The ameloblastoma is a benign tumour of jawbones with locally invasive capacity. It is a true neoplasm of enamel-organ type of tissue which does not undergo differentiation to the point of enamel formation. Ameloblastoma is the best-known odontogenic tumour, very often used as the norm by which other odontogenic tumours are judged. Its unique clinical and pathologic behaviour was described by Robinson (1937) as being “usually unicentric, non-functional, intermittent in growth, anatomically benign and clinically persistent”.
Guzack in 1826 reported a tumour of the jaw, which may be the first recorded instance of an ameloblastoma. But the credit of reporting the first neoplasm of this nature goes to Broca (1968). The first detailed description of ameloblastoma was given by Falkson in 1879.
The name ‘adamantine epithelioma’ was introduced by Malassez (1885) and subsequently many synonyms like adamantinoma, adamantinoblastoma, epithelial odontoma and multilocular cyst, were used to describe the lesion. The name ameloblastoma was suggested by Churchill (1920) and Ivy & Churchill (1930).
A full account of historical aspect of ameloblastoma was detailed by Baden in 1965.
The literature consists mainly of many single-case reports and small series. A few extensive series with statistics of age, sex, race, site of growth etc. include that of Robinson (1937) who reported 379 cases, and that of Small and Waldron (1955) who listed 1036 cases including those of Robinson. More recent series include those of Mehlisch et al (Mayo Clinic Review-1972 – 126 cases), Sehdev et al (1974 – 92 cases), Regezi et al (1978 – 78 cases)and Ademola et al (1993 – 315 cases). The last mentioned series include the cases of Mosadoni (1975 – 29 cases), Doranola et al (1975 – 16 cases) and Adekeye (1980 – 109 cases).
Ameloblastoma is said to account for about 1% of all oral tumours. Many tumour registries list it as the most prevalent odontogenic tumour, but because this data is based on biopsied lesions and because innocuous lesions like compound odontomas are often not removed, this data may not reflect the true frequency.
Small and Waldron (1955) found the average age of patients at the time of reporting to hospital to be 38.9 years, but the average age at the time of discovery of the lesion was 32.7 years. All series have reported that more than half of all the cases was reported in patients in the age-group of 20 to 50 years. But the tumour can occur in any age, and have been reported in young children (Young & Robinson – 1962 and Lewin – 1966). The oldest patients have been over 80 years of age.
The occurrence of ameloblastoma is approximately equally divided between the sexes. Some authors have reported a slight preponderance in males, but the difference is considered insignificant.
The tumour is thought to be more frequent in Africans than in white race (Kegel). In the U. S. and in Denmark, it accounts for 0.07% and 1% respectively of all oral tumours. In Africa, this figure is 3.6%. But this data is difficult to interpret because of the lack of standardised data collection procedures in third world countries and because many people do not report for treatment until the disease becomes troublesome. This has prompted many authors to believe that the concept of higher incidence of the tumour in black races cannot be supported. However, a more recent report by Shear and Singh (19780 from South Africa showed that the incidence of ameloblastoma is very much higher in blacks than in whites. Chung et al (1969) reported that tumours of jaws including ameloblastoma have a higher incidence in Korea.
About 80% of the tumours occur in the mandible. This figure was as high as 99.1% in one case (Adekeye – 1980). Nearly three-fourth of the mandibular tumours occur in the molar-ramus area in almost all the series. But in Nigerians (Akinosi and William – 1969) and in Indians (Potdar – 1969), a predeliction to mandibular symphysis was noted, but by contrast, Adekeye noted a preponderance in the horizontal ramus of the mandible. The less common lesions of the maxilla mainly occur in the molar area, antrum and the floor of the nose. Lesions have even been described to occur in the tuberosity area, zygomatic bone and base of skull.
Very little is known about the causative factors. Robinson in 1937 noted that in one-third of the cases, there was a history of trauma, oral infection or impacted third molars. But considering that these factors are common in normal individuals also, this data is not considered significant.
Dietary deficiency has been considered a possible factor. An irregularity in the ameloblastic layer of enamel was seen in pigs maintained on rachitogenic (Vit. D deficient) diet, but no unequivocal conclusion could be made.
Ameloblastoma-like tumours could be produced in mice by injection of polyoma virus, and particles with characteristics of paramyxovirus have been noticed in ameloblastoma. Similar tumours have also been produced in animals by the injection of nitrosureas.
The earlier workers themselves had noted the resemblance of the tumour epithelium to the normal odontogenic apparatus and had suggested that the neoplasm was derived from a portion of this apparatus or from cells potentially capable of forming dental tissue, but the precise point of origin is unknown. Malassez had noted small collection of epithelial cells near the roots of teeth and suggested that ‘adamanto-epithelioma’ arose from these cells.
At present, most authorities consider the tumour to be of varied origin. It conceivably may be derived from
1. Enamel organ
Early histologists considered ameloblastoma to be of origin from enamel organ due to the obvious histologic similarities. The main contesting point (Bland & Sutton – 1922) is that the age of onset (approx. 32 years) belies this concept. But considering the early symptomless character, slow growth of the tumour and the fact that it is seen most often in the region of the mandible where supernumerary tooth germs are generally present, it is suggested that the cells of enamel organ give rise to this neoplasm.
2. Cell rests of enamel organ
After the tooth buds have separated from dental lamina, that structure regresse4s and disappears, although isolated groups of epithelial cells remain in the connective tissue as rests of Serres. These cell rests in the periodontal membrane were first demonstrated by Malassez, who along with many others suggested that ameloblastoma originated from these rests.
3. Basal cells of oral mucosa
Many histologists have noted the connection of ameloblastoma with oral mucosa but it is generally agreed that the tumour probably grew up from beneath and then established a connection with the surface epithelium. That the tumour is essentially intra-osseous in origin lends credence to this theory, but some authors do raise the question of mucosal origin, and in line with this concept, some have considered the tumour to be a type of basal cell carcinoma. There are striking histological similarities between the two. They also resemble each other in their clinical growth (slow growth and local invasiveness).
