Temporal lobe changes as a key diagnostic flag for hypochondroplasia

We report an infant referred for apnoeic episodes and a facial port-wine stain, prompting brain magnetic resonance imaging (MRI) to assess for Sturge-Weber syndrome. MRI showed no leptomeningeal angiomatosis but revealed abnormal temporal lobe morphology with altered sulcation and bilateral hippocampal non-inversion, a pattern previously associated with fibroblast growth factor receptor 3 (FGFR3)-related skeletal dysplasia. This unexpected finding led to targeted genetic testing, which confirmed a de novo FGFR3 variant diagnostic of hypochondroplasia. Skeletal features were subtle in early infancy and became more obviously apparent later. This case highlights temporal lobe morphology as a diagnostic clue for FGFR3-related dysplasia on brain MRI performed for unrelated indications, potentially enabling earlier genetic diagnosis before clinical skeletal features emerge.