Conversion of Aneurysmal Bone Cyst into Fibrous Dysplasia: A Rare Pediatric Case Report

Abstract

Aneurysmal bone cyst (ABC) is an uncommon, non-neoplastic, expansive and erosive bone lesion. Considered as a pseudocyst due the lack of epithelial lining, the presence of giant cells and similarity to other lesions can make preoperative diagnosis difficult; biopsy findings must be co-related to complete clinical and radiological assessment. ABC's controversial etiopathogenesis and variable clinicopathological presentations have been widely described, but to date, there are just a few reports in literature describing the development of fibrous dysplasia (FD) from an ABC, and even less cases occurring in the jaws. We describe the case of an ABC in an 8 year-old male patient, affecting the body of the mandible, which showed accelerated growth associated to thinning of the buccal, lingual and lower cortical plates. The treatment consisted of repetitive surgical resection, curettage of the lesion and mandibular reinforcement with osteosynthesis reconstruction plates. A 16-month follow-up showed self-limitation of the overgrowth. The final histopathological and radiological analysis confirmed the FD diagnosis.

Keywords: Aneurysmal bone cyst; Fibrous dysplasia; Jaws.

Fig. 1

Clinical photograph of the patient, taken on November 2013, showing facial asymmetry caused by ovoid swelling over the left mandible

Fig. 2

Intraoperative pictures taken during the third surgery, which was executed on early November 2013. (a) Surgical removal of the lesion (b) Placement of a well contoured mandibular reconstruction plate

Fig. 3

Histologic image of the third surgery, compatible with ABC diagnosis. H&E 10×. Histologic plate that shows mononuclear fusiform and giant multinucleated cells within hemorrhagic stroma

Fig. 4

Clinical photograph taken on April 2014, 5 months after the third surgery, showing evident facial asymmetry

Fig. 5

Panoramic X-ray taken on April 2014, showing mandibular low cortical expansion on the left side, caused by new bone formation around the defect. Multilocular lesions can be observed in left ramus and body of the mandible

Fig. 6

Picture of the fourth surgical approach executed in early May 2014, showing a bone deposition over the reconstruction plate. b Intra-operative pic that shows the span of the entire new plate from anterior to posterior

Fig. 7

a Photograph showing the removed bone and teeth during fourth surgery. b H&E 10×. Histological appearance of the sample, showing bone trabecular calcified tissue, with typical osteocytes, immerse into fibrous stroma

Fig. 8

Clinical appearance of the patient after 16 months of the last surgery

Fig. 9

Orthopantomogram of the patient after 16 months of the last surgery, showing adequate radiopacity of the left ramus and body of the jaw that suggests bone neoformation