COURSE.—It may be said, in a general way, that the etiology has much to do with its course. If the cause be pneumonia, the course will be such as the detail of symptoms already given shows. In some unknown way the natural course of the disease is interrupted, and what promises to be an average case is followed by the characteristic features of abscess. If pyæmia be the precedent condition, a peculiar form of pneumonia, embolic in origin, appears, and abscesses again follow. Greater septicity and rapidity of destruction are probable sequences. The perforating abscesses are subject to modifying influences of mechanical effect, such as gravitation and the resistance of tissues, and have their peculiar course, which is often marked by great chronicity.
TERMINATION.—In the course of seventeen years the reports of the Cincinnati Hospital show that there have been 6 cases of abscess of the lung treated there. Of these 4 died and 2 were discharged as improved. These figures show the infrequency of such cases, and also represent a greater mortality than probably occurs in the non-hospital class. We know of no large statistics which show what is the percentage of recoveries. Our own experience in private practice gives a majority of recoveries. They were cases following typhoid fever, croupous and catarrhal pneumonia, and hepatic abscess. A termination in a chronic cavity now and then happens: perforation of the pleural cavity, with subsequent pyo-pneumothorax, discharge externally through an intercostal space, or even extension into the abdominal cavity, are among the actual events of such abscesses.
DURATION.—The duration of an ordinary case is subject to wide variations between one and six months. A few cases are recorded of several years' duration. Previous constitutional condition has much to do with this element. The degree of infectiousness in the pyæmic class is important as to time. The abscesses become a subordinate condition in the fate of the case. In this connection we may also refer to Leyden's third variety, a so-called chronic abscess.
PATHOLOGY.—A close parallelism, etiologically and otherwise, is observable up to certain points between gangrene and abscess of the lung. Both are products of, or associated with, pneumonia. That which finally determines whether the result shall be gangrene or abscess is unknown to us. In the article on [GANGRENE OF THE LUNG] some investigations are referred to which point to a probable solution in the existence of specific forms having special pathogenetic force. The tendency of experimental and clinical investigations is to connect the suppurative process closely with the product of specific germs. Ogston in 65 cases of acute abscess found micrococci present in all of them. Obstruction of blood-vessels in the centre of the pneumonic area or on the margin of the abscess walls is an important anatomical element in the production of abscess, and it is claimed that it is often due to colonies of micrococci within their calibre; so that it is probable that there are both mechanical and biological or chemical influences at work. If the view of the zymotic and infectious character of pneumonia be tenable, the contingency of an abscess developing in its course would seem not very remote. Yet the proportion of cases of abscess from pneumonia is not more than 2 per cent. Leyden's high authority supports the idea of the essential and specific differences in the chemical and morphological peculiarities of gangrene and abscess of the lung, but the subject is as yet on a hypothetical basis.
MORBID ANATOMY.—The fresh cavity, generally in the upper lobe, has rough, ragged, and irregular walls, and may have bridles of the more resistant structures, as bronchi and vessels, crossing it. Such a cavity is quite likely to contain portions of undissolved parenchyma or more or less malodorous pus. The older cavity becomes smoother walled, and of more regular limits and cleaner contents. A gradation from granular hepatization through congested to crepitant tissue is almost uniform in the varieties of abscess, whether simple or pyæmic. In addition, some peculiarities are observable in the latter. These are usually several, varying in size from a pea or less to a walnut, some round and others wedge-shaped; others lying superficially and forming slight elevations on the pleural surface. In proportion to the curative progress the cavity will contract and disappear, occasionally leaving behind a cicatricial mark. A lining pus-secreting membrane will sometimes form, resulting in such a limitation of morbid action and such a disappearance of reactionary symptoms as to make the disease entirely local, but quite chronic.
DIAGNOSIS.—The more or less sudden and copious expectoration of pus, without a specially offensive odor, in the course of a case having up to that time the history of a pneumonia, would be considered as due to the development of an abscess in the lung. Some degree of fetor in breath and expectoration is observed, but it is far different from that of gangrene. The detection of the débris of lung-structure in coarse particles, and the microscopic discovery of elastic lung-tissue, are important diagnostic points in contradistinction from the solution of tissue that gangrene usually effects upon the parenchyma of the lung. According to Leyden's3 very complete investigations, the microscope reveals fatty crystals, mostly in roundish fragments, of the size of the epithelium of the lung and of a brilliant structure; pigment-débris of a yellowish-brown or brownish-red color; hæmatoidin and bilirubin, which Traube thought were due to hemorrhagic infarction, but which Leyden has observed in all of his cases; and, lastly, micrococci, in the well-known form of the round, granular micrococci colonies, which differ from those in gangrenous fragments in that they show very little movement and do not give the iodine reaction.
3 "Ueber Lungenabscess," Volkmann's klin. Vorträge, p. 994.
Difficulties of diagnosis arise in the case of an empyema discharging through the bronchi, or of an encysted empyema discharging through the third or fourth intercostal space in front; also, between abscess of the superior portion of the liver and one in the base of the lung, or between the latter and a pyo-pneumothorax. Very careful study of the history in each case is of the first importance. Where this is not attainable the difficulty is often much increased. In the case of the empyema the discharge is more profuse at each time, the whole amount in a given period is much greater, and the time of opening is much delayed beyond that of the pneumonic abscess. Trousseau gives the case of a child who brought up for more than six months 200 grammes of pus daily. He makes children an exception to the rule as to the late opening of the pleural abscesses. In the encysted empyema discharging either internally or externally the difficulties are greater. A portion of the lung-tissue may be so near behind the deposit of matter as to make the physical signs confusing if the pus has opened externally. Some of these and of the interlobular deposits it is almost impossible to diagnose.
In hepatic abscess opening into the lung and bronchi the discharge is copious, dirty brown, paroxysmal, and will generally, on careful observation, show the bile color or its chemical reactions or some microscopic débris of the liver. In Leyden's third class, or the chronic abscess arising in the course of chronic pneumonia, the history is so much like that of some forms of phthisis as scarcely to serve in diagnosis. He thinks there are some macroscopic and microscopic appearances which may serve for diagnosis. There are in the expectoration dark and compact pieces of greenish-black color, not unlike plugs of pus, and larger, black-pigmented fragments of parenchyma, from a pin's head to a hempseed in size. Microscopically, they consist of a close and strongly-pigmented parenchyma, which seldom reveals alveolar structure. They show fatty degeneration and cholesterin plates. This class of cases is mostly without fever. The application of the bacilli-tuberculosis test would seem to offer some assistance in diagnosis.
PROGNOSIS.—A grave prognosis may be formulated if there be a history of feeble constitution, and especially if it be further impaired by habits of intemperance, if the patient belong to either extreme of age, if there has been a recent debauch, or if there be wide variation from the typical form of pneumonia. Variations will be shown in such a complexus of symptoms as follows: fever of low grade, subject to extremes in range; feeble and frequent pulse, but not so marked as in gangrene of the lung; dyspnoea, objective and subjective; typhoid depression; tongue dryish; delirium; copious and fetid or difficult expectoration; physical signs of extensive lesion, such as a large cavity with a large outlying pneumonic area. A favorable prognosis would be conditioned on the appearance of a fewer number of these symptoms or on their evolution in a milder form.