DEFINITION AND HISTORICAL REVIEW
One runs into difficulties at once in attempting to define optochiasmic arachnoiditis. The concept of this disease is gradually undergoing change ; it is not today what it was, say twelve years ago, and I do not doubt that it will still evolve considerably. Even at present every one is not in complete agreement with regard to this condition.I believe one may best approach the subject by outlining the several lines of converging thought by which the notion of optochiasmic arachnoiditis was arrived at. The first of these starts with acromegaly, which Pierre Marie,1 in 1886, showed was due to a tumor of the pituitary gland. Such a tumor, later identified as acidophilic adenoma, grows upward, presses on the chiasm and causes visual disturbances, with bitemporal field defects. A few years later Babinski2 proved that a pituitary tumor could be linked with a different