These are tumors formed largely of the peculiar fat which is found in bile and brain matter, and that crystallizes in flat oblong scales with a notch at one corner. The tumors are usually connected with the choroid plexus and developed beneath the pia mater, and may be of any size from a pea to a hen’s egg, or in exceptional cases a sheep’s kidney. As a basis there is a stroma of connective tissue permeated by blood vessels from the plexus. Groups of spherical or polygonal cells fill the interstices while fusiform cells are found in the stroma. There is a variable amount of phosphate or carbonate of lime which in oldstanding cases may give a cretaceous character to the mass. These constitute sandy tumors (psammomata).
Cholesteatomata are especially common in old horses and are manifestly connected with congestion of the choroid plexus and exudation. In a recent case or in a case which has shown a recent cerebral hyperæmia, we may find a central mass of yellowish cholesterine, and surrounding this an abundant yellow gelatinoid exudation. This latter is rich in cholesterine which fails to dissolve along with the rest of the exudate on the occurrence of resolution, and is therefore laid up as the solid fatty material. For the same reason the fatty element is usually laid on in layers, one corresponding to each access of local hyperæmia and exudation. The great tendency to calcareous degeneration has been attributed to the abundance of phosphate of lime in the cerebral exudate.
The symptoms of these tumors are exceedingly uncertain. Many such tumors of considerable size have been found after death in animals in which no disease of the brain had been suspected during life. In these it is to be inferred that the accretions were slow, gradual, and without any serious congestion. In other cases the tumor is attended by paroxysms of vertigo, or indications of hyperæmia or meningitis, which will last for several days and gradually subside. It is reasonable to suppose that the tumors are largely the result of such recurrent attacks of encephalitis, and are no less the cause of their recurrence. The intervals of temporary recovery correspond to the subsidence of hyperæmia and the reabsorption of the liquid portion of the exudate. The manifestations during an access correspond directly to those met with in encephalitis. As in that affection there is usually an initial period of excitement and functional nervous disorder tending to more or less somnolence, stupor, paralysis or coma, with long intermissions of apparently good health. In other cases the stupor or paretic symptoms may persist up to the fatal issue.
MELANOMA OF THE ENCEPHALON.
Black pigment tumors have been found in connection with the brain and especially the meninges, varying in size from a pea to a walnut, and as a rule, secondary to similar formations elsewhere. They are most common in gray horses which have turned white, and may give rise to gradually advancing nervous disorder. Bouley and Goubaux record a case of this kind attended with general paralysis. W. Williams reports the case of an aged gray stallion with melanomata on the meninges and in the brain substance which were associated with stringhalt of old standing. Mollereau in a vertiginous horse found a pigmented sarcoma in the right hemisphere between the gray and white matter, and like an olive in size and shape. There were melanomata around the anus. (Annales de Medecine Veterinaire, 1889). So far as such have been examined they follow the usual rule in melanomata in having a sarcomatous structure.
While it is impossible to make a certain diagnosis without opening the cranium, the condition may be suspected, in gray horses, when melanotic tumors are abundant in the usual external situations (anus, vulva, tail, mammæ, sheath, lips, eyelids, etc.), and when brain symptoms set in and progress slowly in such a way as to suggest the gradual growth of a tumor.
Treatment is hopeless, since if they have invaded the brain, the tumors are likely to be multiple in the organ, and numerous and widely scattered elsewhere.
PSAMMOMATA (GRITTY TUMORS) OF THE BRAIN.
As already noted these sandy tumors are often the advanced stage of cholesteatomata, the abundance of the phosphate of lime leading to its precipitation in the neoplasm. The same cretaceous deposit often takes place in old standing tumors of other kinds, as in melanoma, and fibroma so that the sandy neoplasm may be looked upon as a calcareous degeneration of various forms of intracranial tumors. The same tendency to calcareous deposit is seen in the tuber cinereum (pineal body) of the healthy brain which has taken its name from the contained gritty matter. This tendency to the precipitation of earthy salts may be further recognized in the osteid tumors which occasionally grow from the dura mater.
The gritty tumors are especially found in the older horses in which the tendency is greatest to extension of ossification and calcic degenerations.