Mandibular Cysts and Odontogenic Tumors (cont)

Nonodontogenic Mandibular Cysts

Stafne bone cyst

A Stafne bone cyst is an unusual form of slightly aberrant salivary gland tissue wherein a developmental inclusion of glandular tissue is found within or, more commonly, adjacent to the lingual surface of the body of the mandible within a deep and well-circumscribed depression. The oldest described occurrence of this phenomenon is in a skull dated to the sixth to fourth centuries BC. The phenomenon was first recognized by Stafne in 1942, hence the eponym.

However, this cyst has been referred to by many other names, including static bone cavity, defect of the mandible, lingual mandibular bone cavity, static bone cyst, latent bone cyst, and Stafne bone defect. The incidence of occurrence has been reported as 0.1-1.3% in various studies. The general consensus is that this is a congenital defect, although it rarely has been observed in children. These lesions may generally be regarded as developmental rather than pathologic defects. A predilection for males over females seems to exist.

Radiographically, the lesion usually appears as an ovoid radiolucency located between the inferior alveolar canal and the inferior border of the mandible in the region of the second or third molars. It can be differentiated from the traumatic or hemorrhagic bone cyst, which by location almost invariably lies superior to the inferior alveolar canal.

Although the classic Stafne cyst is described in the posterior mandible, an anterior variant presenting as a round or ovoid radiolucency in the area between the central incisors and first premolars exists; however, it is far less common.

These lesions generally represent benign developmental anomalies that normally do not require any treatment. A complication occasionally reported in the literature is the development of a true salivary gland neoplasm in the tissue associated with one of the cortical defects. Therefore, recording the finding of these lesions and periodically observing them radiographically seem prudent. Clinical or radiographic changes may indicate the need for further investigation.

Traumatic bone cyst

The traumatic bone cyst also is known as solitary bone cyst, hemorrhagic cyst, extravasation cyst, unicameral bone cyst, simple bone cyst, and idiopathic bone cavity.

The traumatic bone cyst is a relatively frequent lesion both in the jaws and elsewhere in the skeleton. The specific etiology of the lesion is unknown, although several mechanisms have been proposed. The most widely accepted is that these lesions originate from intramedullary hemorrhage caused by trauma. In these cases, failure of organization of the blood clot occurs followed by subsequent degeneration of the clot, eventually leading to an empty bone cavity. Restricted venous drainage leads to increasing edema, which in turn causes continued resorption of trabeculae and expansion of the lesion. Expansion of the lesion tends to stop when cortical bone is reached, thus these lesions are not characterized by any cortical expansion. Instead, they are usually incidental findings on radiographs taken for other purposes. However, it is not unusual for a patient to be unable to recall any trauma to the involved jaw.

The lesion is most commonly found in young persons (median age, 18 y); the male-to-female incidence ratio is 3:2. The lesions occasionally have been reported in the maxilla but are far more common in the mandible. When the cavities are opened surgically, they are generally either empty or filled with a small amount of straw-colored fluid. Shreds of necrotic clot and fragments of fibrous connective tissue have been reported less commonly. Histologically, these cysts may have a thin connective tissue membrane lining or no lining at all.

Radiographically, these lesions tend to appear as smoothly outlined radiolucencies that scallop around the roots of the teeth. They do not displace teeth or resorb roots, and the lamina dura is left intact. They may range from very small (<1>

These lesions are usually surgically explored to establish a diagnosis, which is made upon finding an empty cavity. No further treatment is generally necessary because surgical manipulation causes the cavity to fill with blood. Soft tissues are closed, and the lesion tends to heal without further intervention. The extreme rarity of such lesions in older patients suggests that the lesions may be self-limiting and/or subject to resolution over time.

Focal osteoporotic bone marrow defect

Bone marrow may be stimulated in response to unusual demands for increased blood cell production. This hyperplastic marrow may present as focal radiolucencies in the jaws. Of jaw lesions, 75% are reported to occur in female patients, and 85% of jaw lesions are found in the mandible. The lesions are almost always asymptomatic and are discovered as incidental findings on radiographs taken for other indications.

Radiographically, these lesions present as ill-defined radiolucencies of variable size, more commonly in edentulous areas. This suggests that in some cases, the lesions represent failure of normal bone regeneration postextraction. Histologically, the tissue in these areas is composed primarily of red marrow, yellow marrow, or a combination of both with long thin irregular trabeculae that are missing the osteoblastic layer.

The radiographic appearance of these lesions is not pathognomonic; therefore, these lesions are usually diagnosed surgically. Once diagnosed, they require no further specific treatment; however, if the etiology for the increased hematopoietic demands is unknown, consider an investigation.

Aneurysmal bone cyst

In 1942, Jaffe and Lichtenstein first classified the aneurysmal bone cyst as a distinct lesion; it is neither a cyst nor an aneurysm. It was not reported in the jaws until 1958, and although theories abound, the etiology and pathogenesis of this lesion are still unknown. Proposed mechanisms for the formation of the aneurysmal bone cyst include alterations in local hemodynamics leading to venous engorgement, resorption, and replacement with connective tissue and osteoid; futile attempts at repair of a hematoma (eg, what occurs in the giant cell granuloma); and microcyst formation secondary to cellular edema associated with other lesions. Often, but not always, these lesions appear in association with other lesions of bone, such as the unicameral cyst, dentigerous cyst, osteoclastoma, central giant cell tumor, fibrous dysplasia, and osteosarcoma.

Aneurysmal bone cysts have been observed in every part of the skeleton, although more than 50% of lesions occur in the long bones and vertebral column. They occur in jaws of people of all ages, but a predilection for younger patients and female patients exists. Aneurysmal bone cysts are more likely to occur in the mandible than in the maxilla. They may displace but usually do not resorb the dentition, and sensory disturbances generally are not present. The radiographic appearance often is described as cystic, honeycomb, or soap bubble with eccentric expansion. Cortical bone may be thinned or destroyed, and a periosteal reaction may be present.

Histologically, the aneurysmal bone cyst reveals a fibrous connective tissue stroma with many cavernous or sinusoidal blood-filled spaces. Young fibroblasts are present throughout the stroma, and multinucleated giant cells are scattered throughout the lesion. Without the cavernous spaces, this lesion would appear almost identical to the central giant cell granuloma.

Treatment of the aneurysmal bone cyst requires complete removal, and complete removal of the lesion with aggressive curettage is the most common treatment modality. Excellent exposure to facilitate this treatment is necessary because these lesions may bleed copiously, and timely but thorough removal of the lesion helps to decrease blood loss. Failure to completely remove all traces of the lesion carries a significant risk (21-59%) of recurrence. Recommendations for bone grafting of the resultant defect vary according to the remaining clinical situation after removal of the lesion. Some authors recommend excision with cryosurgery for recurrent lesions, while other authors advocate block excision or resection with reconstruction. In the past, radiation was proposed for the treatment of these lesions, but radiation may fail to arrest the lesion and, more importantly, can result in sarcomatous changes.