Explain the time course of bronchial, vascular, and alveolar development in the embryonic and pediatric lung and indicate which diseases result from interference of lung growth at various phases of development

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Lecture 38 Pediatric Diseases

  1. Explain the time course of bronchial, vascular, and alveolar development in the embryonic and pediatric lung and indicate which diseases result from interference of lung growth at various phases of development.

    Time Course

    Lung Development

    Associated Diseases

    16 weeks gestation

    Bronchial tree is developed

    Canalicular stage 17-28th weeks

    Acini develop

    60% RDS

    Saccular stage 29-36th weeks

    Saccular development, surfactant appears

    15-20% RDS

    Alveolar stage 37th week +

    True alveoli form and grow

    <5% RDS

  2. Define respiratory distress syndrome and hyaline membrane disease, giving the pathogenesis, clinical features, pathology, and prognosis.

Respiratory Distress Syndrome (RDS) = Hyaline Membrane Disease (HMD) – respiratory distress in premature infants shortly after birth due to lack of surfactant. HMD is so called because of the formation of membranes in the peripheral airspaces of these infants.

Pathogenesis – deficiency in surfactant due to pulmonary immaturity. Surfactant reduces the surface tension in the alveoli requiring less pressure to keep them patent and hence aerated.

Clinical Features – usually premature infants appear OK at birth, but develop respiratory distress soon after. Infiltrates can be seen on chest film. Treatment consists of supplemental oxygen and artificial surfactant.

Pathology – atelectasis and hyaline membranes.

Prognosis – 8% mortality, usually in the first 3-4 days, after that prognosis is good. Recovery of infants of 31 weeks gestation or more can be anticipated without permanent sequelae.

  1. Define bronchopulmonary dysplasia.

Bronchopulmonary Dysplasia - chronic phase of hyaline membrane disease that may last for months to years or even cause death. It is caused by bronchiolar fibrosis with narrowing and interstitial fibrosis, as well as persistent lung immaturity and chronic atelectasis.

  1. List the common causes of pulmonary hypoplasia.

    1. External compression (rib cage anomalies, diaphragmatic hernia)

    2. Renal agenesis or disease (Potter's syndrome)

    3. Oligohydramnios (decreased amniotic fluid)

    4. Anencephaly

    5. Idiopathic

    6. Associated with many complex malformation syndromes

  2. Define foregut cysts; intralobular sequestration; extralobular sequestration.

Foregut Cysts - represent an abnormal detachment of primitive foregut and are most often located in the hilum or middle mediastinum.

Pulmonary Sequestration refers to the presence of a discrete mass of lung tissue without any normal connection to the airway system. Blood supply to the sequestered area arises not from the pulmonary arteries but from the aorta or its branches.

Intralobular Sequestration - within the lung substance, associated with recurrent localized infection (repeated pneumonias) or bronchiectasis.

Extralobular Sequestration - external to the long and may be found anywhere in the thorax or mediastinum, most commonly associated with congenital abnormalities.

  1. Describe the following aspects of cystic fibrosis: Epidemiology, pathogenesis, clinical pattern of disease, pathology, and prognosis.

Epidemiology: incidence of 1 in 3200 live births in the US, cystic fibrosis is the most common lethal genetic disease that affects Caucasian populations. It is uncommon among Asians (1 in 31,000) and African-Americans (1 in 15,000). 2-4% of the white population are heterozygous carriers.

Pathogenesis: the primary defect results from abnormal function of an epithelial chloride channel protein encoded by the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. Over 200 mutations exist; most common (70%) is deletion at 508.

Clinical Pattern of Disease: symptoms are extremely varied and range from mild to severe, from onset at birth (5-10%) to years later, and from involvement of one organ system to many. Exocrine pancreatic insufficiency occurs in the majority (85-90%) patients and is associated with protein and fat malabsorption and increased fecal loss. Cardiorespiratory complications, such as persistent lung infections, obstructive pulmonary disease, and Corp. Homan Alley, are the most common cause of death (about 80%) in the US. Recurrent sinonasal polyps (25%). Significant liver disease (13-17%). Male infertility (95%)

Pathology: Pancreas - from mucus in the small ducts with some dilation of exocrine glands to totally plugged ducts causing atrophy of the exocrine glands and progressive fibrosis. Liver - bile canaliculi are plugged accompanied by a ductular proliferation and portal inflammation with biliary cirrhosis developing overtime. Salivary glands - dilation of ducts, squamous metaplasia of epithelial lining, and glandular atrophy followed by fibrosis. Pulmonary - mucous secretions that obstruct the air passages and predispose to infection. Vas deferens - congenital bilateral absence of vas deferens.

Prognosis: median life expectancy is around 30 years and continues to increase. Advances include improved infection control, gene therapy (possible), and bilateral lung, heart-lung, liver, pancreas, or liver-pancreas transplantation.

  1. List the various types of diseases that can produce bronchiectasis.

Congenital or hereditary: cystic fibrosis, intralobar sequestration of the lung, immunodeficiency states, and primary ciliary dyskinesia and Kartagener syndromes.

Postinfection: necrotizing pneumonia caused by bacteria, viruses, and fungi.

Bronchial obstruction: tumor, foreign bodies, and occasionally mucus impaction.

Other conditions: rheumatoid arthritis, systemic lupus earth produces, inflammatory bowel disease, and post-transplantation (lung rejection and graft-versus-host disease).

  1. Define bronchiectasis and explain common factors in its pathogenesis.

Bronchiectasis -fixed dilation of airways, predominantly bronchi. Considered to be a sequelae of a previous necrotizing inflammatory process in airways.

Obstruction and infection are the major influences associated bronchiectasis. Mucous accumulation, ciliary abnormalities, and airway inflammation.

  1. Describe the gross and microscopic appearance of bronchiectatic airways.

Gross: airways are dilated compared to normal and typically, thin-walled, may be symmetrically dilated or saccular.

Micro: shows absence of normal bronchial wall structures (glands, muscle, cartilage), fibrosis and chronic inflammation, and sometimes superimposed acute infection.

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