(Ultrasound Review) Researchers from the Royal Women’s Hospital, Melbourne, investigated measurement of the transverse cerebellar diameter (TCD) in preterm neonates, and its use in assessment of gestational age (GA). Their aim was to better define the relationship between gestational age and TCD, and establish reliability of TCD measurements.
Published in the September issue of Australasian Radiology, the study confirmed that "TCD correlates closely with GA and predicts GA to 2.33 weeks. Measurements of TCD have excellent reproducibility."
When the LMP is unknown and early ultrasound has not been performed, accurate establishment of GA is difficult. According to the authors, "measurement of TCD in the fetus continues to be a useful indicator for GA even in the presence of abnormal skull shapes, fetal growth restriction, multiple pregnancies and large-for-dates fetuses."
Ultrasound images were obtained of the posterior fossa using the asterion as the acoustic window. The junction of the parieto-occipital and lambdoid sutures forms the asterion which is palpable immediately posterior to the pinna of the ear.
The study involved 96 preterm infants (23-32 weeks) without cranio-spinal malformation or grade 3 or 4 intraventricular haemorrhage. The authors suggested that extrapolation to the newborn infant was reasonable because there was consistency between fetal and neonatal life.
Another test used to determine GA in preterm infants <32 weeks is the New Ballard Score (NBS). Because the NBS requires handling of the fetus it is not always appropriate in sick neonates. Also, if the neonate has had sedation, is paralysed or there is generalized edema this precludes the use of the NBS.
A regression equation was derived with the TCD (mm) as the predictor variable and GA (weeks) as the outcome variable and percentile charts established. These investigators also assessed reproducibility and intra- and interobserver variability. They found TCD measurements to be "readily reproducible with minimal intra- and interobserver differences.’ Regression equation for TCD, GA relationship with 95% confidence interval: GA = (0.470 x TCD) + 13.162.
"Measurement of the transverse cerebellar diameter in preterm neonates and its use in assessment of gestational age"M W Davies et al
Division of Neonatal Services, Royal Women’s Hospital, Melbourne, Australia.
Australasian Radiology 2001(Sept); 45:309-312
By Ultrasound Review
November 6, 2001
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