MR and diffusion tensor imaging of isolated tentorial hypoplasia

We report 3 patients (2 adults and 1 child) with isolated tentorial hypoplasia (ITH) from December 2015 to April 2016. Two patients did not have a visual field defect and ITH was an incidental finding on MRI. One patient was a 5-year-old boy with optic atrophy, who was referred by his ophthalmologist for brain MRI to rule out optic pathway mass. A focal defect in the right tentorium with herniation of the right temporal gyrus was found (figure 1, A and B). The second patient was a 43-year-old woman who was imaged for essential tremor. A focal right tentorial defect with herniation of the right cuneus was identified (figure 1C). In both patients, ITH was an incidental finding. The third patient was a 42-year-old woman who presented with blurry vision and found to have left-sided homonymous hemianopia on formal visual field testing (figure 2), with more prominent left homonymous inferior quadrantanopia (figure 3). The optic disc and central vision were normal. Direct ophthalmoscopy did not detect optic nerve hemihypoplasia. Brain MRI demonstrated a moderate-sized defect in the right tentorium and associated herniation of the medial right occipital gyri (figure 1D). Magnetic resonance DTI/tractography, an extension of diffusion-weighted imaging based on the measurement of Brownian motion of water molecules, demonstrated that at least a portion of the white matter extending into the herniated occipital lobe represents some of the visual pathway tracts (figures 1, E and F). The herniated and displaced white matter tracts correspond to the patient's symptomatology based on visual field testing.