(2) Quantitative measurement: mainly includes ventricular width, cerebellar transverse diameter, and biological indicators (biparietal diameter and head circumference), which in some cases can screen for abnormal proliferation of cranial nerve cells (such as microcephaly and macrocephaly) (good practical evidence).
1) Biparietal diameter and head circumference: used to evaluate gestational age and growth and development status, and can also be used to evaluate craniocerebral abnormalities. The most common method when measuring double parapetal diameter is to place the cursor on the outside of the skull (outer edge-outer edge measurement), but some common parameters are formulated using the outer edge-inner edge measurement method, the main purpose is to avoid measurement errors caused by far-field skull artifacts. If microcephaly is suspected, it is not recommended to include the head circumference indicator when estimating the fetal weight.
2) lateral ventricle width: It is the most effective method to evaluate the ventricular system. The choroidal plexus was displayed in the body of lateral ventricle , with the measurement line perpendicular to the lateral ventricle cavity, and the verb was placed on the medial side of the lateral ventricle wall for measurement (Figure 5). The inner diameter of the lateral ventricle is constant in the middle and late pregnancy and the early stages of late pregnancy, with an average of 6 to 8 mm, and should be 10 mm throughout the pregnancy (recommended grade: Grade C). When the width of the lateral ventricle is ≥10 mm, attention should be paid. It should be emphasized that: ① The width of the ventricle can increase or decrease throughout the pregnancy; ② It is normal when the bilateral ventricle is slightly asymmetric, but the width is 10mm.
Figure 5 A: lateral ventricle width measurement: At the choroid plexus level, the measurement cursor is placed on the medial edge of the lateral ventricle wall; B: The correct position of the cursor when measuring the lateral ventricle, the cursor is placed on the internal edge of the lateral ventricle, and the maximum width of the vertical ventricle (YES).
Other no1, no2, no3 are all wrong measurement methods
3) Transverse diameter of cerebellar and posterior cranial fossa: The transverse diameter of cerebellar increases by 1mm per week between 14-21 weeks. Combined with biparietal diameter and head circumference, the growth and development of the fetus can be effectively judged. When visually detecting that the posterior cranial fossa is wide or narrow, measurements should be performed. In the standard section of cerebellar , the distance between the posterior edge of the cerebellar vermis and the inner edge of the occipital echo is the width of the posterior cranial fossa. The normal value is 2 to 10mm, and the long head may slightly exceed 10mm.
For pregnant women with low risk of moderate pregnancy, if satisfactory translateral ventricle and transcerebellar sections can be obtained, the biometric parameters (especially the head circumference) meet the gestational week, the width of the lateral ventricle is 10mm, and the width of the posterior cranial fossa is 2-10mm, most brain development abnormalities can be ruled out. At this time, the risk of central nervous system abnormalities is very low, and further examination is not recommended.
4. Neurological ultrasound screening before 18 weeks of pregnancy
There are more and more applications of fetal ultrasound examinations in the late early pregnancy and early middle pregnancy, and there is still a lack of relevant clinical application guidelines. This guideline recommends that if ultrasound screening is performed 18 weeks ago, the lateral ventricle and cerebellar sections should be observed and recorded as much as possible (Figure 6) (good practical evidence), but pregnant women should be informed that prenatal ultrasound has not only technical limitations, but also time-consuming.
Figure 6 Normal 16-week fetus A: Terminal ventricle section: The lateral ventricle appears wider than the surrounding thin layer of brain parenchyma, the forehead corner (*) is arc-shaped, filled with cerebrospinal fluid , the choroid plexus (CP) fills the body, chamber cavity, occipital angle and temporal angle of the lateral ventricle, and the boundary may be irregular; B: Cerebellar section, the cerebellum (C) in the early middle pregnancy is dumbbell-shaped, and the upper vermis is present, showing an isoecho (slightly higher echo in the late pregnancy). The observable structures include the anterior angle of the lateral ventricle (shown *), thalamus (th), part of the lateral ventricle occipital angle and CP
Selected from: Jiang Yuting, Xie Hongning (Chinese Journal of Ultrasound Imaging 2021, 30 (7): 553-562.)
(to be continued)
