| Background and PurposeOn T1-weighted (T1WI) MR images of the brain in neonates, it is frequently found that the globus pallidus present symmetric hyperintensity to varying degrees. This sign, which occurs after birth and disappears gradually in late stage, is also called "a transient hyperintensity". At present almost all the studies about the T1WI hyperintensity in globus pallidus have been focused on the bilirubin encephalopathy. Many studies have confirmed bilirubin encephalopathy can cause symmetric hyperintensity in the globus pallidus on T1WI images. However, Using of symmetry hyperintensity in the globus pallidus on T1WI to diagnose bilirubin encephalopathy still have a high false positive rate, as we found in our clinical practice. Although the T1WI hyperintensity in the globus pallidus is often encountered on neonatal MR images, it does not always correspond to a bilirubin encephalopathy, even occurs at lower or normal bilirubin levels. This cause great confusion in the imaging diagnosis and the interpreation of imaging signs. In the present study, we explore the causes of symmetric T1WI hyperintensity of the globus pallidus through analysis of the MRI and clinical data in a group of newboras.Subjects and Methods:1 Clinical dataClinical data of newborns who undertook postnatal brain MRI from January 2013 to June 2014 in our hospital were collected. MRI images were reviewed to exclude the cases which have severe intracranial lesions or severe imaging artifacts. The cases with the time interval of more than 5 days between MR examination and bilirubin test were also excluded. Finally, a total of 427 cases of newborns were included in this study.2 Methods2.1 Qualitative analysis of the T1WI hyperintensity in globus pallidusThe cerebral MR images were reviewed by two senior radiologic physicians who were separated and blind to the clinical information. The signal intensity of globus pallidus was interpreted as normal or hyperintensity, comparing with the background signal of gray matter. For cases with inconsistent interpretations, the two researchers discussed to reach a consensus.2.2 Quantitative analysis of the T1WI hyperintensity globus pallidusSignal intensity values of the bilateral globus pallidus as well as the frontal cortex were measured, and the ratio of signal intensity of the globus pallidus to the frontal cerebral cortex was calculated. In the cases with normal signal, the average ratio of signal intensity was 1.22 ± 0.049, with a 90%limit on the range of 1.30. So,1.30 was used as the threshold value to determine quantitatively whether there is a hyperintensity in the globus pallidus. Further, the signal intensity ratio of the globus pallidus to the cerebral cortex is divided into four levels (<1.30,1.30-1.39,1.40-1.49 and≥1.50).2.3 Analysis of the relationship between the T1WI hyperintensity of the globus pallidus with clinical factorsLogistic regression analysis was employed to investigate the contributions of the clinical factors to the T1WI hyperintensity of globus pallidus.2.4 Analysis of the relationship bewteen the T1WI hyperintensity of the globus pallidus and total serum bilirubin (TSB) levelsLogistic regression analysis revealed hyperbilirubinemia is the main factor contributing to the T1WI hyperintensity of the globus pallidus. Based on the result, we did further analysis of the relationship between the T1WI hyperintensity of the globus pallidus and total serum bilirubin levels. According to serum total bilirubin levels, cases were divided into the normal group (TSB<100.0 μmol/1), mildly elevated group (100.0 umol/1≤TSB<220.6 μmol/1), moderately elevated group (220.6 μmol/1≤TSB <307.8 umol/1) and significantly elevated group (TSB≥ 307.8 umol/1). The relationship between globus pallidus/cerebral cortex signal intensity ratio with the TSB level was analyzed.2.5 Analysis of the relationship between the T1WI hyperintensity of the globus pallidus and postnatal or gestational ageBy using the globus pallidus/cerebral cortex signal intensity ratio as the vertical axis, and postnatal or gestational age as abscissa axis, the scatter diagram was made to analyze the relationship between the signal intensity ratio and postnatal or gestational age in term and preterm infant. 3 Statistical analysisExcel software was applied to establish a database, and all data were presented as (x±s). SPSS 19.0 was employed for statistical analysis. Chi-square test was used to compare the globus pallidus/cerebral cortex signal intensity ratio with the TSB level. The split chi-square test was used for the inter-groups comparison. The relationship between the globus pallidus/cerebral cortical signal intensity ratio between age or gestational age was presented in a scatter diagram, and was analyzed by correlation analysis. P<0.05 was considered statistically significant.Results:1 Signal patterns of the globus pallidus on T1WI imagesT1WI hyperintensity of the globus pallidus was found in 249 of 427 cases (58.3%).2 The relationship between the clinical pathogenesis and the hyperintensity of the globus pallidus on T1WI imagesThe incidence rates of the T1WI hyperintensity of the globus pallidus for various potential clinical pathgenesis were ranked as follows in descending order:72.1%(209/290) of hyperbilirubinemia,61.8%(47/76) of cerebral injury,55.0%(11/20) of hypoproteinemia,48.1%(25/52) of premature delivery,47.8%(32/67) of apnea,33.3%(1/3) of purulent meningitis,28.6%(4/14) of sepsis, and 24.6%(16/65) of other causesLogistic regression analysis showed that hyperbilirubinemia is a major factor contributing to the T1WI hyperintensity of the globus pallidus (OR=5.915,P<0.001).3 The correlation between the total serum bilirubin levels and the T1WI signal intensity ratio of the globus pallidus to the cerebral cortexWith the TSB level increasing, the signal intensity ratio of the globus pallidus to the cerebral cortex increased, with the difference statistically significant (χ2=84.734, P<0.001,r=0.407).4 The correlation between the signal intensity ratio of the globus pallidus to the cerebral cortex and the postnatal age or gestational ageCorrelation analysis showed that the signal T1WI intensity ratio of the globus pallidus to the cerebral cortex was negatively correlated with the postnatal age at MRI examination (r=-0.441, P<0.001), while not correlated with the gestational age.Conclusion:Hyperbilirubinemia is a main factor contributing to the T1WI hyperintensity of globus pallidus in newborns. However, the lower TSB may also cause signal changes, suggesting there are other factors involving in the formation of the T1WI hyperintensity. The T1WI hyperintensity in the globus pallidus is closely related to the postnatal age, but not related to the gestational age. |
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