The radiology of sacral cysts.

The radiological findings in 10 patients with sacral cysts were retrospectively reviewed and classified. The cysts were an incidental finding on computed tomography (CT) in four patients. The expansion of sacral foramina or the sacral canal as seen on plain films suggested the diagnosis in three. In only two of the five patients who had myelograms did the cysts fill with contrast. In eight, CT showed remodelling and expansion of the sacral foramina, or the canal, or both, by a homogeneous mass with a density of 5-20 Hounsfield units. One of the patients underwent magnetic resonance imaging which confirmed that the lesion was fluid-filled. We found that sacral cysts can be either symptomatic or asymptomatic, that they may or may not communicate with the subarachnoid space, and that they have a characteristic CT appearance.