Macrocephaly and Characteristic MRI Findings as Early Clues to a Hereditary Overgrowth Syndrome.

Macrocephaly may be the presenting feature of underlying genetic conditions in childhood. We report a five-year-old boy with persistent macrocephaly above +3 standard deviations since infancy and subtle facial dysmorphisms. Neurological examination revealed hypotonia, a wide-based gait, and fine and gross motor difficulties. Developmental assessment confirmed psychomotor delay without features of autism spectrum disorder. Brain MRI revealed multiple enlarged perivascular spaces involving the bilateral subcortical white matter and the corpus callosum, as well as callosal thickening. Genetic testing identified a heterozygous likely pathogenic variant in the PTEN gene, with maternal transmission confirmed on familial testing. Timely genetic diagnosis allows appropriate genetic counselling and clinical follow-up.