Stafne bone cavity: Report of two case series of Posterior variant with unusual presentation

INTRODUCTION

Edward C. Stafne first described Stafne bone cavity (SBC) in 1942.^1,2 It has various other synonyms such as Stafne bone cyst, Latent Bone cyst, Static Bone cyst, Static bone defect, Lingual cortical mandibular defect and Lingual mandibular Salivary gland depression, Pseudo cyst.^3,4

SBC is an unusual bony pseudocyst without epithelial lining of lingual cortical plate of the mandible.^4,5

SBCs are incidentally discovered during routine conventional oral radiographic examination like orthopantamography (OPG). Diagnosis of SBC is based on clinical and radiographic features, but for accurate diagnosis and in atypical cases, use of advanced imaging such as computed tomography (CT), cone-beam computed tomography (CBCT), magnetic resonance imaging (MRI) and sailography may be advised for definite diagnosis.^3,5 As SBCs are innocuous in nature biopsy or any surgical management is not required to arrive at a final diagnosis.^2,4

The appearance of SBC is usually as an asymptomatic, unilateral, well-defined, radiolucent cavity with corticated edges present on the submandibular salivary gland region, on the lingual cortex in-between the lower border of mandibular canal and inferior border of the mandible.^3,4,5

The etiology is still unclear. It may be due to congenital or developmental in nature. Stafne suggested that it is congenital due to the failure of deposition of bone, which was previously occupied by Meckle’s cartilage. However, the most accepted theory is that these bony defects occur due to constant pressure or deposition of salivary gland tissue on the lingual cortical bone during the embryonic development of the mandible.^2,3

With the above background, two case series of SBC found incidentally on a routine conventional OPG and further confirmation done by CBCT with an unusual presentation are described.

CASE REPORT

1: A 63 years old male patient reported with a chief complaint of generalized sensitivity of the teeth. On clinical examination patient had generalized severe attrition with generalized periodontitis. OPG was advised to see the over view of the dentition and the supporting alveolar structures. OPG showed a generalized attrition and bone loss. Incidentally, a well-defined oval, radiolucency was seen below 48 region between the lower border of the mandibular canal and the base of the mandible.(Figure 1) Patient was asymptomatic and on intraoral examination, no changes were seen on vestibular mucosa, on palpation patient did not have any swelling or tenderness both intra orally and extra orally in 48 region. Based on the patient’s history, clinical and radiographic findings, Stafne bone defect was thought as provisional diagnosis. For further accurate evaluation, CBCT was advised. Examination of sagittal sections of CBCT images revealed a large solitary , oval shaped radiolucent area present below the mandibular canal at level of 48 region measuring about 3.1mm buccolingually, 7.2 mm supero- inferiorly and 9.7 mm antero- posteriorly.(Figure 2) 3D reconstruction of the CBCT images showed a concavity present involving the lingual wall with lower border of the concavity reaching the buccal cortical plate without expansion of the plate, suggestive of perforation of both buccal and lingual cortical plates. Superiorly present in close approximation of the mandibular canal and inferiorly close to the base of the mandible. (Figure 3)

Posterior variant of SBC of mandibular right side was considered as the final diagnosis. The findings and the innocuous nature of the defect was informed to the patient and was suggested regular follow-ups.

CASE REPORT 2:

A local practicing dentist referred a 43 years old male patient with an OPG for an opinion regarding a lesion present on the left posterior mandible. OPG showed missing teeth, multiple root stumps with periapical pathology and a well defined oval shaped radiolucency in the apical region of 37 below the mandibular canal and the inferior border of the mandible. The thinning of mandibular inferior cortex was noticed. (Figure 4) Further on clinical examination patient had multiple clinically missing teeth, multiple root stumps, grossly decayed 38 with severe bone loss extending from 34 to 38 region. On the cumulative findings in relation to the site, history and appearance on OPG, a provisional diagnosis of Stafne bone defect was given. For further evaluation CBCT was advised. The axial and sagittal sections of CBCT images revealed a well defined, oval shaped radiolucency measuring about 9.2mm with hypodense area and narrowing of the lingual cortical bone of the mandible (Figure 5) which was evident on 3D reconstruction as well. (Figure 6)

Stafne Bone Cavity of Left side of mandible was considered as the final diagnosis. Patient was explained regarding the defect and advised for regular follow up.

