by Dr Noreen Norfaraheen Lee Abdullah MD (UKM), MMed Radiology (UKM), AM(Mal)

Answer to Case Of the Month 
Meconium aspiration complicated with left lower lobe pneumonia.

Discussion of Findings
In the first radiograph, there is marked hyperinflation of the lungs with flattening of the domes of both hemidiaphragms. There are numerous patchy asymmetrical nodular opacities in both lung fields. Also in both the lung fields, focal areas of atelectasis are seen and are especially marked at the left lower zone and right upper lobe. The cardiomediastinal contours are normal. The bones and soft tissues are normal. The stomach is outlined in the radiograph and the configuration is normal. The features are compatible with meconium aspiration.

In the second radiograph, the child is intubated. The tip of the endotracheal tube is slightly above the carina. There is worsening of the lung findings. There is now gross over inflation of both lung fields. The left lower zone is opaque with obscuration of the adjacent silhouettes namely the left heart border and the left hemidiaphragm. Air bronchogram is predominant. This feature favor left lower lobe pneumonia. The nodular infiltrates in the right lung is more prominent and numerous. No pneumothorax or pneumomediastinum observed. Bowel gas has outlined the entire gut.

In normal situations, meconium is expelled after birth. Meconium largely consists of mucus, epithelial cells, bile, hair, lanugo and debris. However, when there is intrauterine fetal distress, the hypoxic state of the fetus stimulates increased gastrointestinal peristaltic activity. This leads to premature expulsion of the meconium. Contrary to most beliefs, respiratory activity does occur in the fetus. The breaths are normally shallow but become deeper when there is intrauterine fetal distress. Thus when there is meconium in the amniotic fluid, coupled with the hypoxic fetus taking deep breaths, large volumes of meconium will be aspirated. Hence when the fetus is born, he will be in severe respiratory difficulty. Tachypnea, retractions, grunting and cyanosis almost always are the predominant features.

Radiographically, widespread air trapping is the most prominent finding. This finding results from meconium particles lodged in the small bronchi. If the quantity aspirated is small, the lung findings may be normal in the chest radiograph. If the quantity is large, the findings will be worse. Nodular infiltrates is another feature. It represents areas of atelectasis. This is explained by the deposition of meconium at the bronchi, which totally obstructs the air passageway. The distribution is usually at random with no particular predilection to any lobe of the lung. The atelectatic foci will in turn lead to compensatory over distention of the remaining air spaces. Pneumothorax and pneumomediastinum may follow. Occasionally, a large piece of meconium obstructs the bronchus and this leads to obstructive emphysema. Chemical pneumonitis will follow. Meconium aspiration clears clinically in 3-5 days. Radiographically clearing is slow; sometimes days or even months. The chest radiograph findings nearly always return to normal by 1 year of age.
 

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Last Updated:
Tuesday, 04 January 2005