Any tissue of the body may be the seat of an acute abscess, and there are many routes by which the bacteria may gain access to the affected area. For example: an abscess in the integument or subcutaneous cellular tissue usually results from infection by organisms which have entered through a wound or abrasion of the surface, or along the ducts of the skin; an abscess in the breast from organisms which have passed along the milk ducts opening on the nipple, or along the lymphatics which accompany these. An abscess in a lymph gland is usually due to infection passing by way of the lymph channels from the area of skin or mucous membrane drained by them. Abscesses in internal organs, such as the kidney, liver, or brain, usually result from organisms carried in the blood-stream from some focus of infection elsewhere in the body.
A knowledge of the possible avenues of infection is of clinical importance, as it may enable the source of a given abscess to be traced and dealt with. In suppuration in the Fallopian tube (pyosalpynx), for example, the fact that the most common origin of the infection is in the genital passage, leads to examination for vaginal discharge; and if none is present, the abscess is probably due to infection carried in the blood-stream from some primary focus about the mouth, such as a gumboil or an infective sore throat.
The exact location of an abscess also may furnish a key to its source; in axillary abscess, for example, if the suppuration is in the lymph glands the infection has come through the afferent lymphatics; if in the cellular tissue, it has spread from the neck or chest wall; if in the hair follicles, it is a local infection through the skin.
Formation of an Abscess.—When pyogenic bacteria are introduced into the tissue there ensues an inflammatory reaction, which is characterised by dilatation of the blood vessels, exudation of large numbers of leucocytes, and proliferation of connective-tissue cells. These wandering cells soon accumulate round the focus of infection, and form a protective barrier which tends to prevent the spread of the organisms and to restrict their field of action. Within the area thus circumscribed the struggle between the bacteria and the phagocytes takes place, and in the process toxins are formed by the organisms, a certain number of the leucocytes succumb, and, becoming degenerated, set free certain proteolytic enzymes or ferments. The toxins cause coagulation-necrosis of the tissue cells with which they come in contact, the ferments liquefy the exudate and other albuminous substances, and in this way pus is formed.
If the bacteria gain the upper hand, this process of liquefaction which is characteristic of suppuration, extends into the surrounding tissues, the protective barrier of leucocytes is broken down, and the suppurative process spreads. A fresh accession of leucocytes, however, forms a new barrier, and eventually the spread is arrested, and the collection of pus so hemmed in constitutes an abscess.
Owing to the swelling and condensation of the parts around, the pus thus formed is under considerable pressure, and this causes it to burrow along the lines of least resistance. In the case of a subcutaneous abscess the pus usually works its way towards the surface, and “points,” as it is called. Where it approaches the surface the skin becomes soft and thin, and eventually sloughs, allowing the pus to escape.
An abscess forming in the deeper planes is prevented from pointing directly to the surface by the firm fasciæ and other fibrous structures. The pus therefore tends to burrow along the line of the blood vessels and in the connective-tissue septa, till it either finds a weak spot or causes a portion of fascia to undergo necrosis and so reaches the surface. Accordingly, many abscess cavities resulting from deep-seated suppuration are of irregular shape, with pouches and loculi in various directions—an arrangement which interferes with their successful treatment by incision and drainage.
The relief of tension which follows the bursting of an abscess, the removal of irritation by the escape of pus, and the casting off of bacteria and toxins, allow the tissues once more to assert themselves, and a process of repair sets in. The walls of the abscess fall in; granulation tissue grows into the space and gradually fills it; and later this is replaced by cicatricial tissue. As a result of the subsequent contraction of the cicatricial tissue, the scar is usually depressed below the level of the surrounding skin surface.
If an abscess is prevented from healing—for example, by the presence of a foreign body or a piece of necrosed bone—a sinus results, and from it pus escapes until the foreign body is removed.
Clinical Features of an Acute Circumscribed Abscess.—In the initial stages the usual symptoms of inflammation are present. Increased elevation of temperature, with or without a rigor, progressive leucocytosis, and sweating, mark the transition between inflammation and suppuration. An increasing leucocytosis is evidence that a suppurative process is spreading.
The local symptoms vary with the seat of the abscess. When it is situated superficially—for example, in the breast tissue—the affected area is hot, the redness of inflammation gives place to a dusky purple colour, with a pale, sometimes yellow, spot where the pus is near the surface. The swelling increases in size, the firm brawny centre becomes soft, projects as a cone beyond the level of the rest of the swollen area, and is usually surrounded by a zone of induration.
By gently palpating with the finger-tips over the softened area, a fluid wave may be detected—fluctuation—and when present this is a certain indication of the existence of fluid in the swelling. Its recognition, however, is by no means easy, and various fallacies are to be guarded against in applying this test clinically. When, for example, the walls of the abscess are thick and rigid, or when its contents are under excessive tension, the fluid wave cannot be elicited. On the other hand, a sensation closely resembling fluctuation may often be recognised in œdematous tissues, in certain soft, solid tumours such as fatty tumours or vascular sarcomata, in aneurysm, and in a muscle when it is palpated in its transverse axis.
When pus has formed in deeper parts, and before it has reached the surface, œdema of the overlying skin is frequently present, and the skin pits on pressure.
With the formation of pus the continuous burning or boring pain of inflammation assumes a throbbing character, with occasional sharp, lancinating twinges. Should doubt remain as to the presence of pus, recourse may be had to the use of an exploring needle.
Differential Diagnosis of Acute Abscess.—A practical difficulty which frequently arises is to decide whether or not pus has actually formed. It may be accepted as a working rule in practice that when an acute inflammation has lasted for four or five days without showing signs of abatement, suppuration has almost certainly occurred. In deep-seated suppuration, marked œdema of the skin and the occurrence of rigors and sweating may be taken to indicate the formation of pus.
