This photo illustrates bilateral pulmonary hypoplasia. When the heart and lung block is placed on a flat surface it is normal for the most inferior portions of the lungs to be at the level of the cardiac apex. Pulmonary hypoplasia is also evaluated by lung:body weight ratio. Bilateral pulmonary hypoplasia is usually associated with the oligohydramnios sequence. See renal pathology also.
Diaphragmatic hernia, usually involving the left hemidiaphragm, with movement of abdominal organs into the thoracic cavity during embryonal and fetal life, results in pulmonary hypoplasia, most severe in the ipsilateral lung. In this anterior view of the lungs disparate size is readily apparent.
In order for the lungs to develop normally there must be sufficient space in the thoracic cavity and adequate amniotic fluid entering and exiting the lungs. When these conditions are not present there is inadequate lung development. Insufficient intrathoracic space can result from space-occupying lesions such as diaphragmatic hernia or cystic adenomatoid malformation or from chest wall deformities as in the lethal form of osteogenesis imperfecta or from large chronic effusions as in fetal hydrops. Oligohydramnios results from premature rupture of the membranes with chronic leak or from insufficient fetal urine entering the amniotic cavity as the result of lack of production by the kidneys as in renal agenesis or cystic dysplastic lesions or from obstruction to the flow of urine as in entities such as prune belly syndrome. In the presence of a normal amount of amniotic fluid, pulmonary hypoplasia can result from inadequate movement of amniotic fluid in and out of the lungs because of neurological or neuromuscular conditions in the fetus. A fetal ultrasound examination can discover oligohydramnios, renal absence or malformations, space-occupying lesions, chest wall abnormalities, or decreased fetal movements which would indicate fetal neuromuscular disease. Three dimensional ultrasound can be used to estimate lung volume. In some cases CT scanning or MRI is needed for more definitive diagnosis. Surgical treatment can be applied for space-occupying lesions. ECMO is sometimes needed to allow further postnatal time for lung development.