This information has been written for patients, their families and friends and the general public to help them understand more about a rare benign (non-cancerous) tumour known as ameloblastoma. This section will detail what an ameloblastoma is and how ameloblastomas can be diagnosed and treated.
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What is ameloblastoma?
Ameloblastoma is a rare, benign, tumour of the bone which can occur in the lower or upper jaw bone. Ameloblastoma can appear to be solid or cyst-like. It is very common for this tumour to occur around the position of the third molar tooth (known as the wisdom tooth). Ameloblastomas grow from the cells which give rise to the enamel (outer layer of the teeth). These tumours occur most frequently in the lower jaw bone (known as the mandible), with approximately 80% of reported ameloblastomas occurring here. The remaining 20% of cases occur in the upper jaw bone (known as the maxilla), or present in both the mandible and the maxilla simultaneously(1).
It is important that this non-cancerous tumour is diagnosed early in order to prevent its excessive growth, bone destruction and invasion into soft tissues surrounding the jaw and possible progression to a cancerous tumour.
Ameloblastoma is very rare in Europe, America & Australia. it tends to be more common in Asian and African continents.
Although ameloblastomas tend to be slow-growing, non-cancerous tumours, they can occasionally become aggressive and affect tissues surrounding the jaw area, such as the floor of the mouth, tonsil area, sinuses or eye-sockets as well as nerves and blood vessels. We describe this behaviour as ‘locally aggressive’, which can cause swelling and bone destruction at the site of the ameloblastoma. As this tumour type originates in the tissues that give rise to teeth, bone destruction can result in some facial distortion(2,3).
Statistically, only 1% of all jaw tumours are ameloblastomas and in most cases the growth is benign (non-cancerous) and non-metastatic (they do not spread). The risk of the tumour spreading to other areas of the body is very low, at less than 2%, but if spread does occur it is most likely to be to the lungs, the lymph nodes, the brain or the skin(1,4,5).
The spread of an ameloblastoma to elsewhere in the body can occur over a decade after treatment has taken place, and unfortunately, this rare tumour type has a relatively high risk of the tumour returning at a later date; this is known as tumour recurrence.
Ameloblastoma is known to affect males and females in equal proportions and can affect any age group or ethnicity.
Although ameloblastoma can occur at any age, it is most frequently seen in patients of around 30 to 40 years of age and is relatively uncommon in children under the age of 10 years old(5).
Ameloblastoma patients often experience no symptoms until the tumour is of a larger size. Doctors describe this as being ‘asymptomatic’. Therefore, in many cases, this rare tumour type is discovered during routine dental X-rays before the patient has experienced any symptoms(1,5,6).
The symptoms of ameloblastoma which are most commonly reported are:
- An abnormal growth in the jaw or sinus area
- Painless swelling in the jaw
- Bone pain – which may be continuous or come and go
- Delayed tooth eruption
- Loose movement of multiple teeth
- Difficulty in speaking
- Obstruction of the nasal airways
- Mouth ulcerations
- Imperfect teeth positioning when closing the jaw
For more information on the symptoms or primary bone cancer, please refer to our About Primary Bone Cancer information section
There are a number of different types of ameloblastoma, which can make the final diagnosis of this tumour quite difficult and increase the time taken to reach an accurate diagnosis.
There are four main types of ameloblastoma, which vary due to their different structural make-up(3,7).
These four types of ameloblastoma are:
- Multi-cystic/Conventional Ameloblastoma (also known as solid ameloblastoma)
- Uni-cystic/Cystic Ameloblastoma
- Peripheral Ameloblastoma (also known as extraosseous ameloblastoma)
- Desmoplastic Ameloblastoma
The cause of ameloblastoma is largely unknown, and due to the rarity of this tumour it is hard to assess a possible cause from the small number of cases that have been reported.
Recent research has revealed an association between the mutation of certain genes, which are involved in controlling cell growth, division and survival, and the development of ameloblastoma. Mutations in genes known as BRAF and SMO have been seen in over 80% of ameloblastoma cases and so further investigation into these genes is currently taking place(5,8).
Overexpression of TNFalpha, Matrix metalloproteinases (MMP), vascular endothelila factor and Rank Ligand osteoclasts (bone destroying cells) have also been identified in ameloblastomas.
Although there is currently no identifiable cause for ameloblastoma, there are risk factors that are thought to increase the likelihood of an individual developing this tumour type.
These risk factors include:
- Poor oral hygiene
- Disregard to any swelling in the jaw
- Ethnicity - ameloblastoma is more common in African and Asian populations.
Patients with different types of primary bone cancer are assessed in similar ways. For this reason, diagnostic tests are covered in more detail in our About Primary Bone Cancer information section.
