투고일：2012. 11. 20    심사일：2012. 11. 30    수정일：2012. 12. 19    게재확정일：2012. 12. 21

Traumatic bone cyst resembling a periapical abscess: A case report

Department of Dentistry, Dongsan medical center, College of Medicine, Keimyung University
Ju-Yeon Cho

ABSTRACT

Traumatic bone cyst resembling a periapical abscess: A case report

Department of Dentistry, Dongsan medical center, College of Medicine, Keimyung University
Ju-Yeon Cho

Traumatic bone cyst is known as a symptomless, radiolucent bony lesion incidentally found during routine radiographic examinations. The main characters of traumatic bone cyst are asymptomatic and unicystic radiolucent bony lesion with vital tooth. This case is a confusing case of a traumatic bone cyst with sudden gingival swelling and appearance like a periapical abscess. After surgical exploration and drainage, clinical and radiographic examination showed bony healing with pulpal vitality preserved after 7 months postoperatively.

Key words : traumatic bone cyst, periapical, abscess

Ⅰ. Introduction

The radiolucent areas surrounding the apices of a tooth may be misdiagnosed as apical periodontitis or periradicular cyst with pulpal involvement1). Especially in case of having history of previous trauma, the periradicular radiolucency of the post-traumatic areas tends to be easily considered as a chronic periapical lesion due to pulpal necrosis of affected tooth2). Moreover, if gingival or facial swelling accompanies with such circumstances, erroneous diagnosis of odontogenic abscess as a result of pulpal infection may be led1, 3). So, the accurate diagnosis is essential to consider the lesion to be of endodontic or non-endodontic origin and ensure the maintenance of pulpal vitality4).
The traumatic bone cyst is a vacant intraosseous cystic lesion within bony wall that mainly occurs in the mandible of young patients2, 5). However, it cannot be regarded as a true cyst because of the absence of a capsule and epithelial lining1, 5, 6). The etiology of the lesion is unclear and may be associated with traumatic injury7). The teeth that involved in the area of the cyst remain vital and surgical intervention almost results in complete resolution of the defect4, 8, 9).
The following report presents an unusual case of traumatic bone cyst that could be misdiagnosed as periapical abscess with persistent gingival swelling.

Ⅱ. Case report

A 16-year-old boy was referred for evaluation of chin and gingival swelling that had been persisted for one week in spite of antimicrobial medication. The medical history was unremarkable and the dental history indicated that there was no toothache but tenderness at anterior gingival swelling area of mandible.
The patient informed that he hit his own chin against something 4 months ago and the sudden swelling started one week before visiting our hospital. He has been taking antimicrobial agent for a week at other clinic but the gingival swelling persisted.
Clinical examination revealed a soft swelling on the mucolabial fold of anterior mandibular incisors with slight chin swelling. A periapical abscess, periradi cular cyst or other soft tissue tumor were suspected. 
The panoramic and periapical radiograph showed a small round radiolucency measu ring about 1cm around the periradicular area of left central incisor and lateral incisor of mandible(Fig. 1 ,2), so soft tissue tumor was ruled out and periradicular abscess or cyst was taken into consider ation.

Fig. 1 Periapical x-ray showed periradicular radiolucency around mandibular incisors 

Fig. 2 Dental panoramic view 

A periapical abscess with vestibular swelling of left mandibular central and lateral incisors due to devitalized pulp was strongly suspicious because of prior trauma history and being negative to electronic pulp test(EPT) and cold test. But the color, mobility and percussion test of involved teeth were normal and similar to that of adjacent teeth.
Under local anesthesia, incision and drainage were performed at lower anterior vestibule, but bloody exudate with floating tissue particles was emerged instead of purulent discharge.
Bloody discharge was swabbed for microbial culture, and tissues from incisional biopsy together with the floating tissue debris were sent to laboratory for histological examination after curettage of the lesion. 
Histological examination revealed granul ation tissue rather than cystic lesion due to the absence of epithelial lining(Fig. 3).

Fig. 3 Microscopic view, granulation tissues without epithelial linings
(H&E staining, original magnification × 100) 

Microorganism identified from the culture was streptococcus α-hemolyticus which was frequently found in oral cavity.
Follow-up after 1, 4, 7 month postoper atively showed slight delayed but increa  sing response to EPT and cold test of left mandibular central and lateral incisor, which considered as being vital.
The postoperative course was favorable. There has been no recurrence and the patient is still in follow up periods of 7 months after surgical operation. The radiolucency around left mandibular incisors was also reduced, and the involved teeth showed normal color and nearly normal response to pulpal vitality test(Fig. 4, 5). However, long term follow up is still needed.

Fig. 4 periapical x-ray(7 months after curettage): reduced radiolucency and intact lamina dura 

Fig. 5 Dental panoramic view(7 months after curettage)

Ⅲ. Discussion

The traumatic bone cyst is a rare lesion of the jaws and the pathogenesis remains unclear. The most accepted hypothesis at present is the traumatic-hemorrhagic theory, which suggests that the lesions develop when intramedullary blood clots due to trauma do not dissolve or resolve10).
This theory explains the higher incidence of traumatic bone cysts in young individuals and also explains the presence of blood within the lesions.
Traumatic bone cysts are considered almost exclusively mandibular lesions11), especially the posterior areas although the symphysis may also be a site of predile ction12, 13). The histologic feature reveals only a connective tissue membrane lining the lesion, which is the characteristic of pseudocysts, and hemorrhagic foci, cholesterol crystals and osteoclasts may be found within the lesion14, 15). A final diagnosis of a traumatic bone cyst is usually made at the time of surgery. Surgeons usually encounter an empty or bloody, serous-filled cavity, which may represent different stages in the development of traumatic bone cyst3, 4, 16).
The treatment of choice for traumatic bone cysts is curettage of the lesion, which generally results in short term healing14, 15, 17, 18). Recurrence is rare, but when occurs, it is usually present within three months of surgery5). After conventional therapy has proved unsuccessful, other treatment options like the placement of bone chips, hydroxyapatite, packing the cavity with thrombin sponge or aspiration may be included4, 19).
In this case, intraoral swelling in the labial vestibule of 16-year-old boy was misdiagnosed as odontogenic infection at first, but proved as traumatic bone cyst after clinical, radiographic and histological correlation. There was a prior history of trauma and periradicular radiolucency, which mimic the signs and symptoms of an endodontic lesion. But careful diagnosis avoided unnecessary endodontic treatment of the young patient’s teeth. He had been free of symptom after trauma for four months, and there were no fracture of mandibular incisors. But slight crowding of mandibular incisors was observed which was suspected of producing TFO(trauma from occlusion). Therefore, the cause of sudden gingival swelling might be the result of TFO or other infection of previous traumatic bone cyst, rather than periapical abscess due to pulpal necrosis. Surgical exploration and curettage revealed clear, bloody exudate instead of purulent discharge, and resulted in progressive reduction of the radiolucency and intact lamina dura of the involved tooth at the 7 months follow up appointment. The tooth showed positive to EPT and cold test and there were no clinical symptoms or discoloration. The clinical, radiological and histological findings of traumatic bone cyst are very diverse20), therefore we should put these together for getting accurate diagnosis.

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