Imaging specificities of simple mandibular bone cysts: A three-case report

Abstract

Simple bone cysts (SBCs) are benign, non-neoplastic bone lesions characterized by a single-cavity osteolysis, often discovered incidentally on panoramic radiographs. This article presents three cases of mandibular SBCs with distinct clinical and radiological features, emphasizing their diagnostic challenges and the role of imaging in differential diagnosis and follow-up. The first case involves a 22-year-old female patient with pulsatile mandibular pain, highlighting the lesion’s evolution over 3 years and postsurgical follow-up for 2 years. The second case concerns a 27-year-old patient incidentally diagnosed during prosthetic rehabilitation, underlining the differential diagnosis with periapical cysts and cementoblastomas. The third case describes a 45-year-old patient with a painful left parasymphyseal swelling, highlighting the importance of clinical and radiological correlation. These cases illustrate the variability in SBC presentation and the necessity of imaging for accurate diagnosis and long-term management.

Introduction

Simple bone cysts (SBCs) are benign bone lesions characterized by expansive single-cavity nontumoral osteolysis. They were first defined by Killey and Kay as a pathological cavity surrounded by an epithelium with liquid, semi-solid or sometimes gaseous contents [1]. Later, SBCs were defined as a “pseudo-cysts” without epithelial lining, with intact bony walls, thin connective tissue lining its cavity, and showing no evidence of acute or chronic inflammation [2]. In 2017, the World Health Organization (WHO) classified SBCs under bone cysts and giant cell lesions [3]. This classification was still used in the 5th edition (WHO) (2022) [4]. SBCs, also known as solitary, traumatic, hemorrhagic, or unicameral bone cyst, underscore the unclear pathogenesis of this pathological entity [2].

The first maxillary case was reported by Lucas in 1929; however, the diagnostic criteria were not established until 1946 [5]. This condition affects mainly the mandible, particularly on one side in the premolar-molar area [6]. It can also occur in the maxilla, zygoma, ramus, or condyle; however, occurrence in these locations is very rare [1,[7], [8], [9]].

Radiographically, these lesions typically appear as solitary, unilocular radiolucencies with well-defined borders that can be either scalloped or irregular [10]. Although most of these lesions are unilocular, multifocal and multilocular cases have been reported. When extending into the interdental bone, they typically show a distinctive “scalloping effect” [11]. These lesions rarely cause cortical bone expansion [12], making them frequently identified during routine radiographic examinations. Radiographic assessment is valuable for predicting the prognosis of SBCs. Features, such as scalloped margins, absent lamina dura, nodular bone expansion, or multiple cavities, may indicate a higher risk of recurrence [13].

This article presents three cases of SBCs with distinct clinical features, and it explores the diagnostic challenges associated with this lesion. Given the variation in the signs and symptoms in the present cases, this article aims to improve the dentists’ understanding of its presentation, thus aiding in a more accurate diagnosis and an effective management.

Case reports

Patient 1

A 22-year-old female patient presented with a complaint of pulsatile, radiating pain in the posterior right mandibular region. The patient was in good general health, with no medical, family, or surgical history, and no past traumatic events.

The extra-oral examination was normal, with no notable findings. However, the intraoral examination showed a filling of the vestibular depth adjacent to the impacted tooth (48), with no signs of pus discharge or ulceration. The surrounding mucosa appeared slightly inflamed.

First intention panoramic radiography (PR) was performed, and it revealed that the impacted tooth (48) was mesially inclined, with its crown being in contact with that of tooth (47). Additionally, a well-defined, oval-shaped radiolucency without a peripheral condensation line was detected in the right posterior mandibular region, extending toward the basilar margin (Fig. 1).

Fig. 1.

Panoramic radiograph showing a well-defined, oval-shaped radiolucent lesion (white arrows), extending from tooth 45 to tooth 48.

The relationship between the lesion and the mandibular canal was unclear. It was therefore necessary to perform a computed tomography scan (CT scan) to refine the diagnostic approach.

The CT scan revealed a well-defined hypodense right mandibular image of liquid density (25 Hounsfield Units [HU]). The lesion had a volume of 33.2 × 14.3 × 11.3 mm³. It was associated with buccal extension and cortical bone thinning (Fig. 1A). A scalloped margin was observed around the roots of the mandibular teeth (Fig. 2C). The lesion was in close proximity to the mental foramen (Fig. 2B), and there was an inferior displacement of the mandibular canal with erosion of its superior cortical wall (Fig. 2B and C). The soft tissues adjacent to the lesion remained intact, with no enhancement observed after contrast medium injection (Fig. 2D and E).

Fig. 2.

