Fig. 22.—Regeneration of epithelium over fissures which have been formed in the wall of a bronchus; the epithelium in the neighborhood of and within the fissure is squamous.
Epithelium lining the dilated bronchi is at times completely destroyed (Fig. 28), but more frequently it persists in part. That which remains has almost constantly the character of squamous epithelium (Figs. 22 and 23). The lowermost cells are cubical; those above them are polygonal, tending to become flatter as the surface is approached; upon the surface are cells often much flattened and occasionally they have lost their nuclei and stain deeply with eosin as the result of superficial necrosis. The change should not be regarded as metaplasia, for the epithelium assumes this squamous type when the superficial columnar cells have been lost. Actual necrosis of superficial ciliated columnar cells is occasionally seen (Autopsy 352); injured cells have separated from one another and desquamated into the lumen of the bronchus. The epithelium which remains after the superficial cells are lost consists of cells which become flatter from base to surface, but the intercellular bridges characteristic of the epithelium of the skin are not found. When epithelium is in process of regeneration, a layer gradually diminishing in thickness extends over the denuded surface, the advancing edge being formed by very flat cells in a single layer. The epithelium growing into fissures which have penetrated the bronchial wall may completely cover the exposed alveolar tissue. The newly formed epithelium may follow a fissure into an alveolus which has been opened and come into contact with the fibrin which fills the alveolus.
Fig. 23.—Squamous epithelium growing over the defect in the bronchial wall shown in Fig. 22 more highly magnified; squamous epithelium is present above and columnar epithelium below.
Bronchiectasis usually affects the small bronchi with no cartilage. It is not uncommon to find greatly dilated bronchi with no cartilage in close proximity to cartilage containing bronchi of smaller caliber. In one instance (Autopsy 421) a bronchus of medium size with cartilage measured 3 mm. in diameter, whereas two bronchi with no cartilage were dilated to 4 and 6 mm., respectively. Nevertheless, larger bronchi are occasionally the site of superficial loss of epithelium, necrosis extending into the bronchial wall, formation of fissures and stretching of the wall at the spot which is weakened. In association with these changes atrophy of the cartilage may occur (Autopsies 421, 425, 440, 463). Plates of cartilage in process of atrophy are readily recognized by their irregularly indented outline and often by their small size. The fibrous tissue surrounding the cartilage is the site of chronic inflammation and is densely infiltrated with lymphoid and plasma cells among which polynuclear leucocytes are scant. Nevertheless, polynuclear leucocytes are abundant in immediate contact with the cartilage and appear to have an important part in the solution of its matrix, for about them occur indentations of the edge. Leucocytes penetrate into the cartilage.
The necrosis and tears which occur in the wall of the bronchus are not always limited to the bronchus, but may extend deeply into the surrounding tissue. In Autopsies 312 (Fig. 21) and 423 wide areas of necrosis have penetrated deeply into the tissue about the bronchi.
Autopsy 312.—Illness began with influenza on September 26, seventeen days before death; a diagnosis of lobar pneumonia with consolidation of the right lower lobe was made ten days after onset and Pneumococcus IV, B. influenzæ and S. hemolyticus were found in the sputum. At autopsy there was bronchopneumonia with red and gray lobular and confluent lobular patches of consolidation and right and left serofibrinous pleurisy; there was purulent bronchitis; no abscesses were seen. Small bronchi throughout both lungs were dilated and often surrounded by a zone of hemorrhage.
Hemolytic streptococci were found in the heart’s blood, in the pleural exudate, consolidated lung and bronchus; B. influenzæ was found in the lung and in a small bronchus, and staphylococci in the contents of a small bronchus.
Fig. 24.—Acute bronchiectasis with fissures extending through bronchial wall which is marked by great engorgement of blood vessels; at one point a fissure has penetrated deep into the alveolar tissue and formed a small cavity containing purulent exudate and surrounded by fibrinous pneumonia. Autopsy 312.