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Fetal lungs

The fetal lungs are paired organs in the thoracic cavity that undergo continuous growth and maturation during gestation. Although they are not functional for respiration in utero, they develop structurally in preparation for postnatal gas exchange. Fetal lung evaluation is an essential part of prenatal imaging, as lung development correlates with fetal viability and neonatal outcome.

Synonyms

  • Prenatal lungs

  • Developing lungs in utero

  • Fetal pulmonary tissue

Structure and Development

  • Embryonic stage (weeks 4–7): Lung bud formation from foregut

  • Pseudoglandular stage (weeks 5–17): Branching of airways to terminal bronchioles

  • Canalicular stage (weeks 16–26): Differentiation of respiratory bronchioles; vascularization increases

  • Saccular stage (weeks 24–38): Terminal sac formation; primitive alveoli form

  • Alveolar stage (late fetal life → postnatal): Alveolar multiplication and maturation continue into early childhood

  • Fetal lungs are filled with fluid secreted by pulmonary epithelium, which maintains pressure and supports growth

Relations

  • Medially: Heart and great vessels

  • Inferiorly: Diaphragm separating lungs from abdominal organs

  • Laterally: Thoracic cage

  • Superiorly: Neck structures and trachea

Function

  • In utero: Lungs secrete fluid to maintain lung volume and promote growth

  • Postnatal preparation: Development of airways, alveoli, and surfactant production (type II pneumocytes begin around 24 weeks)

  • Serve as critical maturity markers in predicting neonatal respiratory function

Clinical Significance

  • Pulmonary hypoplasia: Underdeveloped lungs due to oligohydramnios, congenital diaphragmatic hernia, or skeletal dysplasias

  • Congenital lung malformations: CPAM (congenital pulmonary airway malformation), bronchopulmonary sequestration

  • Infections and inflammation: Can alter signal or volume on imaging

  • Fetal lung volume measurement: Performed on MRI to predict neonatal survival in cases of diaphragmatic hernia

  • Imaging relevance: MRI is superior to ultrasound in assessing fetal lung volume and signal patterns

MRI Appearance

T2 HASTE (T2 GRE):

  • Fetal lungs: bright hyperintense signal due to high fluid content

  • Signal intensity increases with gestational age as lungs accumulate more fluid and become more homogeneous

  • Hypoplastic lungs: show reduced volume and lower T2 signal intensity compared to expected gestational norms

T1 GRE:

  • Fetal lungs: low signal intensity (dark) because of fluid-filled tissue

  • Meconium aspiration or hemorrhage (rare in utero): may increase T1 signal focally

  • Surfactant production in late gestation does not significantly alter T1 signal

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Fetal Eyes Anatomy MRI IMAGE

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Fetal lungs MRI axial anatomy image-img-00000-00000