Scalloped border as a possible diagnostic aid for differentiating jaw lesions: A pictorial essay

Radiographic imaging plays a key role in the proper diagnosis of bony lesions in the oral and maxillofacial region.1 Many types of jawbone lesions have several aspects of their radiographic appearance in common, which makes it difficult to differentiate them.2 Therefore, radiographic features such as location, borders, internal structures, ability to expand, perforation, and impact on surrounding tissues can be used as diagnostic aids to reach a timely and correct diagnosis.3 Among the above-mentioned items, the characteristics of the lesion’s border can be helpful in limiting the differential diagnosis. Generally, lesion borders are divided into 2 major groups: well-defined and ill-defined. Well-defined borders also present with different shapes, such as punched out (a sharp demarcation between abnormal and normal bone with no other feature), corticated (a sharp, opaque, and usually curved line), and sclerotic (a sharp opaque border thicker and less uniform than a corticated border).3 Furthermore, the borders of lesions may be smooth or scalloped. Scalloping describes a series of contiguous arcs or semicircles that may develop around the roots of teeth or within adjacent bone or bone cortices. Scalloping may reflect the mechanism of a lesion’s growth. This shape may be seen in cysts, cyst-like lesions, and some benign neoplasms with a unilocular or multilocular internal structure.4

Therefore, the goal of this overview was to assist dental practitioners in making an accurate and timely differential diagnosis by focusing on the relevant radiographic findings. Based on a review of the literature, 5 types of jaw lesions are proposed as cysts and tumors associated with a higher tendency to have scalloped borders. When dentists encounter a lesion with scalloped borders, they should first consider these entities in the differential diagnosis.

General search engines and specialized databases including Google Scholar, PubMed, PubMed Central, and Scopus, as well as an authoritative textbook, were used to find relevant studies by using keywords such as “jaw lesion,” “jaw disease,” “scalloping,” “scalloped border,” “scalloped margin,” “irregular border,” and “irregular margin.”

Out of 289 identified articles, 252 were excluded because they were duplicates (122), had unrelated titles or abstracts (77), or did not mention the term “scalloped” or its synonyms to describe the periphery of lesions or their frequency in this context (53). Finally, 37 articles and 1 textbook closely related to the topic of interest were included. The details of the search strategy are also presented in a flowchart for better understanding (Fig. 1).

Fig. 1
Flowchart of the search strategy.

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Upon comparison of the lesions, ameloblastoma was found to be the most prevalent lesion with scalloped borders, and other lesions in this category were central giant cell granuloma, odontogenic keratocyst, traumatic bone cyst, and glandular odontogenic cyst. Table 1 presents the following 7 characteristics of jaw lesions with scalloped borders: origin, predominant age and sex, most common location and involved jaw, clinical features, and the proportion of lesions with scalloped borders.

Table 1
General characteristics of jaw lesions with a relatively high likelihood of being associated with scalloped borders

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Ameloblastoma

Ameloblastoma is the second most frequent benign odontogenic tumor after odontoma, accounting for 11% to 13% of all odontogenic tumors.5 Most patients are between the ages of 30 and 50 years, and there is a slight sex predilection in men.5, 6 Clinically, it presents as a locally aggressive and slow-growing asymptomatic tumor.6 The mandible is more affected than the maxilla, and most cases (70%) are seen in the molar-ramus area.5 On the other hand, it is in association with an unerupted or impacted tooth, most commonly the mandibular third molar, in 15% to 40% of cases.7 Radiographically, it is characterized by a unilocular or multilocular lesion with coarse and curved septation (Figs. 2 and 3).5 In the mandible, the borders of the lesion are usually well-defined, occasionally scalloped, and frequently corticated; in contrast, maxillary lesions have ill-defined borders because the lesions tend to spread into the bone rather than expanding it.1, 8 Scalloped borders have been mentioned as a characteristic feature of ameloblastoma. In this regard, Kitisubkanchana et al.9 showed that 77.2% of all ameloblastomas had scalloped borders, of which 83% were desmoplastic ameloblastoma, 80% were conventional ameloblastoma, and 66% were unicystic ameloblastoma. In another study, Meng et al.10 categorized the shape of maxillary ameloblastomas according to their radiographic outline as circular, oval, kidney, scalloped-circular, scalloped-oval, scalloped-kidney, and sinus-shaped lesions. In this study, the scalloped-oval type was the second most frequent shape after circular.