CT scan. (A) Axial view (bone window) showing the lesion’s volume and vestibular cortical expansion (white arrows). (B) Cross-sectional view showing the lesion in close contact with the mental foramen (white arrow). (C) Sagittal view showing a scalloped superior contour extending between the teeth roots and an inferior displacement of the mandibular canal (white arrow). (D and E) Axial views (soft tissue window) without (D) and with (E) contrast injection, showing soft tissue integrity and no contrast uptake (white arrows). (F and G) Panoramic radiographs showing the lesion’s progression after 3 years (F) and bone consolidation 2 months postoperatively (G) (white circles).

These radiological findings are consistent with a benign, cystic, and nonvascularized lesion with a slow progression.

Given the clinical presentation and the localized nature of the symptoms, no biological tests were deemed necessary for this case. Typically, such tests might include complete blood counts, inflammatory markers, and possibly serum calcium levels to rule out systemic conditions affecting bone metabolism. However, these tests were not required in the present case due to the absence of systemic symptoms or a significant medical history.

The initial management involved local intervention to remove the impacted debris and to reduce bacterial load, followed by irrigation of the pericoronal space with sterile solutions (chlorhexidine and hydrogen peroxide). Amoxicillin and oral analgesics were prescribed, and the patient was asked to maintain good oral hygiene.

Three years later, the patient presented again with an episode of pericoronitis related to tooth 48. A follow-up panoramic radiograph revealed that the previously described cystic image had evolved distally and inferiorly (Fig. 2F). As a result, tooth 48 was extracted, and a surgical approach to the adjacent lesion was performed. Intraoperatively, an empty cavity was observed, confirming the suspected diagnosis of SBC. Following the standard surgical management, the cavity was curetted to stimulate bleeding and to promote bone healing.

The 2-month postoperative follow-up revealed the beginning of bone healing on PR (Fig. 2G).

Patient 2

A 27-year-old male patient was referred to a dentist for prosthetic rehabilitation of the missing molar (36). The intra-oral examination showed that the adjacent teeth (35) and (37) were intact and vital, as confirmed by the pulp vitality test.

A PR was then performed for a preimplant assessment. A well-limited radiolucent image mimicking a radicular cyst at the apex of the left mandibular second premolar (35) and in continuity with its lamina dura was accidentally noted (Fig. 3).

Fig. 3.

Panoramic radiography: White arrow showing the presence of a radiolucent image associated with the apex of tooth 35.

Diagnosis of an inflammatory radicular cyst was then excluded, given the result of the pulp vitality test.

A CT scan was performed, and it revealed a well-defined radiolucency of liquid density (–10 HU) of 14 × 5.7 mm at the apex of (35). The lesion was accompanied by thinning of the buccal and lingual cortices, proximity to the mental foramen, downward displacement of the mandibular canal, and integrity of the adjacent soft tissues (Fig. 4A-D).

Fig. 4.

(A) Axial bone window CT showing a well-defined hypodense image thinning the vestibular and lingual cortices (white circle). (B) Cross-sectional view showing the radiolucency in close contact with the mental foramen (white arrow). (C) Sagittal view showing continuity with the lamina dura of tooth 35 (white arrow) and downward displacement of the mandibular canal. (D) Axial narrow window CT showing preserved soft tissue integrity (white arrows).

The patient did not report a medical condition, and he was not receiving any medicaments before the diagnosis of the lesion. Surgical exploration via vestibular cortical trepanation revealed a vacant cavity lacking an epithelial coverage, which defined the diagnosis of SBC. In the 6-month follow-up, the patient reported no complaints.

Patient 3

A 45-year-old male patient was referred to our department by his dentist for the evaluation of a painful, progressive left parasymphyseal swelling that had been developing for a month. He was in good general health, and he had no medical or surgical history and no past traumatic events.

The swelling was solid upon palpation, with no signs of labiomental hypoesthesia. The intra-oral examination revealed a filling of the vestibule floor in the area of the teeth 32, 33, 34, and 35.

PR showed a well-defined, oval-shaped radiolucent lesion extending from the left anterior teeth to the posterior mandible, with scalloped upper borders (Fig. 5).

Fig. 5.

Panoramic radiography: White arrow showing an extensive, well-limited radiolucent image around the mandibular teeth roots.

CT scan revealed a well-limited hypodense image of para-fluid density (about 50 HU), extending from tooth 31 to tooth 37 and reaching the inferior mandibular border, with a scalloped upper contour (Fig. 6A and F).

Fig. 6.

