Aneurysmal Bone Cyst
Synonym / Acronym
ABC
Definition
Aneurysmal bone cyst is not classified as a true cyst despite its name because this rare lesion does not have an epithelial lining and it is categorized as a giant cell lesion. Aneurysmal bone cyst cause is unknown but it is considered to be a reactive lesion rather than a cyst or neoplasm. The lesion consists of several blood-filled cavities separated by fibrous septa containing osteo-clast type giant cells, reactive bone and without an endothelial or epithelial lining.
Clinical Features
ABC occurs in young individuals. The majority of those cases occur before third decade of life. The lesion occurs most frequently in the spine and long bones. It appears as a rapid swelling due to expansion of bone. Pain is rarely reported. The area of the lesion can be tender to palpation.
Radiographic Features
The lesion appears as a moderately well-defined and well-corticated unilocular lesion causing extensive expansion of cortical plates. The shape is circular or has ballooning appearance. The lesion could be multilocular with thin septa, giving it a soap bubble appearance. It occurs most commonly in the posterior mandible. ABC share similar radiographic features to CGCG and in most instances the two lesions are indistinguishable. Teeth may undergo resorption or displacement.
Differential Diagnosis
Multilocular ABC has almost the same radiographic appearance as CGCG. However, ABC tends to cause more expansion and it is located in the posterior mandible; while CGCG tends to cause less expansion and usually it occurs anterior to the first molar. Ameloblastoma can be included in the differential; however, it affects older age group. Odontogenic myxoma does not cause much expansion, occurs in older age group, and has well-defined septa.
Treatment
Cone Beam CT scan is recommended to evaluate the location and extension of the lesions. Curettage and surgical resection is the treatment of choice for ABC. Follow-up is indicated due to its high recurrence rate.
Case Reports
HISTORY: A 15-year-old male was referred for a Cone Beam CT scan for evaluation of a left TMJ abnormality noted on a panoramic image.
FINDINGS: There is a well-defined radiolucent lesion in the left condylar head. The margins of the lesion are thinned and exhibit a scalloped endosteal surface. The lesion appears to be multilocular with septations which thin in diameter as they extend into the center of the lesion.. The lesion is affecting the condylar head and neck extending into the ramus area. The anterior boundary of the lesion starts from the sigmoid notch and extends posteriorly to the posterior border of the mandible. There is extensive expansion and the thinning of cortical boundaries. The lesion measures 27 mm H, 23 mm W, and 32 mm L. The inferior margin of the lesion is close to the mandibular foramen. The superior contour of the lesion undulates conforming to the contour of the glendoid fossa and articular eminence.
IMPRESSIONS: The radiographic signs suggest a bengin tumor. They are consistent with osteochondroma. Although benign, the lesion is likely to continue to enlarge and may cause deformity and limitation in function. Surgical consultation is indicated.
RECURRENCE SCAN: Patient was referred for a Cone Beam CT scan for evaluation of his left TMJ area which is status post resection and graft.
FINDINGS: The region of interest (The condylar head) does not include the posterior aspect of the left condyle. The left condyle has expanded extensively by a radiolucent lesion. The lesion extends from just above the mandibular foramen to the top of the condyle. It extends from the posterior aspect of the coronoid process to the posterior aspect of the ramus. The lesion measures approximately 3 cm H and 2.5 cm W and L. A thin cortex can be traced almost all the way in the region of expansion. Perforation may be present although it may not be visualized due to volume averaging artifact. Several septa are present within the lesion.
Impression: The radiographic are suggestive of a benign non-odontogenic neoplastic process. Given an earlier diagnosis of central giant cell tumor, this appears to be recurrence of that lesion.
IMPRESSION: The radiographic signs are suggestive of a bengin tumor. The appearance, location, patient age, and presentation are most consistent with Osteochondroma. Although benign, the lesion is likely to continue to enlarge and may cause deformity and limitation in function. Surgical consultation is indicated.
BIOPSY: A biopsy was taken to confirm the diagnosis and the pathology report’s final diagnosis was aneurysmal bone cyst.
