Tumours are of frequent occurrence in the brain, and produce secondary consequences of great importance. These secondary results are mostly related to the fact that the brain is enclosed in a rigid case, and that either by their own bulk or otherwise the tumours are liable to increase the contents of the cranial cavity. Hence there is pressure exercised on the brain. In addition to this there are various destructive effects produced. The secondary effects are, from a practical point of view, the most important consequences of the presence of tumours, and as these effects are, on the whole, similar whatever the nature of the tumour and whether it be primary or secondary, intra-cranial tumours form a consistent group of lesions. In this view tubercular and syphilitic tumours are in a similar position to other forms.
Pressure effects are of great importance. Any tumour in its growth will press on the parts in its immediate neighbourhood, and the usual result is Softening of the brain substance around, the proper tissue-elements being destroyed. When the growth is slow there may be little pressure, and the nerve structures may partly persist around the tumour or even be contained in its peripheral parts, if the growth is an infiltrating one like a glioma. Pressure is also exerted at a distance. The tumour itself by its bulk added to that of the cranial contents increases the intra-cranial pressure. The action of the pressure will depend somewhat on locality. The dense membranous septa, the falx and the tentorium, but especially the latter, limit its action. A tumour of the cerebellum, being confined by the tentorium, will often cause compression of the parts beneath the latter, and the pons is not infrequently damaged by such tumours (Gowers). Again, tumours often lead to Hydrocephalus, or accumulation of fluid in the ventricles, and this raises the* general intra-cranial pressure. This occurs chiefly when they press on the transverse fissure so as to obstruct veins or lymphatics there (see further on under Hydrocephalus). There may be considerable thinning of the bones from pressure either with or without hydrocephalus, and sometimes even a gap in the bones. In children the sutures may be widened by the intra-cranial pressure. The relation of increased pressure to affections of the optic nerve is referred to in .the section on Diseases of the Eye.
Inflammation is a common result around a tumour. The irritation of the tumour frequently leads to prominent symptoms during life, and its presence causes structural changes. The brain substance in some cases shows sclerosis, although softening is more frequent. The membranes on the other hand are usually thickened by chronic inflammation, over the seat of the tumour and even at a distance. In syphilis the inflammation of the membranes is very great, and in tuberculosis there is sometimes an associated tubercular meningitis.
This form of tumour is peculiar to the nervous system and is of frequent occurrence there. As its tissue somewhat resembles brain substance in consistence, and as the tumour is an infiltrating one, its boundaries are frequently very indefinite and it may even appear as a simple local enlargement of the brain. Some cases described as instances of local hypertrophy are of this kind.
On section the tumour generally shows some difference in colour from the brain substance into which it merges at its boundaries. It is generally redder than the white substance, and sometimes deeply red from excessive develop-ment of vessels. There is not infrequently haemorrhage in the substance of the tumour, and this may be so considerable that the whole softened mass has the appearance of an extravasation of blood, and may be mistaken for this.
Fig. 334. - Glioma of brain.
In its structure the glioma consists of cells usually round and of small size. These are enclosed in a granular, homogeneous, or finely fibrillated intercellular substance (see Fig. 334), which is usually very soft and delicate. Sometimes the intercellular substance has a distinctly fibrous character, and the tumour is then very firm. Sometimes the intercellular substance has a mucous character, in which case the tumour may be designated a Myxo-glioma. On the other hand the tissue may become very cellular and the tumour assume the characters of the. sarcoma.
The glioma usually grows slowly. When it reaches the surface there are sometimes defined growths formed, which may be pedunculated. There may be small separate growths formed on the surface (Gowers).
Ziegler describes under the name Neuro-glioma tumours composed not only of neuroglia, but also of ganglion cells and nerve fibres. Such tumours are due to errors of development, and are congenital. They are better regarded as cases of Heterotopia of the brain substance (see under Malformations of the brain).
