|III. Pediatric Lung Diseases|
|A. Hyaline membrane disease (HMD) or respiratory distress syndrome (RDS):||
- Main etiologic factors include prematurity with relative lack of surfactant, oxygen toxicity and barotrauma. Prophylactic and therapeutic use of surfactant has dramatically decreased morbidity and mortality.
- Grossly the lungs are red, consolidated and hypocrepitant.
- The microscopic hallmark is the formation of pink, acellular membranes lining the terminal and respiratory bronchioles and alveolar ducts. These are formed by necrosis of epithelium, exudation of plasma proteins, and, if there is hemorrhage, fibrin.
- Hyaline membranes are only seen in the liveborn, and are well-developed by 12-24 hrs. By 36-48 hours the reparative phase begins and the membranes are either completely resolved with minimal sequelae or there is varying degrees of fibrosis and loss of alveoli (BPD).
|B. Bronchopulmonary dysplasia (BPD)|
- This is divided into acute, reparative and healed phases. The main features are bronchiolar and interstitial fibrosis of more damaged areas and relative sparing with compensatory emphysema of less damaged acini.
- These patients have limited pulmonary reserve and develop repeated infections. There is often significant pulmonary hypertension which leads to cor pulmonale.
|C. Pulmonary hypoplasia||
- Unilateral or more often bilateral defective development of lung which is fatal.
- The lung weight is less than normal and there are fewer alveoli than expected for gestational age.
- Causes include prolonged oligohydramnios (renal agenesis, rupture of membranes), decreased intrathoracic space (renal cystic disease, diaphragmatic hernia), and decreased breathing movements (anencephaly, musculo-skeletal disorders).
|D. Cystic malformations||These are divided into three types based on morphology.|
- Type I (50%): large cysts, one may predominate, lined by ciliated epithelium with clusters of mucogenic cells.
- Type II (40%): relatively uniform multiple small cysts (<1.2 cm) lined by ciliated epithelium. Malformations of other organs may also occur.
- Type III (10%): Solid, bulky lesion causing mediastinal shift. Whole lobe is replaced by small cysts (<0.5 cm) lined by cuboidal epithelium.