What are the most common fetal ultrasound findings associated with cytomegalovirus (CMV), toxoplasmosis, cystic fibrosis, rubella, and syphilis?

Fetal Ultrasound Findings by Congenital Infection

Cytomegalovirus (CMV)

The most common fetal ultrasound findings in congenital CMV include ventriculomegaly, intracranial calcifications, increased placental thickness, intrahepatic calcifications, ascites, fetal growth restriction, and echogenic bowel 1. Notably, microcephaly is typically NOT seen in fetal CMV, likely due to the associated ventriculomegaly 1.

Key CMV Ultrasound Features:

• Intracranial findings (most common):

  • Ventriculomegaly (most frequent brain finding) 2, 3
  • Intracranial calcifications (periventricular pattern)
  • Subependymal cysts (best seen on MRI) 3
  • Hyperechoic thalamus (may appear in first trimester) 4

• Extra-cranial findings:

  • Hepatic calcifications
  • Echogenic bowel 5
  • Ascites and cardiomegaly 5
  • Fetal growth restriction
  • Increased placental thickness 1

Important caveat: Ultrasound has only 49% sensitivity for detecting congenital CMV, though specificity is 99% 1. A normal ultrasound does NOT exclude CMV infection 1. CMV shows a predilection for intracranial over intra-abdominal findings (61% vs 29%) 6.

Toxoplasmosis

Fetal toxoplasmosis presents with ventriculomegaly, intracranial calcifications, increased placental thickness, intrahepatic calcifications, ascites, fetal growth restriction, and echogenic bowel 1. The ultrasound findings overlap significantly with CMV.

Key Toxoplasma Features:

• Distribution pattern: Unlike CMV, toxoplasmosis shows roughly equal rates of intracranial (49%) and intra-abdominal (42%) findings 6
• Intracranial calcifications (more diffuse/scattered pattern than CMV)
• Ventriculomegaly/hydrocephalus
• Hepatic calcifications
• Echogenic bowel (23.9% of abdominal findings) 6
• Microcephaly is NOT typically reported 1

Critical distinction: While ultrasound findings are similar between CMV and toxoplasmosis, they are NOT pathognomonic for either infection 6. Serological testing and PCR are essential for definitive diagnosis.

Rubella

Congenital rubella syndrome presents with characteristic eye and cardiac anomalies on fetal ultrasound 7, 8.

Key Rubella Features:

• Cardiac anomalies (most characteristic):
  • Patent ductus arteriosus
  • Pulmonary stenosis
  • Ventricular septal defects
• Ocular abnormalities:
  • Cataracts
  • Microphthalmia
• Fetal growth restriction
• Hepatosplenomegaly 7

Important context: In the United Kingdom and similar developed countries, rubella is now uncommon due to vaccination programs, making routine TORCH testing for rubella often unnecessary 5. The 95.5% rubella IgG seropositivity in pregnant women reflects successful immunization 9.

Syphilis

Fetal syphilis typically presents with hepatosplenomegaly, placentomegaly, hydrops fetalis, and polyhydramnios.

Key Syphilis Features:

• Hepatosplenomegaly (most common)
• Placentomegaly (thickened, echogenic placenta)
• Hydrops fetalis (severe cases)
• Polyhydramnios
• Ascites
• Fetal growth restriction

Prevalence note: Syphilis seropositivity in pregnancy ranges from 0.2-0.3% in developed countries 9, making it relatively uncommon but requiring screening due to treatability.

Cystic Fibrosis

Cystic fibrosis is NOT a congenital infection and has distinct ultrasound findings unrelated to the TORCH infections above.

Key CF Features:

• Echogenic bowel (most characteristic finding):
  • Appears as bright as or brighter than surrounding bone
  • Present in second trimester
  • Associated with meconium ileus
• Dilated bowel loops
• Polyhydramnios (late finding)
• Absent or small gallbladder (rare)

Critical distinction: While echogenic bowel appears in both CF and congenital infections (CMV, toxoplasma), CF is a genetic disorder requiring different diagnostic workup (genetic testing, not infectious serology).

Common Pitfalls to Avoid

1. Do not assume normal ultrasound excludes infection: Most infected fetuses appear sonographically normal initially 8. Serial scanning is essential as findings may evolve 7, 8.

2. Do not rely on ultrasound alone: The sensitivity of ultrasound for congenital infections is limited (49% for CMV) 1. Always correlate with maternal serology and consider amniocentesis for PCR when infection is suspected.

3. Do not assume findings are pathognomonic: Ultrasound findings overlap significantly between different congenital infections 6. Specific diagnosis requires laboratory confirmation.

4. Do not forget multiorgan involvement: When any abnormality is detected, perform thorough fetal evaluation as these infections typically affect multiple organ systems 7, 8.

5. Timing matters: For CMV, ventriculomegaly correlates with hearing loss (p=0.0052) 3, and subependymal cysts (best seen on MRI) correlate with neurological complications (p=0.00003547) 3.