Congenital Lung Abnormalities

Question 1

what are the stages of lung development (5)?

Answer 1

1. embryonic: specification of anterior foregut endoderm
2. pseudoglandular: lung bud formation, branching
3. canalicular: formation of gas exchange structures, survival is possible
4. saccular: differentiation of alveolar epithelial cells (Type I/II), surfactant production, generation of blood-air barrier
5. alveolar (postnatal): lung maturation, prime window for therapeutic intervention

Question 2

at which stage of lung development is survival possible?

Answer 2

canalicular stage (24 weeks): formation of respiratory bronchioles, epithelial differentiation begins, intense blood vessel ingrowth

CANalicular SURVIVE

Question 3

at which stage of lung development is the blood-air barrier established?

Answer 3

saccular stage (up to 36 weeks): alveoli develop, blood-air barrier is established, type I/II cells form, surfactant is produced

Question 4

how is lung maturity measured?

Answer 4

increase in lecithin to sphingomyelin ratio (L/S ratio) = lung maturity

more lecithin, less sphingomyelin as fetus develops

representative of surfactant production (required to prevent alveolar collapse)

Question 5

what is pulmonary hypoplasia and during which stage of lung development does it usually occur?

Answer 5

incomplete developed lung parenchyma connected to underdeveloped bronchi

occurs around pseudoglandular phase, mostly associated with other congenital abnormalities

Question 6

how do oligohydramnios cause secondary pulmonary hypoplasia?

Answer 6

oligohydramnios = inadequate amniotic fluid

this is a problem because fetus is supposed to swallow amniotic fluid to create pressure that stretches lung parenchyma, inducing lung development

Question 7

how can Potter syndrome/ sequence cause secondary pulmonary hypoplasia?

Answer 7

Potter syndrome: congenital kidney problems —> reduced fetal urine excretion —> oligohydramnios

oligohydramnios = inadequate amniotic fluid

this is a problem because fetus is supposed to swallow amniotic fluid to create pressure that stretches lung parenchyma, inducing lung development

Question 8

how can congenital diaphragmatic hernia cause secondary pulmonary hypoplasia?

Answer 8

diaphragm fails to develop properly, so separation of abdominal cavity from pleural space doesn’t develop right either

intestines will herniate into chest during critical period of lung development and compress developing lung —> hypoplastic lung, pulmonary HTN

Question 9

what are bronchogenic cysts and how do these present?

Answer 9

bronchogenic cyst: caused by abnormal budding of respiratory tissue from developing respiratory tract, lined with respiratory mucosa including mucus-secreting cells

most commonly within mediastinum

present (10-20yo) as either incidental finding, cause of compression (cough, dyspnea, wheezing), or with recurrent infection

Question 10

what is bronchopulmonary sequestration?

Answer 10

rare, congenital abnormalities of lower airways

non-functional mass of lung tissue that do not communicate with tracheobronchial tree and receive blood supply from systemic circulation

most often intralobar, in lower lobes (within normal lobe of lung)

commonly causes recurrent infection