This section aims to provide information on the specific details of diagnosing an ameloblastoma and to discuss other conditions that may appear diagnostically similar to ameloblastoma.
If patients are experiencing any of the symptoms of an ameloblastoma, they should visit their GP. These may be:
- Jaw pain
- Swelling and/ or numbness of the lips/ chin
Diagnosis of a suspected ameloblastoma usually follows a clinical examination, X-rays and an incisional biopsy under a local anaesthetic. This usually takes no more that 20 minutes to perform an the specimen is looked at under a microscope. is very common to be referred to an Oral & Maxillofacial Surgeon for a second opinion and confirmation of the diagnosis.
Many ameloblastomas are detected at the dentist and are discovered accidentally during routine dental procedures/ X-rays(2). Often the tumour may appear to be an infection, causing pain and swelling in the jaw, and is treated with a course of antibiotics. It is when these symptoms are not relieved by antibiotics that a routine X-ray is carried out to further investigate the symptoms and the suspected ameloblastoma is detected.
It is very common to be referred to an Oral & Maxillofacial Surgeon for a second opinion and confirmation of the diagnosis.
Further tests to confirm the presence of ameloblastoma include: X-rays, CT scans, MRI scans and a biopsy of the bone.
X-rays of the bone may be taken, including the joints above and below, and are studied. These X-rays may show swelling around the bone or areas of abnormal bone growth. A chest x-ray is sometimes taken to show whether the cancer has spread to the lungs.
MRI stands for 'magnetic resonance imaging'. This type of scan is similar to a CT scan but magnetism and radio waves are used instead of x-rays to build up a very detailed 3-dimensional image.
An MRI scan of the entire bone is used to gain more information about the tumour in the bone. An injection of a special dye, known as a contrast agent is also used. This makes certain tissues show up more clearly and with greater detail on the scan. The results of the scan will be examined by a radiologist and a report will be produced. For some patients they may also have a total body MRI scan to look for areas of abnormalities in the other bones such as tumour spread (metastases).
An MRI scan can not only tell the difference between ameloblastoma and other similar conditions, but can also identify the specific type of ameloblastoma that is presenting(6).
CT stands for 'computerised tomography'. They may also be called CAT scans, which stands for 'computerised axial tomography'.
The scanner takes x-rays from many different angles and a computer builds up a 3-dimensional picture of the body in great detail. The pictures show cross-sections of the inside of the body.
CT scanning of the lungs shows up any secondary tumours where the cancer may have spread (metastases). It is used if the MRI scan results have not been able to confirm the diagnosis of osteosarcoma.
A CT scan cannot definitively diagnose an ameloblastoma. However, using a CT scan alongside an MRI scan can provide important information on the exact location of the tumour and the size of the tumour. Additionally, these scans are useful for planning the treatment of individual patients and working out the best way to surgically remove the tumour(3,5).
A bone biopsy is a specialised procedure that can be performed by a maxillofacial surgeon as orthopaedic surgeons do not deal with jaw bones. A biopsy involves taking a small sample of a lump of tumour so that a pathologist can examine the cells in the sample and confirm the presence of ameloblastoma.
The biopsy being taken may be a ‘needle biopsy’ or an ‘open biopsy’.
- Needle biopsy: a needle is inserted into the tumour to draw out a small amount of tumour tissue (this may be done under local anaesthetic). Often, in order to know exactly where to take the sample from, this test is carried out alongside an X-ray or CT scan to guide the doctor.
- Open biopsy (or surgical biopsy): is used less frequently than a needle biopsy. This form of biopsy is carried out during a small, minor, operation to remove a small piece of tumour while under general anaesthetic. This test tends to be used if a needle biopsy does not provide a diagnosis and the doctor wish to investigate further.
The differential diagnosis (conditions which can be the cause of particular symptoms) of destructive bone lesions at this stage include:
- Cysts of the jaw - the most common being Odontogenic Keratocyst and Dentigerous cysts.
- Other tumours that can grow in the bone such as sarcoma and secondary tumours which metastasise (travel) from other part of the body and are cancerous.
An alternative diagnosis?
When diagnosing an ameloblastoma it is important to be able to tell the difference between this rare tumour and any other benign (non cancerous), or malignant, health conditions that may cause similar symptoms(5). It is important the correct diagnosis is made to ensure the treatment provided is suitable(2).
It can sometimes take a long time to confirm a diagnosis of ameloblastoma after a biopsy because these tumours are rare and sometimes difficult to identify.
Other conditions which can present in the same way as ameloblastoma include:
Ameloblastomas are often referred to as the ‘adamantinoma of the jaw’, as they appear to be very similar when they are looked at under the microscope. It is the location of the tumour that allows the differentiation between these two rare primary bone cancer types(10). For more information on adamantinomas please see our information page here.
