Differentiation between cortical atrophy and hydrocephalus using 1H MRS

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Abstract
Quantitative 1H MRS to determine cerebral metabolite patterns and MRI to determine CSF flow were applied to 12 patients with ventricular dilation—Group A, cortical atrophy (N = 5); or Group B, hydrocephalus (N = 7)—and in 9 normal controls. While mean brain water (Group A = 80% ± 6; Group B = 86% ± 5; normal = 85% ± 4) did not differ between the two groups of patients and controls, 1H MRS distinguished those patients with cortical atrophy (Group A) (N‐acetylaspartate/creatine (NAA/Cr) = 0.69 ± 0.17, versus normal = 1.06 ± 0.16; P < 0.002; [NAA] = 5.9 ± 1.3 mmoles/kg, versus normal 8.0 ± 1.4; P < 0.02) from those with hydrocephalus (Group B) (NAA/Cr = 1.16 ± 0.11; [NAA] = 9.2 ± 1.2; P > 0.13 and P > 0.07). Lactate levels were elevated in 3/5 patients with cortical atrophy, but in 0/7 of those with hydrocephalus. Mean absolute concentrations (mmoles/kg) of the five major cerebral osmolytes were 41 ± 4 (Group A), 43 ± 6 (Group B), and 42 ± 4 (normal), so that despite massive brain deformation, constant osmolality was maintained. 1H MRS may directly benefit surgical planning in hydrocephalus infants by clearly identifying those with cortical atrophy who do not require CSF diversion. Thinning of the cortical mantle in hydrocephalus may result from osmotically driven reduction in individual cell volumes, (shrinkage), rather than brain‐compression.