The diagnosis of hydatids will be considered with the individual organs. The disease is more common in certain parts of Australia and in Shetland and Iceland than in countries where the association of dogs in the domestic life of the inhabitants is less intimate. Pfeiler, who has worked at the serum diagnosis of hydatid disease, regards the complement deviation method as the most reliable; he believes that a positive reaction may almost be regarded as absolutely diagnostic of an echinococcal lesion.
The treatment is to excise the cyst completely, or to inject into it a 1 per cent. solution of formalin. In operating upon hydatids the utmost care must be taken to avoid leakage of the contents of the cyst, as these may readily disseminate the infection.
A blood cyst or hæmatoma results from the encapsulation of extravasated blood in the tissues, from hæmorrhage taking place into a preformed cyst, or from the saccular pouching of a varicose vein.
A lymph cyst usually results from a contusion in which the skin is forcibly displaced from the subjacent tissues, and lymph vessels are thereby torn across. The cyst is usually situated between the skin and fascia, and contains clear or blood-stained serum. At first it is lax and fluctuates readily, later it becomes larger and more tense. The treatment consists in drawing off the contents through a hollow needle and applying firm pressure. Apart from injury, lymph cysts are met with as the result of the distension of lymph spaces and vessels (lymphangiectasis); and in lymphangiomas, of which the best-known example is the cystic hygroma or hydrocele of the neck.
Ganglion
This term is applied to a cyst filled with a clear colourless jelly or colloid material, met with in the vicinity of a joint or tendon sheath.
The commonest variety—the carpal ganglion—popularly known as a sprained sinew—is met with as a smooth, rounded, or oval swelling on the dorsal aspect of the carpus, usually towards its radial side ([Fig. 60]). It is situated over one of the intercarpal or other joints in this region, and may be connected with one or other of the extensor tendons. The skin and fascia are movable over the cyst. The cyst varies in size from a pea to a pigeon's egg, and usually attains its maximum size within a few months and then remains stationary. It becomes tense and prominent when the hand is flexed towards the palm. Its appearance is usually ascribed to some strain of the wrist—for example, in girls learning gymnastics. It may cause no symptoms or it may interfere with the use of the hand, especially in grasping movements and when the hand is dorsiflexed. In girls it may give rise to pain which shoots up the arm. Ganglia are also met with on the dorsum of the metacarpus and on the palmar aspect of the wrist.
Fig. 60.—Carpal Ganglion in a woman æt. 25.