DISCUSSION:

The incidence of SBC is 4 in 4000 adults. It is prevalent in males between 50 and 70 years.^2,6 These are commonly found incidentally on the routine oral radiographic examination as unilateral, well-defined, ovoid shaped, radiolucent cavities surrounded by sclerotic border present in between the inferior border of mandibular canal and the lower border of the mandible on the lingual cortex.^3,4,5 These features are in accordance with our case series, but with an unusual finding of perforation of buccal cortical bone in the first case report, which is uncommon.

SBC presents as two most common variantsanterior and posterior.³ Posterior variant is the prevailing type, it is known as classic variant of SBC, which is located at the mandibular angle, in the location amidst the inferior border of mandibular canal and the lower border of the mandible in the submandibular gland region.² They may be unusually located as an anterior variant in the apical region of the premolars and canines of the anterior mandible, associated with the sublingual glands above the mylohyoid muscle.⁴ Other rarely presenting variants are the medial ramus variant, bilateral presentation and bilocular defect, multilocular defect, or perforation of buccal cortical plate.⁶ Both the cases in this case series fall under most common posterior variant of SBC with a rare variant which is described in the first case report, where there is perforation of buccal cortical plate as well. (Figure 3)

SBCs are purely a radiographic entity and do not require any surgical or histopathological interventions as patients are usually asymptomatic and do not present with any signs and symptoms.^4,5 Conventional OPGs are adequate to arrive at a final diagnosis of SBC, however at present in Dentistry CBCT is an advanced imaging modality. The advantages include less radiation exposure and affordable to patients when compared to Computed tomography. CBCT aids in assessing the accurate size, location and extension of the bony defect in all three planes -axial, coronal and sagittal sections and helps in 3D reconstruction of the lesion, which benefits the Oral and Maxillofacial radiologist to give detailed information of a lesion purely based on radiographic interpretation.

In the present case series, SBCs presented as an asymptomatic, ovoid radiolucent cavities on the lingual cortex between the inferior border mandibular canal and the lower border body of the mandible, with an unusual finding of perforation of buccal cortical plate in the first case report. Final diagnosis of Posterior variant of Stafne bone cavity was considered based the history, clinical and radiographic examination.

The Etiology and pathogenesis of the Stafne bone defect are not clearly understood. Many studies and several hypotheses have been suggested. One of the hypothesis suggested by Stafne is the “Congenital hypotheses” which states that it could be due to failure of deposition of bone in the region, which was previously occupied by Meckle’s cartilage.^2,3 Most accepted hypothesis is the “Glandular hypotheses” which states that, SBCs are formed due to ectopic salivary glandular tissue entrapment during the development and ossification of mandible, which appear as radiolucent structures on the radiographs and they are usually located at the region of major salivary glands. The contents in these defects are histologically proven as salivary glandular tissues in most of the cases with surgical intervention.^2,3,5 Other proposed explanation for the formation of SBCs included “Pressure hypotheses” which states that an acquired vascular lesion or lipoma erodes the cortical plate or due to hyperplastic or hypertrophic salivary glands pressure on the bone surface.⁴

The differential diagnosis of SBC includes benign and malignant jaw lesions such as odontogenic cystic lesion, traumatic bone cyst, non-ossifying fibroma, fibrous dysplasia, vascular malformation, focal osteoporotic bone marrow defect, brown’s tumor of hyperparathyroidism, ameloblastoma, basal cell nevus syndrome, giant cell tumor, or a metastasis from a primary malignant tumor.^4,5

Generally, Stafne bone defects do not need any treatment as they are normal anatomical variants rather than pathologic conditions. Clinical and radiological examinations are sufficient to confirm the static nature of these bony defects. Surgical management or biopsy is indicated only when the diagnosis is unclear or in extensive large bony defect which could involve the adjacent vital structures or cause the fracture of the adjacent bone.^2,4 In the present case series both the patients were asymptomatic with no clinical signs and symptoms. Diagnosis of SBC is based on clinical and radiographic findings; hence biopsy or surgical management was not done due to innocuous nature of the lesion especially in view of differential diagnosis. Patients were made aware of the presence of SBC and were advised for regular follow up every 1 year.

CONCLUSION:

Stafne bone cavity is an incidental finding on a conventional radiographic investigation, which are asymptomatic and mainly diagnosed based on the clinical and radiological features. CBCT is adjunctive radiographic modality for the accurate diagnosis of theses squelch lesions. It is important for the Dental surgeons be aware of this nonpathological anatomical variant. This helps in prevention of unnecessary surgical intervention for the patients. These SBCs should be monitored on a regular follow up basis by doing clinical examination and taking a panoramic radiograph one in 1 or 2 years.