Abscess is defined as a circumscribed swelling containing pus (localized collection of pus) surrounded by an inflamed area. It is formed by destructive effect of pyogenic micro-organisms on a tissue. Abscesses can be caused by a wide range of bacterial and fungal infections.
An abscess is different from cellulitis in that it has a defined edge and shape. Characteristics:
1-Raised skin surface
3-Tenderness and pain
4-Redness of the skin (in white people)
6-Foul smell if it has begun to discharge
Predilection seats: -
Abscesses can be formed at any part of the animal body. In equines, sheep and goats it is predominant in the parotid region and inter-mandibular space while in cattle it is formed in left chest region behind elbow joint, in the front of udder and at the umbilicus.
Occasionally it ensues as a result of entrance of microorganisms through a break down in the skin or mucous membrane through:
1-Foreign body as nail, needle, sharp piece of bone, wood or glass.... etc.
2-Injuries, accidents and skin wounds
3-During injection, as the wide bore needle that may drive a piece of skin or hair into the muscle or the improper sterile technique of injection Pathogenesis: -
Abscess is the last stage of a tissue infection that begins with inflammation. Initially, the invading germ activates the body's immune system that causes increase in the temperature of the affected area due to the increased blood flow, swelling due to the accumulation of water, blood, and other liquids, redness and pain due to the irritation from the swelling and the chemical activity. These four signs (heat, swelling, redness, and pain) characterize inflammation. As the process progresses, the tissue begins to liquefy, and an abscess forms. As the chemical digestion liquefies more and more tissue, the abscess increases in size and spreads following the path of least resistance tissues that are easily digested. A good example is an abscess just beneath the skin that continues beneath the skin rather than working its way through the skin. The contents of abscess leak into the circulation and produce symptoms like any other infection including chills, fever, aching, and general discomfort. Sterile abscesses are a milder and does not caused by germs but by nonliving irritants such as drugs. If an injected drug like penicillin is not absorbed, it stays in place and may causing irritation to generate a sterile abscess (sterile because there is no infection involved). In general, sterile abscesses are likely to become hard as they scar rather than remaining as pockets of pus. Although there are sterile abscesses, most abscesses are caused by bacterial infections that produce large amounts of pus in the tissues. Abscesses commonly develop after bite wounds, scratches, or when objects penetrate the skin and then the skin heals over. Since the infection cannot drain, pus builds up under the skin and an abscess develops. As the pus continues to build, the skin over the abscess undergoes necrosis by the infection and the abscess will eventually rupture. Unfortunately, unless the abscess is treated correctly, the skin will heal over again and the abscess will redevelop.
There are two types of abscesses, septic and sterile. Most abscesses are septic, which means that they are the result of an infection. Septic abscesses can occur anywhere in the body and only a germ and the body's immune response are involved in such process. In response to the invading germ, the white blood cells gather at the infected site and produce enzymes which attack and digest the germ. These enzymes act like acid, killing and breaking down the germs into small pieces that can be picked up by the circulation and eliminated from the body. Unfortunately, these enzymes also digest body tissues and in most cases, the germ produces similar chemicals resulting in thick, yellow, liquid pus containing digested germs and tissues, white blood cells and enzymes.
Abscesses are classified according to the clinical features into;
a-Acute or hot abscess of rapid evolution and it may be superficial or deep
b-Chronic or cold abscess of slow evolution and it may be hard or soft
Each of the above types may be distinguished as;
c-Metastatic (there are multiple foci)
d-Critical when it resulted from grave disease or develops in connection with vital organ
I-ACUTE or HOT ABSCESS
Formation and structure of an acute abscess: -
1-An acute abscess is formed within 3-5 days after entrance of the pyogenic micro-organism.
2-It is composed of wall (pyogenic membrane) and contents (pus)
3-The character of the pus varies according to tissue involved and causative agent.
4-The germs, which gained access to the tissues, multiply and produce toxins that diffuse into surrounding structures causing acute inflammation, vasodilatation, accelerating blood stream (but finally retarding the blood stream), thrombosis and leucocytic emigration and microscopically, the lesion shows two well differentiated zones;
a-Central area of dead tissues that have lost their staining properties and contain the causative pyogenic bacteria
b-Peripheral zone of acute inflammation which is highly infiltrated with leucocytes and fades gradually into the surrounding healthy tissues
Fate of pus: -
1-Usually the pus directed to the external body surface, but if it is unable to escape superficially due to tissue resistance, as horn of the hoof, it extends in the direction of the least resistance until it finds a means of escape.
2-An abscess in vicinity of joint or visceral cavity may open into it leading to serious consequences.
3-Abscess formation on ligament, tendon or bone may cause necrosis of these structures and interferes with healing even after the abscess burst.
4-Retained pus in an abscess cavity for a long time, without evacuation, causes resorption of the liquid part of the abscess, inspissation, caseation, and finally calcification.
Generally, there is no specific clinical signs except presence of lump or swelling, reduced appetite, and increased water intake or fever.
