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Neuroradiology Case of the Week

Case 118

Clinical Presentation: A 2-day-old, three-week premature, male presented with seizures, microcephaly, and metabolic acidosis.  The pregnancy was reportedly uncomplicated, however routine prenatal care was infrequent.

Radiological Findings: There is marked tissue loss involving the bilateral parietal, occipital, and temporal lobes (Figure 1). There is secondary widening of the bilateral occipital horns and the right temporal horn (Figure 1, white arrowhead) of the lateral ventricular system. Additionally, there are foci of increased hyperattenuation in a periventricular distribution representing calcifications (Figure 2). Incidental note is made of enlarged venous sinuses secondary to an elevated hematocrit (Figure 1, black arrowhead).

Discussion: Congenital CNS infections are typically caused by toxoplasmosis, rubella, cytomegalovirus (CMV), and herpes simplex virus. Other important causes include human immunodeficiency virus (HIV) and syphilis. Together, these form the classic “TORCH” CNS infections of the fetus and neonate. Of these, CMV is one of the most common.
     CMV is a linear double-stranded DNA virus that is a member of the herpes virus group. The virus is transmitted to the fetus in utero via the placenta during either maternal primary infection or reactivation. CMV infection causes a necrotizing inflammation with a predilection for the subependymal germinal matrix of the lateral ventricles. This results in paraventricular cystic lesions, characteristic periventricular post-inflammatory calcifications, disturbed neuronal migration, and cerebellar dysplasia. The severity of the findings is directly related to the gestational age of the fetus at the time of infection. Earlier infection leads to more severe migrational and developmental anomalies. Congenital CMV infection affects approximately 1% of newborns in the United States. Five to 10% of these are symptomatic at birth, while an additional 10 to 15% become symptomatic during the first year of life.
     Infants infected with CMV are often born prematurely. Microcephaly, hepatosplenomegaly, jaundice, thrombocytopenia, pneumonitis, and chorioretinitis are common manifestations during the newborn period. Seizures, mental retardation, optic atrophy, sensorineural hearing loss, and hydrocephalus are later manifestations. Cardiovascular and musculoskeletal anomalies may also be present. Prognosis depends on the extent of brain and visceral organ injury.
     A variety of imaging features have been described in congenital CMV infections. Antenatal ultrasound findings include growth retardation, hydrocephalus, periventricular calcifications, and microcephaly. Ascites, bilateral pleural effusions and cardiovascular anomalies can also be detected if present. CT scan of the brain demonstrates atrophy, ventricular dilatation, subependymal cysts, and periventricular/ lenticulostriate calcifications. MRI is typically not required for diagnosis, but can detect additional findings such as cerebellar dysgenesis, polymicrogyria, abnormal myelination and other migrational abnormalities.
     The differential diagnosis of subependymal and periventricular calcifications includes toxoplasmosis, rubella and tuberous sclerosis. In toxoplasmosis, the basal ganglia and cortex are more commonly involved. Calcifications in rubella are evenly distributed in the necrotic brain substance. Tuberous sclerosis can mimic CMV infection on imaging; however subependymal enhancing nodules in the region of the foramen of Monro and the presence of hypodense cortical tubers help in differentiating the two conditions.

References:

1. Barkovich AJ, Lindan CE. Congenital cytomegalovirus infection of the brain: imaging analysis and embryological considerations. AJNR 15:703-715, 1994. [Medline]
2. Boesch C, Issakainen J, Kewitz G, et al. Magnetic resonance imaging of the brain in congenital cytomegalovirus infection. Pediatr Radiol 19:91-93, 1989. [Medline]
3. Stagno S, Pass RF, Cloud G, et al. Primary cytomegalovirus infection in pregnancy: incidence transmission to fetus, and clinical outcome. JAMA 1986; 256: 1904-1908. [Medline]