4. Cysts of dental origin
A number of reports have showed lesions which appeared clinically and radiographically as ordinary odontogenic cysts but was proved in fact to be ameloblastoma. Cahn (1933) argued that dentigerous cyst should be considered a potential ameloblastoma. Shteyer et al has reviewed the concerned literature. In a review of 641 cases by Stanley and Diehl, 17% of the cases were definitely associated with an impacted tooth or a dentigerous cyst. So it is suggested that ameloblastoma arises not infrequently from dentigerous cyst.
5. Heterotopic epithelium
Lesions histologically similar to ameloblastomas have been discovered in sites other than jaws like the pituitary and long bones. These lesions are discussed separately.
The typical ameloblastoma begins insidiously as a central lesion of bone, which is slowly destructive but tends to expand the bone rather than perforate it. The tumour is seldom painful unless secondarily infected and shows few or no symptoms in the early stages. Quite frequently, it is first noticed during routine dental examination.
Later there is a gradually increasing facial deformity. As the lesion grows in size, an ovoid or fusiform swelling is noted, which is hard but not tender. Because of the slow growth of the tumour, it is probable that even in apparently early cases, it has already been present for a significant time before its discovery. In the absence of treatment, the tumour continues to enlarge in size and the surrounding bone becomes thin and fluctuence or ‘egg-shell crackling’ may be elicited. Perforation of bone is a very late feature.
Teeth in the area may become loosened and usually many teeth are extracted before the tumour is discovered. Resorption of roots of teeth is an extremely common finding.
In the maxilla, the sinus becomes involved and the tumour may extend into the orbit or nasopharynx.
In lesser-developed countries, it has been common to see the tumours having grown to enormous size by the time treatment is sought. Another presentation is a history of a series of operations in the jaw for a ‘cyst’ or an ‘abscess’ carried out over a period of years with recurrence after each one.
The ameloblastoma has been described classically as a multilocular cyst of the jaw. The tumour exhibits a compartmental appearance with septa of bone extending into the radiolucent tumour mass.
The radiograph may present either a polycystic (multilocular) or a monocystic (unilocular) appearance. In the polycystic type, the bone is replaced by a number of small well-defined radiolucent areas, giving the whole lesion a ‘honey-comb’ or ‘soap-bubble’ appearance and at the same time, the jaw is expanded. In the unilocular type, there is a well-defined area of radiolucency resembling a single cyst. It is not uncommon to misdiagnose an ameloblastoma as a dentigerous cyst or a radicular cyst because of its positional relationship with teeth.
Other characteristics like thinning of cortical plate and root resorption are also observed radiographically.
Biopsy is the removal of tissue from a living individual for diagnostic examination. It is the least equivalent (most diagnostic) of all diagnostic procedures and should be carried out whenever a definitive diagnosis cannot be obtained using less invasive methods. Aspiration or incisional/excisional biopsy may be performed for hard- tissue lesions like ameloblastoma.
Any radiolucent lesion that requires biopsy should undergo aspiration biopsy before surgical exploration, to rule out vascular lesions and to obtain a more confirmative clinical diagnosis.
Most lesions of the hard tissue have to be approached through a mucoperiosteal flap. Lesions totally within the jaw require the use of a cortical window, which is cut using burs or chisels. A trephine bur may also be used. If the cortex is resorbed, the opening is made larger using rongeurs and burs. The specimen is removed as a V-shaped section and the remaining lesion is left undisturbed. Then the flap is closed.
The specimen is immediately placed in 10% formalin solution. The tissue must be totally immersed in the solution. The biopsy data sheet is filled, mentioning the clinical and radiological aspects in detail. The specimen and the data sheet are sent to a pathologist who has expertise in oral pathology.
The specimen as received by the pathologist consists of the tumour with a surrounding margin of normal bone or of the completely resected tumour-bearing area of the jaw. The tumour presents as a cylindrical or fusiform swelling which expands the bone. If perforation has occurred, the tumour extends to the soft tissues.
On section, the tumour appears as a greyish-yellow mass replacing the bone. There may be cystic spaces, particularly in advanced cases. The cysts have a more or less smooth epithelial lining and contents vary from straw-coloured fluid to semisolid materials. There may be minute nodules of growth protruding from an otherwise smooth lining. This is true in the case of unicystic ameloblastoma also. One or more teeth may be involved in the tumour.
The ameloblastoma closely resembles the enamel organ. The typical multilocular ameloblastoma has two main histological patterns – follicular and plexiform. The unicystic variety shows a different histologic picture from these two.
Follicular (simple) ameloblastoma
This is composed of many small discrete islands of the tumour consisting of a peripheral layer of cuboidal or columnar cells whose nuclei are generally well polarised. The cells resemble ameloblasts or pre-ameloblasts and shows fine cytoplasm or fine granulation in some cases. These enclose a central mass of polyhedral, loosely arranged cells resembling the stellate reticulum. Thus each islet resembles an enamel organ.
The tumour islets are separated from each other by a variable amount of connective tissue stroma that caries the blood vessels. The general resemblance of ameloblastoma to the normal enamel organ has also been emphasised in a number of histochemical and ultrastructural studies. But some workers have found that the enzyme activity is more similar to that squamous cell carcinoma.
Microcyst formation within the tumour follicle is a common occurrence. In some cases, the central stellate cells undergo degeneration. In other cases, the cyst formation is accompanied by well-marked cellular changes like swelling of cells and homogenisation of cytoplasm. The coalescence of small cysts to form larger ones is responsible in course of time for macroscopic cyst formation. Apart from a rare case of ‘odonto-ameloblastoma’, enamel is not found in the tumour.
The follicular type shows a large number of histologic variants like
- Acanthomatous ameloblastoma (Pindborg – 1970)
In this case, the cells occupying the central region undergo squamous metaplasia, sometimes with keratin formation.
- Granular cell ameloblastoma (McCallum et al – 1957, Mallick – 1957)
The cytoplasm of the central cells takes on a very coarse, granular, eosinophilic appearance. This character often extends to the peripheral cells as well. The cytoplasmic granules are eosinophilic and PAS positive. The ultrastructural studies (Tandler & Rossi – 1977) have shown that the granules represent lysosomal aggregates.
- Basal cell ameloblastoma
This variant resembles basal cell carcinoma of skin. The epithelial tumour cells are more primitive and less columnar, and are generally arranged in sheets.
