Ameloblastoma
Encyclopedia
Ameloblastoma is a rare, benign tumor of odontogenic epithelium
(ameloblasts, or outside portion, of the teeth during development
) much more commonly appearing in the lower jaw than the upper jaw
. It was recognized in 1827 by Cusack. This type of odontogenic neoplasm was designated as an adamantinoma in 1885 by the French physician Louis-Charles Malassez
. It was finally renamed to the modern name ameloblastoma in 1930 by Ivey and Churchill.
While these tumors are rarely malignant
or metastatic (that is, they rarely spread to other parts of the body), and progress slowly, the resulting lesions can cause severe abnormalities of the face
and jaw
. Additionally, because abnormal cell growth easily infiltrates and destroys surrounding bony tissues, wide surgical excision is required to treat this disorder.
Ameloblastoma also occurs in long bones, and another variant is Craniopharyngioma (Rathke's pouch tumour, Pituitary Ameloblastoma.)
, an important diagnostic feature. Ameloblastoma is tentatively diagnosed through radiographic examination and must be confirmed by histological examination (e.g., biopsy
). Radiographically, it appears as a lucency in the bone of varying size and features—sometimes it is a single, well-demarcated lesion whereas it often demonstrates as a multiloculated "soap bubble" appearance. Resorption of roots of involved teeth can be seen in some cases, but is not unique to ameloblastoma. The disease is most often found in the posterior body and angle of the mandible, but can occur anywhere in either the maxilla or mandible.
Ameloblastoma is often associated with bony-impacted wisdom teeth—one of the many reasons dentists recommend having them extracted.
. This process is referred to as "Reverse Polarization". The follicular type will have outer arrangement of columnar or palisaded ameloblast like cells and inner zone of triangular shaped cells resembling stellate reticulum
in bell stage. The central cells sometimes degenerate to form central microcysts. The plexiform type has epithelium that proliferates in a "Fish Net Pattern". The plexiform ameloblastoma shows epithelium proliferating in a 'cord like fashion', hence the name 'plexiform'. There are layers of cells in between the proliferating epithelium with a well-formed desmosomal junctions, simulating spindle cell layers.
The acanthomatous variant is extremely rare.
One-third of ameloblastomas are plexiform, one-third are follicular. Other variants such as acanthomatous occur in older patients. In one center, desmoplastic ameloblastomas represented about 9% of all ameloblastomas encountered.
, radiation therapy
, curettage and liquid nitrogen have been effective in some cases of ameloblastoma, surgical resection or enucleation remains the most definitive treatment for this condition. In a detailed study of 345 patients, chemotherapy
and radiation therapy
seemed to be contraindicated for the treatment of ameloblastomas. Thus, surgery
is the most common treatment of this tumor. Because of the invasive nature of the growth, excision of normal tissue near the tumor margin is often required. Some have likened the disease to basal cell carcinoma (a skin cancer) in its tendency to spread to adjacent bony and sometimes soft tissues without metastasizing. While not a cancer that actually invades adjacent tissues, ameloblastoma is suspected to spread to adjacent areas of the jaw bone via marrow space. Thus, wide surgical margins that are clear of disease are required for a good prognosis. This is very much like surgical treatment of cancer. Often, treatment requires excision of entire portions of the jaw.
Radiation is ineffective in many cases of ameloblastoma. There have also been reports of sarcoma being induced as the result of using radiation to treat ameloblastoma. Chemotherapy is also often ineffective. However, there is some controversy regarding this and some indication that some ameloblastomas might be more responsive to radiation that previously thought.
While the Mayo Clinic
recommends surgery for almost all ameloblastomas, there are situations in which a Mayo Clinic physician might recommend radiation therapy. These include malignancy, inability to completely remove the ameloblastoma, recurrence, unacceptable loss of function, and unacceptable cosmetic damage. In the case of radiotherapy, oncologists at the Mayo Clinic would use intensity-modulated radiotherapy.
may inhibit the local invasiveness of ameloblastoma, however, this was only demonstrated in vitro
. There is also some research suggesting that α5β1 integrin
may participate in the local invasiveness of ameloblastomas.
and curettage
. Follicular variants appear to recur more than plexiform variants. Unicystic tumors recur less frequently than "non-unicystic" tumors. Persistent follow-up examination is essential for managing ameloblastoma. Follow up should occur at regular intervals for at least 10 years. Follow up is important, because 50% of all recurrences occur within 5 years postoperatively. Recurrence within a bone graft (following resection of the original tumor) does occur, but is less common. Seeding to the bone graft is suspected as a cause of recurrence. The recurrences in these cases seem to stem from the soft tissues, especially the adjacent periosteum
. Recurrence has been reported to occur as many as 36 years after treatment.
