Skull base polyostotic fibrous dysplasia with secondary aneurysmal bone cyst

Case contributed by Ralph Nelson
Diagnosis certain


Incidental finding of skull base fibrous dysplasia with subsequent new facial numbness and worsening headache a few years later.

Patient Data

Age: 20 years
Gender: Female

Incidental increased uptake in the left maxillary bone and sinus with increase uptake along the left sphenoid wing and central sphenoid bone and sinus, suggestive of fibrous dysplasia.

Patient underwent a whole body bone scan to assess for sacroiliitis and spondylitis, which was negative.

Confirming polyostotic fibrous dysphasia with numerous sclerotic osseous lesions, some of which demonstrate ground glass matrix and heterogeneous density with associated thickening and expansion of the left parietal bone, greater wing of sphenoid bone, clivus, ethmoid and sphenoid sinuses.

MRI findings of left skull base polyostotic fibrous dysplasia.

Known polyostotic fibrous dysplasia in the left skull base with development of lytic-appearing lesion mainly along the superior left clivus. There is interval associated cortical disruption.

Confirming new osteolytic lesion within the area of fibrous dysplasia at the level of the body of the sphenoid and clivus, which shows isointense signal on T1, a definite fluid-fluid level on T2. Smooth oeripheral enhancement without associated central contrast enhancement within the cystic lesion.

The lytic lesion extends into the left foramen rotundum and pterygopalatine fossa.

The superior orbital fissure, orbital apex, and petrous apex appear uninvolved. 

H&E stain with original magnification x 20. Fibroblast like stromal composed of elongated cells without marked atypia,giant multinucleated cells, fragments of woven bone and blood filled lakes. Focal deposits of hemosiderin are present.

H&E stain with original magnification x 200. Irregular trabeculae of woven bone with no rim of osteoblasts, within a stroma containing bland spindle cells.

Case Discussion

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.

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