Idiopathic Bone Cavity of the Mandible

A 14-year-old male patient presented to the department of maxillofacial surgery for further work-up of a radiolucent lesion within the left mandible, which was incidentally found on a routine panoramic radiograph. There is a history of trauma from a previous fall on the chin 5 years prior to the current admission.

Cone Beam Computed Tomography (CBCT) showed a unilocular, well-defined radiolucent lesion with thin sclerotic margins in the body of the mandible (Fig. 1A, B). The lesion had a slight polylobular morphology and caused thinning of the buccal and lingual cortex. Although there was an intimate relationship with the apex of tooth 43, erosion was absent (Fig. 2B).

Fat-suppressed (FS) T2-weighted MR images demonstrated a hyperintense, well-delineated lesion with slight polylobular margins in the median aspect of the mandible body (Fig. 3A,3B).

Coronal T1-weighted MR images before (Fig. 3C) and after (Fig. 3D, 3E) intravenous gadolinium contrast injection showed subtle peripheral rim enhancement.

Idiopathic Bone Cavity (IBC) or Simple Bone Cyst (SBC) is a benign intraosseous cavity of unknown aetiology, frequently observed among young adults [1-5].

IBC is a pseudocyst as it lacks epithelial lining and is either empty or filled with serous or sanguineous fluid and is therefore sometimes designated as a “haemorrhagic bone cyst”. IBC is also referred to as Traumatic Bone Cyst because association with trauma has been reported in some cases with symptoms including pain, tooth sensitivity and paraesthesia. However, in most cases, the lesion is asymptomatic with inapparent traumatic events and is incidentally discovered on radiographs performed for dental purposes [1,4].  

It is important to distinguish IBC from more worrisome odontogenic lesions. The main imaging modalities are panoramic radiography and (CBCT), and in selected cases, Magnetic Resonance Imaging (MRI) may be helpful for further characterisation and additional information regarding soft tissue extension [2,3,4].

The typical radiographic appearance of IBC is a radiolucent and unilocular lesion with well-circumscribed borders, expanding between the roots of teeth, with no or slight cortical expansion. The corpus of the mandible is the most frequently affected area. Despite its potential expansile nature, teeth displacement or root resorption are rare, and the lamina dura is usually intact or only partly disrupted [1-4].
 

(CB)CT scan usually demonstrates a central, well-defined, mildly expansile or nonexpansile, thin-walled lytic lesion, with little or no marginal sclerosis.
 

MRI usually confirms the cystic nature of the lesion by showing its fluid content. Fluid-fluid levels are rarely seen in non-complicated lesions. However, fractured IBCs may contain blood products and fluid-fluid levels. On MRI, the lesion shows low signal intensity on T1-weighted images, and high signal intensity on T2-weighted or Short Tau Inversion Recovery (STIR) images [1-4].

The above described radiological features are pathognomonic and usually sufficient to establish the diagnosis of IBC without any need for further invasive assessment. However, in rare cases, clinical imaging is in conclussion necessitating histopathological examination of biopsy specimens to reach a final diagnosis and distinguish the lesion from other radiolucent lesions of the jaws [1,2,4]. Histological examination in our case revealed the absence of epithelial lining.

IBC is mostly a self-limiting benign lesion that heals spontaneously after skeletal maturity. Therefore, a short-term follow up would mostly be the best approach and unnecessary extensive surgical intervention should be avoided. Symptomatic cases could warrant a limited exploration and curettage with appropriate follow-up. The overall prognosis is excellent [1-5].

Written informed patient consent for publication has been obtained.