Solitary bone cysts of the mandible (also known as traumatic bone cyst of the jaw, haemorrhagic cyst of the mandible, extravasation cyst, progressive bone cavity or unicameral bone cyst) are an uncommon nonepithelial lined lucent mandibular lesion. It is one of a myriad of potential mandibular lesions.
They are also described in the long bones and are known as a simple/unicameral bone cyst occurring mostly in the humerus or femur, close to the epiphyseal plate.
The lesion is mainly diagnosed in young patients (10-30 years) most frequently during the second decade of life. Some reports suggest that it is more common in males while others report equal distribution between males and females.
Clinically the lesion is asymptomatic in the majority of cases. It is often accidentally discovered on routine radiological examination, usually as an unilocular radiolucent area with a "scalloping effect”.
The definite diagnosis of traumatic cyst is invariably achieved at surgery. Since material for histologic examination may be scant or non-existent, it is very often difficult for a definite histologic diagnosis to be achieved. Biopsy material consists of fragments of viable bone and loose connective tissue. It is a cystic cavity without an epithelial lining. Osteoclast-like giant cells have also been described in a few cases.
Trauma has been suggested as the etiology along with other non-substantiated theories, such as cystic degeneration of a pre-existing tumor or of the fatty marrow in the area. Less than half are associated with prior trauma.
The majority of them are located in the mandibular body between the canine and the third molar. The second most common site is the mandibular symphysis. Fewer cases are reported in the ramus, condyle, and the anterior maxilla. Traumatic bone cavity is not unique to the jaw bones.
They are usually unilocular, non-expansile (~75%) and radiolucent, typically above the alveolar canal and in many cases with a scalloped superior border spreading between the roots of vital teeth. Large, expansile and multilocular traumatic bone cavities have been rarely described. Expansion is not characteristic of these cysts, but it is described in ~25% of cases.
The margins of these lesions range from very well defined to corticated to punched out radiolucency.
Plain radiograph in the form of an OPG is typically the only imaging performed. On occasion, CT of the jaw may be undertaken.
Plain radiograph (intra-oral / OPG )
Well defined non-expansile radiolucent mandibular lesion. No association with the teeth. No cortical destruction.
Well-defined, corticated, non-expansile radiolucent mandibular lesion.
- T1: homogeneous hypointensity
- T2: homogenous hyperintensity
- T1 + C: mildly enhancing
Treatment and prognosis
Surgical exploration is often undertaken to exclude other more worrisome mandibular lesions. Typically the surgeons report an empty cavity at the entrance in about two-thirds of the cases and straw-colored fluid filled cavities in about one-third of the cases. Blood clot is also present occasionally. The bony cavity is scraped to generate bleeding, which is considered the treatment of choice for this condition. Other methods of treatment have been tried, such as packing the curetted cavity with autologous blood, autologous bone, and hydroxyapatite. Exploration surgery usually leads to healing. Recurrence is rare.
Pathological fractures are rarely associated with traumatic bone cavity have been described in the jaws.