Simple bone cyst occurring in calvarium.

A 60 year-old female presented with a non-specific headache that she had experienced for 4 years. A simple skull X-ray indicated a well-defined, lobulated and radiolucent lesion with a thin sclerotic rim involving the parietal bone (Fig. 1A). Computed tomography revealed a hypodense lesion. Magnetic resonance imaging showed a 2 cm-sized cystic lesion in the diploic space with both tabular involvement. This lesion was not enhanced by contrast agent. It was well defined and the periosteum was intact. The cyst paralleled the CSF in signal intensity on all pulse sequences. No fluid levels were detected (Fig. 1B, C, D). After the scalp was incised, a semi-translucent and light yellow- to white-coloured bony lesion was easily identified. The outer bony cortex of this lesion was slightly elevated, and the consistency was same as that of the normal skull. A craniectomy was performed and the cystic skull lesion was removed. The inner surface of this cystic lesion was intact but appeared irregular. The cystic cavity was empty and the dura did not appear to be involved. Histologically, it was a simple cystic cavity without lining epithelium, and the surrounding bony structures were normal (Fig. 1E, F). It was diagnosed as a simple bone cyst (SBC). The postoperative course was uneventful.