Page 478 - Textbook of Pathology, 6th Edition

462 2. Pulmonary vascular disease
3. Pulmonary infections
4. Chronic obstructive pulomonary disease
5. Chronic restrictive pulmonary disease
6. Tumours of lungs.

PAEDIATRIC LUNG DISEASE
A number of congenital anomalies (e.g. agenesis, hypoplasia,
heterotopic tissue, vascular anomalies, tracheal and bronchial
anomalies, congenital pulmonary overinflation or lobar
emphysema, congenital cysts and bronchopulmonary
sequestration) and certain neonatal acquired lung diseases
(respiratory distress syndrome or hyaline membrane disease,
bronchopulmonary dysplasia, meconium aspiration
syndrome, persistent foetal circulation, atelactasis, collapse
and bronchiolitis) have been described. Some of the
important conditions from point of view of pathology are
discussed below.

CONGENITAL CYSTS

Developmental defects involving deficiency of bronchial or
bronchiolar cartilage, elastic tissue and muscle result in
Figure 17.2 Histologic structure of alveolar wall (alveolar septa). It congenital cystic disease of lungs. A single large cyst of this
shows capillary endothelium, capillary basement membrane and scanty
interstitial tissue and the alveolar lining cells (type I or membranous type occupying almost a lobe is called pneumatocele. Multiple
pneumocytes and type II or granular pneumocytes). small cysts are more common and give sponge-like
appearance to the lung. The cysts are thin-walled and dilated
and generally lined by flattened ciliated epithelium overlying
about 95% of alveolar surface, while type II or granular a thin layer of supportive connective tissue. These cysts may
pneumocytes project into the alveoli and are covered by
SECTION III
microvilli. Type II pneumocytes are essentially reserve cells contain air or may get infected and become abscesses. Cysts
which undergo compensatory hyperplasia when type I may rupture into bronchi producing haemoptysis, or into
pneumocytes are injured and are also the source of the pleural cavity producing pneumothorax.
pulmonary surfactant rich in lecithin. The main functions of
coating of surfactant are to lower the surface tension of the BRONCHOPULMONARY SEQUESTRATION
alveolar lining cells and in maintaining the stability of the Sequestration is the presence of lobes or segments of lung
alveoli. tissue which are not connected to the airway system. The
4. The alveolar macrophages belonging to mononuclear- blood supply of the sequestered area is not from the
phagocyte system are present either free in the alveolar pulmonary arteries but from the aorta or its branches.
spaces or are attached to the alveolar cells. Sequestration may be intralobar or extralobar.
5. The pores of Kohn are the sites of alveolar connections
Systemic Pathology
between the adjacent alveoli and allow the passage of bacteria Intralobar sequestration is the sequestered broncho-
and exudate. pulmonary mass within the pleural covering of the affected
lung.
FUNCTIONS. The primary functions of lungs is oxygenation
of the blood and removal of carbon dioxide. The respiratory Extralobar sequestration is the sequestered mass of lung
tract is particularly exposed to infection as well as to the tissue lying outside the pleural investing layer such as in the
hazards of inhalation of pollutants from the inhaled air and base of left lung or below the diaphragm. The extralobar
cigarette smoke. There exists a natural mechanism of filtering sequestration is predominantly seen in infants and children
and clearing of such pollutants through respiratory and is often associated with other congenital malformations.
epithelium, tracheobronchial lymphatics and alveolar
macrophages. Besides, the lungs are the only other organ ACUTE RESPIRATORY DISTRESS SYNDROME
after heart through which all the blood of the body passes (HYALINE MEMBRANE DISEASE)
during circulation. Therefore, cardiovascular diseases have Acute respiratory distress syndrome (ARDS) is a severe, at
serious effects on the lungs, and conversely, diseases of the times life-threatening, form of progressive respiratory
lungs which interfere with pulmonary blood flow have insufficiency which involves pulmonary tissues diffusely i.e.
significant effects on the heart and systemic circulation. involvement of the alveolar epithelium, alveolar lumina and
Following groups of diseases of the respiratory tract are interstitial tissue. ARDS exists in 2 forms: neonatal and adult
studied in this chapter: type. Both have the common morphological feature of
1. Paediatric lung disease (congenital and acquired) formation of hyaline membrane in the alveoli and hence is