- Spindle cell ameloblastoma
The central cells undergo metaplasia to spindle cells.
- Clear cell ameloblastoma (Waldron et al – 1985)
This tumour has histopathological characteristics of ameloblastoma but also shows clear cells. It closely resembles ameloblastic carcinoma. The more recent view (Gardner – 1993) is that they are different lesions and that the presence of clear cells are rare occurrences in both lesions.
- Ghost cell ameloblastoma
Some workers have demonstrated ‘ghost cells’ (degenerated empty cells) which could be differentiated from the ‘clear cells’ of Waldron.
- Desmoplastic ameloblastoma
A newly described variant, occurring predominantly in anterior maxilla, it shows the radiographic picture of a benign fibro-osseous lesion.
There is considerable controversy regarding the relationship of these histological variations to the aggressiveness of the tumour. But most studies in this direction remain inconclusive.
In this case, the tumour cells are arranged in irregular masses, or more frequently, as a network of interconnecting strands of cells. Each of these masses show a lining of columnar/cuboidal cells and a central mass of stellate reticulum like cells although the latter is much less prominent. Cyst formation is also seen in this type of growth.
First described by Robinson and Martinez (1977), the unicystic ameloblastoma resembles dentigerous, radicular or residual cyst clinically and radiographically. It is differentiated by one or more of these features (Ackerman-1988).
- Lining epithelium exhibiting early ameloblastomatous changes of cyst lining, as described by Vickers and Gorlin (1970). This variety is called mural ameloblastoma.
- Nodules of tumour projecting intraluminally. This type is mentioned as luminal/ intraluminal ameloblastoma.
- Ameloblatomatous lining epithelium proliferating into the connective tissue wall.
- Islands of ameloblastoma occurring isolated in the connective tissue wall.
The latter two types are includes in the group ‘invasive unicystic ameloblastoma’.
‘Plexiform unicystic ameloblastoma’ is the term used by Gardner (1970) to designate a plexiform type of epithelial proliferation occurring in the dentigerous cyst, which otherwise exhibit the usual histologic features of a dentigerous cyst.
Local spread and metastases
Ameloblastoma is a tumour that causes expansion of bone rather than destruction. At the same time, there is a certain amount of local invasion of the surrounding bone, though it is generally limited in extent. Compact bone forms a much more efficient barrier to invasion by ameloblastoma than does cancellous bone and because of this, the extent of tumour encroachment upon it is reflected reasonably accurately in the corresponding radiograph. Extension of tumour into the cancellous bone, on the other hand, is much less readily gauged, since neither the radiograph nor naked eye assessment at the time of operation can reveal the extent to which cancellous spaces have been infiltrated, since this process occurs well in advance of actual bone destruction, to the magnitude of several millimetres. Because of its tendency to infiltrate cancellous bone, the lesions of posterior maxilla, and rarely large mandibular tumours may in fact kill the patient by direct extension into the cranium.
However it is found that in the unilocular type of ameloblastoma, the infiltration into cancellous bone is minimal, if ever present.
There appears to be little correlation between the histological pattern in ameloblastoma and its clinical course. Ultrastructural and histochemical studies have been conducted by many authors for this purpose, but most studies remain inconclusive.
Regarding distant spread, ameloblastoma is rather like basal cell carcinoma, which means that metastatic dissemination of ameloblastoma is rare, but has been reported to occur. This brings us to two new terms – malignant ameloblastoma and ameloblastic carcinoma. These terms are often used for each other, and they continue to confuse clinicians even now.
As used by most investigators, malignant ameloblastoma is defined as the ameloblastoma that has been shown to metastasise. To qualify for this designation, the metastatic lesion must also be cytologically benign and must closely resemble the original lesion in the jaws histologically.
In early reviews by Small and Waldron, over 30 cases were collected from the literature in which metastatic deposits were reported to have occurred. On further review of them (Carr and Halpenin – 1968), many of them were found to be either cases of misdiagnosis or ones where the metastatic lesion could not be undoubtedly proven to have disseminated from the ameloblastoma. In those few cases where a metastasis of ameloblastoma has been accepted, the feature is a long standing disease, operated upon a number of times over the course of years, and finally presenting with metastatic deposits in the lungs (Vorzimer and Perla – 1932; Schweiter and Banfield – 1943).
The literature dealing with metastatic ameloblastoma was reviewed by Lee et al (1959). It has been argued that the demonstrable lung lesions are a result of aspiration implantation, although this is difficult to prove and unlikely considering the routine precaution taken to avoid such and occurrence. What lends credence to this argument are the history of previous surgeries and the fact metastases are usually found in sites where aspirated foreign bodies are usually found.
Though pulmonary metastases seem to be the usual form of dissemination, metastases have also been noted in other sites, such as cervical and media stinal lymph nodes, bone and liver, and other viscera. These are considered by some as result of haematogenous spread.
This is generally defined as that type of ameloblastoma in which there has been obvious histological malignant transformation of the epithelial component, and in which the tumour has behaved in malignant fashion so that the metastatic lesion do not have resemblance to the primary odontogenic tumour but to a less well-differentiated carcinoma
There seems to be difference of opinion in the relation of ameloblastic carcinoma to primary intra-osseous carcinoma of odontogenic origin. While the WHO publication (Pindborg –1971) classifies odontogenic carcinoma into malignant ameloblastoma, primary intra-osseous carcinoma and other carcinoma arising from odontogenic epithelium. But Elzay (1982) has liberalised this concept and classifies primary intra-osseous carcinoma into
- Those arising from odontogenic cysts
- Those arising from ameloblastoma (malignant ameloblastoma and ameloblastic carcinoma)
- Those arising de novo
Diagnosis of ameloblastoma
Non-neoplastic epithelial proliferation
While typical tumours present no problems in microscopic diagnosis, some difficulties may arise in cases of non-neoplastic epithelial proliferation, such as in the walls of odontogenic cysts.
