What are the typical fetal ultrasound findings in congenital Cytomegalovirus (CMV) infection?

Fetal Ultrasound Findings in Congenital CMV Infection

Congenital CMV infection presents with a spectrum of intracranial abnormalities on ultrasound, most commonly including increased periventricular echogenicity, ventriculomegaly, and intracranial calcifications, often accompanied by extracranial findings such as hyperechogenic bowel. 1, 2

Intracranial Findings (Most Common and Diagnostically Important)

The brain is the primary target organ in congenital CMV infection, and intracranial abnormalities are present in virtually all affected fetuses when carefully examined:

Primary Brain Abnormalities

• Increased periventricular echogenicity - the most frequently observed finding, present in approximately 88% of infected fetuses 1, 2
• Ventriculomegaly - occurs in approximately 63% of cases, ranging from mild to severe 1, 2
• Intracranial calcifications - seen in approximately 50% of infected fetuses, typically periventricular in location 1, 3, 2
• Intraventricular adhesions - present in approximately 50% of cases 1

Additional Brain Abnormalities

• Thalamic hyperechogenicity - observed in approximately 38% of cases 1
• Mega cisterna magna - present in approximately 38% of infected fetuses 1
• Lissencephaly (smooth brain surface due to abnormal neuronal migration) - seen in approximately 25% of cases 1
• Vermian defects - cerebellar abnormalities present in approximately 25% 1
• Cerebellar cysts - less common but reported 1

Extracranial Findings

CMV infection is a systemic disease, and extracranial findings are present in all infected fetuses with brain abnormalities:

Gastrointestinal System

• Hyperechogenic bowel - the most common extracranial finding, present in approximately 75% of infected fetuses 4, 1
• CMV is the most commonly observed infection causing echogenic bowel, with rates of 2-10% of fetuses with this finding having congenital infection 4
• In one series of 650 maternal primary CMV infections, 7 fetuses had isolated echogenic bowel as the sole ultrasound finding 4

Cardiac Findings

• Cardiomegaly - present in approximately 38% of cases 1
• Pericardial effusion - seen in approximately 25% of infected fetuses 1

Hepatic and Splenic Findings

• Hepatosplenomegaly - less commonly detected prenatally but clinically significant 1

Growth Parameters

• Intrauterine growth restriction (IUGR) - present in approximately 38% of infected fetuses 5, 1
• Microcephaly may be detected prenatally 5

Hydrops Fetalis

• Nonimmune hydrops fetalis (NIHF) can occur with CMV infection, accounting for 5-10% of NIHF cases in most series 4
• CMV is among the most commonly observed infections causing NIHF, along with parvovirus, toxoplasmosis, and syphilis 4

Timing and Diagnostic Approach

When to Perform Detailed Ultrasound

• Following diagnosis of maternal CMV infection, detailed ultrasound should be performed no sooner than 2-4 weeks after onset of maternal illness to allow time for fetal manifestations to develop 4
• Serial ultrasound examinations every 2-4 weeks are recommended following diagnosis of fetal infection to detect evolving abnormalities 5, 3

Optimal Imaging Technique

• Targeted transvaginal fetal neurosonography provides superior visualization of intracranial structures compared to transabdominal approach and correlates well with MRI findings 2
• Detailed fetal echocardiogram should be included as part of the comprehensive evaluation 4

Prognostic Implications

Predictive Value of Ultrasound Findings

• Positive ultrasound findings in combination with confirmed fetal infection predict high risk of cytomegalic inclusion disease (CID) 3
• Detection of CMV-specific IgM in fetal blood combined with ultrasound abnormalities is significantly correlated with severe outcome (p = 0.0224) 3

Critical Caveat

• Normal ultrasound at 22-23 weeks does NOT exclude fetal infection or guarantee normal outcome 3
• Abnormalities may develop later in gestation, and some manifestations (particularly hearing loss) are not detectable by ultrasound 3
• Approximately 12.5% of infected infants will have clinically detectable signs at birth, but all require follow-up for at least 2 years to assess hearing and neurodevelopment 6

Differential Diagnosis Considerations

When these ultrasound findings are present, CMV should be strongly suspected, but other congenital infections can present similarly:

• Toxoplasmosis - can cause intracranial calcifications and hydrocephalus 4
• Rubella - associated with cardiac defects and growth restriction 4
• Varicella and parvovirus - less commonly cause similar patterns 4
• Polymicrogyria - CMV accounts for 12-30% of cases, particularly when associated with white matter hyperintensities and calcifications 4

Diagnostic Confirmation

When suspicious ultrasound findings are identified:

• Amniocentesis with CMV DNA PCR is the gold standard for confirming fetal infection, performed at least 7 weeks after presumed maternal infection and after 21 weeks gestation 5, 3
• Maternal CMV IgG and IgM with IgG avidity testing should be performed 4
• MRI of the fetal brain at 28-32 weeks gestation (sometimes repeated 3-4 weeks later) provides additional detail for assessing brain injury 6