They are largely the effect of peculiar occupation, as in housemaids and carpet-layers there are formed frequently prepatellar bursæ, while miners get them upon the elbow, porters upon the shoulder, plasterers upon the forearm, etc. In the same way, by the pressure of ill-fitting boots, an adventitious bursa is developed over the expanded head of the first metacarpal bone, thus forming a condition known as bunion.

Neural Cysts.

—This term has been applied by Sutton to pseudocystic dilatation of certain cavities found in the brain and central nervous system. Hydrocephalus is in one sense a pseudocyst of this variety. Corresponding to it in fetal life is hydramnios. Hydrocele or cystic dilatation of the fourth ventricle is well known. Cranial meningoceles, which are hernial protrusions of brain membranes, are also pseudocysts, to be included in this category. They will be considered in Chapter XXXVI. Cephalhematoma may be also included in the same way. Spina bifida, a condition which will be described in Chapter XXXVIII, is, nevertheless, practically a cyst of congenital origin involving the spinal meninges. One form of spina bifida is constituted by cystic dilatation of the central canal of the spinal cord, and produces syringomyelocele. These conditions will be treated more fully in their appropriate places.

Sutton has rendered a great service by showing that the brain and spinal cord are evolved from a segment of the primary intestines, and that the intestinal canal and the neural canal communicate in fetal life at their lower terminations; while it has been shown by several that in the earlier forms of mammalian life they were also connected by their anterior terminations. It is in this way that certain complex tumors of the sacral and coccygeal region are to be explained. So also is the collection of lymphoid tissue in the vault of the pharynx, known as Luschka’s tonsil, and in the coccygeal region, known as Luschka’s gland, it being a curious and instructive fact that lymphoid tissue of this character is always met with in the neighborhood of obsolete canals.

Hydatid Cysts.

—These cysts are the indirect product of the eggs of the Tænia echinococcus, a form of tape-worm which infests the alimentary canal of dogs. The eggs reach in some direct or indirect way the food or water taken into the human stomach and are there hatched; the young animals migrate through vessel walls and are deposited in some tissue or organ where the cyst later develops. These cysts have a thick, elastic wall, with a lining containing cells, involuntary muscle fibers, and a water-vascular system. After such a cyst has attained the size of an inch or more, small vesicles, or “brood capsules,” begin to develop, which present at one point a retractable head, with scolices so arranged in crown form as to produce sucking disks. According to the date at which the cyst is opened appearances will differ. Sometimes a large cavity will be filled with multiple “daughter cysts,” and sometimes these will have disappeared, so that the cyst fluid contains nothing distinctive. After having ceased to develop, hydatids frequently undergo atrophy and even become calcified; the characteristic hooklets are the last of the distinctive features to disappear.

These growths may be rapid, even to the point of producing necrosis and rupture, or may be very slow and persist almost unchanged for years. The disease is uncommon among the native-born population of the United States, and most of its examples are seen in emigrants. It is exceedingly prevalent in Iceland and in New Zealand. It occurs most often in the liver, but is frequently met with in these countries in the lungs, the brain and spinal canal, and the bones, but may be encountered in any part of the body. When located near the intestinal tract or the air tract the cysts are more liable to penetration by ordinary germs of sepsis, and then may suppurate. It is not infrequent to have conversion of an hydatid cyst into an abscess. Before or after such change it may undergo rupture, spontaneous or traumatic, and this, according to the nature and amount of its contents, and the location of the opening, will promptly produce more or less grave symptoms. While spontaneous recovery has, in rare instances, followed rupture, it has perhaps more often led to fatal result. At all events, it will produce serious and perhaps distressing symptoms.

The only radical treatment for hydatid cysts is extirpation. When this is not possible the cyst may be opened and the margins of the opening attached to those of the skin wound. After being evacuated it should be packed and drained, and then may be expected to slowly contract, perhaps even to the point of obliteration. The contents of such a cyst should not be allowed to escape into any of the body cavities, since their sterility can not be always relied upon.

Cystic Degeneration.

Hematocele is an expression meaning a tumor composed originally of effused blood which has undergone chemical and other changes, which consist of lamination and thickening of its exterior portion and fluidification of the interior, until in course of time such an internal blood clot may be converted into a distinct and plainly walled cyst. This condition may be seen in two locations—namely, in the pelvis and between the cranium and the brain, or in the brain. The hemoglobin gradually disappears, and the contents of these cysts are translucent or even watery in appearance. Hematoceles may form where there has been internal hemorrhage in certain locations which has failed to absorb, and where no pyogenic infection has occurred.