In surgery of the brain the policy has been evolved of pronouncing final judgment as to the operability and prognosis of a tumor only after exploration and microscopic examination. In few instances will the experienced surgeon feel prepared to predict with finality even the pathologic type of the tumor, not to mention its operability. Although a properly made ventriculogram will localize a tumor to a satisfactory degree, it usually cannot be relied on to show the type of tumor. In any instance in which the ventriculogram can be relied on to indicate an inoperable tumor, it provides valuable information to the surgeon.
Tumors arising in the thalamus are unique in this respect. The ventriculographic picture is unmistakable, and the tumor, because of its position if not because of its cell type, is clearly inoperable. Four cases are presented here to illustrate the cardinal ventriculographic features of tumor of the thalamus.