First described in 1942, Stafne bone defects (SBDs), are well-defined, radio-lucent lingual depressions of the lower jaw bone that are asymptomatic and most frequently diagnosed in middle-aged men. These lesions are also known as static bone cysts, idiopathic bone cavities, lingual bone defects, or Stafne’s bone cavities.
An American dentist, Edward C. Stafne, discovered that these lesions present unilaterally in the posterior aspect of the mandible between the third molar and the mandibular angle. He further noted that they were located slightly above the basis of the mandibulae and underneath the inferior dental canal. SBDs are usually found incidentally, and the term cyst is a misnomer because they do not contain any fluid.
Clinical Presentation and Etiology
SBDs are typically found incidentally, as they cause no signs or symptoms in affected patients. They are believed to be caused by lingual cortical plate bone remodeling, which results from ectopic segments of the salivary submandibular glands. In his investigations, Stafne suggested that a deficiency in bone deposition leads to cartilaginous tissue occupation of the defect during development. Other investigators posit that pressure from the glandular tissue is what leads to the bony depressions. This theory is accepted by many and implicates the submandibular gland in SBDs.
In rare cases, SBDs are completely encased by the bone. Investigators believe that this finding may result from salivary gland tissue entrapment within the bone during its embryonic stages. In even rarer cases, some patients may present with SBDs in the anterior aspects of the mandible (anterior SBDs [ASBDs]). These lesions are believed to be associated with the salivary sublingual glands. ASBDs are more prevalent in the middle-aged male population, but have an incidence of only 0.009% or less. In contrast to SBDs, ASBDs typically present at the canine and premolar segments of the mandible, adjacent to the first molars. This localization and their features make ASBDs more prone to being mistaken for other mandibular lesions.
Traumatic bone cysts, giant cell granulomas, sialadenosis, bone marrow defects, and residual cysts are just some of the pathologies that ASBDs may be misdiagnosed as, owing to their rarity. These other pathologies, however, have their own characteristic features that will aid in establishing a correct diagnosis. For example, residual cysts, which are odontogenic inflammatory lesions that develop after the removal of an affected tooth, have well-defined sclerotic bone margins.
Diagnosis and Treatment
SBDs are usually discovered during dental radiography for carries screening. They are generally 1 to 3 cm, monolocular, well-circumscribed, and radiolucent on radiographic film. Particularly helpful with the diagnosis is the observation that SBD radiographic appearance usually does not change over time. They tend to remain the same size and retain their basic features. This unchanging size is the basis for their labeling as “static” bone cysts.
Owing to the benign and static nature of SBDs, surgical treatment is usually not indicated. However, in taking this approach, it is imperative to thoroughly rule out the presence of neoplastic conditions using imaging studies and further clinical investigations, where applicable. Very rarely, neoplastic transformation to a salivary gland tumor can occur because this type of tissue is present in the bony defect. However, malignant transformation of the SBD is not associated with a higher overall risk of oncogenesis in these tissues in their normal locations.
Surgical management with biopsy is employed in cases where the diagnosis of SBDs cannot be established. Surgery is also considered when SBDs grow or when they are large, as they can significantly increase the risk of mandibular fractures. In nearly all other cases, a ‘wait and see’ approach is usually preferred and is undertaken with the help of periodic follow-up using various imaging modalities. Follow-up is important to avoid unnecessary surgical interventions that may be associated with many potential risks and complications.