Any part of the body may be affected and usually the lesions are multiple.

Structure.-Microscopically the structure of the tumors is allied to that of lymphadenomata. There is a proliferation of connective-tissue cells about the blood-vessels and glands at the base of the papillæ of the skin, forming a network or reticulum in which round (lymphoid) cells are embedded. Epithelioid cells and giant-cells may occur. The tumors are poorly supplied with blood-vessels, and to this is attributed the tendency to central necrosis. Inflammatory infiltration (polymorphous leukocytes) is not observed to any considerable degree, excepting in the latter stages around and in the areas of necrosis. Mast-cells are often abundant.

Associated Conditions.-In some cases enlargement of the lymphatic glands, liver, and spleen has been observed, and has suggested the term pseudoleukemia cutis. Occasionally the blood presents leukemic char

acters.

Nature. The disease presents many resemblances to sarcoma or lymphadenoma, and it has frequently been described as multiple sarcoma of the skin. In other respects it is allied to the infectious inflammations, though there is much less evidence of true inflammatory infiltration than in these. The relationship to leukemia and pseudoleukemia is unsettled.

ENDOTHELIOMA.

This tumor, which is also sometimes designated endothelial cancer, resembles cancer very closely in histologic appearances in

FIG. 58.-Endothelioma of pleura: the pleural cavity was distended with effusion and the lung was compressed and invaded by secondary nodules.

some cases. It appears, however, to be purely endothelial in origin, and therefore rather of the connective-tissue group or sarcomata. It affects the pleura, peritoneum, and membranes of the brain most frequently, but may be found in the skin, walls of the blood-vessels, periosteum, bone-marrow, lymphatic glands, and elsewhere. The serous membranes when affected become greatly thickened, tough, and white in color (Fig. 58), and irregular elevations or nodules may occur. Metastasis is infrequent, but the adjacent organs are sometimes involved, and occasionally more distant structures.

FIG. 59.-Microscopic section from the above (Fig. 58).

Histologically the tumor is characterized by more or less tubular or acinus-like aggregations of endothelial cells. The latter vary in character from those which are distinctly endothelial to the most differentiated, which may be almost typical cylindrical epithelium (Fig. 59). Between these cellular columns or acini the connective tissue of the part affected may be seen in a normal state, though it is more frequently thickened by proliferation. In the endotheliomata of serous membranes inspection of the sections shows that the columns of epithelioid cells occupy lymph-channels, and it may be possible to demonstrate that the endothelium of the latter has been the starting-point of the cellular proliferation. In cases of carcinoma with penetration into the lymphatic channels it is notable, on the other hand, that the endothelial lining of the channels is uninvolved.

GLIOMA.

Definition. The term glioma is applied to tumors composed of neuroglia. It is difficult to distinguish between the circumscribed tumors of this structure and the diffuse neurogliar hyper

plasia or gliomatosis is met with in certain cases. (See section on Diseases of the Nervous System.)

Etiology. It is probable that congenital defects of development play some part in the causation of these tumors, particularly in the forms more frequently spoken of as gliosis.

Appearance.-A typical glioma is usually a solitary tumor, rounded in outline, though its limits are difficult to determine, as it merges gradually into the surrounding nervous tissue. Gliomata are somewhat harder than the normal brain-substance, and often the color is a little different, either more grayish or pink or reddish. Sometimes they are quite vascular and dark red. The normal shape of the part may be a little disturbed, or there may be indefinite elevation. In size the tumor varies up to masses as

FIG. 60.-Glioma of the corpora quadrigemina (Peris).

large as a lemon. Diffuse gliomatosis causes a swelling of the affected parts, sometimes quite regular, at other times irregular. When the spinal cord is affected its thickness may be considerably increased. On section the area of gliomatosis is rather firm and grayish in color. Nearly always there is a tendency to excavation or cyst-formation. In the cord this leads to the development of considerable cavities, as a rule communicating with the central canal.

Seats.-Gliomata occur in the brain and less frequently in the spinal cord. In rare cases the cranial nerves have been involved. Glioma of the eyeball will be referred to below. Diffuse gliomatosis is particularly common in the cord. It is usually met with in the vicinity of the cavities of the brain or cord.

Structure. The minute structure of glioma varies considerably according to the type of neuroglia represented. In the typical glioma the cells contain rounded or oval nuclei, and the protoplasm is scanty, but drawn out in fine interlacing extensions. These give the section a granular appearance when seen under low magnification. In other cases the cells are of the ependymal type, and occasionally they may be arranged around the bloodvessels in rosette-forms. These formations, however, constitute only a small part of the structure, the bulk being composed of round glia-cells. The number of cells and the density of the intercellular network vary greatly. As a rule, the cells are larger than the normal neuroglia-cells, and sometimes they contain several nuclei.

