Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation

Abstract

Purpose Pilocytic astrocytomas (PAs), the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and show excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation (PA-GD), a recently defined PA variant that includes glial and neuronal elements like a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiological and histopathologic features. This study investigated whether imaging could distinguish between posterior fossa PA-GDs and PAs. Materials and Methods Pre-operative MRIs (± CTs) of 41 children (7mo-15 years, mean 7.3±3.7 years; 58.5% male) with PA-GD (n=7) or PA (n= 34) were evaluated; differences in tumor location, morphology, and minimum rADC between tumor types were compared (Wilcoxon rank sum test, Fisher’s exact test). Histopathology and BRAF fusion / mutation status were reviewed. Associations of progression-free survival (PFS) with diagnosis, imaging features and BRAF status were examined by Cox proportional hazards models. Results PA-GDs appeared similar to PAs, but had lower minimum rADC (mean 1.01±0.17 compared to 2.01±0.38 for PAs; p=0.0005), and were more commonly located within midline structures (p=0.0034). BRAF status was similar for both groups. Non-total resection (hazard ratio 52.64, p=0.0002), PA-GD diagnosis (hazard ratio 4.66, p=0.0104) and midline involvement (hazard ratio 3.32, p=0.0433) were associated with shorter PFS. Conclusion Minimum rADC and tumor location may be useful adjuncts to histopathology in differentiating PA-GD from PA. Shorter PFS in PA-GD is likely due to a propensity for involvement of midline structures and poor resectability.

Role of diffusion weighted imaging for differentiating cerebral pilocytic astrocytoma and ganglioglioma BRAF V600E-mutant from wild type

“…Molecular analyses were performed to test the presence of BRAF V600E mutation which was confirmed by sequencing. In particular, the BRAF V600E mutation hotspot was sequenced in genomic DNA, and quantitative reverse-transcription polymerase chain reaction was performed by using first-strand complementary DNA synthesized from total RNA, as previously described [20].…”

Comparison of conventional, diffusion, and perfusion MRI between infratentorial ganglioglioma and pilocytic astrocytoma

“…(11) demonstrated in a case series that the signal intensity of the tumors was isointense to slightly hyperintense on DWI (without calculated ADC value) in the nine infratentorial gangliogliomas. In a more recent study that reported imaging features of ganglioglioma, the minimum rADC ratios were 1.01 ± 0.17 in the six tumors (16). In this study, our results are similar to the previously published reports in the DWI signal and minimum rADC ratios of infratentorial ganglioglioma.…”

“…DWI with ADC measurements could offer quantitative information regarding the Brownian movement of water molecules and partly reflect the tissue cellularity (14,19,20). Although there are several diffusion imaging reports of ganglioglioma in supratentorial and infratentorial brain, dedicated diffusion MRI studies of infratentorial ganglioglioma are rare (11,16,17,22,23). Lou et al.…”

“…Advanced MRI techniques including diffusion-weighted imaging (DWI) and dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI) can supplement functional and physiological information not available from conventional MRI, such as the tissue cellularity and vascularity of infratentorial brain tumor (13–15). To the best of our knowledge, there have been limited studies concerning the use of DWI and DSC-PWI for distinguishing infratentorial ganglioglioma from pilocytic astrocytoma (16). In this study, we investigated whether an infratentorial ganglioglioma can be discriminated from pilocytic astrocytoma with conventional MRI, DWI, and DSC-PWI.…”

Volumetric voxelwise apparent diffusion coefficient histogram analysis for differentiation of the fourth ventricular tumors

“…Also, many pilocytic astrocytomas-classically described as cystic tumors with mural modularity-localize to cerebellar hemisphere, particularly those without gangliocytic differentiation. 4 Medulloblastomas characteristically present as midline masses along the 4th ventricle roof in pediatric patients; whereas, cerebellar hemisphere medulloblastomas typically belong to the sonic hedgehog molecular subtype and are commonly seen in adults. 5,6 On the other hand, infratentorial ependymomas tend to present as 4th ventricle floor lesions extending through the foramina of Luschka and Magendie.…”