- Odontogenic Keratocyst
An odontogenic keratocyst is a benign tumour of the jaw, which commonly occurs in the lower jaw much like an ameloblastoma. Patients experience symptoms of pain and swelling and the presence of cysts in the jaw, which will need treatment to remove(11,12)
- Ameloblastic Fibrosarcoma
Ameloblastic fibrosarcoma is a rare but highly malignant tumour of dental origin. The symptoms are pain and swelling of the jaw which is very similar to an ameloblastoma(13), however the swelling increases at a rapid rate and needs urgent attention.
- Ameloblastic carcinoma
Ameloblastic carcinoma is another extremely rare type of tumour. It can be classified as metastasising (malignant) ameloblastoma or ameloblastic carcinoma.
Metastasising ameloblastoma is an ameloblastoma which metastasises (spreads) to the lungs and other parts of the body. The primary and metastatic tissues demonstrate benign (non cancerous) features when examined under the microscope. It is unclear whether the ameloblastoma tissue is inhaled into the lungs and hence causes the growth in the lungs.
Ameloblastic carcinoma exhibits cancer/ malignant features. Ameloblastic carcinoma consists of two subtypes; primary and secondary. Surgery remains the main course of treatment with a radical margin of 1-2cm.
Due to the rarity of ameloblastoma, and therefore the smaller number of reported cases, it is difficult to work out the most effective and safest treatment for this tumour. Different countries seem to have developed their own treatment protocols for this type of tumour..
Research suggests that chemotherapy is of little-to-no benefit in treating this tumour type and is used purely to relieve patients’ symptoms(4,14).
The most effective and common treatment method for ameloblastoma is the surgical removal of the tumour. Surgery can either be ‘conservative’, which attempts to retain as much tissue as possible in the area, or surgery may be ‘radical’, a more invasive procedure which requires reconstruction of the area following tumour removal(1,6).
Depending upon the location, size and the subtype of ameloblastoma the surgical treatment is tailored accordingly.
Smaller tumours confined to bone with no perforation (hole) in the bone or expansion of the jaw can be treated by curettage and marginal resections, keeping the continuity of the jaw intact. This is a simple procedure which takes 2 hours, can be carried out local anaesthetic but usually requires a general anaesthetic and a night in hospital.
Sometimes there is a pack inserted to ensure good healing and removed in stages. The patient is then followed up every 4-6 months with X-rays to ensure that the bony infill is happening and to detect recurrences early.
Unicystic ameloblastomas with variants of a small size without any evidence of expansion of bone, can be treated conservatively.
Larger tumours which have perforated the bone (made holes in the bone) and invaded the soft tissues are treated radically by removing the entirety of the jaw with a 5-10 mm margin on either side. This procedure is known as a mandibulectomy in the lower jaw and maxillectomy in the upper jaw.
If less than half of the jaw is removed, it is known as partial mandibulectomy/ maxillectomy.
If half of the jaw is removed, it is called hemi mandibulectomy/ hemi maxillectomy
If more than half of the jaw is removed, it is called subtotal mandibulectomy/ maxillectomy and if all the jaw is removed it is called total mandibulectomy and maxillectomy.
If the ameloblastoma is 2 cm in its maximum dimension then radical treatment results in a 4 cm defect of the jaw. However most aggressive ameloblastomas are nearly 3-4 cms in size when they are detected, hence the treatment leaves larger defects.
The surgical treatment of ameloblastomas requires a ‘wide surgical margin’ in order to achieve effective and adequate surgery. A ‘wide surgical margin’ usually 5-10 mm, meaning the tumour is removed alongside a small amount of healthy tissue. This method ensures all tumour/ cancerous cells are removed and lowers the risk of the tumour returning at a later date (which is known as tumour recurrence). If the tumour does return, a second round of surgery may be carried out(1,7).
For marginal mandibulectomy/alveolectomy, a bone graft which is usually sourced from the hip or the side of the jaw can be anchored to keep the thickness of the jaw. However in marginal mandibulectomy, the continuity of the jaw is maintained so there is no absolute need for reconstruction.
For small mandibular resections (less than 4 cm), a bone graft could be considered from the hip bone and a titanium plates and screws are used to anchor the bone. It takes 4-6 months for the bone to take up. Subsequent to this, implants could be planned.
Transport Distraction of the Jaw
Transport Distraction is another method of reconstructing lost continuity of the jaw. Usually for small defect, this technique uses the adjacent intact bone, fracturing a slice and moving it after one week at the rate of 1mm per day thereby spreading the clot. Just as a fracture heals with a clot, ultimately the expanded clot forms the bone and fills up the defect. The advantage is that there is no need to harvest any additional tissue thereby minimising morbidity.
