CASE
A post-orthodontic panoramic radiograph was acquired on a 27-year-old female patient. On this panoramic radiograph, an altered bone pattern with a mixed radiolucent/radiopaque density was noted in the periapical region of the right mandibular premolar and molar teeth. A periapical radiograph and a posterior mandibular standard occlusal radiograph were acquired to further characterize the region. The patient is asymptomatic and clinical examination is within the range of normal (Figs. 1-3).
FIGURE 1. Panoramic radiograph showing an unusual bone pattern in the right mandible.
FIGURE 2. Intraoral periapical radiograph of the mandibular right premolar and molar regions.
FIGURE 3. Mandibular standard occlusal radiograph of the posterior right mandible.
QUESTIONS:
– Which are the important radiographic features present?
– What is your diagnosis?
Interpretation:
There is a well-defined relatively radiolucent region located in the posterior right mandible apical to teeth 45 and 46. Internally, there is a mixed pattern of long curvilinear and short granular bone trabeculae. The periphery is corticated and scallops around the apices of the first molar. However, the periodontal ligament space and the lamina dura of the adjacent teeth are unaffected. On the occlusal radiograph, no expansion of the buccal or lingual cortices of the mandible is noted; however, there is scalloping of the buccal cortex adjacent to the first molar.
Diagnosis: Healing Simple Bone cyst
A conebeam CT examination of a similar case demonstrates the same type of scalloping on the periphery and small areas of thinning of the endosteal surface of the cortices without expansion (Fig. 4). The teeth and inferior alveolar nerve canal are unaffected. These are characteristic features of simple bone cysts. However, as in the challenge case, a fine granular bone pattern is seen internally, which suggests healing of the lesion.
FIGURE 4. Healing simple bone cyst. (A) Conebeam CT examination, sagittal image, demonstrating a sclerotic periphery with a homogeneous granular internal structure and scalloping between the roots of the teeth. (B) Conebeam CT, cross-sectional image, showing an intact cortex around the inferior alveolar nerve canal and lack of bucco-lingual expansion.
FIGURE 4(A). FIGURE 4(B).
A series of panoramic radiographs and conebeam CT examinations shows the spontaneous healing of a simple bone cyst in the mandibular right ramus (Figs. 5A-E). Over a period of 2.5 years, the radiolucent region, seen initially, is gradually replaced by fine granular internal bone pattern. As well, the cortex initially thickened and then it gradually remodeled into normal trabecular bone. An abnormal bone pattern can also remain in a region where a simple bone cyst has completed healing. This is demonstrated in Figure 6, where the outline of a simple bone cyst can be appreciated on both intraoral radiographs. However, internally there is a mix of granular and trabecular bone that presents with a density similar to the normal surrounding bone. Over time, this area might remodel into normal trabecular bone or remain with an abnormal bone pattern.
FIGURE 5. Cropped panoramic radiographs and axial cone beam CT images showing a healing simple bone cyst in the mandibular right ramus. (A & B) In March 2010, the periphery presented with a thick cortex. (C & D) In February 2011, the cortex was thickened. (E) In September 2012, there was a homogeneous granular bone pattern internally.
FIGURE 5(A). FIGURE 5(B).
FIGURE 5(C). FIGURE 5(D).
FIGURE 5(E).
FIGURE 6. Mandibular anterior occlusal radiograph (A) and intraoral periapical radiograph (B) demonstrating a healed simple bone cyst. The outline of the simple bone cyst can still be seen; however, a mixture of granular and trabecular bone is present internally.
FIGURE 6(A). FIGURE 6(B).
The usual treatment of simple bone cysts is surgical exploration with or without curettage of the bone cavity. However, some cases kept under observation demonstrate spontaneous healing. Spontaneous healing of simple bone cysts was first described by Blum in 1955. In his case review, all cases, which were kept under his observation, demonstrated bone regeneration without any type of treatment.1 Since then, there have been few reports on spontaneous healing of simple bone cysts. White and Pharoah described the internal structures of a healing simple bone cyst as having a granular bone pattern.2
A recent case series aimed to evaluate the radiographic features associated with spontaneously healing simple bone cysts. One hundred twenty three cases of simple bone cysts were retrieved from the database of the Radiology Department at the Faculty of Dentistry, University of Toronto. Cases of spontaneously healing simple bone cyst were interpreted following these inclusion criteria:
• Well-defined, corticated or partially corticated entity;
• Radiolucent or presenting with a fine internal granular bone pattern;
• No bucco-lingual expansion or very slight expansion relative to the size of the lesion;
• No effect on surrounding tooth structure;
• No previous history of surgical treatment.
Out of the 123 cases of simple bone cysts, 25 cases met the inclusion criteria. Two oral and maxillofacial radiology residents reviewed these cases and recorded whether the internal pattern and density of the entity were homogeneous, the presence of a corticated border, and the thickness of the cortex.
Most cases presented with a partial cortex and a homogeneous granular internal bone pattern. When the simple bone cyst was heterogeneous, the more radiopaque component was seen at the periphery. These results suggest two types of healing patterns: one with a homogeneous internal bone formation and the other with more bone formation at the periphery. Similarly, previous publications evaluating the radiographic findings of healing simple bone cyst after steroid injection, reported cortical thickening at the periphery.3,4 Chigira et al. suggested that cortical thickening could be a first step in the healing of a simple bone cyst.5
The cases presented illustrate the features of spontaneously healing simple bone cysts. When radiographic signs suggest the presence of a simple bone cyst, careful evaluation of the internal pattern for granular bone or thickening of the cortex should be made in order to determine if the lesion could already be healing. In these cases, periodic monitoring of the patient to ensure continued resolution is recommended. Completely healed simple bone cysts may be encountered incidentally and present as an irregular bone pattern. Awareness of this entity can aid the clinician to recognize the etiology and prevent unnecessary treatment. OH
Dr. Catherine Nolet-Lévesque is a third year Oral Radiology resident at the University of Toronto’s Faculty of Dentistry and a fellow at the Women’s College Hospital. Dr. Nolet-Lévesque obtained her Doctor of Dental Medicine with a minor in International Study from Laval University. After obtaining her dental degree, she completed a one year general practice residency at McGill University at the Montreal Children’s Hospital.
We would like to acknowledge Dr. Michael Pharoah for his contribution to the case review discussed in this article.
Oral Health welcomes this original article.
REFERENCES:
1. Blum T (1955). An additional report on traumatic bone cysts; also a discussion of Dr. John G. Whinery’s paper, “Progressive Bone Cavities of the Mandible”. Oral Surg Oral Med Oral Pathol 8(9):917-939.
2. White, S. C., & Pharoah, M. J. (2009). Oral Radiology: Principles and Interpretation (6th ed.). St. Louis, Mo.: Mosby/Elsevier.
3. Capanna R, Dal Monte A, Gitelis S, Campanacci M (1982). The natural history of unicameral bone cyst after steroid injection. Clinical orthopaedics and related research 166):204-211.
4. Scaglietti O, Marchetti PG, Bartolozzi P (1982). Final results obtained in the treatment of bone cysts with methylprednisolone acetate (depo-medrol) and a discussion of results achieved in other bone lesions. Clinical orthopaedics and related research 165):33-42.
5. Chigira M, Shimizu T, Arita S, Watanabe H, Heshiki A (1986). Radiological evidence of healing of a simple bone cyst after hole drilling. Arch Orthop Trauma Surg 105(3):150-153.