Fig. 2
Scalloped borders of ameloblastoma in the posterior mandible on cone-beam computed tomographic images. A. Low-thickness multiplanar reformatted (MPR) image. The superior border of the inferior alveolar nerve canal cannot be clearly detected adjacent to the lesion. B. High-thickness MPR image. C. Three-dimensional volumetric image. D. Maximum intensity projection (MIP) panorama image shows extensive destruction along the anterior border of right mandibular ramus E. A scalloped border of the lesion (arrow) is seen in an axial image. F. Three-dimensional surface rendering image shows septation (arrow) between adjacent locules and destruction of the superior border of the inferior alveolar canal is also observed.

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Fig. 3
Multilocular ameloblastoma on cone-beam computed tomographic images. A. Coronal section shows septation (arrow) in an expansile lesion. B. Sagittal view shows a typical scalloped border. C. Axial view shows an expansile multilocular radiolucent lesion, causing extensive destruction in the right ascending ramus. The lesion has well-defined, corticated, and sclerotic scalloping borders (arrows). D. Three-dimensional surface-rendering cone-beam computed tomographic image shows curved and coarse septa in ameloblastoma (arrows), which partially divide a unilocular cavity into multiple, smaller, variably sized cavities.

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Central giant cell granuloma

Central giant cell granuloma is a locally aggressive, non-neoplastic intraosseous lesion, accounting for about 7% of benign lesions of the jawbones.11 It usually occurs in the second and third decades of life and there is a sex predilection in women.11, 12 Clinically, it appears as an expansile lesion causing a swelling that can cross the midline in 50% of mandibular cases.13 The mandible is more frequently affected than the maxilla, and most cases are seen in the anterior portion of the jaws.11 Radiographically, it is characterized as a unilocular or multilocular radiolucency with well-defined, smooth, or scalloped margins and a honeycomb or soap bubble-like appearance (Fig. 4).11, 12, 13, 14 The same radiographic features have also been reported in other giant cell lesions such as giant cell tumors and brown tumors of hyperparathyroidism.14 In a systematic review, Stavropoulos and Katz11 showed that 53% of all central giant cell granulomas had scalloped margins. The presence of scalloped margins in this entity has also been reported by Kahlon et al.14 In addition, they also pointed out that this radiographic feature can be seen in giant cell granulomas associated with genetic disorders such as Noonan syndrome, neurofibromatosis, cherubism, and arteriovenous malformations.14 The same findings were also reported by Vaidya et al.15 and Jeyaraj.16

Fig. 4
Central giant cell granuloma extends from the right first molar to the midline of the mandible. Panoramic reconstructed cone-beam computed tomographic image with 2-mm thickness shows scalloped borders (arrows).

