Normal values of the resistivity index of the pericallosal artery with and without compression of the anterior fontanelle.

BACKGROUND: Resistivity index (RI) of the pericallosal artery as is commonly measured during head ultrasound (US) examination in neonates. Some studies have shown that RI measured with gentle compression of the fontanelle provides additional information in cases of neonatal brain anomalies.

OBJECTIVE: The purpose of this study was to establish normal RI values with and without compression in a large population of neonates with normal cranial ultrasound as a function of gestational age.

MATERIALS AND METHODS: The authors of this retrospective study reviewed the RI of 323 infants with normal gray-scale cranial US and with a gestational age ranging 26-42 weeks. We conducted the exams both with and without compression of the anterior fontanelle and we studied changes in RI depending on gestational age, gender and type of delivery.

RESULTS: Infants with a gestational age of more than 35 weeks tended to have a lower RI (P=0.011). The compression of the anterior fontanelle emphasized the change in RI with increasing gestational age, with higher gestational ages having a lower RI (P<0.001). The results concerning the percentage change between baseline RI and RI with compression showed that infants with higher gestational ages have a smaller percentage change in RI (P=0.002).

CONCLUSION: We established the normal values for RI from 26 weeks to 42 weeks of gestation. The results of the study show the importance of taking the gestational age into consideration when evaluating the RI.