Churchill (1938) has demonstrated that the walls of dentigerous cysts may show non-neoplastic proliferation comparable to the appearance of ameloblastoma and emphasised that the two lesions were separate entities. Again Vickers and Gorlin (1970) has shown that cells of mural ameloblastoma might flatten down by the pressure of cyst contents to look like a non-neoplastic proliferation. Close examination of the lesion considering the size of the cells, and shape and size of the nuclei, is essential to differentiate the two in certain cases
Relationship with dentigerous cyst
This is a controversial subject. The statement that ameloblastoma may arise in dentigerous cyst implies neoplastic change in an initially non-neoplastic lesion. A monocystic lesion with the clinical and radiographic characteristics of dentigerous cyst may prove histologically to be a simple cyst or an ameloblastoma. It is particularly necessary to make a thorough examination of the cyst wall with special attention to all mural nodules and thickenings.
From the treatment point of view, the histologic variations of ameloblastoma are not very significant, and the basic diagnosis of the tumour whether it is the typical multilocular type, unicystic type or peripheral (extra-osseous) type, is considered adequate. In all cases, the typical palisading, hyperchromatism, reversed polarity and vacuolisation of basal cells are present.
One potential error is confusing the acanthomatous pattern of ameloblastoma with squamous cell carcinoma. Here the basal cells should be looked for typical features of ameloblastoma, and squamous cells looked for signs of dysplasia.
The basal cell ameloblastoma is confused with basal cell carcinoma of skin and adenoid cystic carcinoma. The diagnostic problem of the latter occurs primarily in maxilla. The differential diagnoses of ameloblastoma exhibiting mucous cells or clear cells include muco-epidermoid carcinoma, renal cell carcinoma and various salivary gland tumours.
Other tumours that should be included in differential diagnosis include odontogenic ones like ameloblastic fibroma, squamous odontogenic tumour, calcifying odontogenic cyst and metastatic carcinoma.
Another potential misdiagnosis is the failure to recognise the ameloblastic carcinoma. This has the same histologic features as ameloblastoma, except that it exhibits dysplasia. Since it behaves like a carcinoma, it requires different treatment.
Before discussing management of ameloblastoma, it is important to mention two different lesions – extra-osseous ameloblastoma and extra-oral similar tumours.
Extra-osseous (peripheral ameloblastoma) is a tumour which histologically resembles the typical central or intra-osseous ameloblastoma, but which occurs in the soft tissue outside and overlying the alveolar bone. Although there were some earlier reports, Stanley and Krogh (1959) were the first to describe a peripheral ameloblastoma in the lingual surface of molar-premolar area of the mandible.
The peripheral ameloblastoma appears to have a predilection for the acanthomatous and basal cell patterns. The relationship of tumour cells to overlying epithelium is highly variable.
Greer and Hammond (1978) have shown that the ultrastructure of peripheral ameloblastoma is the same as that of intra-osseous ameloblastoma. Most important factor in the diagnosis is a distinction between a peripheral ameloblastoma and extra-osseous component of an intra-osseous ameloblastoma. Another factor is its histological similarity to basal cell carcinoma and basal cell pattern of ameloblastoma. Other differential diagnoses include squamous cell carcinoma and other odontogenic tumours.
The peripheral ameloblastoma is considered a less invasive lesion than its intra-osseous counterpart, and they do not require excessively drastic treatment.
Extra-oral tumours resembling ameloblastoma
Tumours somewhat similar in structure and histological picture to ameloblastoma occurs in pituitary gland, the tibia and ulna, the ovary and elsewhere.
Zulch in 1963 reported after reviewing 6000 CNS tumours that the pituitary craniopharyngioma accounts for 2.5% of all CNS tumours. This tumour occurs in the anterior lobe which is derived from the Rathke’s pouch, an outgrowth of the oral ectoderm. Even after the degeneration of the craniopharyngeal duct, some squamous epithelial residues remain in the infundibulum, giving rise to ameloblastoma-like tumours. Its greatest incidence is in children and in young adults below 25 years of age. It grows as a pseudo-encapsulated mass, usually in suprasellar area, and often destroys the pituitary gland. Microscopically, the resemblance to ameloblastoma is very close.
Adamantinoma of long bones
This lesion was first reported by Fischer in 1913. Discussed by Baker, Dockerty & Coventry (1954), the tumour has a superficial microscopic resemblance to ameloblastoma of the jaws. Most cases have been reported in the tibia but rare cases have been reported to occur in ulna, fibula and femur. Chagus et al has suggested that the lesion is actually a malignant angioblastoma, but electron microscopic studies have pointed towards an epithelial origin.
Management of ameloblastoma
Over the years, a wide variety of treatment modalities have been advocated by different authors in the management of ameloblastoma. These range from a very conservative enucleation through an intra-oral approach to a radical hemimandibulectomy or maxillectomy with liberal removal of a good amount of uninvolved bone. A detailed discussion of the various treatment options is given below.
For decades, it has been almost universally accepted that radiotherapy is not an appropriate treatment modality in the treatment of ameloblastoma. Most series have reported poor result with this method.
It is not that the tumour is inherently radioresistant. It has been found that the extra-osseous component of large ameloblastomas can be markedly reduced by irradiation (Hair-1963; Singleton-1970). Also, the other similar tumours are relatively radiosensitive. The reason why ameloblastoma is not controlled by radiation is that they are primarily intra-osseous lesions and their location within the bone provides resistance to radiotherapy, just as squamous cell carcinoma turns radioresistant once the tumour has invaded bone.
The objections to the use of radiotherapy are mainly three-fold.
- It is ineffective in controlling the tumour
- There is danger of inducing osteoradionecrosis
- There is possibility of inducing malignancy, post-radiation carcinoma (in the form of ameloblastic carcinoma) or post-radiation sarcoma (Becker et al – 1967).
However, Atkinson, Harwood and Cummings, in a reputed journal (Cancer – 1984), have argued that there is, in fact, a role for megavoltage radiation in the treatment of ameloblastoma. Nevertheless, considered as a whole, radiotherapy is not an acceptable means of treating ameloblastoma, except in inoperable cases, primarily when it has invaded the cranium. In such cases, its use is one of last resort.
Curettage is the removal of the tumour by scrapping it from the surrounding normal tissue. Excision is the local surgical removal with an attempt to include a rim of uninvolved tissue. Currently most surgeons conclude that curettage is the least desirable form of therapy. Sehdev et al (1974) reported that repeated curettage for mandibular ameloblastoma has given a cure rate of only 10%. Taylor (1968) reported a 63% recurrence rate and Rankow and Hickey (1954) gave a 91% recurrence rate.
