MRI imaging characteristics of brainstem and midbrain aqueduct in patients with iNPH

Idiopathic normal pressure hydrocephalus (iNPH) is frequently difficult to diagnose due to the absence of specific symptoms, yet early detection and surgical intervention are essential for preventing sequela such as irreversible dementia. This study explores the specific magnetic resonance imaging (MRI) features of the brainstem and mesencephalic aqueduct in patients with iNPH. Head MRI data of 50 iNPH patients and 30 healthy matched controls were compared for mesencephalic aqueduct length, diameter, and angle, structural features of the brainstem at the sagittal plane, brainstem component volume ratios, angle between the brainstem and spinal cord, and the area and morphology of the pontine cisterns. Compared to healthy individuals, iNPH patients exhibited significant dilation of the mesencephalic aqueduct diameter, a reduced aqueduct angle, and a decrease in the sagittal plane area of the brainstem, with the most pronounced reduction in the midbrain region. Notably, the CSF spaces surrounding the brainstem were dilated, resulting in the prepontine cistern presenting a "hammer-like" shape on the sagittal plane. The prevalence of this hammer shape was positively correlated with prepontine cistern area in patients with iNPH. These unique imaging characteristics may facilitate the clinical recognition of iNPH for early diagnosis and treatment.