Transverse Cerebellum Essay

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3. Transverse cerebellar diameter measurement (TCD) : The cerebellar view is obtained by rotating the transducer in the axial plane centered on the thalamus to show the cerebellar hemispheres. This view shows the cerebellum, the cistern magna and the cavum septum pellucidi. The cerebellum characteristically appears as two lobules in either side of midline in the posterior cranial fossa. The widest diameter of the cerebellum is measured(16).

Fig. 5: Ultrasonographic Measurement of Transverse cerebellar Diameter

Table 5: Predicted Menstrual Age for Transverse Cerebellar Diameter (TCD) measurements (29) TCD (mm) Menstrual Age (weeks) TCD (mm) Menstrual Age (weeks)
14 15.2 35 29.2
15 15.8 36 30.0
16 16.5 37 30.6
17 17.2 38 31.2
18 17.9 39 31.8
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It lies dorsal to the pons and the medulla, separated from them by fourth ventricle. Cerebellum is separated from the cerebrum by a fold of duramater called the tentorium cerebelli. The cerebellum consists of a midline part called the vermis and two lateral hemispheres. It is roughly spherical but somewhat constricted in its median region and flattened, the greatest diameter being transverse.
The cerebellum develops from the dorsolateral part of the alar lamina of the metencephalon. In the embryo cerebellum appears at the end of the fifth week as a swelling overriding the fourth ventricle.
Since cerebellum lies in the posterior cranial fossa, surrounded by the dense petrous ridges and the occipital bone so it can withstand deformation by extrinsic pressure better than the parietal bones. The fetal cerebellum can be visualized with ultrasound easily. Therefore imaging the posterior fossa is becoming an integral part of many routine fetal sonogram. Several authors working on transverse cerebellar diameter (TCD) have correlated it well with gestational age, even in the presence of growth retardation and found it as a better marker for GA estimation as compared to other clinical and biometric
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Although the size of the fetal liver may be reduced as a result of fetal malnutrition, this is a less sensitive marker for FGR than AC(47,48).
Most studies report reduced AC is the most sensitive single morphometric indicator of FGR(49-54). The performance of AC measurement was illustrated by a study of 3616 pregnancies over 25 weeks of gestation that had a single ultrasound examination performed within two weeks of delivery(53). AC measurement predicted small for gestational age (SGA) infants (ie, birth weight below the 10th percentile for GA) with sensitivity, specificity, positive and negative predictive values of 61, 95, 86, and 83 percent, respectively. Measurement of AC was more predictive of FGR than measurement of either head circumference (HC) or biparietal diameter (BPD) or the combination of AC with either one of these two variables. The optimal time to screen for FGR was at approximately 34 weeks of gestation.
The following factors affect the sensitivity of the AC

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