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.