Our patient was a previously healthy young woman known for left skull base polyostotic fibrous dysplasia, discovered incidentally on whole body bone scan. Approximately three years later she represented with new and worsening headaches and numbness in the V2 distribution. 

Skull base MRI demonstrated a predominantely cystic lesion at the body of the left sphenoid and clivus, which encroached on the left foramen rotundum, consistent with the patient's symptomatology. 

The working diagnosis was that of polyostotic fibrous dysplasia with development of an aneurysmal bone cyst.

On histopathological study, both pathologies were indeed present with clear transition from the fibrous dysplasia to the aneurysmal bone cyst. There have been case reports of such rare combination (please refer to references).

Our patient was treated with a transsphenoidal endoscopic drainage of the aneurysmal bone cyst with associated septoplasty.

Review of our patient last clinic note, 3 months postsurgical treatment, shows that she "no longer has headaches... area of left CN V2 numbness improving".

Special acknowledgments to Drs. Kovacina, B., Lam S., and Torres, C., for being exemplary teachers and to Dr. Guiot, MC., a respected pathologist, for being generous with her time.