The image being shown here is the base of  a cranium of patient who has a confirmed diagnosis meningeal tumor with bone invasion. Which of the following sentence is most appropriate regarding the meningeal tumor?

A.  The tumor is a WHO grade I meningioma.

B.  The tumor is a WHO grade II meningioma because of bone invasion.

C.  The tumor is a WHO grade II or III meningioma because of bone invasion.

D.  The tumor is a WHO grade III meningioma because the tumor is invading into the adjacent bone.

E.  The WHO grade of the tumor cannot be determined because bone invasion is not a diagnostic criteria for WHO grading of meningioma.

Answer and Discussion: The answer is (E). Bone invasion is not a diagnostic of histologic grade in WHO classification. Brain invasion, however, would make a meningioma at least WHO grade II. It is not uncommon for meningioma arising from the cranial base to have extensive invasion of the cranial bone. This feature makes these tumor difficult to be entirely resected in some occasions.