目的

探讨超声诊断胎儿后颅窝池畸形的准确性，进一步提升对后颅窝池畸形的认识及鉴别诊断能力。

方法

回顾性分析2020 年8 月至2023 年8 月于湖北省妇幼保健院经超声诊断为胎儿后颅窝池畸形的281 例孕妇（异常组）的病例资料，所有病例经MRI 或产后病理检查进行了确认，并与同时期2000 例正常孕妇（正常组）的年龄与孕周分布进行对比。总结胎儿后颅窝池畸形的超声诊断特征，统计超声诊断符合率，分析畸形类型分布特征及漏误诊病例的影像学特征和原因。

结果

后颅窝池畸形胎儿中超声诊断与MRI 诊断相符的病例为268 例（95.37%），超声诊断与MRI诊断不相符的病例为13 例。异常组与正常组孕妇年龄均主要集中于25～34 岁之间，分别为74.3%（199/268）和79.9%（1598/2000），差异无统计学意义（P＞0.05）；超声诊断胎儿后颅窝池畸形多数于孕晚期（30～34⁺⁶ 周，67.5%，181/268），常可伴发神经系统畸形或其他类型的先天性异常，正常孕妇的检查孕周主要是20～22 周及30～32 周的2 次系统检查，2 组检查孕周比较差异具有统计学意义（P＜0.001）。超声检出的后颅窝池畸形病种包括单纯后颅窝池增宽255 例，Dandy-Walker 畸形8例，Blake 囊肿3 例和小脑蚓部发育不良2 例。13 例误诊病例中，2 例蛛网膜囊肿误诊为Blake 囊肿，1 例蛛网膜囊肿、1 例Blake 囊肿及1 例小脑蚓部发育不良漏诊。22.8%（61/268）的病例合并其他系统畸形。后颅窝池宽度≥1.20 cm 的病例合并其他异常率为24.8%（34/137），高于宽度＜1.20 cm组的13.6%（16/118）。

结论

超声检查在胎儿后颅窝池畸形的产前筛查中具有较高的诊断价值，但对于小脑蚓部发育不良及Blake 囊肿等复杂畸形还存在一定漏误诊率。孕晚期（30～34⁺⁶ 周）是超声诊断后颅窝池畸形确诊的关键时期，对超声检查可疑病例建议进行全面神经系统评估及多系统联合筛查，同时进行多模态影像学验证，以提高诊断准确性。

Objective

To assess the diagnostic accuracy of ultrasound in detecting fetal cystic malformations of the posterior fossa in order to further enhance their diagnostic recognition and differential diagnosis.

Methods

Data of 281 fetuses (abnormal group) diagnosed with cystic malformations of the posterior fossa via ultrasound at Hubei Maternal and Child Health Hospital from August 2020 to 2023 were retrospectively analyzed.All cases were confirmed by MRI or postpartum pathological examination and compared with 2000 normal pregnant women (normal group) in the same period.The ultrasound diagnostic features of cystic malformations of the posterior fossa were summarized, the diagnostic concordance rate was calculated, the distribution of malformation types was examined, and the imaging features and causes of misdiagnosed cases were analyzed.

Results

Among all fetal posterior fossa malformation cases, ultrasound and MRI diagnoses showed concordant results in 268 cases (95.37%) and discordant results in 13.Most pregnant women in both the abnormal (74.3%, 199/268) and normal (79.9%, 1598/2000) groups were aged 25-34 years, with no significant difference between the two groups (P=0.104).Most ultrasonographic diagnoses of cystic malformations of the posterior fossa were made in late pregnancy (30-34⁺⁶ weeks, 67.5%,181/268).These malformations often coexisted with nervous system malformations or other congenital abnormalities.In contrast, normal pregnant women mainly had check-ups at 20-22 and 30-32 weeks (two systematic checks), with a significant difference in peak timing of check-ups compared to the abnormal group (P＜0.001).The posterior fossa cisterna malformations detected by ultrasound included 255 cases of mega cisterna magna, 8 cases of Dandy-Walker malformation, 3 cases of Blake’s pouch cysts, and 2 cases of cerebellar vermis hypoplasia.Among 13 misdiagnosed cases, 2 arachnoid cysts were misdiagnosed as Blake's pouch cysts, and 1 case each of arachnoid cyst, Blake's pouch cyst, and cerebellar vermis hypoplasia was missed.Approximately 22.8% (61/268) of the cases had malformations in other systems.The abnormality rate was 24.8% (34/137) in the posterior cranial fossa width ≥1.20 cm group, higher than the 13.6% (16/118) in the＜1.20 cm group.

Conclusion

Ultrasound is valuable for prenatal screening of cystic malformations of the posterior fossa but has a misdiagnosis rate for complex malformations like cerebellar vermis hypoplasia and Blake’s pouch cysts.Late pregnancy (30-34⁺⁶ weeks) is the critical time point for confirming these diagnoses.For suspicious cases, a comprehensive neurological assessment, multi-system screening, and multi-modality imaging verification are recommended to enhance diagnostic accuracy.