There are cases on record where rapidly growing sarcomatous and angiomatous tumours, aneurysms, and the bruises that occur in hæmophylics, have been mistaken for acute abscesses and incised, with disastrous results.
Treatment of Acute Abscesses.—The dictum of John Bell, “Where there is pus, let it out,” summarises the treatment of abscess. The extent and situation of the incision and the means taken to drain the cavity, however, vary with the nature, site, and relations of the abscess. In a superficial abscess, for example a bubo, or an abscess in the breast or face where a disfiguring scar is undesirable, a small puncture should be made where the pus threatens to point, and a Klapp's suction bell be applied as already described (p. 39). A drain is not necessary, and in the intervals between the applications of the bell the part is covered with a moist antiseptic dressing.
In abscesses deeply placed, as for example under the gluteal or pectoral muscles, one or more incisions should be made, and the cavity drained by glass or rubber tubes or by strips of rubber tissue.
The wound should be dressed the next day, and the tube shortened, in the case of a rubber tube, by cutting off a portion of its outer end. On the second day or later, according to circumstances, the tube is removed, and after this the dressing need not be repeated oftener than every second or third day.
Where pus has formed in relation to important structures—as, for example, in the deeper planes of the neck—Hilton's method of opening the abscess may be employed. An incision is made through the skin and fascia, a grooved director is gently pushed through the deeper tissues till pus escapes along its groove, and then the track is widened by passing in a pair of dressing forceps and expanding the blades. A tube, or strip of rubber tissue, is introduced, and the subsequent treatment carried out as in other abscesses. When the drain lies in proximity to a large blood vessel, care must be taken not to leave it in position long enough to cause ulceration of the vessel wall by pressure.
In some abscesses, such as those in the vicinity of the anus, the cavity should be laid freely open in its whole extent, stuffed with iodoform or bismuth gauze, and treated by the open method.
It is seldom advisable to wash out an abscess cavity, and squeezing out the pus is also to be avoided, lest the protective zone be broken down and the infection be diffused into the surrounding tissues.
The importance of taking precautions against further infection in opening an abscess can scarcely be exaggerated, and the rapidity with which healing occurs when the access of fresh bacteria is prevented is in marked contrast to what occurs when such precautions are neglected and further infection is allowed to take place.
Acute Suppuration in a Wound.—If in the course of an operation infection of the wound has occurred, a marked inflammatory reaction soon manifests itself, and the same changes as occur in the formation of an acute abscess take place, modified, however, by the fact that the pus can more readily reach the surface. In from twenty-four to forty-eight hours the patient is conscious of a sensation of chilliness, or may even have a rigor. At the same time he feels generally out of sorts, with impaired appetite, headache, and it may be looseness of the bowels. His temperature rises to 100° or 101° F., and the pulse quickens to 100 or 110.
On exposing the wound it is found that the parts for some distance around are red, glazed, and œdematous. The discoloration and swelling are most intense in the immediate vicinity of the wound, the edges of which are everted and moist. Any stitches that may have been introduced are tight, and the deep ones may be cutting into the tissues. There is heat, and a constant burning or throbbing pain, which is increased by pressure. If the stitches be cut, pus escapes, the wound gapes, and its surfaces are found to be inflamed and covered with pus.
The open method is the only safe means of treating such wounds. The infected surface may be sponged over with pure carbolic acid, the excess of which is washed off with absolute alcohol, and the wound either drained by tubes or packed with iodoform gauze. The practice of scraping such surfaces with the sharp spoon, squeezing or even of washing them out with antiseptic lotions, is attended with the risk of further diffusing the organisms in the tissue, and is only to be employed under exceptional circumstances. Continuous irrigation of infected wounds or their immersion in antiseptic baths is sometimes useful. The free opening up of the wound is almost immediately followed by a fall in the temperature. The surrounding inflammation subsides, the discharge of pus lessens, and healing takes place by the formation of granulation tissue—the so-called “healing by second intention.”
Wound infection may take place from catgut which has not been efficiently prepared. The local and general reactions may be slight, and, as a rule, do not appear for seven or eight days after the operation, and, it may be, not till after the skin edges have united. The suppuration is strictly localised to the part of the wound where catgut was employed for stitches or ligatures, and shows little tendency to spread. The infected part, however, is often long of healing. The irritation in these cases is probably due to toxins in the catgut and not to bacteria.
When suppuration occurs in connection with buried sutures of unabsorbable materials, such as silk, silkworm gut, or silver wire, it is apt to persist till the foreign material is cast off or removed.
Suppuration may occur in the track of a skin stitch, producing a stitch abscess. The infection may arise from the material used, especially catgut or silk, or, more frequently perhaps, from the growth of staphylococcus albus from the skin of the patient when this has been imperfectly disinfected. The formation of pus under these conditions may not be attended with any of the usual signs of suppuration, and beyond some induration around the wound and a slight tenderness on pressure there may be nothing to suggest the presence of an abscess.
Acute Suppuration of a Mucous Membrane.—When pyogenic organisms gain access to a mucous membrane, such as that of the bladder, urethra, or middle ear, the usual phenomena of acute inflammation and suppuration ensue, followed by the discharge of pus on the free surface. It would appear that the most marked changes take place in the submucous tissue, causing the covering epithelium in places to die and leave small superficial ulcers, for example in urethritis, the cicatricial contraction of the scar subsequently leading to the formation of stricture. When mucous glands are present in the membrane, the pus is mixed with mucus—muco-pus.