1-Acute Superficial Abscess
General signs of acute inflammation (swelling, redness, hotness and pain). It starts as a very painful firm circumscribed inflammatory swelling. The center of such swelling gradually becomes softer while its periphery remains firm, and gradually the wall becomes thin and the abscess appears to be fluctuated. Later on, it points at the skin surface, forming a shining hairless patch at its center which is thin on palpation giving a sensation of softening combined with elasticity. At the end it burst allowing escape of pus through the orifice.
2-Acute Deep Abscess
As a result of the deep position of that abscess, local manifestations can't be noticed except slight edema in its vicinity. Deep abscess is first indicated by febrile condition of the animal due to absorption of toxins. It may interfere with normal function of surrounding organs like pharynx or larynx. When the pus reaches near the surface, features of a superficial abscess may be detected.
Diagnosis of superficial abscess is always easy by symptoms while deep one may present some difficulties as a result of absence of local manifestation. The common findings of inflammation (heat, redness, swelling, and pain) easily identify superficial abscesses. Deep abscess is indicated only by generalized symptoms such as fever and discomfort. Pain and tenderness on physical examination are common findings. Sometimes a deep abscess will eat a small channel (sinus) to the surface and begin leaking pus. Generally, edema at the vicinity, interference with normal function of surrounding organs and febrile condition may be helpful. A sterile abscess may cause only a painful lump deep in the buttock where a shot was given.
Differential diagnosis: -
Abscess may be confused with hematoma, cyst, hernia, bursitis or tumor.
1-It appears directly after severe trauma, and immediately fluctuating beneath intact skin
2-It causes transient inflammatory reactions that can be seen for few days then disappear, but generally pain is not as severe as in abscess
3-Crepitation ensues when coagulation occurs
4-It never points as the abscess
1-It is uniformly fluctuating and lined with epithelium or endothelium
2-It is either congenital or it takes longer time to develop
1-Presence of hernial ring, and reducibility of contents in case of reducible hernias
2-Absence of inflammatory reaction except when it is recent and traumatic
1-It is abnormal benign or malignant overgrowth of tissue
2-Benign tumors are firm, grow slowly, single or multiple, remains localized and with a regular and well-defined borders without any sign of inflammation. In some cases it may be subjected to friction leading to ulceration and infection.
An inflammatory swelling of the bursae (known from anatomical positions)
1-The hair must be clipped off the area
2-If the mature abscess has not ruptured, it can be surgically lanced. Lancing is a lot better for healing than allowing the abscess to rupture without surgery.
3-Thus, the pus must be drained from the abscess. The surgeon determines when the abscess is ready for drainage and opens a path to the outside, allowing the pus to escape. Ordinarily, the body handles the remaining infection, sometimes with the help of antibiotics or other drugs.
4-The sooner the mature abscess is lanced, the less tissue damage will occur and the quicker that healing will occur.
5-After the abscess is lanced, flushing of the pocket with sterile fluids is critical to prevent the abscess from recurring.
- Keeping the incision open for 7 to 10 days is required to flush out all of the infection and sometimes the surgeon may leave a drain (a piece of cloth or rubber) in the abscess cavity to prevent it from closing before all the pus has drained out.
- If the incision closes too quickly, the infection will recur and possibly the infection could spread and infect bones in the area. Since skin is very resistant to the spread of infection, it acts as a barrier, often keeping the toxic chemicals of an abscess from escaping the body on their own.
1-Systemic antibiotic for control of septicemia and bacteremia and it should be continued even after evacuation of abscess
2-Anti pyretic or anti-inflammatory according to need
3-Fluid therapy if the animal refuses to eat as a result of toxemia
2-Ripening or Maturation
It is a process aims at faster maturation of the abscess to come close to the skin surface, become fluctuating and the pus lies within a thin wall cavity beneath a thin circle of skin, and inflammation of the surrounding tissues subsides.
Ripening can be done by using;
1-Fomentation and/or poultices
2-Antiphlogistic preparations such as icthyol ointment
4-Blister like bin-iodide of mercury ointment
3-Evacuation and Drainage
It is a process of incising of the mature abscess for evacuation of pus and drainage. The incision must be wide enough to prevent re-accumulation and it should be made at a suitable level for good drainage (lowest point).
Technique of evacuation: -
1-The area should be shaved, washed with soap and water, dried, and suitable antiseptic like Tr. Iodine is applied prior to incision.
2-Generally speaking it is not advised to open an abscess which is not fully ripe or mature to avoid secondary abscess formation, although abscesses that situated close to a joint or peritoneum should be opened before they are fully mature and this in fact is made to avoid rupture of the abscess into the joint or the peritoneal cavity.
3-Incision should be performed by using sterilized abscess knife or scalpel that incises the abscess from its point and downward so that drainage occurs by gravity when the animal stands in normal position.
4-Sometimes it is necessary to make another opening to provide drainage and it is called a counter-opening.
5-After evacuating the pus, the cavity should be irrigated with antiseptic solution like hydrogen peroxide, to promote the complete evacuation and removal of the contents then after the abscess cavity should be explorated for the presence of foreign body.
