Which ultrasound finding is most characteristic of congenital toxoplasmosis?

The most characteristic ultrasound finding of congenital toxoplasmosis is ventriculomegaly. This condition is often associated with a triad of findings: chorioretinitis, hydrocephalus (which is reflected as ventriculomegaly on ultrasound), and intracranial calcifications. In cases of congenital toxoplasmosis, the fetal brain can be affected significantly, leading to the accumulation of cerebrospinal fluid within the ventricles. This results in an enlargement of those ventricles, indicative of ventriculomegaly.

Microcephaly can occur in various congenital infections and conditions, but it is not specific to toxoplasmosis. Hydrops, which refers to an abnormal accumulation of fluid in fetal compartments, might also arise in various maternal and fetal conditions but is less characteristic of congenital toxoplasmosis compared to ventriculomegaly. Neural tube defects could present as other anomalies seen on ultrasound, but they are fundamentally different pathologies and are not directly linked to the spectrum of findings associated with congenital toxoplasmosis. Thus, the prominence of ventriculomegaly as a consistent finding in cases of congenital toxoplasmosis makes it a definitive characteristic diagnosis with imaging.