Wet Lung Disease (Transient Tachypnea of the Newborn) (TTN) (Retained Fetal Lung Liquid)

Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed

Etiology/Pathophysiology:
Retention or delay in clearing fetal lung liquid. Prior to birth the fetal lungs and airways are filled with fluid formed from an ultrafiltrate of plasma. During a normal vaginal delivery, 30% of this fluid is expelled by thoracic compression during transit through the vagina, 30% is cleared by the pulmonary lymphatics, and 40% is cleared by the pulmonary capillaries. When the thoracic compression is lacking or inefficient, such as in delivery via cesarean section or a precipitous delivery, there is retention and subsequent delay in the resorption of normal fetal lung liquid. Other causes of delay in the resorption of fetal lung liquid include prematurity, maternal diabetes, oversedation, and hypervolemic states.

Pathology:
Greater than normal amounts of fluid in the airways, alveoli, capillaries, and lymphatics.

Imaging Findings:
Symmetrical pattern of pulmonary congestion consisting of bilateral reticulonodular densities that are most prominent in the perihilar regions along with a slightly enlarged heart. Peripheral air trapping is present, leading to increased lung volume and scattered atelectasis. Small bilateral pleural effusions may be present. Air leak is rare. The chest x-ray returns to normal in 48-72 hours.

DDX:

• Hyaline Membrane Disease - usually has a uniform distribution of pulmonary opacities, never has pleural effusions, has a decreased lung volume.
• Meconium Aspiration - usually has nodular non homogeneous densities, may have pleural effusions, usually has an increased lung volume.
• Neonatal pneumonia - usually has non homogeneous densities, may have pleural fluid, usually has a normal lung volume.

References:
See References Chapter.

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