COM March 2005 Diagnosis

Unilocular Radiolucency Associated with an Impacted Third Molar

Can you make the correct diagnosis?

This is a 47-year-old male with an incidental discovery of a left mandibular radiolucency around an impacted tooth #17.

1. Dentigerous Cyst

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Dentigerous cyst is the most common developmental cyst in the oral cavity, accounting for 20% of the developmental cysts of the jaws, and is almost always associated with the crown of a tooth attached to the cemento-enamel junction. It is believed to originate from the accumulation of fluid between the reduced enamel epithelium and the tooth crown thus expanding the follicle beyond the 3 mm normal diameter (1-3). It is usually associated with an unerupted or impacted tooth. This cyst can present as an asymptomatic radiolucency discovered during a routine dental examination or can act aggressively by expanding the jaws, leading to facial asymmetry with extreme displacement of adjacent teeth as well as the involved tooth (1-2). It can be painful and cause root resorption of the adjacent teeth, especially if the cyst is infected. It is more common in the third molars and upper canines and can also involve supernumerary teeth and odontomas. Radiographically, it presents as a smooth border, usually unilocular or sometimes multilocular radiolucency, located around the tooth circumferentially, laterally or in the form of a “doughnut” ring. The size varies from small to extremely large, extending into the ramus of the mandible. The borders are usually corticated and smooth unless it is inflamed when loss or cortication (usually partial) is present (1). Histologically, the cyst has non-specific features lined by variable thickness of stratified squamous epithelium and supported by connective tissue. Clusters of mucous cells are frequently present, especially in the mandibular third molar areas. Treatment depends on its size, and ranges from thorough curettage to marsupialization. It usually has a good prognosis. Recurrence is uncommon if properly removed. Occasionally this cyst is associated with ameloblastoma, epithelial dysplasia and/or squamous cell carcinoma or mucoepidermoid (1-3). The clinical and radiographic features of this case are consistent with a dentigerous cyst. The presence of mucin does not exclude the diagnosis of a dentigerous cyst. However, the presence of microcystic structures, the superficial lining, with cuboidal epithelial cells is not in support of a dentigerous cyst.

2. Odontogenic Keratocyst

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Odontogenic keratocyst (OKC) is an aggressive odontogenic cyst and is known for its rapid growth and its tendency to invade the adjacent tissues, including bone. It has a high recurrence rate and is associated with basal cell nevus syndrome (4, 5). The majority of patients are in the age ranges of 20-29 and 40-59, but cases in patients ranging in age from 5 to 80 years have been reported (4). The distribution between sexes varies from equal distribution to a male-to-female ratio of 1.6:1. OKC predominantly affects Caucasian populations and, if one may judge from the limited evidence provided by the literature, is chiefly of Northern European descent (4). Odontogenic keratocysts may occur in any part of the upper and lower jaw, with the majority (almost 70%) occurring in the mandible. They occur most commonly in the angle of the mandible extending superiorly into the ramus (4, 5). Posterior mandible is an area common to many benign odontogenic tumors such as ameloblastoma and is also a typical location for dentigerous cysts. Radiographically, OKCs present predominantly as unilocular radiolucencies with well-defined or sclerotic borders; they may also present as multilocular radiolucencies or unilocular with scalloped borders (more common) (4-6). They usually penetrate the bone rather than expand; they grow in an anterior and posterior manner with little to no expansion. The larger OKCs, however, tend to expand bone, but mildly. Obvious clinical expansion should be viewed with suspicion for a neoplasm. OKCs can also present as small and oval radiolucencies between teeth simulating a lateral periodontal cyst, in an area of an extracted tooth simulating a residual cyst, at the apex of a vital tooth mistaken for a periapical cyst, or in the anterior maxilla between the central incisors simulating an incisive canal cyst (4-6). OKCs grow to sizes larger than any other odontogenic cysts. Despite this aggressive growth, they often remain asymptomatic, thus growing to large sizes and hollowing the bone (4-6). Like dentigerous cysts, if infected, they can be painful, thus symptomatic. Multiple OKCs are frequently associated with bifid-rib basal cell nevus syndrome (Gorlin syndrome). Odontogenic keratocysts are significant clinical entities due to their tendency for recurrence and destructive behavior. They are known to have a high recurrence rate, ranging from 13% to 60% (4). Complete surgical removal is the treatment of choice. Enucleation combined with Carnoy’s solution or liquid nitrogen treatment has been effective in reducing recurrence rate (5). Both the clinical and radiographic findings of this case are consistent with OKC. The histology however is not.

