[Case of cervical monostotic fibrous dysplasia with a large cyst].

We report a rare cervical monostotic fibrous dysplasia with a large cyst in the C2 region in a 55-year-old man complaining of headache. MRI revealed an expanding bony tumor at the C2 spinous process. Gd-DTPA MRI showed slight enhancement around a cystic mass. We performed C2 laminectomy and removed the tumor. It was comprised of soft tissue in the C2 spinous process and right lamina and contained a large septated cyst filled with xanthochromic fluid. Histopathology confirmed fibrous dysplasia with typical woven bony trabeculae. His postoperative course was uneventful and outpatient follow-up detected no deficits. Cervical fibrous dysplasia with a distinct cyst is a rare entity and few cases have been reported in the literature. Such cysts are considered to reflect a tumor regression process. Diagnosis based on MRI and CT study alone is difficult. We suggest that these lesions be surgically resected.