Is it true that we can insert a microcamera through our mouths to check on the top of the spine, inside of our heads, if we wish? If so, why is it that neurologists are not checking on tumours in the region like that yet?

By the top of the spine, I presume you must mean the uppermost parts of the vertebral column.  They are not actually visible through the oral cavity, though the first and second cervical vertebrae (the atlas and the axis) can be visualized by an x-ray taken through the open mouth.  Anomalies such as tumors may or may not be visible with X-rays taken of that region.  However, health care providers such as dentists and M.D.s will make a visual examination of the oral cavity during regular checkups, and any abnormalities that might be noted at that time would be further examined by other methods.  But as regards your question, the top of the vertebral column is not immediately visible.

Robert A. Walker, Ph.D.
New York Chiropractic College