The Psammoma is not a frequent tumour of the brain substance, being much more common in the choroid plexus and dura mater. But it does occur in the substance of the brain, as in the case from which Fig. 90, p. 232, is taken. Here a hard calcareous tumour, which was with difficulty incised, measured 3/8 by 1/4 of an inch, and to that extent completely replaced the brain substance. It was seated at the surface of the convolutions. As shown in the figure it was composed of the characteristic sand granules held together by a very small quantity of connective tissue. These bodies also occur in other tumours, chiefly sarcomas.
The sarcoma of the brain substance is a circumscribed tumour, in this respect contrasting with the glioma (see Fig. 335). It occurs in the midst of the brain substance, and usually in a more or less rounded form, being free to expand in all directions on account of the softness of the tissue around. The round-celled sarcoma is the commonest form, but spindle-celled tumours and those with variously shaped cells are not infrequent.
Fig. 335. - Spindle-celled sarcoma of brain. It forms a defined tumour. The affected hemisphere is considerably enlarged by its presence.
Fig. 336. - Primary cancer of the brain, a, Tumour; b, corpora quadrigeminu stretched over it. The aqueduct of Sylvius is visible between tumour and corpora quadrigemina; the tumour bulges into fourth ventricle, c, Thalamus opticus; d, third ventricle.
The sarcomas vary in consistence, the softer ones being usually round-celled. They may soften in the central parts and form cysts. Most demarcated tumours of the brain, excluding tubercular masses, are sarcomas.
Primary cancer occurs in the substance of the brain, but is perhaps usually connected with one of the ventricles, from which it probably derives its epithelial elements. In the case figured (see Fig. S36) the tumour had its seat chiefly in the fourth ventricle and aqueduct of Sylvius, bulging into these. The tumour consisted of a vascular stroma and cylindrical cells which impinged on the brain substance.
Fig. 337. - Secondary cancer in brain. Cysts developed.
The Cholesteatoma or Pearl tumour is a rare form of tumour which occurs chiefly in the membranes, but is also met with in the substance of the brain. It consists of a cyst containing epidermic cells which have a glancing character and are arranged in rounded masses. The tumour has a soapy appearance. It probably originates from the epithelium of the spinal canal or ventricles, and is therefore an epithelioma. Ziegler mentions that small hairs may be present in the tumour.
Secondary cancer is not common in the brain, but it may form single or multiple tumours. In a case recorded by the author in which the primary tumour was presumably in the lung, the secondary tumours occurred chiefly in the form of Cysts, of which there were twenty-four discovered in the brain (see Fig. 337). In one of the tumours which was not yet entirely cystic the cancerous structure was apparent (see Fig. 338).
The Cysticer-cus cellulosse, which is the scolex form of the taenia solium, has occasionally its seat in the brain, mostly in the cortical portions, but it may be in any situation. It forms a small round structure enclosed in a connective-tissue capsule. Inside this the proper stratified membrane of the parasite, as well as the head (see Fig. 178, p. 391) and other structures, are to be found. Sometimes the parasite is dead and calcified. As a rule it produces little disturbance, and is often found by accident after death. If situated in the peduncular portions it may produce serious symptoms, but even here its slow growth and small size generally allow of accommodation. Sometimes several cysticerci, as many as 10 to 20, have been found.
The Echinococcus more rarely develops in the brain, forming its usual cysts, which are generally in the substance of the cerebral hemispheres. They also occur in other parts of the brain, and between the dura mater and the bone.
Fig. 338. - Secondary cancer in brain developing cysts, a, a, Duct-like canals; b, b, larger spaces, the beginnings of cysts.
Gowers, 1. c, ii., and Syphilis of the nervous system, 1892; Hale White, Guy's Hosp. Rep., xliii., 1886; Virchow, (Glioma) Geschwiilste, ii., 123; Various authors and tabulation of 54 tumours, Path, trans., 1886, xxxvii., p. 6-89; Coats, (Cancer) Path, trans., 1888, xxxix., p. 5, (Multiple cysts) do., p. 326; Eppinger, (Cholesteatoma) Prag. Vierteljahrschr., 1875; Rokitansky, (do.) Hand-buch, ii.; Muller, Virch. Arch., viii.; Bruns, Die Geschwulste d. Nervensystems, 1897.