Malformations of the trachea usually consist of a fistulous opening, the result of failure of closure of the third or fourth branchial cleft. Generally appear along the anterior border of the sternomastoid, a little above the clavicle.

The trachea is the seat of inflammatory processes secondary to those in the neighboring portions of the respiratory system, the larynx, and the bronchi.

Bronchitis may be either acute or chronic. When severe it may extend to the capillary bronchi and involve the adjacent lung tissue, giving rise to an important form of broncho-pneumonia. In the acute variety the mucosa becomes congested with swelling, and in the beginning secretion is decreased. There is soon an increased exudation, at first thin and with but few pus cells, but soon becoming thick and tenacious and containing more cells. There is a desquamation of the epithelium and the walls will show a round cell infiltration.

If there is much expectoration of a serous type the condition is known as bronchorrhea serosa; if purulent in character, broncho-blennorrhea. Blood may be present as a result of congestion or rupture of capillary vessels.

The cause of bronchitis is not definitely known. It is probably bacterial in origin, but it commonly follows exposure to cold which lowers resistance against infection.

Chronic bronchitis may follow repeated acute attacks or accompany various chronic diseases of the lung or heart, particularly in those in which there are marked circulatory disturbances. The mucosa is much congested, the secretion may be scant or plentiful, and there may be distinct projections on the walls. The epithelial cells may undergo hyperplasia or atrophy. Instead of proliferative changes there may be atrophy with weakening of the bronchial walls and dilatations.

Fibrinous bronchitis is a condition in which a small area of the terminal bronchi and bronchioles are involved. It is marked by the expectoration of a dense yellowish-white substance moulded in the shape of the air-passages from which it came. The larger stalk is usually hollow, the smaller branches being solid and the walls commonly laminated. Although resembling fibrin it does not always give the characteristic reaction and may be evidently inspissated mucous. In the meshes of the bronchial cast are leukocytes, broken-down epithelium, and Charcot-Leyden crystals such as are found in asthma. Curschmann's spirals are also found. These are collections of fine fibrils twisted like a corkscrew. They are present at the end of the smallest branches of the cast.

In diphtheria and in croupous pneumonia there may be the formation of a true fibrinous exudate. The mucosa of the bronchi is reddened and is more or less completely covered by a pseudo-membrane.

Bronchiectasis, or dilatation of a bronchus, may follow chronic bronchitis in which there has been atrophy and weakening of the bronchial wall, or it may be due to an increase in the air-pressure. The medium-sized bronchi of the lower and middle lobes of the right lung are the ones most frequently involved. The enlargements are usually saccular, but may be fusiform or cylindric. There may also be several in the course of a single bronchus. The walls may appear of normal thickness, but this is due to fibrous tissue formation, as the normal tissues are atrophic, particularly the mucous membrane.

In fibroid phthisis the contraction of the new formed fibrous tissue may drag upon the bronchi and cause them to dilate.

The walls of the cavity may be smooth, lined with epithelium and may contain remnants of the normal bronchial wall. If the cavity be roughened by ulceration it will be at the most dependent point as it is there that the retained secretions will act.

Chronic Fibrinous Bronchitis.

Fig. 139. - Chronic Fibrinous Bronchitis.

Fibrinous Casts of the Bronchi, Similar to those Shown in the Photograph, were Coughed up at Irregular Intervals for Several Years (Delafield and Prudden).

The openings of entrance and exit may be evident. There will be no shreds of blood-vessels, or of other bronchi or bronchioles present.

As the walls become weakened, secretions in large amounts may be retained and by their weight cause extensive bronchiectasis. The various dilatations may, on account of atrophy of the intervening tissues, communicate. They may be filled with secretion, with cyst formation resulting. The wall of the cavity is, as a rule, smooth or only slightly granular.

This material may undergo decomposition with subsequent gangrene or it may dry up.

Obstruction of a bronchus may be the result of inflammatory changes within the wall, of tumors or foreign bodies inside, or of pressure from the outside.

Foreign bodies more commonly lodge in the right bronchus, and may cause ulceration and pneumonia or gangrene of the lung.

Ulceration of the bronchi may follow acute or chronic bronchitis, or be due to the presence of foreign bodies. The most common cause of severe ulceration is tuberculosis. The lesion may be superficial or so deep as to cause necrosis of the cartilage with perforation of the bronchus. In such a case the material may escape into the lung and cause suppuration.

Tumors

Primary growths are uncommon, but secondary tumors are more frequent, particularly carcinomata.