Monash Ultrasound for Women, Melbourne, Australia.
Ultrasound Obstet Gynecol. 2011 Dec;38(6):640-5. doi: 10.1002/uog.10088. Epub 2011 Nov 1.
To describe a new first-trimester sonographic landmark, posterior displacement of the midbrain and aqueduct of Sylvius, which may be useful in early screening for neural tube defects.
This was a prospective study of 457 normal fetuses at 11 + 0 to 13 + 6 weeks' gestation. We measured the distance from the posterior border of the aqueduct of Sylvius to the anterior border of the occiput (AOS-to-occiput distance) in the axial plane and created a reference range. In the nine fetuses with abnormal midbrain position identified in the first trimester and with neural tube defect subsequently confirmed, we analyzed ultrasound images to determine the position of the aqueduct of Sylvius.
The lower limit of normal AOS-to-occiput distance (mean minus 2 SD) ranged from 1.7 mm at a crown-rump length (CRL) of 45 mm to 3.7 mm at a CRL of 84 mm. In the nine cases with abnormal position of the midbrain and confirmed neural tube defect, juxtaposition of the midbrain to the occiput was the clue to diagnosis of the spinal abnormality. In all nine cases, the AOS-to-occiput distance was below the established normal range.
Examination of the midbrain in an axial plane may prove a reliable marker for the first-trimester diagnosis of neural tube defects. In contrast to recently reported subtle changes in the mid-sagittal view of the posterior cranial fossa, axial imaging of the midbrain reveals striking displacement of this structure, with virtual juxtaposition to the occiput, in fetuses with confirmed open spina bifida. This anatomical distortion of the midbrain can be quantified by measurement of the AOS-to-occiput distance.
描述一种新的早孕期超声标志，即中脑和第四脑室后移位，这可能有助于神经管缺陷的早期筛查。
这是一项对 457 例 11+0 至 13+6 孕周正常胎儿的前瞻性研究。我们在轴平面上测量了第四脑室后缘到枕骨前缘的距离（AOS 到枕骨距离），并创建了参考范围。在 9 例早孕期中脑位置异常且随后证实存在神经管缺陷的胎儿中，我们分析了超声图像以确定第四脑室的位置。
正常 AOS 到枕骨距离的下限（均值减去 2 个标准差）范围从 45 毫米头臀长（CRL）时的 1.7 毫米到 84 毫米 CRL 时的 3.7 毫米。在 9 例中脑位置异常且证实存在神经管缺陷的病例中，中脑与枕骨毗邻是诊断脊柱异常的线索。在所有 9 例病例中，AOS 到枕骨距离均低于既定的正常范围。
在轴平面上检查中脑可能成为神经管缺陷的早期诊断的可靠标志。与最近报道的后颅窝正中矢状面的细微变化不同，中脑的轴向成像显示，在确诊开放性脊柱裂的胎儿中，该结构明显移位，与枕骨几乎毗邻。这种中脑的解剖学扭曲可以通过测量 AOS 到枕骨的距离来定量。
