Objectives <p>To compare serial prenatal MRI findings in valacyclovir-treated vs untreated fetuses with confirmed congenital cytomegalovirus (cCMV) infection, focusing on the occurrence and timing of minor brain lesions.</p> Materials and methods <p>In this retrospective single-center cohort study, fetuses with confirmed cCMV infection and at least two prenatal brain MRI examinations were included. Fetuses with major brain malformations at baseline were excluded. Treated fetuses received oral valacyclovir (8 g/day) from diagnosis to delivery. Two senior neuroradiologists assessed MRI examinations in consensus, focusing on minor lesions (temporal pole T2 hyperintensity, focal temporal horn dilation, small cysts). Lesion timing was categorized as absent, late-onset, or early-onset. Statistical analyses included Fisher’s exact test, χ²-test, and odds ratios.</p> Results <p>Seventy-seven fetuses were included (62 untreated, 15 treated). Persistently negative MRI findings were observed in 73.3% of treated fetuses vs 37.1% of untreated fetuses (<i>p</i> = 0.018; OR 4.67, 95% CI: 1.29–16.9). Early-onset minor lesions were observed only in untreated fetuses (11.3%). A significant difference between groups was confirmed when analysis was restricted to temporal pole lesions (<i>p</i> = 0.02).</p> Conclusion <p>Maternal valacyclovir therapy was associated with a significantly higher likelihood of persistently normal prenatal MRI findings and absence of early minor brain lesions, suggesting a protective effect on fetal brain involvement in cCMV.</p> Key Points <p><Emphasis Type="BoldItalic">Question</Emphasis> <i>Minor temporal pole lesions are common early MRI findings in cCMV</i>.</p> <p><Emphasis Type="BoldItalic">Findings</Emphasis> <i>Valacyclovir-treated fetuses showed fewer and later-onset minor lesions</i>.</p> <p><Emphasis Type="BoldItalic">Clinical relevance</Emphasis> <i>Serial fetal MRI may serve as an imaging surrogate marker of treatment response</i>.</p> Graphical Abstract <p></p>