(A) Sagittal CT scan (bone window) showing the radiolucency’s mesiodistal extent and its proximity to the mandibular canal (white arrows) and the adjacent teeth. (B) Axial CT scan (bone window) revealing vestibular cortical displacement and partial effacement. (C) Cross-sectional CT scan (bone window) showing the image’s proximity to the mental foramen. (D) Cross-sectional CT scan (bone window) showing its proximity to the mandibular canal. (E) Axial CT scan (soft tissue window) confirming soft tissue integrity. (F) 3D CT reconstruction demonstrating the lesion’s full extent.

Vestibular cortical expansion with partial erosion and lingual cortical thinning, without perforation or invasion of the adjacent structures, was noted (Fig. 6B and E). The lesion was closely associated with the mental foramen (Fig. 6C). The mandibular canal was displaced lingually, with erosion of its superior cortex (Fig. 6D).

The radiological features were suggestive of a SBC, with a differential diagnosis of a benign tumor-like cystic lesion. The patient was referred to the maxillofacial department for a minimally invasive treatment. The examination found no tissue inside the lesion, except for a thin epithelial layer in some areas of the margin. The intraoperative diagnosis was then in favor of SBC. The patient was lost to follow-up for the assessment of the clinical progression.

Discussion

SBCs usually occur in the metaphyseal region of the long bones (90%), and are rare in the maxillafacial region (1%) [6,14]. In case they occur in this area, the posterior mandible is the most common site [13]. In the three reported cases, the cyst location matches the findings in the existing literature.

The exact etiology and pathogenesis of SBC remain unclear, but several theories have been proposed in the literature [15]. One widely accepted theory is the “trauma-intramedullary hemorrhage,” leading to bleeding within the bone and resulting in the formation of a cavity [16]. However, in the present cases, there was no reported history of trauma.

The epidemiological features of SBCs remain inconsistent across studies. While some reports suggest no gender predilection, others indicate a higher prevalence in males [17]. This is reflected in the cases herein, where two out of three patients were males. Similarly, SBCs are typically diagnosed in the second decade of life [11]; however, our patients were mostly between the age of 22 and 27 years, except for one who was diagnosed at the age of 45 years. This age difference may be due to delayed diagnosis, as these lesions often remain asymptomatic.

Clinically, SBCs are often found incidentally during routine radiological examinations, with no clinical symptoms, as seen in the first two cases reported in this article [16,18]. The symptoms, reported in 2.27% to 30.43% of cases [19], can include pain, swelling, tooth sensitivity, and other complications such as fistula formation, root resorption, paresthesia, and pathological fractures [10]. In 85% of cases, adjacent teeth remain vital [17]. In some cases, SBCs can grow significantly large, causing facial asymmetry [20]. This was evident in the third case reported herein, where the patient sought treatment due to swelling and facial asymmetry caused by the lesion.

On imaging, SBCs typically appear as well-defined unilocular radiolucency with margins that may be irregular and partially sclerotic [13,21]. Scalloped borders, often suggesting the diagnosis, are a key feature of SBCs. This scalloping effect is particularly noticeable when the cyst extends toward the dental roots, and it can also be observed in the edentulous areas [21]. Another radiographic feature of SBCs is the widespread nature of the lesion, which does not lead to bone expansion. Instead, the cortical bone is often thinned due to erosion within the bone [21]. The radiographic findings in the present three cases are consistent with the features described, as seen in the CT scan images, showing cortical thinning, scalloped effects, and no displacement or resorption of the adjacent teeth.

In cases of large lesions, a multilocular appearance may be observed, which can lead to misdiagnosis as keratocysts or ameloblastomas. These multilocular lesions may also present intralesional septa [8]. SBCs are typically found away from teeth or may surround fully developed teeth without inducing resorption or affecting the lamina dura [19]. However, in the second case reported in this article, the lamina dura of an adjacent tooth appeared similar to that of a periapical cyst, which is an unusual finding.

The radiographic appearance of SBCs can share features with other lesions, especially root cysts when placed at the teeth apexes, leading to potential misdiagnosis. However, combining radiographic evaluation with pulp vitality testing helps to differentiate SBCs from root cysts [22]. In the second case reported in this article, simple cyst mimicking a peri-apical cyst was ruled out based on pulp vitality and the absence of dental symptoms. Similarly, the potential diagnosis of cementoblastoma was excluded due to the lack of mixed radiographic features. However, this might be attributed to the early stage of lesion development, which can present as a hypodense image. Nonetheless, the size of the lesion ruled out this diagnosis, as cementoblastomas typically show calcifications earlier in their development. The differential diagnosis also includes central giant cell granuloma, myxoma, ameloblastoma, and keratocystic odontogenic tumor because of little expansive growth and scalloped borders [1,23]. These conditions, along with cementoblastoma and periapical cysts, highlight the importance of a thorough diagnostic approach, considering both the clinical and radiographic findings to ensure an accurate diagnosis and an appropriate treatment planning.

