(1) Becario F.P.D.I.
(2) Profesor Asociado de Cirugía Bucal
(3) Profesor Titular de Cirugía Bucal. Departamento de Estomatología. Facultad de Odontología. Universidad de Sevilla

Correspondencia / Address:
Daniel Torres Lagares
C/ Sta Mª Valverde 2 3ºC
41008 Sevilla
Tlfno: 661 336 740
Fax 954 481 129
E-mail: danieltl@us.es

Recibido / Received: 1-02-2004 Aceptado / Accepted: 30-05-2004

Of all swellings of the oral cavity, 9% are odontogenic tumours, and within this group, ameloblastoma accounts for 1% of lesions (1-4). The WHO defines it as a locally-invasive polymorphic neoplasia that often has a follicular or plexiform pattern in a fibrous stroma. Its behaviour has been described as being benign but locally aggressive (5,6).

It localises to the maxilla in 20% of cases, most often in the canine and antral regions. In the mandible (80% of ameloblastomas), 70% are located in the area of the molars or the ascending ramus, 20% in the premolar region, and 10% in the anterior region (5). They are usually diagnosed between the fourth and fifth decades of life, except in the case of the unicystic variety, which is diagnosed between the ages of 20 and 30 years, with no gender predilection. About 10-15% of the tumours are associated with a non-erupted tooth (7). There are practically no symptoms except the occurrence of swelling in most cases. However, it is still infiltrative in character in terms of local malignant behaviour.

Ameloblastoma is observed as a radiolucent area, which may present in three different patterns. The most common form is the multilocular with various cysts that are in groups or separated by osseous reinforced septa (soap bubble appearance). Another image we sometimes see is a beehive pattern, this being the second most common type. A third radiographic manifestation, which is very important in terms of a differential diagnosis, is the unilocular form. In choosing a treatment for ameloblastomas, the clinical type (solid, multicystic, unicystic, peripheral), localisation, size of the tumour, and age of the patient should be assessed. Resection should be as wide as possible to include healthy tissue, since recurrence is fairly common with this disease (8-10).

Articles have recently been published with the purpose of providing updated knowledge and therapeutic approaches related to ameloblastoma. Of significance among these is the work of Reichart et al. (11), which has prompted the appearance of other publications criticising, supporting, or completing their work. The aim of this article is to review the concepts that have been published recently and assess their influence on the clinical attitude taken when facing this pathology, using our experience with ameloblastoma as a starting point to illustrate this discussion.

CLINICAL CASES

We present six cases of ameloblastoma treated during the period of January 1995 to December 2001 in the Maxillofacial Surgery Service of the "Virgen del Rocío" Hospital in Seville (Table 1).

All cases involved mandibular localisation. The most commonly-affected areas were the body of the mandible (four cases) with or without involvement of surrounding areas, followed by the symphysis (one case), and the angle of the mandible (one case). In terms of gender, females outnumbered males by a 2:1 ratio. Mean age of the patients was 42.3 years. The youngest individual was 25 years old, and the oldest was 65 years old.

The follow-up period was variable between patients, ranging from 1 year 7 months to 5 years 11 months, with a mean of 4 years 8 months. None of the patients has experienced recurrence of the disease. The mean size of the lesion was 2.5x2.25cm, with the largest being 4x3cm and the smallest 1.5x1cm.

Case 1.- Woman, 65 years old, presenting for a tumour localised to the horizontal ramus of the mandible extending to the incisors (Figure 1). The lesion was resected, preserving the base of the mandible, and extraction of 41, 42, and 43 was performed. An anatomic pathology analysis indicated the presence of a follicular and acanthomatous ameloblastoma measuring 1x0.7cm.

Case 2.- Woman, 59 years old, with a history of chronic bronchitis, hypertension under treatment, and tonsillectomy. She was referred by her dentist who a marked swelling in the mental region detected two months previously, and observed on radiographic examination a unilocular radiolucent lesion extending from 35 to 45 (Figure 2). Intervention under general anaesthesia was prepared, and an intraoperative biopsy was taken, which confirmed the presence of a cystic ameloblastoma. Surgical excision of the lesion, peripheral osteotomy, and extraction of 41 and 42 were performed.

Case 3.- Woman, 33 years old, presented with a mass in the area of the right first lower molar (Figure 3). The patient had undergone intervention for a residual inflammatory cyst in the same area 8 years previously. A medullary and vestibular cortical bone biopsy was taken at the level of 46, which yielded a diagnosis of cystic acanthomatous ameloblastoma. It was elected to perform curettage of the lesion and drilling of the perilesional bone. The osseous cavity was then filled with Medpore® (expanded porous polyethylene). A few months later, a foreign body reaction occurred, and the rejected material had to be removed.

Case 4.- Woman, 42 years old, presented with a locally-expansive osteolytic lesion in the body and angle of the mandible, which involved the ascending ramus and appeared unilocular and ovoid (2.7x3.5 cm) and well delimited (Figure 4). It extended from the beginning of the inferior dental canal to the first molar that was present, 48, the distal root of which had been partially resorbed. A cystectomy with intraoperative biopsy was performed, which confirmed the presence of ameloblastoma in the cystic wall. Extraction of 48 was also performed. Upon eruption, 48 had resorbed the entire distal root of 47. Therefore, because of the grave prognosis for that tooth, it was also extracted at that time.

Case 5.- Male, 25 years old, presented with haemorrhagic, painful swelling at the level of the right retromolar trigone. Following a biopsy of the lesion, ameloblastoma was diagnosed. On radiography, a 2x3 cm lesion was observed, which involved the lower third molar (Figure 5). Treatment consisted of extraction of 48 and osteotomy of the angle of the mandible, preserving the basal cortex. The anatomic pathology analysis reported ameloblastoma infiltrating and ulcerating the gingival mucosa.

