Answer:
D. Idiopathic bone cavity (IBC)
D. Idiopathic bone cavity (IBC) (also known as traumatic
bone cyst or simple bone cyst) is a bone lesion with an
unknown etiology. It presents as either a fluid-filled cavity
or (more commonly) an empty cavity, but it can mimic other
types of bone lesions radiographically. One hypothesis about
the etiology is that it is the result of trauma. However, this
theory is inconsistent and it has been present without a
history of trauma.1 Other theories include degeneration
of a bone tumor or cyst, ischemic bone marrow necrosis,
disturbances in bone formation, venous obstruction, altered
calcium metabolism, and synovial development. Clinically,
IBCs can present in any bone, with the long bones as the
most common site. When they present in the jaws, they
have a predilection for the premolar-molar area or the
symphyseal area of the mandible, but can present anywhere.1
Jaw lesions do not have a gender predilection, however long
bone lesions have a male predilection. They commonly
present in the second or third decade of life. IBC typically
presents without symptoms, but up to 20 percent can
present with painless swelling.1 Usually they present as single
lesions, but occasionally multiple lesions can present.2 Due to
their lack of symptoms, they are commonly detected incidentally on routine radiographs. Radiographically, they commonly
present as a well-circumscribed, unilocular radiolucency;
however, ill-defined multilocular radiolucencies are possible.
The borders may be well-corticated, diffuse, oval, or rounded.
They can range from a few millimeters up to 10cm and
commonly scallop around the roots of teeth. Teeth in the
area usually remain vital, however, some cases of root
resorption, cortical plate expansion, and loss of cortical plates
have been reported. Cases of extensive lesions are reported,
involving a large portion of the ramus and the body of the
mandible.1, 2 Occasionally, the lesion may arise in association
with fibro-osseous lesions or cemento-osseous dysplasia,
typically in older females.1 Histologically, the lesions contain
fragments of thin, vascular, fibro-collagenous soft tissue, free
of epithelial cystic lining. Due to the lack of epithelial lining,
the lesion is better classified as a pseudocyst, rather than a
cyst. Hence, traumatic bone cyst and simple bone cyst are
misnomers and IBC is preferred. Occasionally red blood cells
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and osteoid-like material may be seen along with osteoclastic,
multinucleated giant cells and calcifications. Treatment involves
surgical exploration and curettage; typically the area appears
as an empty cavity upon surgical exposure. Exposure with or
without curettage is enough to induce bone regeneration.
Although minimal tissue is usually obtained from curettage,
it is advisable to submit the tissue for histopathologic review
to confirm diagnosis. Most studies report recurrence rates as
low (1-2 percent) whereas other report recurrence rates up to
27 percent.1 It is advisable to follow-up patients periodically
to confirm bone fill in the area.
In the case described above, surgical exploration was performed
on the patient. The area was found to be an empty cavity and
minimal tissue was curettaged from the area. It was noted that
septations were present between the lesion and the teeth; the
teeth in the area were not involved with the lesion. Bone graft
material was placed into the cavity after curettage. The patient
had bony fill in the area as is noted on a post-operative
panoramic radiograph (Figure 4).
Figure 4:
Post-surgical panoramic radiograph showing a bony fill of the anterior mandible.