

• Periventricular calcifications (linear or punctate pattern along ventricular margins) are the hallmark finding 1, 2
• Lenticulostriate vasculopathy (echogenic vessels in basal ganglia region) appears in the majority of cases 1
• Periventricular pseudocysts (occipital, temporal, or fronto-parietal location) occur in approximately 50% of cases 1
• Mild to moderate ventricular dilatation is commonly associated with calcifications 1

Brain MRI Findings (Provides Critical Additional Information)

• Polymicrogyria (particularly perisylvian region) detected in approximately 50% of cases 1
• Hippocampal dysplasia present in approximately 40% of cases 1
• Cerebellar hypoplasia identified in approximately 50% of cases 1
• Abnormal white matter signal intensity on T2-weighted sequences 3, 1
• Microcephaly frequently present 4, 1

Important Technical Note

• Ultrasound is superior to MRI for detecting calcifications, while MRI provides essential information about cortical malformations and white matter abnormalities that ultrasound cannot detect 1, 2
• CT scanning should be avoided due to radiation exposure; combined ultrasound and MRI is the recommended approach 1

Toxoplasmosis

Head Ultrasound/CT Findings

• Randomly distributed intracranial calcifications (scattered throughout brain parenchyma, not periventricular) are characteristic 3, 4
• Ventricular dilatation or hydrocephalus (may be obstructive or ex vacuo) 3
• Punctate focal calcifications (≥3 calcifications indicates severe disease) 3

Brain MRI Findings

• White matter signal abnormalities on T2-weighted and FLAIR sequences 3, 4
• Resolution or diminution of calcifications occurs in 75% of treated cases by 1 year of age, associated with improved neurologic function 3
• Persistent or increasing calcifications in 25% of cases may reflect healing rather than progression 3

Prognostic Imaging Features

• Hydrocephalus ex vacuo with elevated CSF protein predicts poor outcome 3
• Obstructive hydrocephalus requiring shunt still allows 75% chance of normal/near-normal neurodevelopment with treatment 3

Herpes Simplex Virus (HSV)

Brain MRI Findings (Preferred Modality)

• Medial temporal lobe involvement (gyral edema and high signal on T2/FLAIR) is the hallmark finding 5, 6
• Cingulate gyrus involvement occurs early in disease course 5, 6
• Diffusion-weighted imaging (DWI) abnormalities are especially sensitive for detecting early changes 5, 6
• Hemorrhagic transformation develops later in affected areas 5
• Bilateral temporal hypermetabolism on FDG-PET may be more sensitive than MRI early in disease 5

Critical Timing Considerations

• MRI is abnormal in approximately 90% of cases within 48 hours of hospital admission 5, 6
• Initial MRI can be normal in 10% of cases, particularly within first 24-48 hours 5, 7
• CT scanning has only 25% sensitivity for initial HSV encephalitis diagnosis 5, 6, 7

Clinical Pitfall

• Normal imaging never excludes HSV encephalitis and should never delay empiric acyclovir treatment 5, 6, 7

Rubella

Neuroimaging Findings

• Microcephaly is the primary manifestation 3
• Specific detailed neuroimaging patterns are less well-characterized in recent literature compared to other TORCH infections 3

Zika Virus

Head Ultrasound/CT Findings

• Severe microcephaly (often with overlapping cranial sutures and redundant scalp) 3, 4
• Periventricular calcifications (similar distribution to CMV) 4
• Ventriculomegaly associated with brain volume loss 4

Brain MRI Findings

• Severe brain atrophy (disproportionate to head size) 4
• Brain surface smoothness (simplified gyral pattern/pachygyria) 4
• Spectrum of brain malformations including cortical malformations 3
• White matter abnormalities 3

Distinguishing Feature

• The severity of microcephaly and brain atrophy in Zika is typically more profound than other congenital infections 4

Syphilis

Neuroimaging Findings

• Specific CNS imaging findings are less prominently featured in recent high-quality guidelines
• Clinical diagnosis relies more heavily on serologic testing and CSF analysis than distinctive neuroimaging patterns

General Diagnostic Approach

Imaging Modality Selection

• MRI with DWI should be performed within 24-48 hours of suspected congenital infection diagnosis 5, 6, 2
• Head ultrasound is valuable for detecting calcifications and can be performed at bedside in unstable neonates 1, 2
• Combined ultrasound and MRI provides complementary information: ultrasound for calcifications, MRI for cortical malformations and white matter disease 1, 2

Critical Clinical Caveat

• Neuroimaging findings cannot reliably distinguish between genetic and infectious causes of brain malformations 3
• Diagnosis requires correlation with maternal history, serologic testing, PCR studies, and CSF analysis 8, 4, 9
• Treatment decisions should never be delayed while awaiting imaging results 5, 6, 7