The tumor is usually soft and can be removed with small surgical instruments called curettes. In order to remove a large tumor through a small hole, the tumor itself has to be cut into small pieces. As the surgeon cores out the center of the tumor, the peripheral margin of the tumor has to fall into an area that can be reached by the surgeon. Some tumors, which have grown beyond the area of the sella, cannot be completely removed. Tumors that grow sideways into the cavernous sinus, a collection of veins next to the sella, usually cannot be completely removed. This is because that area contains important nerves controlling muscles of the eye and the carotid artery, which supplies the brain. Tumors which have a large amount of supra-sellar extension (up into the brain) can be removed in one operation if they fall downward into the sella during the procedure. Sometimes the removal of large tumors has to be staged into two operations, to allow time for the uppermost portion of the tumor to fall into the sella where it can be reached on a subsequent operation.