Are false "negatives" possible?

VonnieKai

My husband had rectal cancer and we found in October 2003 that it has spread to his lungs. He had CPT-11 in November and stopped because he suddenly became very delusional about me, thinking I was not his wife. His other memories and functioning is intact, except he complains of increasing back pain. He had a CT-Scan on his brain last week and it was negative for mets, but I am wondering if it's possible that he actually does have mets to the brain, but the tumors are too small to see on the CT scan yet. Is it possible that tumors that small would cause symptoms? I am grasping at straws to try and figure out what is wrong with him so I can help him.
Thanks