MRI Features Of Intracranial Pilocytic Astrocytoma In Children Correlative With Pathology

Part?MRI features of Intracranial Pilocytic Astrocytoma in Children Correlative with PathologyObjective : To study the MRI features of intracranial pilocytic astrocytomas in children correlative with pathology.Methods: Seventy nine patients with pilocytic astrocytomas were retrospectively analyzed from Xinhua Hospital in 2008~2014. There were 56 boys and 23 girls. The mean age of these patients was 4.92±3.65 years, ranging from 2 months to 18 years. We study the clinical materials, MR images and pathologic pictures. The ADC values of the masses were measured, whose ROIs were located in the solid regions. According to the age, location and enhancement type, we divided the patients into several groups. The differences between the ADC avlues of each groups were analyzed.Results: The initial symptoms of the patients included headache, nausea, vomit,motor impairment, convulsion, epilepsy, visual deterioration, strabismus and so on.There were 33 supratentorial masses, 45 subtentorial masses and one multifocal lesion.Pilocytic astrocytomas involved different parts of the brain such as cerebellum(n=37),sellar region(n=21), brainstem(n=8), pineal region(n=4), basal ganglia region(n=3)and cerebral hemisphere(n=5). The appearances of pilocytic astrocytomas were various, including predominantly solid type(n=46), solid-cyst type(n=13), cystic with mural nodules type(n=16) and pure cyst type(n=4). The solid components of pilocytic astrocytomas in this study were predominantly iso-to-hypointensity on T1-weighted image, iso-to-hperintensity on T2-weighted image. On contrast-enhanced T1-weighted images, the lesions show different enhancement patterns, including intense enhancement(n=56), heterogeneous enhancement(n=15), slight enhancement(n=6)and non enhancement(n=2). 94.94%(75/79)pilocytic astrocytomas had slight peritumoral edema or non peritumoral edema. 9 cases definitely had calcification(on CT scan). 5 pilocytic astrocytomas located in sellar region were accompaied with CSF dissemination. 5 cases of type-I neurofibromatosis were included. In this study, 59.49%(47/79) pilocytic astrocytomas appeared with typical imaging features, while 40.5%(32/79) with atypical imaging appearance. 78 cases(98.73%) were iso-to-hypointensity on DWI. The ADC values were(1.647±0.315)×10-3mm2/s. The ADC values of different groups has no statistical difference(P>0.05). At histologic examination,pilocytic astrocytomas manifest in a noteworthy biphasic pattern composed of loose glial area and dense tissue. Some tumors have a predominance of the piloid tissue,whereas others show more of the glial component. The vessels in some cases may appeared glomeruloid, hyalinization and angiomatoid. Microscopially, calcification and hemorrhage may occur in some tumors, which also can be observed on radiologic images.Conclusion: Pilocytic astrocytomas most commonly occur in cerebellum and sellar region. More than half pilocytic astrocytomas have typical image appearance, including cystic with mural nodules pattern and predominantly solid pattern. On contrast-enhanced T1-weighted image, the classic pilocytic astrocytomas have intense enhancement with slight peritumoral edema or without peripheral edema. Atypical pilocytic astrocytomas are not rare in this study, including solid-cyst mass, pure cyst mass, calcification,tumor hemorrhage, obvious peritumoral edema, slight or non enhancement, CSF dissemination and multifocal lesions. Pathology, the different percentages of loose area,dense area and vessels may lead to various atypical appearances of pilocytic astrocytomas. The iso-to-hypointensity on DWI plays an important role in the differential diagnosis. Age, location, enhancement types and morphology patterns do not affect the ADC value of pilocytic astrocytomas.Part ?MRS features of Intracranial Pilocytic Astrocytomas in ChildrenObjective: To study the MR spectroscopy of intracranial pilocytic astrocytomas in children.Material and methods: 33 patients with pilocytic astrocytomas confirmed by pathology were collected from Xinhua hospital in 2009-2014. All of the patients had proton MR spectroscopy before the surgy. There are 20 boys and 13 girls. The mean age of the patients was 5.61±3.61 years, ranging from 7 months to 13 years. We analyzed the clinical materials and images of these patients. We measured the N-Aceytl Aspartate(N-AA) peak, Choline(Cho) peak and Creatine(Cr) peak in the selected regions. The ratios of NAA/Cr?Cho/ Cr?Cho /NAA?NAA/Cho were calculated. Lactate(Lac) peak and Lipids(Lip) peak were observed. The patients were divided into two groups, the statistic difference was analyzed between the two groups.Results: The 33 pilocytic astrocytomas had high Cho peak and low N-AA peak.The Cho/NAA ratio of 29 cases were >1, and the Cho/NAA ratio of 16 cases were >2. The mean Cho/NAA ratio was 2.396±0.947, the maximum was 4.610. The mean NAA/Cho ratio was 0.489±0.206, the minimum was 0.213. The mean NAA/Cr ratio was 2.047±1.630, ranging 0.482 to 6.425. The mean ratio of Cho/Cr ratio was 2.747± 1.943, ranging 0.96 to 8.5. The ratios of NAA/Cr, Cho/Cr, Cho/NAA,,NAA/Cho between two groups(?2 years, <2 years) had no statistic difference(P>0.05). Lac peaks were observed in 15 cases. Lip peaks were observed in 9 cases.Conclusion: The MR spectroscopy of pilocytic astrocytomas in about half of patients have characteristic features, with high Cho/NAA ratio which >2. The Cho/NAA ratio of PA may higher than 4, and the mean was 2.396±0.947. Some tumors had Lac peak. Seldom tumors show Lip peak. Even though the MR spectrocsopy features of pilocytic astrocytoma may suggest a more malignant tumor, conventional MR images, DW image and ADC value should be considered together to do the correct diagnosis.