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HISTOLOGICAL TRANSFORMATION IN RECURRENT AMELOBLASTOMA
Ivanov A.,
Department of General and Clinical Pathology, Medical University of Plovdiv, Bulgaria Department of Clinical Pathology, UMHAT "Sveti Georgi" - Plovdiv, Bulgaria
Ivanov G.,
Department of General and Clinical Pathology, Medical University of Plovdiv, Bulgaria Department of Clinical Pathology, UMHAT "Sveti Georgi" - Plovdiv, Bulgaria
Bivolarski I.,
Department of General and Clinical Pathology, Medical University of Plovdiv, Bulgaria Popivanova M., Department of General and Clinical Pathology, Medical University of Plovdiv, Bulgaria Department of Clinical Pathology, UMHAT "Sveti Georgi" - Plovdiv, Bulgaria
Tomova M.
Department of Clinical Pathology, UMHAT "Sveti Georgi" - Plovdiv, Bulgaria
ABSTRACT
Ameloblastoma is a benign tumour with a slow, locally aggressive growth and high recurrence rate. Macro-scopically it is a unicystic or multicystic tumour formation. The histological variants of ameloblastoma are - fol-licular, plexiform, basal cell, acanthomatous, granular and desmoplastic, the latter being the most commonly diagnosed recurring type. We present a case of a 79-year-old woman, who, in the year 2000, was operated, due to a tumour formation, 6cm in diameter, of the mandible, that limited her mouth movement. In 2014 another operation was performed, due to the tumour reappearing and the defect was substituted with a metal plate. Contrary to the usual histological transformation diagnosed, the tumour from the first operation was defined as desmoplastic and from the second one - plexiform. We are discussing the differences between the two variants and the reasons for the histological transformation observed.
Keywords: plexiform ameloblastoma, desmoplastic ameloblastoma, recurrent ameloblastoma.
Introduction
Ameloblastoma is a benign tumour arising from the odontogenic epithelium. It has a relatively slow growth, but it's aggressive, destroying the adjacent bones and sometimes leading to facial deformities. What is characteristic about it is that even after surgical
removal it has the tendency to reappear [2]. It represents 1% of tumours in the oral cavity and around 10% of odontogenic ones. It occurs most often between the 3rd and 5th decades of life. Macroscopically it is a unicystic or multicystic tumour formation. The histologi-
cal variants of ameloblastoma are - follicular, plexi-form, basal cell, acanthomatous, granular and desmo-plastic [4], the latter being the most commonly diagnosed recurring type [1].
Case report
A 79-year-old woman was admitted in the Craniofacial surgical clinic in UMHAT "Sveti Georgi" - Plovdiv, in the year 2000. She complained of a painless lump in the mandible that limited the mouth from opening. The X-ray showed a tumour formation, 6cm in diameter. The clinical examination determined facial asymmetry from a focal oedema around the left section of the mandible. It limited the opening of the mouth. There was dilatation of the bone, more pronounced on the mucosal surface. Under general anaesthesia a surgical procedure was performed, consisting of total excision of the tumour tissue with a subsequent adaptation and a mucoperiosteal flap. A surgical drain was placed.
In 2014 the patient was admitted again in UMHAT "Sveti Georgi" - Plovdiv with a nodule-like dense formation in the area of the previous operation. The clinical examination found a pathological area with a firm-elastic consistency. A surgical resection of the alveolar ridge as well as the newly formed tumour mass was performed under general anaesthesia. The defect was replaced with a metal plate.
Material and metods
The tissue samples were fixated in 10% neutral formalin and embedded in paraffin. The cut sections were 4 |im thick and stained with hematoxylin and eosin (HE).
Results
The histological result from the first operation (back in the year 2000) is ameloblastoma, desmoplastic variant. The tumour parenchyma is composed of elongated tumour nests, comprised of epithelial cells, surrounded by a fibrotic stroma, with areas of hyaliniza-tion(fig. 1).
Fig. 1. Desmoplastic variant of ameloblastoma, H-E, magn.x100
The histological result from the second operation (2014) gives the diagnosis ameloblastoma, plexiform variant, comprised of anastomosing nests of odontogenic epithelial cells with a classic palisade arrangement at the periphery (fig. 2).
Fig. 2. Ameloblastoma, plexiform pattern, H-E, magn.x100
Discussion
Ameloblastoma is a recurring, locally aggressive tumour [2] with a high risk of malignant transformation (70%) and capable of metastasizing (2%). It represents 1% of all tumours of the oral cavity and 9%-11% of odontogenic ones. It is often diagnosed late, due to the slow growth and scarce symptoms. Etiopathogenet-ically, on a molecular level, the genetic factors that take part in the teeth development are connected to the appearance of ameloblastoma. An analysis of 34 different genes demonstrates 11 overexpressed and 23 underex-pressed ones. Some of the former include collagen type VIII, alfa 1 (COL8A1), macrophage elastase (MMP-12) and collagenase 3 (MMP-13). It has also been proven that the BRAF-mutations are found more frequently in the mandible, in younger patients [3]. This mutation correlates with some clinico-morphological specificities of the tumour - jaw localisation and age. Ameloblastomas highly express also MMP-1, MMP-2 h MMP-9 [5]. Changes in the complexes of matrix met-alloproteinases MMP- 14/MMP-2/TIMP2 have also been proven in different histological variants of ameloblastoma [6]. Local aggression of ameloblastomas is connected to the activity of MMP-2, that can degrade collagen type IV in the basement membrane [7]. The histological picture of vast stromal collagenization with hyalinosis is considered pathognomonic for desmo-plastic ameloblastoma [1].
Conclusion
The histological transformation in recurrent ame-loblastoma with the development of a new phenotype is connected to the change in tumour gene expression. The tumour variants are not of great prognostic importance, but the desmoplastic type is the far more common recurrent one, not plexiform, as it is in our case.
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