CT scan is considered a valuable diagnostic tool for initial diagnosis [23], helping to assess the lesion’s contents, typically showing fluid-like density. Contrast injection may reveal vascularity [1]. However, magnetic resonance imaging (MRI) enhances the lesion’s characterization by providing additional diagnostic insights. It distinguishes SBCs from benign tumors based on signal intensity: low on T1 and high homogeneous on T2, indicating fluid but not specifying the lesion’s nature [24].

For a more detailed assessment, dynamic contrast-enhanced MRI offers further differentiation by showing contrast agent diffusion from the periphery inward, suggesting interaction with the surrounding bone marrow. This dynamic contrast enhancement helps to differentiate SBCs from true cysts with epithelial linings, which lack this enhancement [25].

The treatment approach for SBCs depends on several factors, such as the patient’s age, lesion size, symptoms, and location [13]. Different treatment modalities are available, each with varying recurrence rates, except for complete resection [17]. For small asymptomatic SBCs in the mandible, conservative treatment is recommended. It includes intra-oral management of the lesion and the use of antibiotics and anti-inflammatory drugs. Alternatively, a wait-and-see approach can be taken, with regular radiographic follow-ups [13,26]. For large symptomatic cysts, whenever boundary changes or size and cortical expansion occurs, complete curettage and bone grafting are the most common and effective methods. Indeed, the surgical approach is considered a secure way for both diagnosis and treatment [13,17,26]. However, in some cases, spontaneous resolution of SBCs has been reported [26].

The management of teeth involved in SBCs remains a controversial topic. Newton and Zunt [27] recommend endodontic treatment before, during, or after the surgery of teeth with compromised pulp vitality, as it helps to eliminate potential sources of inflammation. On the other hand, Peñarrocha-Diago et al. [14] reported that endodontic treatment should be avoided for teeth with apexes within the lesion, as spontaneous healing is often sufficient and normal healing occurs without complications.

Other treatment modalities, such as careful curettage with bone regeneration techniques [28], endoscopic curettage [29], intra-lesional corticosteroid injections [30], decompression [31], and the use of bone grafts or biomaterials have also been explored [5].

Histological examination plays a crucial role in diagnosis. However, the limited availability of material for analysis can be challenging to gather enough evidence for a conclusive diagnosis [21]. Despite this limitation, most histological results show fibrous and normal bone tissue. In most cases, no epithelial lining is present, although a thin fibrous membrane may occasionally surround the cavity. Furthermore, areas with fibrin, erythrocytes, osteoclastic giant cells, cholesterol, granulation tissue, and vascularity may also be present [21,32,33].

The prognosis of SBCs is generally favorable, but recurrence remains a concern [13]. According to Suei et al. [34], the radiographic features are useful for both diagnosis and predicting the recurrence risk, providing valuable prognostic insights. In this context, a scalloped margin may suggest a potential recurrence, but it should not be confused with interdental scalloping, which is observed when the lamina dura remains intact. Since an unbroken lamina dura is a sign of probable healing, lesions with this feature tend to heal either spontaneously or after treatment. Additionally, the presence and characteristics of bone expansion play a crucial role in prognosis. Indeed, lesions without expansion or with a smooth expansion pattern tend to heal, whereas those with nodular expansion have a higher risk of recurrence. Furthermore, the multiplicity of lesions or their association with osseous dysplasia are strongly linked to a higher risk of recurrence. Given these predictors of recurrence, the need for long-term follow-up and the possibility of repeated surgery should be considered.

In conclusion, SBCs remain a controversial entity due to their unclear etiopathogenesis and diagnostic challenges. Histological examination is often limited by tissue availability, and diagnosis primarily relies on the clinical evaluation during surgery. Imaging plays a crucial role not only in guiding the diagnosis but also in ruling out misleading differential diagnoses when combined with clinical correlation. Additionally, imaging is essential for assessing both prognosis and recurrence risk. Radiographic features, such as absent lamina dura, scalloped margins, and nodular bone expansion, are key predictors for determining the likelihood of recurrence and guiding long-term management.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethics approval statement

Ethical approval was not required for this study as it did not involve human participants or animal subjects.

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No material from other sources requiring permission was used in this study.

Declaration of Generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the authors used ChatGPT and perplexity. AI in the writing process in order to improve the readability and language. After using this tool, the authors reviewed and edited the content as needed, and they therefore take full responsibility for the content of the publication.

Patient consent

We confirm that the three patients involved in this publication have provided informed consent for their cases to be published with full respect for their anonymity. The information included in this article is limited to radiological examinations and does not contain any identifiable patient images, such as facial features or other recognizable details. All ethical aspects regarding patient privacy have been strictly respected in accordance with international guidelines for medical publications.