The results of curettage for maxillary ameloblastomas are even worse than those in the mandible because of structural difference in the bone. The maxilla lacks a thick compact cortical bone and has an intimate relation to the nasal cavity, paranasal sinuses, orbital contents, pharyngeal tissues and structures entering and leaving the base of skull.
In 11 cases of Sehdev et al, all of them had recurrences. 63% either died of the disease or had massive recurrences. It is possible that opening of maxillary antrum to a direct and clinically invisible tumour by curettage might have contributed to delay in early recognition and hence the inadequate treatment of a recurrence.
The failure of curettage is probably related to the fact that nests of tumour cells extend beyond the clinical and radiographic margins of the lesion and are therefore impossible to eradicate by a scrapping procedure. Many types of chemical and electrical cauterisation have been used by surgeons in conjunction with curettage but they have reported only a slight improvement in cure rate.
Curettage generally implies the removal of pathological tissue by vigorous scrapping. It is primarily approached intra-orally. A mucoperiosteal flap is reflected to create adequate access. In the mandible, the approach is usually restricted to the buccal aspect. Hazards of lingual access include injury to lingual nerve & mandibular neurovascular bundle and exposure of facial spaces in the floor of the mouth. When the lesion occurs in the maxilla, either a palatal or buccal / labial approach may be used.
Depending on the thickness of the cortical bone, either a rongeur or surgical bur is used to remove sufficient bone to expose the underlying pathoses. Then the lesion is removed from the underlying bony cavity by the use of angular / straight curettes, using a teasing motion with the convex surface of the curette placed against the bony wall. Usually the vital structures like the contents of the mandibular canal are displaced to the distal wall of the surgical defect; sometimes these structures are sacrificed. After the gross lesion is removed using the largest curette that can be employed using the available access, a margin of apparently normal bone should be removed by aggressive scrapping. After thus removing 1 to 3 mm of surrounding bone, all margins are smoothened with a rongeur or a large round bur. Adjunctive treatment like cauterisation may be employed at this stage.
The bony cavity is then irrigated liberally with normal saline. Small wounds are then closed primarily. Large wounds are packed with gauze impregnated with compound tincture of benzoin, balsam of Peru or Whitehead’s varnish. The gauze is layered in tiers. In the case of maxillary procedures, if the procedure has violated the maxillary sinus, the end of the gauze packing may be exited through a nasal antrostomy. The mucoperiosteal flap is then reapproximated and sutured. A topical antibiotic may also be used with the gauze pack.
The pack is removed approximately 2 to 3 inches everyday until the surgical defect is filled with granulation tissue. The patient is put on an antibiotic regimen and scrupulous oral hygiene is maintained.
Numerous complications have been reported following conservative therapy, particularly extensions to vital structures. Other reported complications are seeding into the lungs, direct extension into the brain and malignant transformation (Tekeuchi et al – 1981). Moreover, the curettage procedure breaks the cortical barrier, thus paving the way for residual tumour to grow into the soft tissues, which then becomes more difficult to treat.
Various types of cautery have been used in the treatment of ameloblastoma, primarily as an adjuvant to curettage, but in some cases as a primary mode of therapy. Chemical agents (most recently Carnoy’s solution), electrocautery and cryotherapy have all been used. Cauterisation is basically an attempt to eradicate the tumour that has infiltrated beyond the clinical and radiographic margins of the tumour. In general, the use of cautery is empirical because of our lack of knowledge as to
- how far the tumour in each case has extended into the cancellous bone
- how far the caustic agent (heat / chemicals) penetrates into the cancellous bone
- how effective is the agent in eradicating the tumour cells and
- the possible harmful effects to normal tissue
Electrocoagulation (thermal cautery)
Mehlisch et al (1972) states that cautery when used as primary treatment resulted in a 50% recurrence rate. Thus it is potentially a more effective therapy than curettage. The secondary ischaemia and necrosis that occurs for some distance from the margins of the tumour may destroy the invading tumour cells.
Cautery has frequently been employed as an adjuvant to other methods of therapy to give a better result (Gardner and Pecak – 1980). Mehlisch et al reported no recurrences in 2 patients treated with this method.
In recent years, Carnoy’s solution (a fixing agent consisting of a mixture of absolute alcohol, chloroform and glacial acetic acid, which is sometimes modified by the addition of ferric chloride) has been advocated as a treatment for odontogenic keratocysts. Stoelinga and Bronkhorst (1988) have used it after enucleation in the treatment of unicystic ameloblastoma and reported no recurrences.
The depth of penetration of Carnoy’s solution is known. It penetrates cancellous bone up to 1.5 mm after 5 minutes and up to 1.8 mm after 1 hour (Voorsmit et al – 1981). In 1982, Voorsmit further reported that the injurious effect of this agent on adjacent soft tissue is negligible.
Eventhough Carnoy’s solution has been used in the treatment of classical multilocular ameloblastoma also, there is no information in the literature concerning its efficacy. Nevertheless, the use of Carnoy’s solution appears to be harmless and has the potential of reducing recurrences after curettage.
In the past two decades, cryotherapy has also been advocated in the treatment of ameloblastoma (Bradley-1986, Holland and Mellor-1981). It is used mainly as an adjunct to curettage in the hope of reducing recurrences. The obvious advantage of cryotherapy is that it is possible to devitalise the tissue with liquid nitrogen to a depth of 1.5 cm, the margin that is frequently used for surgical resection. In fact, the jaw can be frozen through its entire thickness if necessary.
However, there are potential complications such as sequestration, pathological fracture, transient anaesthesia of mandibular nerve etc. In general, the more extensive the freezing, the greater the risk. This is a comparatively new treatment method, and has not been used extensively as yet in the treatment of ameloblastoma.
Another method which has been described (Weaver and Smith-1963, Bradley-1978) in which the affected segment of bone is excised, frozen in liquid nitrogen to devitalise the tissue, and then reimplanted as an autogenous graft. This is only in experimental stages at present.
En bloc resection
The en bloc or marginal mandibular resection is a surgical procedure in which the entire tumour is removed intact with a rim of uninvolved bone while maintaining the continuity of the jaw. This procedure is advocated for the treatment of ameloblastoma when the lesion does not extent closer than 1 cm to the inferior border of the mandible.
