Pulmonary Abscess

We have already described the termination of pneumonia in purulent infiltration, that is to say, in purulent solution of the inflammatory product, which occurs without any separation of continuity or ulcerous destruction. The reverse takes place when accumulations of pus are formed in the lung. This termination of pneumonia is extremely rare; but this rarity need not excite our wonder, nor do we require the explanation attempted by Laennec, if we adhere to our view of the pneumonic process. The conditions giving rise to the formation of pulmonary abscesses and the mode in which it is formed are, however, little known. Of all the theories which have been advanced, that is most conformable with the nature of the pneumonic process, which regards it as a consequence of a peculiar character of the inflammatory process, causing the pulmonary mucous membrane, which has been deprived of its epithelial investment, and the other tissues entering into the composition of the parenchyma, to become disintegrated and to suppurate, - a process analogous to that which occurs in many cases of true croup of the mucous membrane, and still more so to other exudative processes occurring on the same structure.

A recently formed, fresh pulmonary abscess presents the appearance of a cavern of irregular form filled with pus formed from the disintegration of the lung and surrounded by a softened parenchyma infiltrated with pus, and in some places hanging in shreds. It is perfectly similar to those rents which may be produced by pressure, when we are carelessly handling a lung in the stage of purulent infiltration, or on attempting to separate it from adhesions to the costal wall, and which we have already warned our readers against mistaking for pulmonary abscess.

The abscess either enlarges in the same way in which it originated, by the continued solution of the inflammatory product and of the tissue of its walls, or else by the confluence of other neighboring abscesses. As a general rule the suppuration extends over the whole of the inflamed portion of the lung, and hence the abscesses consequent on the lobular inflammation (of which we have already spoken) are always very considerable. According to their size we observe one or more bronchial tubes opening into them with transverse or oblique mouths, and their tissues also become the seat of purulent solution. These abscesses represent the true but very rare ulcerous 'pulmonary phthisis which is based on inflammation.

It proves fatal either by the supervention of fresh pneumonia around it, or pleuritis, or by the absorption of pus into the blood, with the symptoms of pyaemia and hectic fever. In rare cases it perforates the pulmonary pleura, and causes suppuration of the adjacent tissues, after having given rise to pleuritis and adhesion of the lung to the wall of the chest. Finally, in some very rare cases, it opens freely into the thorax before pleuritis and adhesion of the lung to the walls of the chest have been established; a general or circumscribed pleuritis then follows. If any of the bronchial tubes open into the abscess there will also be pneumothorax, and it may happen that the pleuritic effusion will be ejected through the air-passages, - a phenomena which however occurs much more frequently as a consequence of a reverse succession of the processes, namely, from primary pleurisy and consecutive corrosion and suppuration of the pleura. (See Pleuritis.) Finally, pulmonary gangrene sometimes arises in its vicinity, and the purulent solution of the tissues is converted into gangrenous ichor.

When the abscess has existed for a long time, its inner wall appears smooth, and its form is as nearly as possible round, and in the surrounding parts a secondary, interstitial inflammation may be observed, in consequence of which the parenchyma becomes converted into a cellulo-fibrous tissue, which surrounds the cavity of the abscess, and isolates it from the remainder of the pulmonary tissue. When an abscess is large-its perfect closure is very difficult; the process by which this is effected is by agglutination of its walls, which causes the obliteration of the bronchi entering into it; when the abscess has been a very large one, there is a depression of the thorax over it; and when its position is near the surface of the lungs, there is a puckered cicatrix left.

A pulmonary abscess may be confounded with a tuberculous vomica, and with certain accumulations of pus, which are developed from a secondary inflammation of the capillaries of the pulmonary tissue* of which we shall speak presently, and also with saccular dilatation of the bronchi.

The diagnosis may be established from a comparative view of the positive signs attending each of their conditions.