摘要： 研究背景 毛细胞型星形细胞瘤为好发于儿童和青少年的低级别胶质瘤，其中发生于小脑者（WHOⅠ级）的组织形态学呈典型的毛细胞型星形细胞瘤表现。本文报告1 例小脑毛细胞型星形细胞瘤患儿的临床表现、影像学和组织病理学特征及其与其他中枢神经系统肿瘤之鉴别要点。方法与结果 女性患儿，8 岁。临床表现为间断性头痛伴呕吐。MRI 显示左侧小脑半球、小脑蚓部类圆形占位性病变，病灶内信号不均匀。术中可见肿瘤组织质地柔软，血运较差，呈胶冻状。肿瘤细胞胞核呈圆形或卵圆形，胞质两端突起呈发丝样，围绕血管排列；部分区域肿瘤细胞胞核伸展呈长梭形束状致密排列或疏松星网状排列，除具有典型毛细胞型星形细胞瘤病理表现外，血管异常丰富，且Rosenthal 纤维和嗜酸性颗粒不明显。肿瘤细胞弥漫表达胶质纤维酸性蛋白、突触素、波形蛋白和P53，不表达细胞角蛋白、神经元核抗原和神经微丝蛋白，Ki-67 抗原标记指数为2% ~ 5%；血管内皮细胞表达CD34、散在表达CD68。结论 毛细胞型星形细胞瘤好发于小脑，肿瘤组织中无明显Rosenthal纤维和嗜酸性颗粒有助于诊断，但不是诊断的必要条件；应注意与毛细胞黏液型星形细胞瘤、血管中心型胶质瘤和胚胎发育不良性神经上皮肿瘤等相鉴别。

关键词: 星形细胞瘤, 小脑, 免疫组织化学, 病理学

Abstract: Background  Pilocytic astrocytoma (PA) is a low-grade glioma that occurs mainly in children and young adults. The histomorphology of PA located in the cerebellum (WHOⅠ) is very typical. This article is to report one case of PA in the cerebellum of an 8-year-old child, and to discuss the clinical, imaging and pathological features of PA and clinicopathological differentiations from relevant tumors.  Methods and Results  An 8-year-old girl presented intermittent headache for one month and the headache was aggravated for 7 d. MRI showed circular space-occupying lesion in the left cerebellar hemisphere and cerebellar vermis, and the lesion revealed uneven signals. During the surgery, the tumor was soft and jellylike, with poor blood supply. Histologically, tumor cell nuclei were round or oval; cytoplasmic projections on both ends were slender hair-like, and were arranged around the blood vessels. Part of tumor cells had spindle nuclei, and showed fascicular compact arrangement or loose reticular arrangement. The pathomorphism of this tumro was slightly different from that of typical PA. It had unusually rich blood vessels, and Rosenthal fibers and eosinophilic granules were not obvious. Tumor cells were diffusely positive for glial fibrillary acidic protein (GFAP), synaptophysin (Syn), vimentin (Vim) and P53, but negative for cytokeratin (CK), neuronal nuclei (NeuN) and neurofilament protein (NF). Ki-67 index was 2%-5%. Vascular endothelial cells were positive for CD34, and scatteredly expressed CD68. Pathological diagosis was pilocytic astrocytoma (WHOⅠ).  Conclusions  Pilocytic astrocytoma usually happens in children and adolescents and often occurs in the cerebellum. Rosenthal fibers and eosinophilic granules are helpful to make a clear diagnosis, but they are not necessary conditions of diagnosis. Differential diagnoses should be paid attention, such as pilomyxoid astrocytoma, angiocentric glioma and dysembryoplastic neuroepithelial tumor (DNT).

Key words: Astrocytoma, Cerebellum, Immunohistochemistry, Pathology