Kramer (1963) reported that although there is an invasion of cancellous spaces of the bone by finger-like projections, the tumour does not invade the haversian systems of compact bone. He concluded that in relation to cortical bone, the clinical and radiological margin may be regarded as the true margin. However, in the cancellous bone, a margin of 1 to 2 cm beyond the clinical and radiological limit is considered the minimum acceptable margin. Various authors have reported good results with en bloc resection (Mehlisch et al – 1972, Sehdev et al – 1974). But most surgeons are of the view that for lesions of the maxilla, en bloc resection is not as successful and recommend segmental resection (Björklund – 1979, Chaudhuri – 1975).
En bloc resection can be done from either an intra-oral or an extra-oral approach. The former is used when there is a good access and when the lesion is anterior to third molar region. The extra-oral approach is used when the lesion involves the ramus of the mandible or when immediate reconstruction is planned.
For large mandibular lesions requiring the removal of large sections of bone, a midline lip-splitting incision is often made to increase the access into the posterior region. This is not necessary for lesions requiring less bone removal.
Connecting vertical incisions are made on the buccal and lingual sides through the mucoperiosteum 2 cm anterior and posterior to the anticipated area of resection. These incisions should extend deep into buccal and lingual folds. The teeth bordering the surgical margin should be extracted. Next, horizontal incisions connecting the lower ends of vertical incisions are made. The buccal and lingual mucoperiosteal flaps are then developed, but not reflected superiorly over the region of bone to be removed.
On exposure of the mandible, the bony segment is sectioned with an air-driven saw or bur, at least 1 to 1.5 cm from the radiographic margin of the lesion. For segmental resection of the same region, a continuity defect is created by removing an entire segment of the mandible, including the lower border.
Haemorrhage arising from the bony segments can be controlled by crushing the bone over small blood vessels with a blunt instrument or by using bone wax. The mucoperiosteum is then undermined both lingually and facially to relieve tension. They are approximated with interrupted silk sutures.
Post-operatively, good oral hygiene should be maintained and antibiotic coverage is necessary. The use of intermaxillary fixation depends on the amount of remaining bone.
This is similar to that used in segmental mandibular resection except that a margin of inferior border of mandible is left intact.
Segmental (partial) mandibular resection / hemimandibulectomy
Segmental resection of jaws, including maxillectomy and hemimandibulectomy has been the most commonly used treatment for ameloblastoma. Obviously, those who used this method have reported the least number of recurrences.
Depending on the size of the mandibular segment to be removed, a lip-splitting incision may or may not be necessary. When the lower lip is being split, finger pressure should be applied on either side of the vertical incision to control bleeding from labial arteries. After the lip split, larger arteries may be ligated, and the smaller ones cauterised.
A submandibular incision about 1 to 2 cm below the inferior border of the mandible, is made from the angle of the mandible to join the vertical lip incision. This incision is made through the skin and subcutaneous tissue, exposing the platysma.
Next, intra-orally, a horizontal incision is made through the mucoperiosteum on the facial and lingual aspects of alveolar ridge. These are then curved on to the retromolar region. The facial and lingual flaps are advanced below the horizontal incision using a periosteal elevator. The lingual flap is raised as deep as to expose the mylohyoid attachment.
A vertical mucoperiosteal incision is made 0.5 cm proximal to the anticipated anterior bony cut. The buccal flap beneath the horizontal incision is reflected to expose the mental neurovascular bundle, which is ligated and sectioned. Preservation of the marginal mandibular branch of the facial nerve, which would be located in the lateral aspect of the facial flap, is important for the normal function and appearance of the lower lip post-operatively.
The masseter is resected at the lower border of the mandible, and reflected from the ascending ramus using periosteal elevators. The medial pterygoid is then reflected from the lingual surface. The temporalis is incised and reflected off the coronoid process. The lingual flap is retracted to expose the mylohyoid, which is then severed off its attachment. The facial flap should expose the entire lateral surface of the body and ramus of the mandible.
Using an air-driven saw, bur or a Gigli saw, a vertical cut is made through the mandible anterior to the lesion. Using bone forceps, the proximal part of the mandible is rotated laterally, exposing the inferior alveolar nerve and vessels, at the lingula of the mandible. They are ligated and cut adjacent to the mandibular foramen. The lateral pterygoid muscle is sectioned from the condyle and TMJ capsule. The capsule is cut with a scalpel and the segment of mandible is disarticulated and removed using bone-holding forceps. Bleeding ensuing from the severed muscles is controlled by digital pressure, coagulation or ligation, depending on the size of the bleeding vessel.
In order to obliterate the dead space and for haemostatic purposes, the opposing surfaces of medial pterygoid and masseter are sutured together, and a drain is placed in the region. When immediate reconstruction is planned, the graft is inserted at this stage. The submucosal surfaces are approximated and sutured with buried chromic gut or vicryl. Mucosal surfaces are then closed with interrupted sutures. The vertical and horizontal mucoperiosteal flaps are approximated and closed, covering all exposed bone. The vermilion border of the lip is re-approximated and sutured. The mucosal surface inside the lip is restored in layers. The deep tissues in the submandibular region are re-approximated to obliterate the dead space. The platysma is then re-approximated and sutured. The subcutaneous tissues are sutured with gut / vicryl. The skin is closed with silk or prolene sutures. The external portion of the drain is secured with a binding suture.
A firm pressure dressing is applied on the lateral surface of the resected area. Intermaxillary elastic traction using previously placed archbars will minimise mandibular deviation, and encourage a more ideal wound healing. The patient should be fed through a naso-gastric tube for a week and scrupulous oral hygiene should be maintained. Dressings should be changed daily. Removal of drain depends on the amount of drainage. Alternate skin sutures are removed after 4 days and the remaining ones, after 6 days. After that, the naso-gastric tube may be removed and oral feeding may be begun.
Marginal (partial) maxillectomy
The marginal maxillectomy is the surgical procedure most often used for ameloblastoma of maxilla when the maxillary sinus is not involved.
