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目的：探讨低龄儿童 Chiari 畸形 I 型( chiari malformation type I，CMI )伴脊髓空洞患者后颅窝减压( posterior fossa decompression，PFD )术后小脑的位置及形态变化，并分析其对脊髓空洞转归的影响。方法对2006年9月至2012年9月，在我院接受治疗并符合入选标准的32例低龄儿童 CMI 伴脊髓空洞患者的资料进行回顾性分析，其中男20例，女12例；年龄5～9岁，平均(7.5±1.3)岁；随访时间12～71个月，平均(33.8±18.5)个月。选取正中矢状位 MRI 图像，并测量术前及随访的第四脑室顶点、小脑扁桃体下端的纵向及横向位置、空洞的最大前后径与同水平处脊髓前后径的比值( S / C 最大比值)及空洞的长度。分析 PFD 术前和随访时上述指标间的差异，并分析末次随访时差异有统计学意义的指标变化值与空洞改善之间的相关性。结果末次随访时22例(68.8％)患儿小脑扁桃体下端上移，26例(81.3％)后移；平均上移(2.6±4.2) mm (P＝0.002)，后移(5.2±5.1) mm (P＜0.001)。31例(96.9％)患者脊髓空洞改善，S / C 最大比值及空洞长度的改善率分别为(49.5±25.7)％和(51.5±27.7)％。小脑扁桃体的上移与空洞长度的改善率具有显著相关性(P＝0.035)。术前31例(96.9%)患儿小脑扁桃体下端为钉状或舌状，其中90.3%(28/31)在末次随访恢复为钝圆状。结论低龄儿童 CMI 患者 PFD 术后小脑的形态大多会通过小脑扁桃体的回缩和变圆而恢复正常。小脑扁桃体下端的回缩与空洞的改善具有显著相关性。“,”Objective To evaluate the changes of the position of the cerebellum following posterior fossa decompression ( PFD ), and to investigate their influences on the prognosis of the syringomyelia in children with Chiari malformation type I ( CMI ).Methods A retrospective review was performed on all CMI patients treated at our scoliosis clinic between September 2006 and September 2012. A subset of 32 patients, including 20 males and 12 females, was ifnally enrolled according to the inclusion criteria. The initial age and duration of follow-up averaged ( 7.5±1.3 ) years ( range: 5-9 years ) and ( 33.8±18.5 ) months ( range: 12-71 months ), respectively. On mid-sagittal magnetic resonance images ( MRI ), the following parameters were evaluated pre- and postoperatively: the longitudinal and transverse positions of the fourth ventricle vertex, the tip of cerebella tonsil, the maximal syrinx / cord ( S / C ) ratio and the syrinx length. Changes in these parameters pre- and postoperatively were analyzed. For those reaching statistical signiifcance, an additional bivariate correlation analysis was performed to investigate their relations with syrinx resolusion.Results At the last follow-up, upward shifting of the tip of cerebella tonsil was observed in 22 ( 68.8% ) patients [ mean: ( 2.6±4.2 ) mm,P=0.002 ], and backward shifting presenting in 26 ( 81.3% ) patients [ mean: ( 5.2±5.1 ) mm,P<0.001 ]. Significant resolution of the syrinx was demonstrated in 31 ( 96.9% ) cases. More speciifcally, the average improvement rates of the maximal syrinx / cord ( S / C ) ratio and the syrinx length were ( 49.5±25.7 ) % and ( 51.5±27.7 ) %, respectively. The upward shifting of cerebellum was significantly correlated with the improvement of syrinx length (P=0.035 ). Pegged cerebella tonsils were found in 31 ( 96.9% ) patients preoperatively and 90.3% ( 28 / 31 ) of them acquired round cerebella tonsils at last follow-up.Conclusions Normalization of the cerebellum morphology is observed in most children with CMI, presenting upward shifting and round revert of the cerebellar tonsil. The upward shifting of the cerebellar tonsil is signiifcantly correlated with the improvement of syrinx length.