Assessment of spontaneous resolution of idiopathic bone cavity

Abstract Idiopathic Bone Cavity (IBC) or Simple Bone Cyst (SBC) is a non- epithelialized bone cavity with serosanguinous fluid content or empty. There is a literature debate regarding its pathogenesis that remains unclear. The main treatment option is the surgical exploration, although there are successful cases described in the literature in which just a follow-up with clinical and radiographic evaluation was performed. Objective This study aimed to assess the spontaneous resolution of idiopathic bone cavity untreated by surgery. Material and Methods Twenty-one patients diagnosed with surgically untreated IBC were submitted to a follow-up protocol modified from Damante, Guerra, and Ferreira 5 (2002). A clinical and radiographic evaluation was performed in 13 patients (13/21), while eight patients (8/21) were only radiographically evaluated. Three observers evaluated the panoramic radiographs of 21 patients and the Kappa test was performed by intra and inter-examiners. Inductive and descriptive statistics were applied to the results. Results Only one patient had a positive response to palpation and percussion of the teeth in the cyst area. Most of the cysts evaluated were rated as 3 (lesion “in involution”), 4 (lesion “almost completely resolved”), or 5 (“completely resolved”). Conclusions We observed progressive spontaneous resolution of IBC. Most cysts were found in the recovery process in different follow-up periods. Patient's follow-up, without surgery, may be considered after the diagnosis based on epidemiological, clinical, and radiographic features of the lesion.


Idiopathic Bone Cavity (IBC), Traumatic Bone
Cyst, or Simple Bone Cyst (SBC) is a commonly asymptomatic intraosseous cavity not covered by epithelium, empty or partially filled with serous/bloody fluid. It has a thin membrane of connective tissue, only microscopically visible, overlying the bone surface.
It is almost totally located in the cancellous bone of the lower jaw, most in the premolars and molars region 8,15,16,22 . A supposed etiology may be linked to a hemorrhagic or ischemic vascular phenomenon with subsequent bone necrosis and resorption 9 . This lesion affects young people between the 1 st and 2 nd decades of life 8 . The IBC image appears as a radiolucent limited area, usually oval or circular shaped, partially limited by a well-defined, sometimes radiopaque, line. Lesion boundaries are usually below the roots and may be superimposed to -or bypass -the roots. Extension of the crest involvement presents a "scalloping" aspect.
The body of the mandible is the most frequently affected area 8,12,16 .
Clinically, the alveolar ridge is covered by normal oral mucosa, and the expansion of buccal and lingual cortex are rare. The teeth involved are vital, with rare displacement 8,12 . Besides the panoramic radiograph, occlusal and periapical X-rays are sometimes required.
Cone beam computed tomography (CBCT) may be prescribed in some cases 14 .
IBC are mostly incidentally found in radiographic examinations performed for other reasons, especially when prescribed in the assessment of an orthodontic patient 8,5,12,13,19 .
Few studies described cases of untreated IBC with spontaneous resolution, highlighting possible non-surgical treatment for IBC cases, reducing risks of morbidity 9,20,22,23 . This study aimed to assess the spontaneous resolution of surgically untreated IBC cases by panoramic radiographs and CBCT images.

Clinical evaluation
Twenty-one cases of untreated IBC were requested to a clinical evaluation. Clinical data regarding all patients included in this study is presented on Table   1.

Panoramic evaluation
The intra-examiner agreement (concerning the bone remodeling stage of the lesion) was satisfactory ("substantial agreement"), whereas the intra-examiner Kappa test was 0.8 for Examiner A; 1.0 for Examiner B, and 0.75 for Examiner C. The concordance was also considered good, with a Kappa value of 0.75.
There was a higher tendency of the cases to be classified as 3, 4, or 5 according to the follow-up period in years (Group A, B, or C). However, three cases from Group A (1 to 5 years) were classified as stage 5 ("completely resolved"). Most of the lesions were classified as stages 3, 4, and 5 within the observation period of 5 to 10 ( Figure 1; Figure 2).

Discussion
The IBC is a benign lesion with unknown pathogenesis and etiology 9 . Since it was first   Panoramic analyses showed a tendency of the lesions to be classified as stages 3 (lesion "in involution"), 4 (lesion "almost completely resolved"), and 5 (lesion "completely resolved") (Graph 1). Most cases that were followed from one to 20 years in this study showed that idiopathic bone cavity is a disease which affects children and young people ( Table 1).
The IBC underwent complete resolution with no intervention in eight cases. Thus far, this is the biggest report of IBC spontaneous resolution. Our results

Conclusions
The results of this study indicate that a spontaneous resolution of untreated idiopathic bone cavity may occur. The IBC follow-up without surgical intervention is possible after the diagnosis, based on epidemiological, clinical, and radiographic characteristics described in the literature. The long period need for the complete resolution of the lesion, in some cases, must also be considered while electing this protocol.