Abscess of the Brain.
As indicated in the last article, there formerly existed much confusion in the minds of pathologists regarding the terms softening and abscess of the brain. As long as softening was regarded as an inflammation, so long was abscess of the brain regarded as a suppurative form of softening. Aside from the fact that there is some resemblance in mechanical consistency between a spot of ordinary softening and one of inflammatory softening, there is no essential similarity of the two conditions. True softening is to-day regarded as the result of a death of brain-tissue produced by interference with the blood-supply; it is therefore a passive process. Inflammatory softening, of which abscess is a form, is due to an irritant, usually of an infectious nature. It is to the results of such irritation that the term suppurative encephalitis should be limited.
MORBID ANATOMY.—In all well-established inflammatory brain troubles the active part is taken by the blood-vessels and connective tissue; the ganglionic elements undergo secondary, usually regressive or necrotic, changes. The brain, considered as a parenchymatous organ, is not disposed to react readily in the way of suppurative inflammation unless some septic elements are added to the inflammatory irritant. Foreign bodies, such as knitting-needles, bullets, and slate-pencils, have been found encapsulated in this organ or projecting into it from the surrounding bony shell without encapsulation and without any evidences of inflammatory change. As a rule, a foreign body which enters the brain under aseptic conditions will, if the subject survive sufficiently long, be found to have made its way to the deepest part of the brain, in obedience to the law of gravity, and through an area of so-called inflammatory red softening which appears to precede it and facilitate the movement downward. This form of softening derives its color from the colored elements of the blood, which either escape from the vessels in consequence of the direct action of the traumatic agent; secondly, in consequence of vascular rupture from the reduced resistance of the perivascular tissue in consequence of inflammatory œdema and infiltration; or, thirdly, in obedience to the general laws governing simple inflammation.
A cerebral abscess may present itself to the pathological anatomist in one of three phases—the formative, the crude, and the encapsulated. In the first it is not dissimilar to a focus of yellow softening, being, like the latter, a diffuse softened area varying from almost microscopical dimensions to the size of a walnut, and of a distinctly yellow tinge. Microscopic examination, however, shows a profound difference. In pure yellow softening there are no pus-cells; in the suppurative encephalitic foci they are very numerous, and congregated around the vessels and in the parenchyma in groups. The crude abscess is the form usually found in cases rapidly running to a fatal termination. Here there is an irregular cavity in the brain, usually the white central substance of the cerebrum or cerebellum, formed by its eroded and pulpy tissue; it is filled with yellow, greenish, and more rarely brownish pus. In the most furibund cases broken-down brain-detritus may be found in the shape of whitish or reddish flocculi, but in slowly-formed abscesses the contents are free from such admixture, and thus the third phase is produced, known as the encapsulated abscess. The cavity of the abscess becomes more regular, usually spheroid or ovoid; the pus is less fluid, more tenacious, and slightly transparent; and the walls are formed by a pseudo-membrane48 which is contributed by the sclerosing brain-substance, which merges gradually into the outlying normal tissue. I have seen one acute cerebral abscess from ear disease which might be appropriately designated as hemorrhagic; the contents were almost chocolate-colored; on closer inspection it was found that they were true pus, mingled with a large number of red blood-discs and some small flocculi of softened brain-substance. This hemorrhagic admixture was not due to the erosion of any large vessel, for the abscess had ruptured into the lateral ventricle at that part where it was most purely purulent. In a case of tubercular meningitis, Mollenhauer in my laboratory found an abscess in the white axis of the precentral gyrus, with a distinct purulent infiltration following the line of one of the long cortical vessels. The abscess was not encapsulated, the surrounding white substance exhibited an injected halo, and the consistency of the contents was that of mucoid material.
48 There is considerable dispute as to the real nature of the tissue encapsulating cerebral abscesses. It is known, through the careful observations of R. Meyer, Goll, Lebert, Schott, and Huguenin, that the capsule may form in from seven to ten weeks in the majority of cases, about eight weeks being the presumable time, and that at first the so-called capsule of Lallemand does not deserve the name, being a mucoid lining of the wall. At about the fiftieth day, according to Huguenin, this lining becomes a delicate membrane composed of young cells and a layer of spindle-shaped connective elements.
In cases where the symptoms accompanying the abscess during life had been very severe it is not rare to find intense vascular injection of the parts near the abscess, and it is not unlikely that the reddish or chocolate color of the contents of some acutely developed abscesses is due to blood admixture derived from the rupture of vessels in this congested vicinity. Sometimes the entire segment of the brain in which the abscess is situated, or the whole brain, is congested or œdematous. In a few cases meningitis with lymphoid and purulent exudation has been found to accompany abscesses that had not ruptured. It is impossible to say whether in this case there was any relation between the focal and the meningeal inflammation, as both may have been due to a common primary cause.49 In such cases, usually secondary to ear disease, thrombosis of the lateral sinus may be found on the same side. Where rupture of an abscess occurs, if the patient have survived this accident long enough—for it is usually fatal in a few minutes or hours—meningitis will be found in its most malignant form. A rupture into the lateral and other ventricles has been noted in a few cases.50
49 Otitis media purulenta in the two cases of this kind I examined.
50 In one, observed together with E. G. Messemer, intense injection of the endymal lining, with capillary extravasations, demonstrated the irritant properties of the discharged contents.
Some rare forms of abscess have been related in the various journals and archives which have less interest as objects of clinical study than as curiosities of medical literature. Thus, Chiari51 found the cavity of a cerebral abscess filled with air, a communication with the nose having become established by its rupture and discharge.
51 Zeitschrift für Heilkunde, 1884, v. p. 383. In this remarkable rase the abscess, situated in the frontal lobe, had perforated in two directions—one outward into the ethmoidal cells, the other inward into the ventricles, so that the ventricles had also become filled with air. This event precipitated a fatal apoplectiform seizure.