6-After opening the abscess and its irrigation, it should be packed with gauze moisten with Tr. iodine to destroy infection and to stimulate the healing process. The gauze packs are removed after 24 hour and then the abscess cavity is irrigated with diluted solution of mild antiseptic solution like acriflavin, potassium permanganate, dettol, savlon, or povidone iodine.
7-The abscess cavity should be dressed daily and drain should be changed till the healthy granulations are seen filling its gap.
The actual functions of the gauze: -
1-To carry the antiseptic solution (Tr. iodine)
2-To maintain the opening of the abscess and prevention of its closure
3-To bring exudates out of the abscess progression or retardation of healing
4-To induce mild irritation that stimulates granulation formation
The average period required for the complete healing of an abscess is about three weeks and it should be obliterated from inward to outward, otherwise, secondary abscess is formed. However, the persistent discharge from an opened abscess indicates; inadequate drainage due to either small orifice; retention of dead tissue as sequestrum or foreign body; or persistence of suppuration as a result of secondary infection or the use of ineffective antiseptics. The use of systemic antibiotics may be indicated in some cases.
Critical abscess found in vicinity of serious area (has great blood vessels, nerves) or vital organs such as parotid region or sub-pharyngeal region. Convential treatment of such abscess should be performed over the skin only without deep puncturing by a blunt instrument (artery forceps or blunt scissors) that is inserted through the underlying tissues to reach the abscess cavity and when the two jaws are inside the abscess cavity, the jaws of the instrument is opened without sharp cutting to widen the abscess opening bluntly. However the rest steps of treatment are the same adopted for treatment of abscess and mentioned before including evacuation, washing with antiseptics and insertion of drain.
Abscess in mucous cavity like pharynx, rectum or vagina may be opened by; thrusting the finger into its thin wall, using a concealed knife, trocar and canula, or an ordinary pointed scalpel guarded or enveloped in gauze or cotton wool just up to its point.
II-CHRONIC or COLD ABSCESS
These abscesses grow very slowly and show very slight inflammatory reactions, therefore pain in these cases is either very slight or absent.
Repeated simple wounds as those induced by the saddle, leading to wounds of the bony prominences as the ribs or the pelvic bones.
1-Cold Soft Abscess
An abscess of soft surface and contains a large amount of pus
2-Cold Hard Abscess
An abscess that is surrounded by fibrous tissues and the pus contents are small in quantity.
1-Absence of inflammatory symptoms or presence of only mild inflammation
2-The abscess appears as cyst in cold soft abscess or fibroma in cold hard one
2-Clinical examination and exploratory puncturing
The same treatment adopted in case of hot abscesses by maturation and evacuation, however blister may be applied to change the cold abscess into acute one and bring the pus near to the surface before opening it.
When pus is inspessiated, curetting of the abscess cavity is necessary that is followed by application of a drain immersed in Tr. Iodine, and a counter opening for drainage may be necessary in some cases.
Encapsulated abscess can be excised surgically within its intact capsule then the skin wound is sutured
Special forms of abscesses: -
I-ACNE, FURUNCLE or BOIL
Acne, furuncle or boil is an abscess involving the sebaceous gland affecting all domestic animals but it is common in the horse and dog. In the dog it is more common in short haired breeds in the region rich in sebaceous glands like nose, lips ... etc.
Local irritation from any cause (e.g. friction of saddle or collar) predisposes to the infection (mainly staphylococci)
The lesion appears as a single or multiple pustules that have the size of a pea that release grayish white pus. At the same time, grayish white core of necrotic tissue comes out when the pustule is compressed between fingers.
1-Wash thoroughly with soap and warm water and apply an antiseptic and salicylic acid ointment
2-Some of the pustules may require to be incised to remove the necrotic core, and then they are wards with Tr. iodine
3-Topical and systemic antibiotics are very effective
It is a diffuse inflammatory swelling which fades gradually into the surrounding structures without any definite demarcation
It is either caused by bacterial invasion or infiltration of the tissues by one of the body excretions as urine or feces
It is caused by infiltration of the subcutaneous tissues by an irritant sterile material as turpentine oil, chloral hydrate or concentrated saline solution
1-Formation of local diffuse swelling which fades gradually in the surrounding structures
2-Local tenderness and hotness
3-The lymphatic glands draining the area are usually inflamed
4-The body temperature rises and sharply fluctuates
1-Trauma followed by infection by microorganisms.
2-Infiltration of the tissues by body excretions or an irritant material
3-Secondary to local suppurative lesion as abscess, lymphadenitis or arthritis
1-Keep the affected part in complete rest
2-Apply hot antiseptic fomentation with compression, antiphlogestic poultices and bandage if practicable
3-If the phlegmon is so voluminous, incise it several times (scarification) to provide drainage then dress it as septic wound
4-Administration of systemic antibiotics
5-Administration of anti-titanic serum for animals susceptible to tetanus
III-FISTULA and SINUS
It will be discussed at topic sinus and fistula