Thanks for writing in.
Since you have said that the meningioma
was in the olfactory groove and 6 cms in size, there must have been some involvement of the olfactory tract.
During the tumor
removal, there must be some olfactory stimulation and that is the cause of the constant smell.
In some cases it can disappear after a while, and for few patients it can remain for a long time. This is a harmless condition.
Hope this helps.