Unicystic ameloblastoma: a case of mistaken identity

I was astonished to find a case report (Bisinelli JC, Ioshii S, Retamoso LB, Moysés ST, Moysés SJ, Tanaka OM. Conservative treatment of unicystic ameloblastoma. Am J Orthod Dentofacial Orthop 2010;137:396-400) in the “Clinician’s corner” of the March issue. This article slipped through the review process despite a serious diagnostic error in surgical pathology.

Although one is always at a disadvantage in viewing only photomicrographs rather than the actual slides, Figure 2, C and D , clearly indicates that the lesion is, in fact, an example of adenomatoid odontogenic tumor (AOT) and not unicystic ameloblastoma (UA). It is curious that the figure legends and described histologic findings are much more suggestive of AOT than of UA. The radiographic picture of a well-corticated, pericoronal radiolucency extending apically beyond the crown (Fig 1) and containing small radiopacities (Fig 2, B ) is also typical of AOT, but it is not characteristic of dentigerous cysts. Moreover, the operative findings, “The lesion had an evident cleavage plane . . . It came away from the bone tissue easily,” appear to be equally if not more applicable to AOT than to ameloblastoma.

Except for the controversial histologic subtype of ameloblastoma reported in the literature under the name “adenoid ameloblastoma,” there is no real differential diagnostic alternative for AOT. Because odontogenic tumors might not be seen routinely, and their histologic classification can be overly complex, a general pathologist with limited experience in evaluating jaw specimens appropriately places ameloblastoma at the head of the differential diagnosis. In addition, AOT rarely occurs in the posterior mandible, making its diagnosis at that site unusual from the onset. As emphasized in the recent literature, the diagnosis and classification of odontogenic tumors might pose the greatest diagnostic challenge for general surgical pathologists. A prime example of this problem is indeed this article.

A diagnosis of ameloblastoma will alert the oral surgeon to aggressively curette the bone cavity or to even plan resection with wide margins. Although there is still a feeling that UA is an inherently innocuous lesion, its recurrence rate is similar to other types of ameloblastoma after simple enucleation. Also, UA, when it does recur, has a potential risk of evolving to a conventional infiltrating ameloblastoma. In marked contrast, AOT always responds well to conservative enucleation. Even in AOTs that were incompletely removed, there has been no recurrence in any of the follow-up cases. Among more than 1082 reported cases of AOT, there have been only 2 convincing examples with recurrence. Because of its completely benign nature, retreatment of recurrent AOT never becomes problematic. Although not considered an optimal therapy, an unerupted or impacted tooth associated with AOT can be brought into its proper position either orthodontically or surgically after subtotal excision of the tumor. In certain cases, spontaneous eruption can also be expected. Given that the histologic diagnosis has a direct impact on treatment and prognosis, the biggest threat to a patient with AOT is to have it misdiagnosed as ameloblastoma. Fortunately, both initial overtreatment and unnecessary retreatment were avoided. Surgeons and pathologists who are familiar with AOT will assume nothing will happen to their lesion postoperatively.

I fear that the article by Bisinelli et al might have the adverse potential of promoting inappropriate undertreatment of patients with UA. The article should be retracted and an explanation published. Considering the fact that AOT enclosing the lower third molar is exceptional, with only 4 unequivocal cases in the literature, the lesion is rare enough to republish the article as a “nonclassic” example.

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Apr 13, 2017 | Posted by in Orthodontics | Comments Off on Unicystic ameloblastoma: a case of mistaken identity
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