Syphilis attacks the brain chiefly in conjunction with the membranes. It is very rare to meet with a syphilitic tumour in the brain substance without some connection with the surface, and probably the lesion, in almost every case, begins in the membranes. The lesions are those of the tertiary stage, and have the characters already described; gummata associated with more or less inflammation around, and affection of the arteries.

The Gumma occurs as a grey or yellow mass, or is variously composed of both grey and yellow material. The grey structure consists of more or less fresh granulation tissue, while the yellow is due to caseous necrosis, and hence is older. The caseous part consists of granular structureless matter, in which may be recognized some traces of the original tissue, along with fat and blood-pigment. The mass presents these two constituents in varying abundance (see Fig. 333), and the outline of the tumour is indefinite, shading off on the one hand into inflamed and thickened membranes, and on the other into the brain substance infiltrated with round cells.

Fig. 333. - Gumma of membranes affecting brain. a, Thickened niniit>i-a:if-adherent to brain; b. b; arteries with syphilitic endarteritis; c, c, round-celled tissue in brain substance; d, caseous structures, involving occluded capillaries e, e,e.

Sometimes the gumma obviously grows from the Soft membranes, the pia-arachnoid. The membranes are thickened and matted, and adherent to the brain beneath. From their under surface rounded masses bulge against the brain substance, adhering to it and causing destruction. There is usually a zone of softening at the advancing margin of the tumour, and there may be considerable areas of softening deeply in the brain substance due to disease of the arteries in connection with the gumma (see below). In other cases the gumma is seated chiefly in the brain substance, but it is superficial, and the soft membranes are involved in the process. On the other hand, the Dura mater may be the primary seat of the tumour, and here we have tumours of considerable size, as large as a pigeon's or even a hen's egg. The dura mater is thickened and adherent to the soft membranes, and the tumour is usually to a large extent caseous. These tumours have a special tendency to form in the duplicatures of the dura mater, such as the falx cerebri. The projecting tumours impinge on the brain substance like those of the soft membranes, but they also, when seated over the convexity, project against the bone, producing erosion which may be considerable (dry caries).

The gumma may occur at any part of the convexity of the brain, and is also frequent at the base, affecting especially the optic chiasma, pons, and crura. By the latter it may extend to the optic thalamus, but otherwise scarcely attacks the basal ganglia. It not infrequently involves the cerebral nerves as they issue from the brain, especially the optic, and those emerging from the peduncles and pons (third, fourth, and fifth).

It has been already stated that inflammation and thickening of the membranes occur around the gummata, but sometimes a condition exists which may be designated a Gummatous meningitis. The gummatous tissue is formed more diffusely in the form of a grey gelatinous layer, covering a considerable surface at the base or on the convexity. In the former case there may be some resemblance to tubercular meningitis. In the latter, the whole membranes are thickened and matted together by gummatous tissue, and the brain substance beneath is softened. If, under treatment or otherwise, the proper gummatous tissue disappears, then the thickened membranes may present the appearance of an old simple inflammation.

Syphilitic disease of the blood-vessels, although not confined to those of the' brain, is most frequent and most characteristic in them (see p. 301). The lesion is, in many cases, simply a part of the phenomena in connection with a gumma and presents itself in a number of small arteries, as an endarteritis obliterans (see Fig. 333, b, b). But it also occurs as an -isolated affection of the larger cerebral vessels, chiefly those which contribute to the circle of Willis. The appearances are like those of atheroma, but the affection is more localized, occurring mostly in a few patches and not, as in atheroma, extending to a large number of branches. The patches are greyish white and opaque, and the wall is firm, so that the vessel preserves its cylindrical shape. The new-formation has a dense character, and as it consists of thickened internal coat, the calibre is diminished or even obliterated, especially if thrombosis ensue.

The lesion is a gummatous new-formation in the wall of the artery. It has its seat, according to Heubner, especially between the elastic lamina and the endothelial layer. The new-formation consists of granulation tissue and rudimentary connective tissue in the form of spindle and stellate cells. The lesion is apt to extend some distance along vessels, sometimes involving communicating branches.

An important result of this affection of the arteries is local Softening of the brain. This may occur either in relation to a proper gumma, or independently, from the affection of an artery alone. It is due to the narrowing of the calibre and occlusion, and has the same nature as softening from embolism, etc. The softening may be seated at some distance from the gumma or arterial lesion, especially where a long artery is distributed without intervening branches. According to Heubner the lesion affects most frequently the carotid and its branches, especially the middle cerebral, so that we may have softenings in the basal ganglia as in embolism.

The Functional effect of these various. lesions depends largely on their Localization. The gummata and resulting inflammations of the convexity, occurring as they do on the surface, will, at first, irritate the surface of the convolutions. If a motor part be affected then there will be muscular spasm, often progressive and ending perhaps in general convulsions of a quasi-epileptic character. Any sort of local spasm may be produced according to the particular part irritated. If the lesion be over a sensory part there will be subjective sensory impressions. We have already seen that the brain substance commonly gets involved in the gumma, and that outside it there is also softening of the brain. This destruction of brain substance involves loss of function, namely, motor paralysis or loss of sensation; but there will still be irritation of the marginal parts, and though paralyses and anaesthesia? may develop, the signs of irritation generally remain prominent. At the base the gumma is very apt to involve motor tracts. The motor fibres of the pons and peduncles are anterior, and are therefore more exposed to the inroads of the tumour. But these paralyses are apt to be complicated by the lesion extending to the cerebral nerves which issue here, mainly the optic, third, fourth, and fifth, and so we have very complex conditions brought about, such as crossed paralysis, etc. Again, the syphilitic disease of the arteries occurs most frequently in the carotid and middle cerebral, and the resulting softening is usually most manifest in the region of the corpus striatum and motor convolutions. In this way a hemiplegia may be produced which imitates that from, embolism. It will be seen that a great variety of symptoms may be produced from syphilitic lesions of the brain and its membranes.

Literature

Heubner, Die luetische Erkrankung der Hirnarterien, 1874; Greenfield, Gowers, Hutchinson, Goodhart, and others in Path, trans., xxviii., 1877, pp. 249-360; Greenfield, Path, trans., xxix., 1878; Gowers, Syphilis of the nervous system, 1892.