Simple bone cyst. Evaluation of contents with conventional radiography and computed tomography.

To evaluate whether gas is present in the cavity of simple bone cysts, the clinical and histologic findings of 53 patients with simple bone cysts were examined and compared with an experimental model. The model consisted of a dry mandible with the medullary bone removed and the resulting cavity injected with water. Although an air-liquid level was observed on all radiographs for the experimental model, none was observed in the clinical cases of simple bone cysts. When the experimental cavity was completely filled with water, the density in the cavity was similar to that of the surrounding water on computed tomography, but when it was filled with air, the density was lower than that of the surrounding water. In contrast, in simple bone cysts said to contain air at surgery, the cavity contents were not consistent with the density for gas on computed tomography. These results indicate that the operative finding of air in the cavity of simple bone cysts may have been in error at least in some cases.