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Malignant Ameloblastoma and Ameloblastic Carcinoma

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Metastasizing Malignant Ameloblastoma and Ameloblatic Carcinoma: Introduction, Clinical features, Radiology, Histopathology and Treatment

Author: Sanketh DS, MDS

Ameloblastoma is considered to be a benign odontogenic tumor that is locally aggressive with a high recurrence rate. This tumor however has two malignant counterparts called metastasizing malignant ameloblastoma and ameloblastic carcinoma, two very rare entities.

METASTASIZING MALIGNANT AMELOBLASTOMA (MMA) AND AMELOBLASTIC CARCINOMA

Introduction

Metastasizing malignant ameloblastoma(MMA) is that ameloblastoma that metastasizes, most often to the lungs (80%).

However, it has to be noted that, both the primary tumor and metastatic deposits of the tumor show the same histopathologic features of conventional solid ameloblastoma without any features of malignancy.

Other sites of metastases that have been reported are bones like skull & vertebrae and cervical lymph nodes.

Ameloblastic carcinoma on the other hand, is a malignant tumor where both the primary tumor and the metastatic deposits of the tumor, to an extent, resemble conventional ameloblastoma histopathologically, and also clearly exhibits malignant cytological features.

This tumor usually has a local aggressive clinical course and may show metastasis to the lungs, cervical lymph nodes and other distant sites.

If AC arises from existing benign ameloblastoma, it is called carcinoma ex ameloblastoma. In such cases either the conventional ameloblastoma slowly over time becomes AC or ameloblastic carcinoma may arise as a recurrent lesion after treatment of a conventional ameloblastoma. AC arising with no evidence of previous conventional ameloblastoma is called de novo AC.

METASTASIZING MALIGNANT AMELOBLASTOMA (MMA)

Clinical features, radiology and histopathology

Malignant ameloblastomas are very rare and have been reported in patients with mean age of 30 years and have no gender predilection.  The primary tumor of malignant ameloblastoma is indistinguishable from conventional ameloblastoma and occurs most commonly in the mandible. Also, it radiologically shows no difference from the benign tumor. Interestingly, most of the malignant ameloblastomas show a plexiform pattern under the microscope. Unfortunately, there is no way to know, if an ameloblastoma might potentially be a metastasizing malignant ameloblastoma, until it has metastasized.

Prognosis and Treatment

The prognosis for the lesion is poor and is best treated with surgery. If lungs are involved, lobectomy is done and if cervical lymph nodes are involved, the tumor is managed by neck dissection.

AMELOBLASTIC CARCINOMA (AC)

Clinical and Radiologic features

Clinically, AC is reported to occur in the elderly usually in the sixth decade. The lesion’s clinical behaviour is similar to conventional ameloblastoma, except that it may in addition show rapid growth and paraesthesia. Radiographic findings are also similar to its benign counterpart, although it may sometimes show ill-defined radiolucencies and pathologic fractures.

Histopathology

Under the microscope, histopathology resembles ameloblastoma but shows cytologic atypia. The peripheral cuboidal cells are hyperplastic and stellate reticulum like cells may become polygonal, squamoid or basaloid with hyperchromatic and pleomorphic nuclei. Mitotic figures, keratin pearls and necrosis may also be observed.

Prognosis and Treatment

Ameloblastic carcinoma shows a very aggressive clinical course and radical surgery with neck dissection is the treatment of choice. Recurrence is common and metastasis may occur commonly to the lungs.

REFERENCES

Reichart PA,  Philipsen HP. Odontogenic tumors and allied lesions. Quintessence Publishing;2004. 

Neville BW, Damm DD, Allen CM, Chi A. Oral and Maxillofacial Pathology. South Asian ed. Elsevier; 2016.

Rajendran R, Sivapathasundaram B. Shafer’s Textbook of Oral Pathology. 8th ed. Elsevier; 2016.

OTHER (HACKDENTISTRY) PRACTICE/STUDY RESOURCES

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