The parovarium consists of a series of fine tubules lying between the layers of the mesosalpinx. It may be seen in the fresh specimen by holding the mesosalpinx stretched between the eye and the light (Fig. 145).

The typical parovarium consists of three parts: a series of vertical tubules; a series of outer tubules free at one extremity; and a larger longitudinal tubule.

The vertical tubules range from five to twenty-four in number. They converge somewhat toward the ovary, where they end in blind extremities and become closely associated with the paroÖphoron. At the other end they terminate in the larger longitudinal tubule.

The series of outer tubules are called Kobelt’s tubes. They are free and closed at the distal extremity, while at the proximal extremity they join the longitudinal tubule. The larger longitudinal tubule is called the duct of GÄrtner. It may sometimes be traced traversing the broad ligament to the uterus, and through the walls of this organ and of the vagina to its termination at the urethra. It corresponds to the vas deferens in the male. When persistent in the vaginal wall it may become the starting-point of a vaginal cyst.

The vertical tubes of the parovarium are from 0.3 to 0.5 millimeters in diameter. They are occasionally found lined with ciliated columnar epithelium. Usually they contain a granular detritus representing the remains of broken-down epithelium.

Cysts may arise from any of the parts of the parovarium.

Kobelt’s tubes frequently become distended, and form small pedunculated cysts about the size of a pea. They are of no clinical importance (Fig. 145). They are often observed in operations for ovarian disease, and are very often mistaken for the hydatid or the cyst of Morgagni which springs from the Fallopian tube, and which has already been described.

The difference between these two varieties of small cysts may be determined by careful examination of the point of origin and by means of the microscope. Sutton states that the cyst of Morgagni has muscular walls and is lined by ciliated columnar epithelium. In the cyst of Kobelt’s tubes the walls are fibrous and the lining is cubical epithelium.

Large cysts of the parovarium originate from the vertical or the longitudinal tubules, and usually remain sessile and develop between the layers of the mesosalpinx and the broad ligament. As the cyst grows and separates the layers of the mesosalpinx, it comes into close relationship with the Fallopian tube. This structure, being held by its uterine connection and the tubo-ovarian ligament, becomes stretched across the surface of the cyst and very much elongated. The elongation of the Fallopian tube is a very constant accompaniment of parovarian cysts. The tube may attain a length of 15 or 20 inches. The fimbriÆ may also become much stretched and elongated by the traction of the growing cyst, and may attain a length of 4 inches.

The ovary is unaffected unless the cyst be of very large size, in which case the ovary may be stretched upon the surface of the cyst, so that its position becomes difficult to determine.

There are two varieties of parovarian cyst—the simple and the papillomatous.

The simple parovarian cyst has a very thin wall of uniform thickness. In small cysts, less than the size of a child’s head, the wall may be transparent. It is of a light yellowish or greenish color, and the fine vessels ramifying upon the surface are plainly visible. As one would expect from the direction of growth, the outer covering of the cyst is peritoneum, which is not adherent and may be readily stripped off. The middle coat is composed of fibrous tissue containing unstriped muscle. The lining membrane is ciliated columnar epithelium, stratified epithelium, or simple fibrous tissue, according to the size of the cyst. The changes in the character of the epithelium are due to pressure. The cyst-contents are a clear, limpid, opalescent fluid of a specific gravity below 1010.

In the papillomatous parovarian cyst the interior is covered with warts or papillomatous growths resembling in every respect those that occur in the cyst of the paroÖphoron, already described. The papillomatous parovarian cyst exhibits the same clinical features, and is liable to the same accidents, as the paroÖphoritic cyst. It may become perforated and infect the general peritoneum.

The walls of the papillomatous parovarian cyst are somewhat thicker than those of the simple parovarian cyst; the fluid contents are not so clear and limpid, and may contain altered blood that has escaped from the papillomata.

Parovarian cysts are almost invariably unilocular. Only a few cases have been reported in which two or more cavities were present.

The cysts are of small size, not often exceeding that of a child’s head. They may, however, attain large dimensions and contain several quarts of fluid.

Parovarian cysts are of very slow growth, and refill but slowly after tapping or rupture. On account of the thinness of the cyst-walls, these cysts seem especially liable to the accident of rupture. Unless the cyst be papillomatous, the bland, unirritating fluid is readily absorbed by the peritoneum, and the cyst may remain quiescent for a long period.

Cysts of the parovarium occur most frequently during the period of active sexual life. Unlike dermoids and cysts of the oÖphoron, they are unknown in childhood.

Cysts of the parovarium are much less common than cysts of the oÖphoron and paroÖphoron. In 284 tumors of the ovary and parovarium operated upon by Olshausen, about 11 per cent. originated in the parovarium.

Some authorities maintain that in rare instances dermoid cysts may arise from the parovarium.

The symptoms of parovarian cysts resemble those of ovarian cysts of similar development. On account of the intra-ligamentous development of the tumor, pressure-symptoms may appear early. The cyst is of such slow growth that the simple parovarian cyst may exist for a long time without giving any trouble whatever. The slow growth is the only clinical feature that would enable one to make a diagnosis between parovarian and ovarian cyst.

COMPARISON OF OÖPHORITIC, PAROÖPHORITIC, AND PAROVARIAN CYSTS.

The chief characteristic features of the large cysts of the. ovary and the parovarium—the glandular cyst, the paroÖphoritic cyst, and the parovarian cyst—may be tabulated for comparison as follows:

Glandular OÖphoritic Cyst.—Intra-peritoneal in development; no peritoneal investment. Ovary destroyed early in the course of the disease. Cyst multilocular.

Fluid contents thick, colored; specific gravity greater than 1010.

Tumor of rapid growth.

Usually unilateral.

Fallopian tube distinct from tumor, and not much, if any, elongated.

ParoÖphoritic Cyst.—Often extra-peritoneal in development, in which case there is a detachable peritoneal investment.

OÖphoron not at first involved by the growth.

Unilocular.

Fluid contents less thick and viscid than in oÖphoritic cyst.

Interior filled with papillomata.

Tumor usually of slower growth than the oÖphoritic cyst.

Very often bilateral.

Fallopian tube more likely to be involved than in oÖphoritic cyst.

Cysts of the Parovarium.—Intra-ligamentous in development. Peritoneal investment which may be stripped off.

Ovary pushed aside, but shape not affected unless the cyst be very large.

Cyst unilocular.

Wall thin. Fluid contents watery, opalescent; specific gravity below 1010.

May or may not have papillomata in interior.

Tumor of very slow growth.

Usually unilateral.

Fallopian tube much elongated and stretched immediately over the surface of the cyst.