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Odontogenic keratocyst

Odontogenic keratocyst is an odontogenic cyst representing the third most frequent cyst of the jaw bones, accounting for 10% to 14% of all odontogenic cysts.5 There is a slight sex predilection in men, with the peak incidence occurring in the third decade of life.17 More than 80% of cases have been detected in the mandible, mostly in the body (20%), angle (18%), and ascending ramus (10%).5 This entity usually tends to grow in an anteroposterior direction within the bone without causing considerable clinical expansion, and this finding has also been reported for odontogenic myxoma.5 It is usually asymptomatic, but pain and discharge have been reported by 40% of patients.5 Radiographically, it appears as a unilocular or multilocular radiolucency with well-defined, smooth, or scalloped, and often corticated margins (Figs. 5 and 6).5, 9 In some cases, dystrophic calcification may be seen in long-standing lesions.5 According to Veena et al.,18 most cases of odontogenic keratocyst are unilocular with scalloped borders when present at the periapex. Lesions with scalloped borders have also been reported in 40% of cases by Kitisubkanchana et al.9 In another study by Ong and Siar,19 the presence of scalloped borders in unilocular odontogenic keratocysts was reported to be 12.12%, and 12.12% of multilocular odontogenic keratocysts had scalloped borders as well. In this regard, Borghesi et al.20 pointed out that multilocular lesions with scalloped borders were more frequent than unilocular lesions, and stated that this appearance seems to be characteristic of this entity.

Fig. 5
Odontogenic keratocyst on cone-beam computed tomographic images. A. Coronal view shows a scalloped border in the lateral border of the left ramus (arrow). B. Sagittal view shows a scalloped border in the posterior border of the ramus (arrow). C. Axial view shows a scalloped border in the lateral border of the ramus (arrow). D. Three-dimensional surface-rendering image shows a scalloped border in the posterior border of the left ramus (arrow).

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Fig. 6
Odontogenic keratocyst from the angle of the right mandible extending to the opposite side. Panoramic reconstructed cone-beam computed tomographic image with 2-mm thickness shows scalloped borders (arrows).

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Simple bone cysts

Simple bone cyst is a non-odontogenic pseudocyst with no epithelial lining that is also known as solitary bone cyst, extravasation cyst, traumatic bone cyst, progressive bone cavity, unicameral bone cyst, and hemorrhagic bone cyst.21, 22 It mostly occurs in the second and third decades of life, with a mean age of 20 years.23 There is a slight male predominance or no sex predilection.23 Most cases are in the mandible between the canine and third molar, followed by the mandibular symphysis, ramus, condyle, and anterior portion of the maxilla.21 Trauma is the most commonly discussed etiologic factor in the formation of this lesion, and the presence of a traumatic experience in patients’ history has been reported to be up to 70% in the literature.24 Clinically, it usually presents as an asymptomatic lesion with no considerable expansion; however, pain and buccal expansion have been reported in 10% to 30% and 18% to 50% of long-lasting lesions, respectively.23, 24 Radiographically, it appears as a unilocular or multilocular, well-defined lesion, with irregular or scalloped borders often suggesting the diagnosis (Figs. 7 and 8).23 In this regard, a scalloping pattern has been reported in 68% of cases occurring between and away from the teeth.24 In a review article, Xanthinaki et al.21 described that the scalloping pattern is characteristic of traumatic bone cyst and can be seen either in dentate or edentulous areas.21 The same descriptions were also reported by Suei et al.25

Fig. 7
Simple bone cyst on cone-beam computed tomographic images. A. Coronal view shows a scalloped border in the medial border of the mandibular body (arrow). B. Sagittal view shows a scalloped border in the anterior border of the lesion (arrow). C. Axial view shows scalloped borders in the buccal and lingual aspects of the lesion (arrows). D. Three-dimensional surface-rendering image shows a spatial view of the lesion on the left side of the mandible.

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Fig. 8
Simple bone cyst in the posterior aspect of the left mandible. Panoramic reconstructed cone-beam computed tomographic image with 2-mm thickness shows scalloped borders and scalloping between roots (arrows).

