title: Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: From the Departments of Diagnostic Imaging (J.H.H., S.N.H.) julie.harreld@stjude.org.
authors.forename: J H
authors.identifier: 0000-0002-8814-9373
authors.initials: JH
authors.lastname: Harreld
authors.affiliation: From the Departments of Diagnostic Imaging (J.H.H., S.N.H.).
authors.forename: S N
authors.identifier: 0000-0002-6496-2087
authors.initials: SN
authors.lastname: Hwang
authors.affiliation: Neuro-Oncology (I.Q.).
authors.forename: I
authors.identifier: 0000-0002-6645-4895
authors.initials: I
authors.lastname: Qaddoumi
authors.affiliation: Pathology (R.G.T., J.D., K.H., D.W.E.).
authors.forename: R G
authors.identifier: 0000-0002-1653-3026
authors.initials: RG
authors.lastname: Tatevossian
authors.affiliation: Biostatistics (X.L., Y.L.), St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: X
authors.identifier: 0000-0003-1653-4886
authors.initials: X
authors.lastname: Li
authors.affiliation: Pathology (R.G.T., J.D., K.H., D.W.E.).
authors.forename: J
authors.identifier: 0000-0002-9824-5043
authors.initials: J
authors.lastname: Dalton
authors.affiliation: Pathology (R.G.T., J.D., K.H., D.W.E.).
authors.forename: K
authors.identifier: 0000-0001-5283-7660
authors.initials: K
authors.lastname: Haupfear
authors.affiliation: Biostatistics (X.L., Y.L.), St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: Y
authors.identifier: 0000-0002-7046-4316
authors.initials: Y
authors.lastname: Li
authors.affiliation: Pathology (R.G.T., J.D., K.H., D.W.E.).
authors.forename: D W
authors.identifier: 0000-0003-1239-7757
authors.initials: DW
authors.lastname: Ellison
mesh_terms: D000293:Adolescent; D001254:Astrocytoma / Q000000981:diagnostic imaging* / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D005260:Female; D006801:Humans; D007223:Infant; D015192:Infratentorial Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D008297:Male; D059906:Neuroimaging / Q000379:methods