Purpose: To report the observation of brown adipose tissue (BAT) with low fat content in neonates with hypoxic-ischemic encephalopathy (HIE) after they have undergone hypothermia therapy.
Materials and methods: The local ethics committee approved the imaging study. Ten HIE neonates (3 males, 7 females, age range: 2-3days) were studied on a 3-T MRI system using a low-flip-angle (3°) six-echo proton-density-weighted chemical-shift-encoded water-fat pulse sequence. Fat-signal fraction (FF) measurements of supraclavicular and interscapular (nape) BAT and adjacent subcutaneous white adipose tissues (WAT) were compared to those from five non-HIE neonates, two recruited for the present investigation and three from a previous study.
Results: In HIE neonates, the FF range for the supraclavicular, interscapular, and subcutaneous regions was 10.3%-29.9%, 28.0%-57.9%, and 62.6%-88.0%, respectively. In non-HIE neonates, the values were 23.7%-42.2% (p=0.01), 45.4%-59.5% (p=0.06), and 67.8%-86.3% (p=0.38), respectively. On an individual basis, supraclavicular BAT FF was consistently the lowest, interscapular BAT values were higher, and subcutaneous WAT values were the highest (p<0.01).
Conclusion: We speculate that hypothermia therapy in HIE neonates likely promotes BAT-mediated non-shivering thermogenesis, which subsequently leads to a depletion of the tissue's intracellular fat stores. We believe that this is consequently reflected in lower FF values, particularly in the supraclavicular BAT depot, in contrast to non-HIE neonates.
Keywords: Brown adipose tissue; Fat-signal fraction; Hypothermia; Infants; Water-fat MRI.