Marginal maxillectomy is accomplished through an intra-oral approach. A mucoperiosteal incision is made approximately 1.5 to 2 cm in all directions from the underlying tumour. It may be necessary to extract one or more teeth to complete these incisions. A small mucoperiosteal flap is reflected on the uninvolved bone. Using an air-driven saw or bur, the vertical bony cuts are made at the height of the alveolar ridge. These cuts extent into the maxillary sinus. If the tuberosity is to be removed, a separation of the pterygoid plates can serve as the distal cut. A horizontal buccal osteotomy is made to connect the buccal cuts. A similar osteotomy is performed on the palatal aspect also. The saw blade / bur is directed to enter the maxillary sinus or the nasal cavity as is necessary. Then the resected portion of maxilla is easily removed.
A gauze strip impregnated with a suitable medicament is firmly packed into the maxillary sinus and is held in position with a pre-fabricated obturator. The surgical defect is later repaired with a permanent obturator, which permits inspection for recurrence.
Maxillectomy is the surgical procedure of choice when an ameloblastoma extends into the maxillary sinus or when a maxillary lesion has recurred.
A full-thickness midline incision is made in the upper lip from skin to the mucous membrane. The incision is continued along the inferior portion and lateral aspect of the nose, to the medial canthus of the eye, and is joined by a transverse infra-orbital incision close to the margin of lower eyelid (Weber-Ferguson incision). An intra-oral incision is made through the mucosa at the height of the labio-buccal sulcus from the anterior vertical incision to the tuberosity. This incision should be made deep to touch the lateral wall of the maxilla.
Using blunt and sharp dissection, a sub-periosteal flap is raised superiorly to the inferior rim of the orbit, exposing the whole lateral surface of the maxilla. The infra-orbital vein and nerve are identified and ligated. The periosteum of the floor of the orbit is elevated and the contents of the orbit are safely retracted, exposing the inferior orbital fissure.
The facial flap should be retracted posteriorly, exposing the zygoma, which is sectioned vertically using a saw / bur / chisel and mallet. The cut is directed medially at an oblique angle extending through the zygoma along the floor of the orbit to the inferior orbital fissure. The nasal soft tissues are reflected from the maxilla and the adjacent surface of the nasal bone.
The fronto-nasal process of the maxilla is sectioned vertically from the orbit to the nasal fossa. The cut is directed laterally and obliquely, extending along the floor of the orbit to the inferior orbital fissure.
A vertical incision is made over the midline of maxilla, and a gingival flap is reflected. The central incisor is extracted, and a bone cut is placed through the tooth socket and alveolar process to the floor of the nose. A midline incision on hard palate is made which is turned transversely at its junction with soft palate to join the buccal incision. The hard palate is sectioned along the floor of the nose just medial to the nasal septum. The muscles of soft palate and superior constrictor are divided. Retraction of the cut muscles expose the pterygoid plates of the sphenoid bone and the muscles attached to it. Pterygomaxillary disjunction is done with a chisel. The sectioned maxilla is made free of any remaining skeletal attachments.
Pressure / ligation is used to control bleeding from the severed muscles. Often the greater palatine vessels have to be ligated and sutured. The exposed surfaces of sphenoid and ethmoid are smoothened and a split-thickness skin graft is placed in the raw bony and soft tissue surfaces. The raw edges of facial surfaces are reapproximated in layers. A 1-inch wide gauze strip impregnated with a suitable medicament is packed firmly against the skin graft. This packing should be layered firmly and may be maintained with a pre-fabricated maxillary surgical splint.
A firmly placed pressure bandage is applied over the lateral facial area of the surgical defect. Post-operative feeding is through naso-gastric tube, inserted through the intact nostril and antibiotic therapy is instituted. Proper oral hygiene should be maintained. Extra-oral dressings are changed daily, and after six to eight days, the facial sutures and packing are removed.
Factors governing the choice of treatment method
Since the aggressiveness and recurrence of ameloblastoma are controversial issues, there is still no single accepted treatment method for ameloblastoma. Before arriving at a final decision as to which treatment is best suited for a particular patient, a number of actors need to be considered.
Age and health of the patient
These are of prime importance in selection of treatment method. A mutilating radical surgery would be unwarranted in a small child or a very elderly patient, but for different reasons. In the case of the former, it is a question of post-surgical morbidity i. e. leaving the patient with a crippling surgical defect for the rest of his/her life. Again, for the very old patients, conservative therapy may be considered as the recurrences are known to take several years to occur.
It needs to be assessed whether the general health of the patient permits any radical procedure. It would not be preferable to do a radical surgery in medically compromised patients and in those with advanced systemic disease.
Clinical type of ameloblastoma
The unicystic type of ameloblastoma is known to have a much better prognosis than the typical intra-osseous type, and a conservative therapy is considered adequate. Some workers consider certain variants like basal cell ameloblastoma and granular cell ameloblastoma as more aggressive than the other types. Even in the unicystic type, the ‘invasive’ type (involving the connective tissue) is thought to be a more aggressive variety.
Site of the lesion
The porous nature of the maxilla, along with the proximity to the maxillary sinuses and nasopharynx, means a poorer prognosis for maxillary lesions than mandibular ones. So the maxillary tumours always need a more radical therapy than mandibular tumours.
The adjacent vital structures like neurovascular bundles and maxillary sinus should be preserved when possible, but may be sacrificed if the tumour has grown very close.
A tumour which is confined to the bone without perforation of cortical plates offer a better prognosis than one that has invaded soft tissues. Tumours with extra-osseous component make complete removal more difficult and require sacrifice of more (apparently) normal tissue.
An ameloblastoma in an inaccessible site like the base of the skull or pterygo-maxillary fissure area present a difficult surgical problem. Other measures like megavoltage radiotherapy has a role in such cases.
Size of the lesion
A small tumour confined to the mandible may be treated by conservative measures at the first instance while the larger ones require more radical surgery.
Chances of recurrence
The chance of recurrence after the procedure should always be borne in mind. Obviously the conservative methods like curettage and cauterisation have a higher risk of recurrence than the radical methods.
Morbidity and complications
The expected post-surgical morbidity and the complications related to the particular method are very significant factors since resection of jaw bones has serious implications on the functional and psychological well-being of the patient.
The patient should be informed of all treatment options, complete with the advantages and risks of each treatment modality, and reconstruction options. He/she should then be given a role in the final decision making.