3. Cystic Ameloblastoma

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Ameloblastoma is defined as a benign neoplasm of tooth origin and as a benign but locally aggressive neoplasm with potential for invasion of the surrounding bone and soft tissue (7). It also has the potential for local extension to the brain and death of the patient. However, not all ameloblastomas behave in that aggressive manner. Ameloblastoma is a family of diseases with different biological behavior. Therefore, it is necessary to distinguish between the various types before a definitive treatment is rendered (7-8). Three clinical types are described, beginning with the solid type (radiographically multilocular) which is treated with complete resection or en bloc (partial) resection depending on the size. The unicytic type includes three histologic types, one of which (the mural cystic ameloblastoma) behaves like the solid type, while the other two types (intraluminal and plexiform unicystic) are less aggressive and treated with curettage. Based on the radiographic presentation of unilocular radiolucency, extending into the ramus and being associated with the crown of an impacted tooth would be more consistent with a plexiform unicystic type of ameloblastoma (7-9). The unicytic type is much less aggressive than the solid type and accounts for about 10% of all ameloblastomas. It occurs in younger patients around 18 to 20 years of age with a strong predilection for the posterior mandible (8). Almost 90% of cases are associated with the crown of impacted third molar teeth with the radiographic presentation similar to a dentigerous cyst. This type of ameloblastoma can arise from a dentigerous cyst or de novo next to a cyst. The former is more commonly seen. In about 10% of times, it can present as a unilocular radiolucency simulating a residual cyst, periapical, primordial cyst or Odontogenic keratocyst (OKC). Radiographically, it is unilocular and corticated radiolucency and at times, the margins are scalloped, simulating an OKC. One study showed a 35% recurrence rate after four years of the initial treatment. Patients should be placed on follow-up for more than five years. The radiographic findings of this case are consistent with a plexiform unicystic ameloblastoma. Neither the age of the patient or the histology is supportive of such diagnosis.

4. Glandular Odontogenic Cyst

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Glandular Odontogenic cyst is a developmental cyst of tooth origin characterized by unusual lining epithelium and occasional aggressive behavior. The uniqueness of this cyst is in the histology where the lining epithelium is stratified squamous in type, but covered by cuboidal or columnar cells (sometimes ciliated) interspersed with microcystic spaces simulating salivary gland ducts (but not true salivary gland ducts), thus the name “glandular.” It is a rare cyst and, though mostly inert, it can sometimes be aggressive in behavior (10). Because it occurs in association with teeth, it is believed to be of tooth origin and not of salivary gland origin. GOC was first described in 1987 and was initially called sialodontogenic cyst, a term later evolved to GOC since it is not of salivary gland origin (10-11). It is more common in adults average age 49, with slight male predominance. It has however been reported in all age ranges including teen-agers. It occurs three times as often in the mandible as in the maxilla, especially in the anterior maxilla. Radiographically, they present as unilocular slightly more commonly and sometimes as multilocular radiolucencies (10-12). The multilocular GOCs tend to recur more than the unilocular. These lesions can grow to large sizes (the majority of cases) and can perforate bone similar to the behavior of Odontogenic Keratocyst, a known aggressive cyst of tooth origin. Like OKCs, the GOCs can be aggressive in terms of bone destruction and recurrence rate (11). Histologically, GOC has features that can overlap with a dentigerous cyst with mucous cell metaplasia, with botryoid Odontogenic cyst and at times with low-grade intra-osseous mucoepidermoid carcinoma. Treatment depends on the size and the radiographic features. Enucleation and curettage have been successfully used with the smaller and unilocular radiolucent lesions, while en bloc resection is used with the larger and more multilocular lesions since they tend to behave more aggressively (10-12). Some are treated with a combination of curettage and carnoy’s or liquid nitrogen cauterization. The recurrence rate ranges between 21-55%. Enucleation and curettage alone carry a high recurrence rate of 25%. Marsupialization has been successfully used; one case the decompression was continued for two years. It showed gradual reduction of the size of the cavity bone fill and reservation of the contour of the maxillary sinus walls.


Under general anesthesia, all four third molars were removed and the area of tooth # 16 was thoroughly enucleated. Post-op medications included dexacort 8 mgX3 IV, zantac 50 mgX2 IV and augmentin 1 gram X3 IV. He had post-operative swelling and trismus which resolved in one week. He demonstrated good healing and normal recovery. Five months follow-up visit demonstrated complete healing.


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