Proton MR spectroscopy of cortical tubers in adults with tuberous sclerosis complex.

BACKGROUND AND PURPOSE Significant advances have been made in understanding the origin of brain manifestations associated with tuberous sclerosis complex (TSC), most recently the idea that cortical tubers and subependymal nodules are a disorder of neocortical formation. The present study was designed to test the hypothesis that MR proton spectra of cortical tubers are abnormal because of the developmental immaturity of the tubers' neurons and glia. METHODS Twenty-six adults with TSC were studied. Proton spectroscopy was performed with a single-voxel point-resolved spectroscopy technique in two 8-mL regions: one over a cortical tuber and the other over a corresponding anatomic area of normal-appearing brain in the contralateral cerebral hemisphere. The results were expressed in terms of the ratio of the area under the three prominent resonances of choline (Cho), creatine + phosphocreatine (Cr), and N-acetyl groups (NA). RESULTS Cortical tubers showed statistically significantly lower NA/Cr (1.54 +/- 0.24 vs. 1.72 +/- 0.23), NA/(Cho+Cr) (0.80 +/- 0.14 vs. 0.91 +/- 0.12), and NA/Cho (1.69 +/- 0.36 vs. 1.97 +/- 0.38) than did normal-appearing brain. No statistically significant difference was found in the Cho/Cr ratios between the tubers and the contralateral brain (0.93 +/- 0.15 vs. 0.90 +/- 0.12). No lactate was identified in any cortical tubers. CONCLUSION Proton spectroscopy can show differences between cortical tubers and normal-appearing white matter in patients with TSC. The reduced NA/Cr ratio is probably due to reduced levels of NA, most likely caused by the presence of immature neurons and glia in tubers that do not express NA, or by the presence of gliosis, a known histologic component of tubers.