Availability for follow-up
This becomes an essential factor particularly if conservative treatment is planned. It is better to perform a radical operation if there is less chance of patient turning up for follow-ups. A follow-up of at least 10 years is essential following curettage.
Controversies concerning treatment
The controversies concerning treatment modalities lie partly in the philosophy of individual surgeons. They should fully understand the clinical behaviour of the tumour and the results to be expected of each treatment method.
Curettage vs. radical surgery
There has been a lot of argument over the years between the surgeons comparing the risk of recurrence of conservative methods to the morbidity following radical surgery.
The recurrence rate for typical intra-osseous ameloblastoma treated by curettage is high, varying from 55-90% in various series (Gardner- 1987, Gardner and Pecak-1980) and in the posterior maxilla, it happens to be100% (Sehdev et al-1974). Muller and Slootweg (1985) have concluded that it is 75% in both jaws put together. This is thought to be because of the infiltrative capacity of ameloblastoma into cancellous bone. In comparison, the recurrence rate is much less for marginal / segmental resection (15% in Muller and Slootweg series). It follows that curettage is not a reliable method in the treatment of multilocular ameloblastoma.
It is generally agreed that curettage should never be used in the treatment of lesions of posterior maxilla since this region lacks a dense cortical plate and there is risk of invasion of the cranium through the foramina leading from the pterygomaxillary fossa, eventually killing the patient. Ameloblastoma of this site should be treated by marginal or segmental resection, depending on the size. Even in the ascending ramus of the mandible, curettage appears to be inadvisable due to the proximity to vital structures.
In the case of the body of the mandible, small tumours may be treated by curettage, provided the surgeon is fully aware of the high risk of recurrence and will be able to follow the patient closely for the next 10 years or more. Moreover, the patient must be fully aware of the risk. In short, the conditions where curettage is thought to be justified are the following.
- A case of ‘non-invasive’ unicystic ameloblastoma in the mandible or anterior maxilla.
- A small tumour in the body of the mandible in a child or a young adult, provided the patient can be followed up for 10 years or more.
- A small tumour in the body of the mandible in an elderly patient, as ameloblastoma takes several years to recur.
- A small tumour in the body of the mandible in a medically compromised patient.
It is always advisable to use some kind of cauterisation as an adjunct to curettage. All teeth in the region should be extracted. These steps might reduce the risk of recurrence.
Feasibility of retaining the lower border of mandible
The decision whether to do a marginal resection or a segmental resection depends largely on the size of the lesion. Obviously a segmental resection needs to be done if the cortical plate has been thinned or expanded, as this situation increases the risk of pathologic fracture.
However, if the lower cortical plate has not been involved with the tumour, a sparing of the inferior border should be performed. This is because the lower border of the mandible consists of a thick layer of dense cortical bone, which is not invaded by ameloblastoma. Thus retaining the inferior border does not increase recurrence.
Timing of reconstruction
In the past, many surgeons were sceptical about doing a primary reconstruction following segmental resection because of the uncertainty regarding the risk of recurrence. The reconstruction was delayed for 6 to 12 months or even more, since it was feared that recurrence might occur in the bone graft. In such cases, a metallic (stainless steel) reconstruction plate is used to maintain the apparent continuity of the jaw and to make the healing occur in near normal positions (El Fattah-1999). Disadvantages of this approach are
- Need for a second surgical procedure
- Fibrosis that accompanies the healing makes dissection more difficult during the secondary procedure.
- The secondary graft is placed in a bed of compromised vascularity, increasing the risk of graft rejection.
Most recent series have reported very good results with primary reconstruction and cases of recurrences on the graft have been very few and far between, especially when segmental resection has included 1 to 2 cm of apparently normal bone tissue.
Radical surgeries like segmental resection, hemimandibulectomy and maxillectomy leave the patient with a thoroughly incapacitating aesthetic and functional deficit. The functions affected include mastication, swallowing, speech and respiration in the case of maxillary surgeries. It is the responsibility of the surgical team to use the best available technique to reconstruct the jaw so that the post-operative quality of life would remain on the high side.
Maxillary reconstruction is a challenging procedure for a reconstructive surgeon because of the complex shape and multiple functions of the region. The reconstruction options include
- Prosthesis – Obturator and splints
- Local soft tissue flaps
Buccal and palatal advancement flaps
Buccal pad of fat
- Regional flaps
Temporalis – myofascial / myo-osseous
Trapezius – muscle / myo-cutaneous / osseo-myo-cutaneous
- Free flaps
The osseous component of these flaps includes rib, scapula, calvarium and mandibular symphysis.
Mandibular reconstruction can also be accomplished by a variety of means. They include
- autogenous vascularised bone by pedicled flaps
- Clavicle pedicled on sternocleidomastoid
- Rib pedicled on pectoralis major
- Scapula pedicled on trapezius
- Calvarium pedicled on temporalis
- Rib pedicled on latissimus dorsi
- autogenous vascularised bone by free flaps
- iliac crest based on deep circumflex iliac artery
- fibula based on peroneal artery
- scapula based on circumflex scapular artery
- radial forearm based on radial artery
- rib based on intercostal artery
- second metatarsal
- calvarium based on superficial temporal artery
- autogenous non-vascularised bone
- iliac crest
- alloplastic materials
- stainless steel reconstruction plate
Allografts and xenografts have fallen out of favour of most authorities. When they are used, it is as banked bone after lyophilisation to prevent antigenicity-related problems.
Autogenous vascularised bone gives the best result because of its reliable blood supply. Free flaps including iliac crest are considered the best choice because of their width which facilitated dental rehabilitation by implants or dentures. Disadvantages of free tissue transfer include longer duration of surgery, and the need for sophisticated and expensive equipment and trained personnel. In the absence of these, autogenous non-vascularised bone is a good compromise option, especially for reconstructing small defects.
Ameloblastoma of jaws is a benign neoplasm of odontogenic origin with local invasive capacity. It presents clinically as a painless swelling and as a multilocular radiolucency in radiographs. It has a number of histologic variants.
Radical resection is the generally accepted treatment modality except in certain specific instances. The defect created by resection may be reconstructed primarily using various means, autogenous vascularised bone being the most preferred choice.
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