Although the skull surrounds the brain, having secondary cancer in the bones (also known as metastases) of the skull is not the same as having cancer in the brain. Many people who get secondary cancers in their skull bones will never get brain metastases.

Both the brain and the bones (including the bones that make up the skull) are common sites for secondary cancers (cancers that have spread from tumours elsewhere in the body).

Some people may develop secondary cancers that are affecting both their brain and their bones. But others will have metastases in just the bones but not the brain, and yet others will have metastases in their brain but not their bones.

A bone scan is a test that looks only at the bones but does not tell doctors anything about other organs or tissues in the body. So the fact that your mother's scan has shown secondaries in her skull simply means that there are metastases in her bones, it does not show whether or not there are also metastases in her brain. In order to look for brain secondaries she would have to have a different type of scan (usually a CT scan or an MRI scan). Doctors would normally only arrange these tests if there were symptoms to suggest that brain metastases could be present, simply having bone secondaries in the skull, without any other symptoms, would not usually be a reason for looking for brain secondaries.