The MR Appearance Of Pilocytic Astrocytoma

[Objective ] To study clinical,pathologic features,MR characteristics,treatment and prognosis of pilocytic astrocytoma(PA).To explore the advantage of MR in diagnosis of PA and improve accuracy of tumor diagnosis.[Materials and Methodes] MR images,pathology reports and clinical information from 15 patients during the past 6 years(from 2003 to 2008)with pathology-confirmed PA were retrospectively studied.Patients ranged in age from 5 years to 58 years(mean=24.1 years).Sex ratio was 7:8(male/female).The patients presented with heterogenous clinical symptoms and signs,including headach,vomit,ataxia,seizure and so on.The mean time from symptom on set to surgery was 12 months(mean=6 months,range,l to 12 months).Prior to treatment,all patients underwent treatment planning using magnetic resonance imaging(MRI,GE signa 3.0T MR or SIEMENTS 1.5T MR).MR findings,clinical diagnosis and pathologic results were tabulated.[Results]1.Age:Seven male patients and eight female patients were studies.The patients age ranged from 5 to 58 years(mean=24.1years).Below age 10 years(including 10):3 cases, 10 to 20 years(including 20):4 cases,20 to 30(including 30):3 cases,above age 30 years:5 cases. 2.Site of involvement:7 of 15 tumors(46.7%) were located in cerebellum, vermis: hemisphere was 4:3.Four (26.7%) occurred in supratentorial place(2 hypothalamus,l cerebrum,l third ventricle).Four(26.7%) located below cerebellum(l midbrain,2 medulla oblongata,l spinal cord).3.Surgical intervention:Surgical resection were not curative in every patients.5 lesions(2 hypothalamus,2 medulla oblongata,l midbrain)performed partial resection. The other 10 lesions performed gross total resection.Noticeable complications occurred in 2 patients,No adjuvant therapy was given.Follow-up MR imaging at 6 months showed gross-total macrosopic resection with no recurrence.4.Gross pathologic features: well-circumscribed , soft, gray mass,only one case without cyst, two cases with mild peritumoral edema.5.Endoscopic pathologic features: All of the 15 tumors demonstrated biphasic patten of growth,consisting of compact elongated bipolar astrocytes associated with Rosenthal fibers,and less cellular areas of multipolar cells with granular bodies and microcyst.Some cases showed atypia of nuclei,and occasional mitoses.Involvement of subarachnoid space was seen in 1 case.Remote hemorrhage and calcification was detected in lcase(MR imaging was negative).No lesion had anaplastic features.6.Immunohistochemistry:All cases showed diffuse positive staining for GFAP and low expression Ki-67.7.MR findings:â‘ According to the cystic degeneration, lesions can be divided into 3 type: cyst type(l case), cystic with mural nodule type(6 cases) and mass type(8 cases, 1 case was predominantly solid mass and the other 7 were cystic-parenchyma).â‘¡Well-circumscribed,two cases with mild peritumoral edema, The medulla oblongata lesion involve leptomeninged metastases.The cystic part appeared obvious hypointensity signal on T₁WI and obvious hyperintensity signal on T₂WI;the solid part of tumor(cystic wall and mural nodule) appeared iso-or hypointensity signal on T₁WI and slightly hyperintensity signal on T₂WI. After injection of contrast media, the tumor cystic wall enhanced or not, the mural nodule and the solid part enhanced markedly, the cystic part of tumor did not enhanced.DWI showed no restricted. 8.Among 15 specimens reviewed,diagnoses were 3 pilocytic astrocytoma,5 unclassifiable astrocytoma,1 craniopharyngioma,1 hemangioblastoma,2 ependymoma, 1 medulloblastoma,1 metastatic tumor, 1 intramedullary tumor,1 neurogenic tumor.[Conclusion]1.Pilocytic astrocytoma are found predominatly in the pediatric population with favorable prognosis. The most commom symptoms are intracranial hypertention,visual loss and ataxia.2.Pilocytic astrocytoma usually involve the cerebellum,then hypothalamus and brainstem as follows. Single lesion is common.3.Most pilocytic astrocytoma in the cerebellum underwent gross total resection but they also can develop in the brainstem and hypothalamus, where gross total resection is not possible.4.We identified four pathological features :bipolar astrocyte,Rosenthal fibers, angiogenesis,and necrosis. Some cases showed atypia of nuclei,and occasional mitoses.Involvement of subarachnoid space, remote hemorrhage and calcification can be seen in rarely case.5.MR fmdings:According to the degree of cystic degeneration,the lesion can be divided into three typesxyst typexystic with mural nodule type,and mass type.T₁WI:solid portions iso-or hypointense,cyst contents obvious hypointense;T₂WI: solid portions hyperintense,cyst contents obvious hyperintense;FLAIR: solid portions hyperintense to grey matter (GM), cyst contents moderately hyperintense relative to CSF.DWI: DWI showed no restricted diffusion areaPost-contrast T₁ image: solid portions heterogeneous enhancement of solid portion;cystic wall occasionally enhances;Rare leptomeningeal metastases.6. Since pilocytic astrocytoma and other cytic tumor (such as craniopharyngioma, hemangioblastoma, ependymoma, medulloblastoma) have similar findings on conventional MR.Additional knowledge and recognition of this entity is necessary to improve accuracy of tumor diagnosis.