Spleen Behind the Heart Complicates Lung‐to‐Head Ratio Measurement in Left‐Sided Congenital Diaphragmatic Hernia

In fetuses with left‐sided congenital diaphragmatic hernia, intrathoracic herniation of the spleen is a common occurrence. The herniated spleen can reside posterior to the left atrium of the heart in the right hemithorax and is increasingly differentiated from the lung with the use of newer sonographic equipment. Estimation of the neonatal prognosis relies on accurate measurement of fetal lung size, particularly with commonly used measurements such as the lung‐to‐head ratio. Here we describe how herniation of the spleen behind the heart can complicate measurement of the lung‐to‐head ratio on sonography and lead to overestimation, with implications for perinatal prognostication and management.