Extravasation cysts, caused by injuries which rupture blood vessels, followed by an increase of fibrous tissue which forms a capsule about the fluid. The hygromata in front of the knee in cattle, so-called tumor of the knee, and serous cysts belong to this variety.
Hygromata, or tumors of the knee.—These consist in the simplest form of a collection of serous fluid mixed with fibrin within a distended bursa. The walls surrounding the fluid become firm, smooth, and dense.
Outwardly the tumor appears fluctuating, though tense, while the skin which covers it may be normal, denuded of hair, or covered with hard epidermal scales, possibly half an inch in thickness, forming a hard, horny plate. The cavity which contains the fluid may have the dimensions of a hen's egg, an apple, or a child's head. Its walls are formed by the diseased secreting membrane of the bursal sac, and are readily detachable from the subcutis of the skin. Their internal surfaces are often uneven or supplied with projections or tufted growths which support a fibrous network within the tumor.
Tumors of the knee may also assume a granular type, as the result of chronic inflammation or following operative or spontaneous evacuation of pus from the part. They are either firmly connected with the skin or are detachable from it, and when laid open disclose a whitish-red, porklike tissue surrounding a central nucleus of pus, or a fistulous tract leading to the outer surface. They are caused by the chronic inflammation which follows the bruises received by cattle in lying down and in rising, or they may be due to falls on uneven, hard ground.
Treatment for hygromata.—When the swelling first appears cold water should be applied, followed later by bandaging with cloths wrung out of warm water. If the swelling is soft, it should be punctured at the lowest point, and afterwards the cavity should be syringed with Lugol's solution. If the tumor is hard and nonfluctuating, a mercurial blister may cause absorption and at the same time prevent further injury to the part by making it more painful, thus sparing it.
Serous cysts.—These swellings are another variety of extravasation cysts, and are caused by such injuries as butting, running against hard objects, and shipping bruises, which are followed by an outpouring of blood and lymph into the tissue spaces. These cysts develop rapidly and may reach the size of a man's head or even larger. They are soft, edematous, and hot at first and contain a serous or blood-tinged fluid. Later, partially organized clots and shreds of a fibrinous nature and of a gelatinous consistence are formed within, and the temperature of the swelling is reduced. They appear on the surface of the body, especially on the belly and flank of cattle.
Treatment of serous cysts.—Treatment consists in opening the cyst at the most dependent point with a sharp knife. The cavity should be washed out twice daily with a 5 per cent solution of carbolic acid, and drainage encouraged by keeping the incision open.
DERMOID CYSTS.
These cysts have a wall which is almost an exact duplicate of the structure of the skin, and frequently contain epidermal structures, such as hair and teeth, which, in the development of the embryo, have been misplaced. Thus we may find in an ovary or testicle a dermoid cyst, containing a tooth or a ball of hair. Dental cysts are included in the class above.
Dental cysts.—It happens occasionally that the teeth of cattle, instead of developing normally within strong supporting alveolæ, remain inclosed within a cystic membrane, which assumes a tumorlike character. One tooth may be included alone in the cyst or a number may be inclosed together. However this may be, the malformation progresses, especially if confined to the incisor teeth, until the remaining teeth that began to develop normally are crowded out of position and rendered useless. The tumor may reach the size of a man's fist. It appears to be fleshy and dents upon pressure, but it may also appear on closer examination as though it contained irregular sections of thin bone. The outer surface is always smooth, and no indication of purulence, softening, or scab formation is ever exhibited. Upon being laid open with the knife the tumor is seen to be surrounded by a firm, smooth membrane which limits it completely from the adjoining tissues. It is filled with material which possesses partly edematous, partly fleshy, and partly bony properties. It is supposed that this mass is composed of rudiments of the jawbone or of the alveolar walls which, becoming spongy, lose themselves in the soft, fleshy mass contained within the capsule of the tumor. It occasionally happens that the tumor is hollow and that the cavity extends back into the body of the lower jaw for a considerable distance.