目的：分析儿童及胎儿半侧巨脑畸形（Hemimegalencephaly，HME）的影像表现，以提高对HME尤其是胎儿HME的认识，减低出生缺陷。方法：回顾2011年9月—2018年12月经临床及MRI证实的11例HME患者资料，其中胎儿3例，出生后8例。11例中8例仅行MRI扫描，2例行CT检查及MRI检查，1例仅行CT检查。手术治疗2例。结果：8例HME中左侧大脑半球受累4例，右侧受累4例，均有患侧的皮层增厚，脑回局部宽大或不规则，呈巨脑回和/或多小脑回样改变，患侧侧脑室增宽、形态失常。7例深部灰质核团异常增大，6例白质T2WI信号减低，3例有胶质增生，1例病变内钙化，1例可见室管膜下灰质异位，1例合并ChiariⅠ型，1例同侧小脑半球受累，1例同侧头面部软组织增厚。胎儿HME，产前超声均提示一侧脑室增宽，产前MRI均明确诊断，3例均可见双顶径大于孕周，患侧颅腔增大、皮层增厚、脑室不规则、脑沟回发育与孕周不符、T2及类T2序列信号较低，其中2例合并明显的巨脑回/多小脑回样改变。结论：HME的MRI表现具有特征性，表现为一侧大脑半球弥漫性增大，侧脑室扩大，脑皮质增厚，失去正常灰白质信号，呈错构瘤样改变。胎儿HME类似儿童表现，另外常伴有双顶径大于孕周、脑沟发育与孕周不符等，能很好地辅助超声检查明确诊断，降低出生缺陷。

Objective: We analyzed the imaging manifestations of hemimegalencephaly(HME) in children and fetuses, in order to improve the understanding of HME, especially in fetuses, and to reduce birth defects. Methods: Eleven cases of HME confirmed by clinical and MRI from September 2011 to December 2018 were retrospectively reviewed, including 3 fetuses and 8 postnatal cases. Of the 11 patients, 8 patients underwent MRI scan only, 2 cases underwent CT and MRI examination, and 1 underwent CT examination only. Surgical treatment was performed in 2 cases. Results: The HME of 8 postnatal cases were 4 involved in the left hemisphere and 4 in the right hemisphere; all the cases had thicken cortex on the affected side, wider or irregular gyrus, pachygyria or polymicrogyria like gyrus pattern and widened and morphologically abnormal ventricles of the affected side. The midline structure shifted and crooked, and abnormal enlargement of deep gray matter nuclei in 7 cases, white matter showed T2WI hypointensity in 6 cases, gliosis in 3 cases, calcification in 1 case, heterotopic subependymal gray matter in 1 case, involvement of ipsilateral cerebellar hemisphere in 1 case, and the thick of soft tissue in the ipsilateral head and face increased. Besides, there was one case with Chiari type I. Fetal HME, prenatal ultrasound showed unilateral ventricular enlargement, and prenatal MRI all gave definite diagnosis. In all 3 cases, the biparietal diameter was larger than the normal one in the gestational week. Increased cranial cavity, cortical thickness, irregular ventricular enlargement, discrepancy between sulcus gyrus development and gestational week, and low signal intensity of T2 and T2-like sequence were found. Two cases were associated with obvious pachygyria and polymicrogyria like gyrus pattern. Conclusion: The MRI manifestations of HME are characterized by diffuse enlargement of the hemisphere, enlargement of the lateral ventricle, thickening of the cerebral cortex, loss of normal grey and white matter signals, and hamartoma-like changes. The MRI manifestations in fetal HME is similar to that of children. In addition, it is often accompanied by biparietal diameter greater than the nomal one gestational weeks, and sulcus development inconsistent with that in gestational weeks. These can be well assisted by ultrasonography to make a definite diagnosis and reduce birth defects.