Case 6.- Woman, 30 years old, smoking 30 cigarettes per day, drinking alcohol on weekends, and allergic to acetylsalicylic acid presented with swelling at the level of the angle of the left mandible (Figure 6). Radiographic examination revealed a multilocular lesion measuring 4x3 cm, involving a wisdom tooth, and extending to the premolar area. With the patient under general anaesthesia, an intraoperative biopsy was taken, which confirmed the presence of a cystic ameloblastoma. The tumour was resected via the intraoral approach and the osseous cavity was drilled.

DISCUSSION

In our small sample, all lesions were located in the mandible. This is the most common localisation (12), while the rate of occurrence of ameloblastoma in the maxilla is lower. In terms of age, our patients fall within the age ranges reported in the literature as standard for this type of pathology (13). Most authors do not report differences in gender, though the majority of these patients may be male (14,15). In terms of clinical presentation, typical findings with this disease include swelling in all cases with the occurrence of other incidents (haemorrhage, pain, etc.) (15).

Although in some of our cases, the follow-up period was short, in four of our patients, it lasted up to five years or more, and in only one case was it less than three years. For this reason, we believe the data on recurrence rates are valid and should be considered. Three types of ameloblastoma have classically been described: solid or multicystic, unicystic, and peripheral. It appears that Melrose was correct in the proposal to group the two forms from the first group under the designation of infiltrative ameloblastoma (16), since that is their primary characteristic, which has determined the need for resection of this type of ameloblastoma with a safety margin of 1-2cm in width (17).

The peripheral ameloblastoma is confined within the gums or alveolar mucosa, and is therefore not the subject of this discussion since none of our cases were of this type. Unicystic ameloblastoma is a form that was described in 1977 by Robinson and Martínez and has been characterised (18) by its histology and its presentation at an earlier age than infiltrative ameloblastoma (20-30 vs. 30-50 years) (19) as well as its capacity for recurrence in the face of conservative treatment, which is lower than the latter (10-20% vs. 45%) (8-10,20).

But even within the group of unicystic ameloblastomas, there are exceptions. Melrose proposed three possible origins of the unicystic ameloblastomas. When it originates from an infiltrative ameloblastoma, treatment should be more aggressive (16,21). Other authors have developed distinct classifications at the histological level, concluding that when a unicystic ameloblastoma displays intramural localisation of growth, treatment should be equally aggressive as in the case of infiltrative ameloblastoma (13,18,21). It cannot currently be concluded that these two groups are identical, although Melrose has proposed the revision of the concept of the unicystic ameloblastoma, specifically to attempt to distinguish forms with different biological behaviour (16).

To this end, attempts have been made to use different markers to differentiate the type of ameloblastoma, though there have been no encouraging results as of yet (22,23). It is therefore of vital importance to consider the differentiating characteristics of these entities, particularly in terms of patient age and radiographic appearance of the lesion (24).

According to recent articles published on this subject (15,25), unilocular or multilocular images may be seen with both types of ameloblastoma. However, with unicystic ameloblastomas, it is more common to see a unilocular image, while a multilocular image is more common with the infiltrative form. There are opinions that contradict this claim (24) and suggest that unicystic ameloblastomas presenting with multilocularity would be due to lesions with imprecise margins, an idea that was previously presented by Ackerman et al. (21). We do not support this theory since two of the three cystic ameloblastomas we presented occurred in patients with multilocular images with fairly well-defined borders (cases 3 and 6).

However, in the case of a unilocular radiographic image, we advocate conservative treatment (cases 2 and 4), without the risk of dealing with an infiltrative ameloblastoma, as occurred in case 4. In the case of a multilocular image, we should seek the clearest possible evidence of osseous trabeculation, which can orient us toward infiltrative ameloblastoma. We should also consider localisation and extent of the lesion. In case 1, we saw a multilocular image with the appearance of trabeculation, and the patient was treated by means of resection preserving the base. In case 6, in which osseous trabeculation could not be compatible with a single space-occupying lesion and the extent was greater and more critical, we opted for conservative treatment. A cystic ameloblastoma was later diagnosed.

This approach of avoiding aggressive treatment when possible even at the risk of increasing the likelihood of recurrence is reflected in the literature, particularly in growing patients in which maintenance of continuity of the mandibular base allows for correct development of the same (26,27). Except in cases that are exceptions to this type, we advocate resection of the lesion with safety margins of 2cm, as we performed in case 5.

In terms of extraction of teeth near or adjacent to the lesion, extraction is indicated for teeth that are within the safety margins of resection around the lesion. The conservation of teeth in the alveolar bone surrounding the lesion presents a risk for later recurrence. Furthermore, it is obvious that a peripheral osteotomy, however small it may be, could affect the viability of adjacent teeth. For this reason, the prognosis for each tooth should be analysed for each case. Following these criteria, the teeth described in clinical cases 2, 3, 4, and 6 were extracted. Moreover, extraction of the lower second molar in clinical case 4 was indicated due to its grave prognosis.

In situations where circumstances point to a tumour with an increased infiltrative potential, as in case 5 (multicystic type, mucosal erosion, significant clinical signs), more extensive extraction would be indicated.

Beyond surgery, there are other alternative therapies for ameloblastoma, such as radiation therapy. There is published evidence on the usefulness of radiation therapy in the treatment of extraosseous ameloblastomas (28-30). However, the tumour was never controlled with this method of therapy. It has not been possible to provoke the occurrence of ameloblastoma in animals, and the closest available model is the so-called acanthomatous epulis in dogs (31,32), which becomes malignant after application of radiation therapy. For this reason, the use of this method is unacceptable in the treatment of ameloblastoma in humans (33).

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