Subcortical morphological alterations and volume loss in infantile hydrocephalus: A surface- and volume-based analysis

Infantile hydrocephalus (IH) can lead to lasting brain structure changes despite early treatment. We investigated deep gray matter morphology in children with treated IH using volumetric analysis and 3D shape modeling. Twenty-one IH patients (diagnosed and treated within the first 2 years of life) and 21 age- and sex-matched controls underwent 3T MRI. We measured volumes of five bilateral subcortical structures (caudate, thalamus, putamen, pallidum, hippocampus) and performed shape analysis with spherical harmonic point distribution models (SPHARM-PDM) to map regional surface deformations. Group differences were assessed by t-tests for volume and vertex-wise general linear models for shape (false discovery rate q < 0.05). IH patients had significantly smaller volumes than controls in all examined structures (p < 0.001). Shape analysis revealed extensive localized differences in the caudate, thalamus, putamen, and pallidum. In IH, the surfaces adjacent to the enlarged ventricles bulged outward, while more distal parts showed inward compression (p < 0.05, corrected). The caudate head lateral surface was displaced outward in IH, whereas the caudate tail was medially compressed. The thalamus and pallidum similarly showed lateral expansion anteriorly and medial inward deformation posteriorly. The hippocampus exhibited a ∼25% volume reduction in IH but no significant regional shape differences. Early hydrocephalus results in persistent atrophy and shape distortion of deep gray matter structures. This is the first application of shape analysis in IH, revealing region-specific deformations consistent with mechanical stretching and compression from ventricular expansion. These findings underscore that measures of parenchymal integrity provide a more direct marker of hydrocephalus-related brain injury than ventricular size alone.