Proton MR spectroscopy of pediatric cerebellar tumors

Purpose: To investigate the role of proton MR spectroscopy in pediatric cerebellar tumor diagnosis. Methods: Single voxel pulse sequences with long echo time (135 or 270 milliseconds, voxel size 8 to 19 cm³), were used to obtain proton spectra of primary pediatric cerebellar tumors. Eleven primitive neuroectodermal tumors (patient age, 2 to 12 years; mean, 7 years), 11 low-grade astrocytomas (age, 2 to 16 years; mean, 9 years), 4 ependymomas (age, 1 to 6 years; mean, 4 years), 1 mixed glioma ependymo-astrocytoma (age, 11 years), 1 anaplastic ependymoma (age, 7 years), 1 ganglioglioma (age, 14 years), and 1 malignant teratoma (age, 6 days) were studied. Control cerebellum spectra were acquired from five patients without abnormality in cerebellum (age, 2 to 15 years; mean, 8 years). The signal intensities from choline-containing compounds (Cho), creatine/phosphocreatine (Cr), N-acetyl-aspartate (NAA), and lactate (Lac) were quantified. The mean and standard deviation of metabolite ratios were calculated. Results: The control spectra ratios (NAA:Cho = 1.49 ± 0.36, Cr:Cho = 1.13 ± 0.23) were distinct from the tumor spectra (NAA:Cho = 0.41 ± 0.27 and Cr:Cho = 0.37 ± 0.23). Most of primitive neuroectodermal tumors had low NAA:Cho (0.17 ± 0.09) and Cr:Cho (0.32 ± 0.19). Compared with primitive neuroectodermal tumors, low-grade astrocytomas and ependymomas had higher NAA:Cho ratio (0.63 ± 0.19 and 0.39 ± 0.12). The Cr:Cho ratio was higher for ependymomas (0.60 ± 0.20) than for astrocytomas (0.27 ± 0.12) and primitive neuroectodermal tumors. No NAA was found in the malignant teratoma. Lac:Cho ratio was 0.66 ± 0.40, 0.58 ± 0.30, and 0.08 ± 0.12 for astrocytoma, ependymoma, and primitive neuroectodermal tumor, respectively. Lactate was elevated in the mixed glioma ependymo-astrocytoma, ganglioglioma, and teratoma. The NAA and lactate signals were sometimes obscured by lipids in the spectra. Discriminant analysis was carried out using NAA:Cho and Cr:Cho ratios to differentiate the three major tumor types. The sensitivity/specificity values for diagnosing astrocytoma, ependymoma, and primitive neuroectodermal tumor were found to be 0.91/0.84, 0.75/0.92, and 0.82/0.89, respectively, based on this study. Conclusion: In many cases, proton MR spectroscopy can be used to help differentiate cerebellar primitive neuroectodermal tumor, low-grade astrocytoma, and ependymoma.