COM Oct. 2008 Diagnosis

Large and multilocular expansile radiolucency, right posterior mandible

Can you make the correct diagnosis?

This is a 46-year-old black female who was referred for evaluation of a right posterior mandiblular mass of unknown duration. A panoramic radiograph and CT scan revealed a large, impressively expansile, multilocular radiolucency involving the body of the mandible (Figures 1 & 2). The patient reported mild pain in the right side of the mandible. She also reported a feeling of swelling intra-orally.

1. Ameloblastoma

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Ameloblastoma is one of the most common benign neoplasms of odontogenic origin. It accounts for 11% of all odontogenic neoplasms/hamartomas. It is a slow-growing, persistent, and locally aggressive neoplasm of epithelial origin. It affects a wide range of age distribution but is mostly a disease of adults, at an average age of 33, with equal sex distribution. Reports from Africa and India show a male predilection; it also has a predilection for occurrence in black patients.

About 85% of ameloblastomas occur in the posterior mandible; most of these occur in the molar-ramus area, and some occur in the anterior mandible. About 15% occur in the maxilla, the vast majority of these in the posterior maxilla, in patients around the age of 60 and tend to have a worse prognosis than those of the mandible.

Ameloblastoma is characteristically expansile, radiolucent and multilocular in nature. However, it can be unilocular and associated with impacted teeth resembling a dentigerous cyst. The latter types of ameloblastoma are known to be less aggressive than the multilocular solid lesions. Three clinical types of ameloblastoma are described: the solid type (radiographically multilocular), the cystic type (radiographically unilocular and usually associated with an impacted tooth), and the peripheral type (soft tissue, usually gingival ameloblastoma). The present case is of the solid type and is multilocular in appearance.

Ameloblastoma, if not treated, can reach very large sizes, causing facial disfigurement. It loosens, displaces and resorbs adjacent teeth. With the exception of jaw expansion, it is usually asymptomatic unless infected, in which case it can be mildly painful. Parasthesia and anesthesia are extremely rare, unless the lesion is very large in size. Also, ameloblastoma tends to expand rather than perforate the cortical bone; if the latter occurs with extension into the adjacent soft tissue, it has a higher tendency for recurrence and therefore a worse prognosis than cases in which the ameloblastoma is completely encased by bone.

As mentioned above, three clinical types of ameloblastomas are described, the solid type being the most common. The solid type is treated with complete surgical removal with clean margins through resection or en bloc. Curettage is not recommended for the solid type because it is associated with a higher recurrence rate. Ameloblastoma has a good prognosis overall but is known to have a high recurrence rate, particularly in the posterior maxilla, from inadequate surgery (tumor extending to the surgical margins). Long-term follow-up is required. Recurrence is related to the treatment modality.


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2. Central giant cell granuloma (CGCG)

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The gender, the site and radiographic presentation are consistent with central giant cell granuloma. The histology, however, is not supportive of this diagnosis.

Central giant cell granuloma is a non-neoplastic condition that can occasionally behave in a very aggressive and expansile manner, destroying bone and displacing teeth. Over 60% of CGCG cases occur in patients younger than 30 years of age, with twice as many occurrences in females as in males. CGCG is classified into aggressive and non-aggressive types; the aggressive type tends to occur in younger patients and is known to cause disfiguration, especially after surgery. Over 70% of cases occur in the mandible anterior to the first molar tooth. This lesion has also been described in other cranio-facial and small bones such as those of the hands and feet.

The usual treatment for CGCG is surgery, ranging from curettage and en bloc to resection. The latter is used in aggressive and recurring cases. Treatment alternatives to surgery have emerged with successful results, including steroid injections, calcitonin injections, nasal spray, and interferon alfa-2a injections; these are administered 2-3 times per week for several months. The latter is the most expensive alternative treatment.

3. Odontogenic Myxoma

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The site, gender and the radiographic presentation are supportive of this condition. However, the histology is not supportive of it.

Odontogenic myxoma should not be mistaken for soft tissue myxoma, which is a relatively common lesion of the soft tissue. It is rare in the mouth; it occurs more commonly in areas such as the heart. When it does occur in the mouth, odontogenic myxoma occurs in the jaw bones, usually in the tooth-bearing areas of the jaw. It is an uncommon, benign, but locally aggressive neoplasm. Nearly all cases so far have been described in the jaw bones. Therefore, it is of tooth origin, and is believed to be from the mesenchymal portion of a tooth germ, most likely of the dental papilla. It has the potential for extensive bony destruction and extension into the surrounding structures. It is less common than odontomas and ameloblastomas, constituting around 17% of all odontogenic tumors. For that reason, a pathologist who is not familiar with the histology of a tooth germ can mistake a myxoid dental follicle for an odontogenic myxoma. Almost 75% of odontogenic myxomas occur in patients around 23-30 years of age with a slight female predilection (1:1.5 male-to-female ratio). It rarely occurs in patients over 50 or under 10 years of age. It occurs almost equally in the maxilla and mandible with a slight predilection for the posterior mandible. A few cases are described in the ramus and condyle, non-tooth bearing areas.

Odontogenic myxoma is slow-growing, persistent and destructive. Most cases are expansile and can displace and resorb teeth. In the maxilla, they usually invade the maxillary sinuses and, in rare cases, cross the midline to the opposing sinus. Radiographically, the majority present as expansile and multilocular, though some are unilocular with or without scalloped borders, and rare cases present with a diffuse and mottled appearance which can be mistaken for a malignant neoplasm. Grossly, this lesion is gelatinous in nature, making curettage alone difficult; the more fibrotic odontogenic myxomas (also known as odontogenic myxofibroma or fibromyxoma) have more body and are easier to curette. Histologically, it is made up of loose and delicate fibrous connective tissue. The fibroblasts are stellate and are suspended on a delicate network of collagen fibrils.

The treatment of choice is surgical excision ranging from segmental resection with clear bony margins of up 1.5cm to prevent recurrence of the neoplasm. Curettage with and without cauterization is used for treatment, but is associated with a high recurrence rate. Reconstruction can be immediate or delayed, and can include an autologous bone graft from the anterior or posterior iliac crest. Fibula-free vascular osteocutaneous bone graft is another reconstructive modality, as is distraction osteogenesis. The patient is usually hospitalized for a short period of time following resection and placed on intravenous antibiotics while in the hospital to prevent secondary infection of the surgical site, especially if immediate bone grafting is accomplished. Immediate postoperative follow up is weekly for approximately one month, then monthly for the next five months and twice a year for the next five years.