TY - JOUR T1 - Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation JF - American Journal of Neuroradiology JO - Am. J. Neuroradiol. SP - 2370 LP - 2375 DO - 10.3174/ajnr.A4892 VL - 37 IS - 12 AU - J.H. Harreld AU - S.N. Hwang AU - I. Qaddoumi AU - R.G. Tatevossian AU - X. Li AU - J. Dalton AU - K. Haupfear AU - Y. Li AU - D.W. Ellison Y1 - 2016/12/01 UR - http://www.ajnr.org/content/37/12/2370.abstract N2 - BACKGROUND AND PURPOSE: Pilocytic astrocytomas, the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and shows excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation, a recently defined pilocytic astrocytoma variant that includes glial and neuronal elements similar to a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiologic, and histopathologic features. This study investigated whether imaging could distinguish posterior fossa pilocytic astrocytoma with and without gangliocytic differentiation.MATERIALS AND METHODS: Preoperative MRIs (± CTs) of 41 children (age range, 7 months to 15 years; mean age, 7.3 ± 3.7 years; 58.5% male) with pilocytic astrocytoma with gangliocytic differentiation (n = 7) or pilocytic astrocytoma (n = 34) were evaluated; differences in tumor location, morphology, and minimum relative ADC between tumor types were compared (Wilcoxon rank sum test, Fisher exact test). Histopathology and BRAF fusion/mutation status were reviewed. Associations of progression-free survival with diagnosis, imaging features, and BRAF status were examined by Cox proportional hazards models.RESULTS: Pilocytic astrocytoma with gangliocytic differentiation appeared similar to pilocytic astrocytoma but had lower minimum relative ADC (mean, 1.01 ± 0.17 compared with 2.01 ± 0.38 for pilocytic astrocytoma; P = .0005) and was more commonly located within midline structures (P = .0034). BRAF status was similar for both groups. Non-total resection (hazard ratio, 52.64; P = .0002), pilocytic astrocytoma with gangliocytic differentiation diagnosis (hazard ratio, 4.66; P = .0104), and midline involvement (hazard ratio, 3.32; P = .0433) were associated with shorter progression-free survival.CONCLUSIONS: Minimum relative ADC and tumor location may be useful adjuncts to histopathology in differentiating pilocytic astrocytoma with gangliocytic differentiation from pilocytic astrocytoma. Shorter progression-free survival in pilocytic astrocytoma with gangliocytic differentiation is likely due to a propensity for involvement of midline structures and poor resectability.GGgangliogliomaGTRgross total resectionMAPKmitogen-activated protein kinaseNTRnon-total resectionPApilocytic astrocytomaPA-GDpilocytic astrocytoma with gangliocytic differentiationPFSprogression-free survivalrADCrelative ADC ER -