Page 482 - Textbook of Pathology, 6th Edition

466 thinner than the systemic arterial system. They are thin elastic secondary pulmonary hypertension. It is the more common
vessels which can be easily distinguished from thick-walled type and may be encountered at any age, but more frequently
bronchial arteries supplying the large airways and the pleura. over the age of 50 years.
General diseases of vascular origin occurring in the lungs ETIOPATHOGENESIS. Based on the underlying
such as pulmonary oedema, pulmonary congestion, mechanism, causes of secondary pulmonary hypertension
pulmonary embolism and pulmonary infarction, have all are divided into the following 3 groups:
been already discussed in Chapter 5. The other important
disease of pulmonary alveocapillary wall, ARDS, has already A. Passive pulmonary hypertension. This is the commonest
been discussed above. Here, an account of pulmonary and is produced by diseases raising pressure in the
hypertension is given. pulmonary veins e.g.
1. Mitral stenosis.
2. Chronic left ventricular failure (e.g. in severe systemic
PULMONARY HYPERTENSION
hypertension, aortic stenosis, myocardial fibrosis).
Normally, the pulmonary arterial circulation is high-flow and B. Hyperkinetic (Reactive) pulmonary hypertension. In
low-pressure system with much lower blood pressure than this group are included causes in which the blood enters the
the systemic blood pressure; it does not exceed 30/15 mmHg pulmonary arteries in greater volume or at a higher pressure.
even during exercise (normally, blood pressure in the For example:
pulmonary veins is between 3 and 8 mmHg). Pulmonary 1. Patent ductus arteriosus.
hypertension is defined as a systolic blood pressure in the 2. Atrial or ventricular septal defects.
pulmonary arterial circulation above 30 mmHg. Pulmonary
hypertension is broadly classified into 2 groups: primary C. Vaso-occlusive pulmonary hypertension. All such
(idiopathic) and secondary; the latter being more common. conditions which produce progressive diminution of the
vascular bed in the lungs are included in this group. Vaso-
occlusive causes may be further sub-divided into 3 types:
Primary (Idiopathic) Pulmonary Hypertension
1. Obstructive type, in which there is block in the pulmonary
Primary or idiopathic pulmonary hypertension is an circulation e.g.
uncommon condition of unknown cause. The diagnosis can i) Multiple emboli or thrombi
be established only after a thorough search for the usual ii) Sickle cell disease
causes of secondary pulmonary hypertension (discussed iii) Schistosomiasis
below). The patients are usually young females between the 2. Obliterative type, in which there is reduction of pulmo-
SECTION III
age of 20 and 40 years, or children around 5 years of age.
nary vascular bed by chronic parenchymal lung diseases e.g.
ETIOPATHOGENESIS. Though the etiology of primary i) Chronic emphysema
pulmonary hypertension is unknown, a number of etiologic ii) Chronic bronchitis
factors have been suggested to explain its pathogenesis: iii) Bronchiectasis
1. A neurohumoral vasoconstrictor mechanism may be invol- iv) Pulmonary tuberculosis
ved leading to chronic vasoconstriction that induces v) Pneumoconiosis
pulmonary hypertension. 3. Vasoconstrictive type, in which there is widespread and
2. The occurrence of disease in young females has promp- sustained hypoxic vasoconstriction and alveolar hyper-
ted a suggestion that unrecognised thromboemboli or amniotic ventilation leading to pulmonary hypertension e.g.
fluid emboli during pregnancy may play a role. i) In residents at high altitude
Systemic Pathology
3. There is a suggestion that primary pulmonary hyper- ii) Pathologic obesity (Pickwickian disease)
tension may be a form of collagen vascular disease. This is iii) Upper airway disease such as tonsillar hypertrophy
supported by occurrence of Raynaud’s phenomenon iv) Neuromuscular diseases such as poliomyelitis
preceding the onset of this disease by a number of years in v) Severe kyphoscoliosis.
many patients, and disease association with SLE, scleroderma
and rheumatoid arthritis. MORPHOLOGIC FEATURES. Irrespective of the type of
4. Pulmonary veno-occlusive disease characterised by fibrous pulmonary hypertension (primary or secondary), chronic
obliteration of small pulmonary veins is believed to be cases invariably lead to cor pulmonale (Chapter 16). The
responsible for some cases of primary pulmonary pathologic changes are confined to the right side of the
hypertension, especially in children. This is generally heart and pulmonary arterial tree in the lungs. There is
considered a consequence of thrombosis or vasculitis. hypertrophy of the right ventricle and dilatation of the
5. Ingestion of substances like ‘bush tea’, oral contraceptives right atrium. The vascular changes are similar in primary
and appetite depressant agents like aminorex are believed and secondary types and involve the entire arterial tree
to be related to primary pulmonary hypertension. from the main pulmonary arteries down to the arterioles.
6. Familial occurrence has been reported in a number of cases. These changes are as under (Fig. 17.5):
1. Arterioles and small pulmonary arteries: These
Secondary Pulmonary Hypertension branches show most conspicuous changes. These are as
follows:
When pulmonary hypertension occurs secondary to a i) Medial hypertrophy.
recognised lesion in the heart or lungs, it is termed as