Developmental Aspects of Lung disease

Question 1

Outline the 5 phases of structural lung development and when they take place.

Answer 1

Embryonic - 3-8 weeks
Pseudogalndular - 5-17 weeks
Canalicular - 16-26 weeks
Saccular - 24-38 weeks
Alveolar - 36 weeks-2/3 years

Question 2

Describe embryonic phase

Answer 2

Embryonic phase - Lung bud starts to develop as respiratory diverticulum from the foetal foregut. At 5 weeks there are two primary lung buds visible these then divide into lobar buds by which there are two on the left and three on the right. Like gut cells they are derived from the endoterm whereas the blood tissues and CT are surrounded by mesoderm.

Question 3

Describe pseudoglandular phase.

Answer 3

Psuedoglandular phase - rapid branching of airways. Eventually there are 16-25 primitive segmental bronchi which are formed and continue to elongate and widen in later phases. Also development of specialised cells such as cilia and mucous glands which start to appear in the airways.

Question 4

Describe canalicular phase.

Answer 4

Canalicular phase - Lungs develop their distal architecture, importantly this is the phase terminal bronchioles, alveoli sacs and capillary vessels form gas exchange units. Type 1 and 2 pneumocytes start to appear in this phase. Type 1 - very thin membranes which allow gas exchange. Type 2 - produces surfactant. Presence of specialised gas exchange units allow the foetus to be delivered prematurely and survive with extensive life support.

Question 5

Describe saccular phase.

Answer 5

Saccular phase - Alveolar sacs grow in size and become well formed, more surfactant produced. Bronchioles continue to elongate and interstitial tissue between sacs reduce. Alveolar walls become thinner improving gas exchange.

Question 6

Describe alveolar phase.

Answer 6

Alveolar stage - Lungs can independently sustain breathing without support. The cells at this stage are well differentiated and the pulmonary vasculature is more developed forming the final alveolar structures.

Question 7

Describe common conginetal abnormalities.

Answer 7

Upper - Laryngomalacia and tracheomalacia. Tracheo-oesophageal fistula.

Lower - CPAM and conginetal diaphragmatic hernia.

Question 8

Describe presentation of conginetal abnormalities.

Answer 8

Presentation of Conginetal abnormalities - Childhood: Stridor/wheeze, recurrent pneumonia, cough, feeding issues. Asymptomatic: Incidental finding.

Question 9

Describe laryngomalacia.

Answer 9

Laryngomalacia - common conginetal abnormality. Malacia is greek for softening. Commonly seen in infants. Present with stridor, worse with feeding or when upset/excited. Will improve within first year, concern if affects feeding, growth or causes apnoeas.

Question 10

Describe tracheomalacia

Answer 10

Tracheomalacia - Can be isolated in healthy infants, associated with genetic conditions. May be caused by external compression. Presentation: Barking cough, recurrent croup, breathless on exertion, stridor/wheeze. Management includes phsyio and antibiotics when unwell, natural history resolution with time.

Question 11

Describe tracheo-oesophageal fistula

Answer 11

Tracheo-oesphageal fistula: Abnormal connection between trachea and oesophagus, majority have associated oesphageal astria. Association with genetic conditions.

Question 12

Describe presentation and treatment of tracheo-oesophageal fistula

Answer 12

Presentation of tracheo-oesophageal fistula - may be diagnosed antenatally or postnatally. Presentation: choking, colour change, cough with feeding and unable to pass NG (Nasogastric tube).

Treatment of tracheo-oesophageal fistula - treatment with surgical repair. Complications include tracheomalacia, strictures, leak and reflux.

Question 13

Describe CPAM (conginetal pulmonary airway malformation)

Answer 13

Conginetal Pulmonary Airway Malformation: Abnormal non-functioning lung tissue, 80% detected antenatally, occurs sporadically. May resolve spontaneously in utero. Conservative Management if Asymptomatic. Surgical intervention may be required. Possible risk of malignant change.

Question 14

Describe Conginetal diaphragmatic hernia.

Answer 14

Conginetal Diaphragmatic Hernia - Diaphragm develops from multiple tissues around 7 weeks and closes by 18 weeks in some cases this does not close properly causing the condition. CDH affects 1 in 2500 births. Different types, most common Bochdalek (90%). Usually left side > right side. Most diagnosed antenatally, some diagnosis late. Management surgical repair. Prognosis depends on degree of lung hypoplasia.

Question 15

Describe neonatal lung disease.

Answer 15

Neonatal Lung disease - Significant changes occur at birth after first breaths. Lungs inflate and fluid in lungs is absorbed. In healthy terms infants, transient tachypnoea of newborn can develop, associated with caesarean section and improves within 1-2 days.

Question 16

Describe RDS and it’s treatment.

Answer 16

Respiratory distress syndrome is a neonatal disease which occurs in preterm infants and some term infants. Due to surfactant deficiency, also called hyaline membrane disease.

Treatment of RDS - Antenatal steroids, Surfactant replacement and appropriate ventilation and nutrition.

Question 17

Describe chronic lung disease.

Answer 17

Chronic lung disease (bronchopulmonary dysplasia) - chronic lung disease associated with prematurity where ongoing oxygen requirement at term. Multifactorial causes. Associated with increased childhood respiratory morbidity. Leads to chronic obstructive picture in later life.

Question 18

Define remodelling.

Answer 18

Remodelling is defined as the alteration of the airway structure following external influences. These could be environmental exposures, chronic disease of childhood or infection. Leads to abnormalities due to interference of inter-cellular signalling.

Question 19

Describe how lung function deficits established at early age may affect adult life.

Answer 19

Lung function deficits which are established at school age can continue in to adult life. This may lead to adult COPD or other obstructive diseases. Early life events can accelerate the decline.