BY SAMUEL C. CHEW, M.D.
DEFINITION.—Enlargement of the calibre of a bronchial tube or tubes, whether confined to a limited portion of one tube, or reaching throughout a great part of its extent, or involving several or many tubes.
SYNONYM.—Bronchiectasis, from [Greek: bronchos], a bronchial tube, and [Greek: echtasis], an expansion.
HISTORY.—The change in the physical condition and size of a bronchial tube, designated as bronchial dilatation, never occurs as a primary affection, but is always the result of some preceding disease, especially of chronic bronchitis or fibroid phthisis. The full consideration of its pathological origin belongs, therefore, to the natural history of those causative affections.
Later writers have in general followed Laennec's description of the different varieties of bronchial dilatation; which, indeed, can hardly be improved upon, for such was the accuracy of that great clinician and pathologist as an observer that nothing was likely to escape him as regards physical conditions, though he may sometimes have been in error as to the theoretical explanation of what he saw. Previously to Laennec's observations dilatation of the bronchial tubes was, as he remarked himself, almost entirely overlooked both by pathologists and practitioners. The reason of this is evident from the considerations that a smaller tube when dilated would, except to the most careful examination, closely resemble a larger tube of normal size, and that a large dilatation might be mistaken by the ear at the bedside and by the eye at the necropsy for a pulmonary vomica.
Two principal forms of bronchial dilatation are met with. In the first, or diffused bronchial dilatation, known also as the cylindrical form, the tube is uniformly enlarged in calibre, so that, whereas in the normal state it would have admitted only a fine probe, in its enlarged condition it may be of the size of a goosequill. In this state it may be readily mistaken, when seen by itself, for a larger tube; but the alteration is conspicuous when the tube is seen to be larger than the branch from which it is given off. In the second or circumscribed form, which is also termed sacculated dilatation, a pouch-like or fusiform distension occurs in the continuity of a tube. In a third form, which is far less common, several successive enlargements are met with in the course of one tube, which thus presents a beaded appearance. It happens at times that all of these different varieties of dilatation may be encountered in the bronchial tubes of the same lung. The second, or sacculated, form is the most common, especially in young persons.
ETIOLOGY.—In both of the more common forms of bronchial dilatation the previous existence of bronchitis is to be regarded as the chief causative agency, though other conditions may serve to increase the dilatation when it has once been established. Laennec's observations led him to connect the occurrence of bronchitis with the production of dilatation of the bronchial tubes, though his explanation of the mechanism of this production was erroneous, inasmuch as he considered the accumulation of secretion in the affected tubes, and the forcible inspiratory efforts made in coughing to dislodge this accumulation, to be the direct causes of the enlargement. The part played by bronchitis in producing dilatation is, however, less immediate and mechanical than Laennec held it to be. It may, in a general way, be considered the direct cause of the cylindrical and the indirect cause of the saccular form of dilatation.
The long continuance of chronic bronchitis gives rise to weakness and atony of the bronchial walls, so that they yield to the pressure brought to bear upon them in the violent or protracted and repeated respiratory efforts that are made in coughing. In such cases the tubes which are themselves affected by the inflammatory process may yield throughout a greater or less extent of their continuity, and thus the cylindrical form of dilatation may be established. The same mechanism may be supposed to give rise to the beaded variety of the disease if the inflammatory action should be greater at several points along the course of a tube, with intervals of tissue in a healthier or less atonic state.
In the saccular form, on the other hand, the dilatation does not occur in the portion of the tube which is chiefly affected with the inflammatory process, but is the consequence of a local capillary bronchitis involving the ultimate ramifications of the affected tube and occasioning collapse of a portion of the lung. This collapse operates in two ways in causing a pouch-like dilatation of an adjacent bronchus—partly through the atmospheric pressure within the affected tube, tending to fill the space created by the collapsed portion, and partly by the traction of this collapsed lung-tissue outside of the tube.