- The solitary bone cyst occurs predominantly in children and adolescents with a peak incidence in the second decade.
- There is no definite sex predilection although some series have shown a slightly higher incidence in males.
- The cyst arises most frequently in the premolar and molar regions of the mandible. Maxillary lesions are rare.
- The majority of solitary bone cysts are asymptomatic and are chance radiographic findings; some degree of bony expansion occurs in about 25 per cent of cases.
- The lesion presents as a radiolucency of variable size and irregular outline.
- Scalloping is a prominent feature particularly around and between the roots of standing teeth (Fig.).
- The margins of the lesion are usually well defined.
Pathological features and pathogenesis
Surgical exploration is undertaken to confirm the clinical diagnosis and characteristically reveals a rough bony walled cavity devoid of any detectable soft-tissue lining. In many cases the cavity appears empty, but in others there is a little clear or blood-stained fluid. Rapid healing follows surgical exploration but even without surgical intervention the cyst will resolve spontaneously with time.
Microscopic examination of curettings from the lesion shows that the bony walls are covered by a delicate layer of loose, vascular fibrous tissue (Fig.) containing extravasated red blood cells and deposits of haemosiderin pigment. There is no epithelial lining.
The pathogenesis of the solitary bone cyst is unknown. It is commonly believed that there is a relationship to trauma, but the evidence is not convincing. Although a history of trauma can be elicited in about 50 per cent of cases, the interval between trauma and discovery of the lesion can range from months to years and the apparent relationship may be purely fortuitous. It has been suggested that the solitary bone cyst, aneurysmal bone cyst, and central giant cell granuloma of bone are related lesions reflecting some haemodynamic disturbance in medullary bone. In the case of the solitary bone cyst it has been argued that trauma produces intramedullary haemorrhage which, for unknown reasons, fails to organize and that cavitation occurs by subsequent haemolysis and resorption of the clot.