The tumor is generally quite vascular, and occasionally teleangiectatic vessels may be observed. Secondary hemorrhages are prone to occur in the latter case. Softening may occur, and occasionally sarcomatous transformation has been described, though with doubtful propriety.

Diffuse gliomatosis has similar microscopic appearances, though the tissue is likely to be more compact and less vascular. In the spinal cord the process begins as a subepithelial proliferation of the glia at the posterior raphé of the central canal, the lining epithelium of this at the same time undergoing a certain amount of proliferation. Subsequently the gliomatosis increases and cavities form within. These may be lined with epithelial or epithelioid cells which are occasionally ciliated. Gliomatosis may also present itself in the form of scattered nodular hyperplasias of the neuroglia.

Nature.-Glioma is essentially benign. It is dangerous mainly on account of the pressure it exerts. Sarcomatous transformation may possibly occur. The growth of the tumor is rather slow.

Glioma of the Retina. This tumor is a primary one of the retina, but may later extend to the eyeball and along the optic nerve. It is composed of round cells with large nuclei, often arranged around blood-vessels in a way suggesting the structure of angiosarcoma. This appearance is due to the fact that the cells surrounding the blood-vessels are preserved, while those at a distance are degenerated. In addition to the round cells, there are often found cells resembling epithelium in their appearance and their arrangement, the latter being that of epithelial rosettes. Ganglional cells have occasionally been discovered. The cells resembling epithelium have been regarded as derivatives of the outer layers of the retina, and the term neuro-epithelioma has therefore been applied by some authors. Others regard it as a glioma in the strict sense of the word. In either case the origin of the tumor is undoubtedly ectodermic, and the growth must be classified among the epithelial tumors. It occurs most frequently in children, particularly in early life (two to four years), and often on both sides simultaneously. Family predisposition, in some cases, is very striking. Extension along the optic nerve or externally, and a tendency to recurrence after removal, indicate the malignant character of the growth.

Glioma Ganglionare.

Definition. This term indicates a form of mixed tumor composed of neuroglia and nerve-fibers with large ganglionar nerve-cells.

Etiology. Probably congenital abnormality of development furnishes the groundwork for the subsequent development of these tumors.

Appearance. A ganglionar glioma may resemble the ordinary glioma, occurring as a solitary tumor, the outlines of which are difficult to distinguish from the surrounding tissue. More frequently it occurs in the form of multiple nodular condensations scattered through the brain or cord. The contour of the affected parts may not be altered, and on section the growths may be recognized only by the light-colored patches and areas of increased density. A few cases of ganglionar gliomata of the spinal or sympathetic ganglia have been described. In these cases the tumors appear as rounded enlargements of the affected ganglia. Occasionally the nerve-roots are seats of these tumors; the suprarenal capsules may also be affected.

Structure. The definition indicates the usual structure. The gliafibrils are generally conspicuous in number, the nuclei being comparatively few. Traversing the tumor there may be more or less abundant nervefibers with or without medullary sheaths. Large ganglionar cells may be found in considerable abundance or in small number. The vascularity of the growths differs greatly.

Nature. The nature of these tumors is the same as that of the ordinary glioma.

NEUROMA.

Definition.-Strictly speaking, neuroma is the term applied to tumors composed of nerve-fibers. Ordinarily, however, the name is given to fibrous growths springing from the perineurium or endoneurium of nerves. The terms true and false neuroma distinguish between the two forms. True neuromata are exceedingly rare.

Etiology. Very little is known regarding the causation. Injury may play a part, as in the case of amputation-neuromata.

Appearance.-False neuromata occur as nodular thickenings along the course of nerves. They may be fusiform or elongated, may extend considerable distances along the nerves, and may form networks of ridges or elevations when the peripheral nerves are involved (Plexiform Neuroma). As a rule they are multiple, and sometimes occur in exceedingly great numbers scattered over the entire body or involving a single part of the body, as the nerves of the arm or leg. After amputations rounded thickenings may occur at the ends of the nerves and cause painful conditions of the stump.

Seats. The peripheral nerves are most frequently involved, but the nerves may be implicated near their roots, or the terminal fibers within the organs may become affected.

More

Structure.-Ordinary false neuroma consists of fibrous tissue in the form of reticular connective tissue with greater or less abundance of cells pushing aside or surrounding the nerve-fibers proper. The latter are prone to degenerate in consequence of the pressure. Proliferation of the nerve-fibers has sometimes been described, but it is doubtful whether such actually occurs. probably the existing fibers increase in length and form a mass by curling at the end. True neuromata of two kinds are described those composed of medullated and those consisting of non-medullated nerve-fibers. The former are called myelinie, the latter amyelinic.

Nature.-Neuromata are painful tumors, but benign in a pathologic sense. Their growth up to a certain point is often rapid.

LEIOMYOMA.

Definition.-Leiomyoma, or myoma lævicellulare, is a tumor containing smooth muscle-fibers. Nearly always there is a certain amount of fibrous tissue associated, and in the most com