Teaching Case

Routine preoperative dental imaging was performed in a 58-year-old male patient.

Routine preoperative dental imaging (OPG) was done in a 58-year-old male patient. There were no systemic or local complaints. OPG showed a sharply delineated lucency of 1 cm diameter at the left mandibular angle, inferior to the mandibular canal. Cone beam CT demonstrated the lesion to be localised at the lingual (medial) border of the left mandibula. The patient was then referred to our hospital for further investigation by means of an MRI-examination. The following sequences were performed: axial T1TSE, axial T2TSE, parasagittal T2TSE, axial T1 VIBE fatsat before and after gadolinium administration (with paracoronal MPR) and coronal T1TSE after gadolinium. These showed that the sharp and corticated lucency was caused by a small protrusion of a part from the left submandibular gland (SMG) in the mandibular angle. No other abnormalities were noted. Findings were pathognomonic for a Stafne bone cavity (SBC).

SBC’s are presumed to form by the remodelling of the mandibular cortex around an extension of submandibular gland tissue. Thereby, the diagnosis can be made when a corticate radiolucency is identified at the mandibular angle, inferior to the mandibular canal, filled with SMG-tissue.
The lesion was first described by Stafne in 1942, hence the eponym. Other synonyms are: Stafne(’s) bone cyst, static bone cavity, developmental bone defect of the mandible, lingual mandibular salivary gland depression and many others, including combinations of the above. The term “cyst” reflects the description on older X-ray studies. Since there is no fluid-filled cavity or lesion, this term should not be used anymore. Most surgical series have noted SMG-tissue inside the SBC, but muscle, lymphatic tissue and blood vessels have also been reported. Maybe this can be explained by intermittent gland herniation or surgical disruption of cavity contents. Plain films are often sufficient for the diagnosis, demonstrating a fully corticated lucency at the mandibular angle, without direct relation to the teeth (non-odontogenic). In atypical cases however, further investigation can be done by cross-sectional imaging (CT or MRI). Preference is given to MRI, because of the absence of ionising radiation and because contrast-administration is not necessary because of the inherent high contrast-resolution of MRI. Gadolinium can be given in atypical cases. The salivary gland content of the SBC should enhance in the same degree as the adjacent SMG.
If uncomplicated, no treatment is needed when a SBC is found.