For this technique to be successful, it is critical that proper case selection is done, ensuring that the soft tissue envelope (the skin of the mouth) has a good seal throughout the process (not allowing the saliva to seep through otherwise the clot will get infected and there will not be any bone formation).
The process of transport distraction is protracted and can take 4 months with multiple steps involved for completing the reconstruction. Due to the prolonged nature and other risk factors, transport distraction is unpredictable in its outcomes especially for large defects.
Most of the evidence for transport distraction studies comes from the Indian subcontinent and the recommendation is that it is to be used for small defects or for elderly patients with pre-existing health conditions where free tissue transfer/transplant of the jaw is not possible or history of failure of more than two free flaps.
Many surgeons/ centres lack the capacity to carry out free flap procedures and this may be a viable alternative in these situations.
Free flap reconstruction
For defects more than 4cm and those involving soft tissue i.e. the tumour has invaded the floor of mouth, free tissue transfer is the gold standard.
In this technique, the correct size of the bone is harvested from either the lower leg (fibula bone), the hip or the shoulder blade (scapula). Along with the bone the blood vessels are also harvested (artery & vein) which is then anastomosed (plumbed) into a artery and vein in the neck using a microscope by a technique called microvascular free tissue transfer.
This is an auto transplant, using the tissues from your own body and transplanting it to form the new jaw.
This is a complex process and the procedure may take up to 12 hours to carry out. There is a 1 in 20 chance that the flap may not work and an alternative flap may be needed.
The commonest flap used is the fibula free flap (lower outer leg bone), This flap can reconstruct the entire jaw if needed and is considered as the gold standard.
Scans are carried out to ensure that there are 3 vessels supplying blood to the leg and are intact, in order to remove the bone along with the blood vessel. This leaves the other two arteries intact to supply the remainder of the leg.
Unless you are an athlete, you don’t require the outer lower leg bone and there is minimal disruption in function, although we would recommend a automatic car to minimise the strain.
Anybody with prior history of claudication (pain in the limbs), is excluded from this type of vascular surgery.
It is common practice in the UK to carry out planning on a computer. 3D models are generated and a custom made plate (patient specific titanium plate, very similar to 3D printing) replaces the contours of the lost jaw, maximising aesthetics and also implant placement for future dental rehabilitation.
The hip bone called a Deep Circumflex Iliac flap is another alternative especially to replace the angle of the mandible. The advantages are that it has good bone height, however it is difficult to replace more than 7-8cm of jaw so is reserved for up to hemi mandibulecomies/ maxillectomies.
The disadvantages are that some patients, especially if obese, can develop hernias, gait changes. It is considered to be a secondary option when compared to the fibula flap (the gold standard).
Another option is the scapula free flap (shoulder blade) which is a good alternative when the fibula cannot be harvested due to medical or technical reasons.
Despite reconstruction with free flaps, depending upon the size of the tumour, some people develop issues with chewing food. Speech and swallowing may be affected. There may also be permanent numbness of the lip/chin and cheek areas.
For more information regarding treatment procedures, including surgery and chemotherapy, please visit our About Primary Bone Cancer information page.
Ultimately, it is highly beneficial to diagnose and treat ameloblastomas as early as possible. Early diagnosis and adequate treatment leads to an excellent outlook for patients in previously reported ameloblastoma cases. The recurrence rate for ameloblastoma is approximately 50-72% if the tumour is not fully removed during surgery, emphasising the importance of correct diagnosis and an adequate surgical procedure(4).
It is important to bear in mind that patients receiving treatment outside of the UK may receive different tests and treatment plans in accordance to the treatment guidelines set out in that specific country. If you have any questions or concerns regarding this please discuss this with your medical team or contact The Bone Cancer Research Trust for more information.
If you would like more information about ameloblastoma please contact us.
Research is being carried out to investigate genes which appear to be commonly mutated in ameloblastomas - such as BRAF and SMO genes. The mutations observed in these genes appear to be associated with a lack of control over the cells growth and division, which ultimately leads to the development of a tumour.
There are developed and approved targeted therapies to these mutations used in other tumour types. Therefore it is hoped that in the near future these targeted drugs, such as Vemurafenib which directly targets the BRAF mutation, can be tested for their efficiency in the treatment of ameloblastoma tumours (5,8).
However these are immunotherapy/chemotherapy agents so come with side effects which include damage to the liver and kidneys, the development of a cough as well as skin & blood cancer. These drugs can currently only be used in a trial setting and may have a role in uncontrolled ameloblastoma which has spread to the skull base/brain. Further trials are needed to substantiate this.
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