A 55-year-old woman presented with persistent right jaw pain for 2 months, with no history of a recent dental procedure and no symptoms to suggest infection. A pantomogram was obtained (Figure 1) followed by CT imaging (Figure 2).
Persistent jaw pain
Expansile cystic/lytic bone lesion within the mandibular ramus without a soft-tissue component or enhancement
Keratocystic odontogenic tumor (OKC)
Dentigerous cyst
Ameloblastoma (unicystic form)
Benign fibro-osseous lesion (ossifying fibroma)
Cystic lesions of the mandibular ramus may first be detected by radiographs and may require CT imaging for further evaluation. The initial presentation is variable with respect to pain. Given that a solid mass can produce lytic changes in bone, it is best to characterize a lesion as “lucent” on radiographs and defer any attempts to differentiate cystic lesions from solid lytic lesions until cross-sectional imaging is available. In this case, the mandibular lesion begins in the retromolar location and extends to the condyle. There is no enhancement, periosteal reaction, or involvement of surrounding musculature to suggest an aggressive malignant neoplasm. The presence of a thick sclerotic cortex suggests a more indolent process as the bone is attempting normal repair around the lesion. Fibrous dysplasia is not included in the differential considerations since there is no evident matrix within the lesion. Dentigerous cyst is considered unlikely since the closest molar tooth is not involved. The most likely consideration is keratocystic odontogenic tumor (OKC) vs unicystic ameloblastoma. Tissue sampling from the cyst wall can be obtained using CT guidance. Although these are benign lesions, they are locally aggressive and may recur.
Keratocystic odontogenic tumor (OKC) is not currently classified as a tumor despite the moniker. An OKC is a benign periapical cyst of the mandible or maxilla that falls into the developmental lesion category of the 2017 World Health Organization classification of odontogenic and maxillofacial bone tumors.1 Most cases are nonsyndromic but multiple lesions are a hallmark of Gorlin syndrome (Nevoid basal cell carcinoma syndrome) due to PTCH mutations. Additional syndromic associations of OKC include Noonan syndrome and Ehlers-Danlos syndrome. Multiple OKCs in these conditions are typically asynchronous, occurring over a lifetime.2 OKCs are mostly seen in younger patients in their teens, 20s or 30s, are locally aggressive and can recur after excision.3 Many patients with keratocystic odontogenic tumors are asymptomatic, but some will present with jaw swelling and pain. The surgical path specimen will reveal a thin-walled cyst with fluid and debris, resulting in a variable consistency.3 These tumors arise from stratified squamous keratinizing epithelium found along the margin of the dental lamina and the periodontal margin of the alveolus.3 When these tumors arise from the mandible they typically arise from the posterior aspect of the mandible.4 These lesions can arise near the roots of teeth similar to radicular cysts from dental caries or can arise near the crown of an unerupted/impacted tooth similar to a dentigerous cyst.4 OKCs may be multilocular and daughter cysts can develop if perforation of the bony cortex occurs.
Dentigerous cysts occur within the mandible or the maxilla, and when large can grow into the maxillary sinus or result in a pathologic fracture of the mandible. These lesions are not seen in childhood because they occur almost exclusively with secondary/permanent dentition, and often with unerupted/impacted teeth. For this reason, third molars are a common location.3 These pericoronal cysts attach to the cementoenamel junction of the tooth. These cysts occur more frequently in Gorlin syndrome but are derived from nonkeratonizing epithelium in contrast with keratocystic odontogenic tumors. Pain is uncommon.3
Ameloblastoma is a locally aggressive benign tumor associated with BRAF mutations located within the mandible or, less commonly, the maxilla. Patients are often in their 20s or 30s, similar to odontogenic keratocysts.4 These tumors arise from the cells responsible for enamel production that form the crown of the tooth. Most conventional (multicystic) ameloblastomas have cystic and variably enhancing solid components with internal septae and present as firm, painless, expansile soap-bubble lesions often with tooth root resorption.4 A unicystic form accounts for less than 15% of cases and can be indistinguishable from dentigerous cysts or odontogenic keratocysts by CT imaging if associated with the crown of an unerupted/impacted tooth and lacking mural nodules or enhancement.4 Another location where dentigerous cyst, odontogenic keratocyst, and unicystic ameloblastoma overlap is the premolar region of the maxillary alveolus where lesions often grow into the maxillary sinus. Treatment of an ameloblastoma with a nodule or solid component is similar to OKC and consists of en-bloc surgical resection. It should be noted that the term “adamantinoma” was historically used for ameloblastoma but is now discouraged since there is no histologic correlate between an ameloblastoma and the adamantinoma that occurs in long bones such as the tibia.
This rare lesion is composed of fibrous tissue that may calcify over time, mostly in a peripheral distribution. The lesion may appear lucent or heterogeneously radiopaque. Most lesions will be small, and cortical breakthrough is uncommon.
Ameloblastoma
>When presented with a cystic-appearing lesion of the mandibular ramus without enhancement or mural nodule, considerations will include unicystic ameloblastoma, dentigerous cyst, and keratocystic odontogenic tumor. The unicystic form of ameloblastoma is less common than the multicystic form that has cystic and soft-tissue components. Dentigerous cyst is usually seen in the setting of an unerupted/impacted tooth, but OKC and ameloblastoma can also be seen with an unerupted/impacted tooth. Dental root resorption is more typical of an ameloblastoma and is uncommon for dentigerous cyst or OKC.
Choudhry F. Cystic Lesion of the Mandibular Ramus. J Am Osteopath Coll Radiol. 2021;10(2):22-23.
