Myxoma

This form of tumour is very rare, but cases have been observed of both central and peripheral origin. The tissue is usually mixed with cartilage or other tissue. The growing tumour, whether central or peripheral, causes atrophy of the bone. The commonest seat is the jaw-bones.

Lipoma is still more rare. Cases have been described in the upper jaw and tibia, and the author has recorded a case of central lipoma of a rib.

Angioma

Tumours composed of blood-vessels are very rare in the bones, but some cases are recorded in which cavities filled with blood have communicated with vessels. These cavities have been chiefly at the ends of long bones. The cavities are variously regarded. Some consider them true vascular tumours, others believe they are produced by rupture of arteries, and are False aneurysms, while others assert that they originate from sarcomas whose vessels have enlarged. The name Hsematoma is also applied in the view that they originate in haemorrhage.

Besides these tumours, others may be so highly vascular as to be pulsatile during life. This applies especially to the soft sarcomas.

Cysts. Cystoma

Cysts occasionally arise in bone by softening of the tissue of other tumours or of "the bone-marrow itself. Fig. 291 represents a case in which the head of the fibula was distended by a unilocular cyst which contained serous fluid and was lined by a vascular membrane.

Cysts of the jaws merit special attention. These originate for the most part near the alveolar processes, and are probably related to the teeth. Some of them are single, Unilocular cysts, and have their origin in teeth which have not undergone the usual eruption. A tooth or pieces of hard substance (dentine) are usually present in the wall of the cyst. Others are Multilocular and develop out of a gland-like tissue, the cells of which undergo colloid degeneration, and in this way form cysts. In its original structure the tumour might be called an adenoma, and a considerable portion of it is sometimes composed of solid glandular or epithelial tissue. According to Eve the tumour arises by penetration downwards of the epithelium of the gums, and he relates this to the normal penetration of this epithelium in the foetus in order to form the enamel organ. These multilocular cysts are mostly innocent, but sometimes the epithelium is less regularly arranged, and they approach in structure and tendencies to the cancers. Both forms of cysts originate in the interior of the jaws and distend them; those in the upper jaw have a special tendency to pass into the antrum which they may fill out.

Sarcomas

These form the most important group of tumours of bone. They are divisible into central and subperiosteal forms.

The Central or Myelogenous sarcomas occur in the lower jaw and in the cancellated tissue of the long bones, especially the femur, tibia, and humerus. They present a somewhat varied structure. Many of them are giant-celled or myeloid sarcomas (see Fig. 101, p. 247). Some are composed of large round cells, which may resemble epithelial cells; some are spindle-celled. There are also cases in which large cells exist in nests, forming an alveolar sarcoma, which resembles cancer.

The central sarcomas, originating in the bone-marrow or in the substance of the bone, destroy in their growth the bone-tissue. In this way they frequently work their way to the surface, destroying the continuity of the bone. Spontaneous fracture is the result. This is well seen in Fig. 292, which represents the upper part of a central myeloid sarcoma. Below there is a bulky tumour distending the lower end of the femur (not shown in figure). A spontaneous fracture has occurred and the upper fragment is shown. The tumour is growing in the medullary cavity of the shaft and has eroded the bone on either side so that the dense bone tapers off. The fracture has been thus produced.

Fig. 291. - Cyst of upper end of fibula. The upper part of the bone is expanded into a cyst which contained a reddish serous fluid.

In some cases the sarcomatous tissue almost entirely replaces the proper bone, the condition suggesting a new-formation in the entire medulla. This is strikingly the case in a preparation in the Museum of the Western Infirmary. Here the entire humerus is replaced by a bulky tumour consisting of round and spindle-shaped cells, no trace of the bone persisting except the condyles. The arm was amputated, but a precisely similar tumour developed in the other humerus, which was also amputated.