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Glandular odontogenic cyst

Glandular odontogenic cyst is a rare, locally aggressive odontogenic cyst that is also known as sialo-odontogenic cyst, developmental odontogenic epithelial cyst, and polymorphous odontogenic cyst.26, 27 It tends to occur over a wide age range, with most cases diagnosed in the fifth to seventh decades of life.26 There is either a slight male predominance or no sex predilection.26, 28 The mandible is more affected than the maxilla, and most cases are seen in the anterior portion of the jaw.28 Clinically, it usually presents as an asymptomatic, slow-growing, invasive lesion with considerable expansion; however, the presence of clinical symptoms has been reported in 24% of cases.29, 30 There may also be tooth displacement and cortical bone perforation, leading to extension of the lesion into the surrounding soft tissue.27 Radiographically, it appears as a unilocular or multilocular, well-defined lesion, often with scalloped and sclerotic borders (Fig. 9).27 In this regard, Manor et al.,28 Opoundo et al.,29 Chrcanovic and Gomez,30 Shah et al.,31 and Fowler et al.32 reported scalloped borders in their case series and review articles as a common radiographical feature in patients with glandular odontogenic cyst. Kaplan et al.33 reported that 54% of glandular odontogenic cysts are multilocular, 93% well-defined, and 13% associated with a scalloped border.

Fig. 9
Glandular odontogenic cyst in the anterior aspect of the mandible. Panoramic reconstructed cone-beam computed tomographic image with 2-mm thickness shows scalloped borders (arrows) and scalloping between roots (arrowheads).

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Bony lesions have 2 types of borders: well-defined or ill-defined. The former usually is indicative of benign lesions with a slow-growing course, and the latter is present in fast-growing and destructive entities like infectious or malignant lesions.3 Well-defined peripheries can be further divided into smooth or scalloped borders, as well as corticated or sclerotic.4

According to the findings of this review article, as summarized in Table 1, scalloped borders are found in 4 groups of lesions: 1) odontogenic cysts (odontogenic keratocyst, glandular odontogenic cyst), 2) pseudocysts (simple bone cyst), 3) odontogenic tumors (ameloblastoma), and 4) reactive lesions (central giant cell granuloma). Due to the structural differences between the maxilla and the mandible and the higher frequency of these lesions in the mandible, it is more likely that a clinician will encounter a lesion with scalloped borders in the mandible than in the maxilla.3, 4 Among those lesions having scalloped borders, ameloblastoma is the most frequent (72.2%), followed by simple bone cyst (68%), central giant cell granuloma (53%), and odontogenic keratocyst (41%).5, 7, 10, 17, 18, 21, 22 Considering this feature along with other characteristics of lesions can help clinicians restrict the differential diagnoses; for example, a multilocular radiolucent lesion with well-defined scalloped borders in the posterior aspect of the mandible that extends to the ramus and causes expansion or tooth movement would prompt the clinician to think about ameloblastoma in the differential diagnosis.5, 6, 7, 8, 9 In contrast, a unilocular or multilocular radiolucency with scalloped borders extending from the mesial aspect of the mandibular first molar to the midline with expansion or fullness of the vestibule might prompt consideration of central giant cell granuloma as the most probable diagnosis and glandular odontogenic cyst as a less likely diagnosis due to its lower prevalence.10, 12, 26, 33 When a clinician faces an extended multilocular radiolucent lesion with a scalloped border, but with minimal expansion, he or she should put forward the diagnosis of odontogenic keratocyst.16 In another instance, simple bone cyst should be ranked first in the differential diagnosis when a solitary or multiple radiolucent lesions in the posterior aspect of the jaws is discovered on routine examination with scalloped borders with a possible history of trauma.19, 20 Generally, these 5 lesions should be considered first in the differential diagnosis. Otherwise, in case of incompatibility with lesion manifestations, rare entities with scalloped borders should be considered, such as odontogenic myxoma, vascular malformations, and multiple myeloma.34, 35, 36, 37, 38 In conclusion, regarding the likelihood of a scalloped feature in the periphery of bony lesions, the clinician should consider ameloblastoma, central giant cell granuloma, odontogenic keratocyst, traumatic bone cyst, and glandular odontogenic cyst in the differential diagnosis list and notice other characteristics of the lesions such as their process, location, and effect on the surrounding tissues to reach the most probable diagnosis. It is recommended to consider other entities with a lower likelihood of having a scalloped border after ruling out the above-mentioned lesions.