Year : 2003 | Volume
: 13 | Issue : 1 | Page : 95--97
Gestational age estimation using transcerebellar diameter with grading of fetal cerebellum and evaluation of TCD/AC (Transcerebellar diameter/abdominal circumference) ratio as a gestational age independent parameter
R Malik, VK Pandya, P Shrivastava
Department of Radiodiagnosis, Gandhi Medical College and Hamidia Hospital, Bhopal (M.P), India
Department of Radiodiagnosis, Gandhi Medical College and Hamidia Hospital, Bhopal (M.P)
Objective : To prospectively evaluate the accuracy of transcerebellar diameter (TCD) in estimation of gestational age (GA), to study foetal cerebellar appearance on USG and its grading and to evaluate the ratio between transcerebellar diameter and abdominal circumference (AC) as a gestational age independent parameter. Material and Method : In 100 pregnant women between 16-40 weeks of gestation TCD, AC and TCD/AC ratio were recorded followed by the study of their predictive accuracy for GA. Simultaneously the US appearance of the cerebella were noted and grouped into «SQ»three«SQ» grades. Result and Conclusion: TCD showed close correlation with gestational age and TCD/AC ratio was fairly constant irrespective of the gestational age and almost all fetuseswith TCD/AC ratio exceeding 2SD were reported to have asymmeteric intra uterine growth retardation (IUGR). In our study, cerebella in 46 percent, 25 percent and 29 percent cases were classified as grade I, II and III respectively and a progressive changeof grade I to grade III was noted with advancing gestation.
|How to cite this article:|
Malik R, Pandya V K, Shrivastava P. Gestational age estimation using transcerebellar diameter with grading of fetal cerebellum and evaluation of TCD/AC (Transcerebellar diameter/abdominal circumference) ratio as a gestational age independent parameter.Indian J Radiol Imaging 2003;13:95-97
|How to cite this URL:|
Malik R, Pandya V K, Shrivastava P. Gestational age estimation using transcerebellar diameter with grading of fetal cerebellum and evaluation of TCD/AC (Transcerebellar diameter/abdominal circumference) ratio as a gestational age independent parameter. Indian J Radiol Imaging [serial online] 2003 [cited 2020 Sep 21 ];13:95-97
Available from: http://www.ijri.org/text.asp?2003/13/1/95/28638
Various biometeric parameters for gestational age (GA) estimation are in vogue. Transcerebellar diameter (TCD) is emerging as a new parameter and is claimed to be more accurate in certain situations. In our study also it revealed a high grade of accuracy. [Table 1]
To conclude that a parameter value is subnormal or above normal, exact menstrual age should be known, but when it is not known a menstrual age independent parameter is needed. We found TCD/AC (abdominal circumference) ratio one such parameter.
Material and Method
The study involved measuring TCD and AC in 100 pregnant women with clinically normal singleton pregnancies, undergoing routine antenatal US screening between 16 to 40 wks using US scanner GE logiq alpha 100 with 3.5 MHz transducer. Measurement of AC was taken in a conventional manner however for measuring TCD the technique described by McLeasy et al (1984) and Goldstein et al (1987) was followed, in which the usual thalamic plane used for BPD is obtained, the transducer is then rotated about 300 below the thalamic plane to see the cerebellum. TCD is now measured and TCD/AC ratio calculated ,. These measurements were compared with standard nomogram given by Chitty et al . In our study the cerebella were grouped into 3 categories according to the following ultrasonographic features:-
Grade I - The cerebellar hemispheres appear as 2 cystic globules, on either side of the midline and the vermis is not developed [Figure 1].
Grade II - The vermis is seen as an echogenic rectangular tissue connecting the two hemispheres with the cerebellum resembling a dumbell with the echogenic margins. [Figure 2]
Grade III - The appearance of the cerebellar hemispheres change to that of a triangular structure, which is homogeneously echogenic and looks more solid. [Figure 3]
The TCD showed 92% predictive accuracy for gestational age as compared to the standard nomogram by Chitty et al.
In this study the TCD/AC ratio was found to be 0.14064±0.059 (SD) which remained fairly constant throughout pregnancy and thus it is a useful gestational age independent parameter. In our study nine out of ten fetuses with TCD/AC ratio more than 2SDs were shown to have asymmeteric IUGR on neonatal examination; while in one case neonatal follow up could not be done.
We found that cerebella in 46%, 25% and 29% cases were grade I, II and III respectively. The grade changed from I to III progressively with advancing gestation. The median GA and TCD were 20 wks and 21 mm for grade I, 31 wks and 36 mm for grade II and 36 wks and 42 mm for grade III [Table 2].
TCD was found to be an accurate parameter in our study and it showed 92% accuracy in predicting GA.
The TCD/AC ratio was fairly constant throughout gestation and we found it to be a good tool to diagnose asymmetric IUGR. It was almost 100% accurate in diagnosing asymmetric IUGR in those with ratio exceeding 2 SDs. All the nine such cases followed up in our study, were subsequently found to have asymmetric IUGR. The reason for this observation is that the cerebellar blood flow is relatively spared in cases of IUGR as demonstrated by Behrman et al in their study on primate models. However the AC is acutely affected in IUGR. The ratio is not sensitive to diagnose symmetrical IUGR where both TCD and AC may be equally affected as noted in two separate studies by Wesley Lee, Scott Barton et al and Winston A Campbell, Anthony M. Viutzileous et al .
The progressive change in cerebellar grade noted in our study probably reflects progressive histological development and purkinje cell differentiation in the cerebellum as studied by Zecevic and Rakic  or it may relate to progressive decrease in cerebellar water content with advancing gestation as studied by Selzer ME, and co-workers .
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