The Subperiosteal sarcomas (Peripheral sarcomas, see Fig. 293) are chiefly round-celled or spindle-celled, but in the case of the jaws they may be giant-celled. The tumour may enclose a considerable portion of the bone, especially in the case of the long bones, and may present a somewhat radiating arrangement from the shaft. The growing tumour is liable to erode the proper tissue of the bone, as shown in Fig. 293. The tissue is very liable to undergo ossification. In some the ossification is so striking a feature that the whole tumour is represented by a mass of dense bone, on the surface of which the sarcomatous tissue is present as a comparatively thin layer. To this form the term Osteoid sarcoma may be applied. The cells on the surface of this tumour are variously shaped, and the bone seems to arise directly from these cells, which act as osteoblasts.

Fig. 292. - Upper part of a central myeloid sarcoma of femur in section. The tumour was growing in the medullary canal and has eroded the bone on either side.

Fig. 293. - Spindle-celled sarcoma of tibia growing from upper end of diaphysis. It is eroding the bone.

The sarcomas of bone show very varying degrees of Malignancy. They grow locally at the expense of the bone as in Figs. 292 and 293, and not infrequently encroach on neighbouring structures, sometimes penetrating into the joints. Many of them show merely this local malignancy, but others extend by metastasis to internal parts. Even the highly ossifying forms may lead to secondary tumours in the lungs, and secondary tumours showing a similar ossifying tendency.

Carcinoma

A primary cancer can scarcely originate in bone, where there are no epithelial elements. In the jaws, however, we meet with what are practically primary cancers. The near connection of the jawbones with the gums and with the teeth, whose enamel organ is an epithelial structure, explains the origin of such tumours. Cysts of the antrum have been already referred to as frequently originating in adenoid tissue, and this tissue may take on a cancerous character. In both jaws, also, cancer, originating at the alveolar surface, may grow into and involve the bone. Cases are not uncommon in which a cancer has originated in connection with an old discharging cloaca, the result of necrosis. The cancer extends into the sinus, and even into the cavity in the bone.

Secondary cancer is very frequent in the bones. Cancer, when it becomes generalized, is very liable to become implanted in the cancellated tissue, especially of the vertebrae, ribs, and ends of the long bones. It there grows as a central tumour, distending and destroying the bone, and sometimes leading to spontaneous fractures as in Fig. 294. In most cases the tumours are multiple. The stroma is sometimes composed of bone and cartilage so that the tumour may be hard.

Secondary thyroid adenoma is a rare form of tumour in bone. A few' cases have been observed in which, with enlargement of the thyroid, secondary tumours composed of glandular tissue have developed, chiefly in the bones of the skull and vertebrae. In a case observed by the author the tumours occurred in the diploe of the skull, and in growing destroyed the bone. One of the tumours in the occipital region caused a gap in the skull an inch and three-quarters in diameter. This was occupied by the tumour which projected inwards and outwards. It formed during life a bulky Pulsatile tumour. (See under Thyroid gland).

Fig. 294. - Spontaneous fracture of nock of femur from a secondary cancer.

Parasites In Bone

The Cysticercus cellulosae has been observed. Targett has given a good account of hydatids in bone. This disease, due to the echinococcus, is very rare in bone. The cysts develop either in the substance of the bone, more particularly the ends of the long bones, the bodies of the vertebrae and the pelvis, or they develop inside a natural cavity such as the frontal or sphenoidal sinuses, this being much less common than the other. The lesion is usually a diffuse one; there is no mother cyst, and the hydatids bud out, forming an exogenous growth. After growing and distending the bone it may burst through it and develop further in the soft parts around.

Literature

Weber, Die Exostosen und Enchondrome, 1856; Virchow, Geschwiil-ste, ii.; Lucre, in Pitha und Billroth's Handb., 1869; Cornil et Eanvier, Man. d'hist. path., i., 1881; Coats (Lipoma), Trans. Glas. Path, and Clin. Soc, iii., 1892; Eve, Cystic tumours of jaws, Brit. Med. Jour., 1883, i.; Heath, Injuries and dis. of jaws, 3rd ed., 1884; Butlin, Oper. surg. of malig. disease, 1887; Jones, Dis. of bones, 1887; Coats (thyroid adenoma), Path, trans., xxxviii., 1887; Targett, Guy's Hosp. Rep., 1., 1893.