To reduce the likelihood of recurrence within grafted bone, meticulous surgery with attention to the adjacent soft tissues is required.
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
(ameloblasts, or outside portion, of the teeth during development
Tooth development
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
) much more commonly appearing in the lower jaw than the upper jaw
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. It was recognized in 1827 by Cusack. This type of odontogenic neoplasm was designated as an adamantinoma in 1885 by the French physician Louis-Charles Malassez
Louis-Charles Malassez
Louis-Charles Malassez was a French anatomist and histologist born in Nevers, department of Nièvre.He studied medicine in Paris, where he worked as an interne from 1867...
. It was finally renamed to the modern name ameloblastoma in 1930 by Ivey and Churchill.
While these tumors are rarely malignant
Malignant
Malignancy is the tendency of a medical condition, especially tumors, to become progressively worse and to potentially result in death. Malignancy in cancers is characterized by anaplasia, invasiveness, and metastasis...
or metastatic (that is, they rarely spread to other parts of the body), and progress slowly, the resulting lesions can cause severe abnormalities of the face
Face
The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...
and jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
. Additionally, because abnormal cell growth easily infiltrates and destroys surrounding bony tissues, wide surgical excision is required to treat this disorder.
Subtypes
There are three main clinical subtypes of ameloblastoma: unicystic, multicystic, peripheral. The peripheral subtype composes 2% of all ameloblastomas. Of all ameloblastomas in younger patients, unicystic ameloblastomas represent 6% of the cases. A fourth subtype, malignant, has been considered by some oncologic specialists, however, this form of the tumor is rare and may be simply a manifestation of one of the three main subtypes.Ameloblastoma also occurs in long bones, and another variant is Craniopharyngioma (Rathke's pouch tumour, Pituitary Ameloblastoma.)
Clinical features
Ameloblastomas are often associated with the presence of unerupted teeth. Symptoms include painless swelling, facial deformity if severe enough, pain if the swelling impinges on other structures, loose teeth, ulcers, and periodontal (gum) disease. Lesions will occur in the mandible and maxilla,although 75% occur in the ascending ramus area and will result in extensive and grotesque deformitites of the mandible and maxilla. In the maxilla it can extend into the maxillary sinus and floor of the nose. The lesion has a tendency to expand the bony cortices because slow growth rate of the lesion allows time for periosteum to develop thin shell of bone ahead of the expanding lesion. This shell of bone cracks when palpated and this phenomenon is referred to as "Egg Shell Cracking" or crepitusCrepitus
Crepitus is a medical term to describe the grating, crackling or popping sounds and sensations experienced under the skin and joints.-Causes:...
, an important diagnostic feature. Ameloblastoma is tentatively diagnosed through radiographic examination and must be confirmed by histological examination (e.g., biopsy
Biopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
). Radiographically, it appears as a lucency in the bone of varying size and features—sometimes it is a single, well-demarcated lesion whereas it often demonstrates as a multiloculated "soap bubble" appearance. Resorption of roots of involved teeth can be seen in some cases, but is not unique to ameloblastoma. The disease is most often found in the posterior body and angle of the mandible, but can occur anywhere in either the maxilla or mandible.
Ameloblastoma is often associated with bony-impacted wisdom teeth—one of the many reasons dentists recommend having them extracted.
Histopathology
Histopathology will show cells that have the tendency to move the nucleus away from the basement membraneBasement membrane
The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...
. This process is referred to as "Reverse Polarization". The follicular type will have outer arrangement of columnar or palisaded ameloblast like cells and inner zone of triangular shaped cells resembling stellate reticulum
Stellate reticulum
The stellate reticulum is a group of cells located in the center of the enamel organ of a developing tooth. These cells are star shaped and synthesize glycosaminoglycans. As glycosamingoglycans are produced, water is drawn in between the cells and stretch them apart...
in bell stage. The central cells sometimes degenerate to form central microcysts. The plexiform type has epithelium that proliferates in a "Fish Net Pattern". The plexiform ameloblastoma shows epithelium proliferating in a 'cord like fashion', hence the name 'plexiform'. There are layers of cells in between the proliferating epithelium with a well-formed desmosomal junctions, simulating spindle cell layers.
Variants
The six different histopathological variants of ameloblastoma are desmoplastic, granular cell, basal cell, plexiform, follicular, and acanthomatous.The acanthomatous variant is extremely rare.
One-third of ameloblastomas are plexiform, one-third are follicular. Other variants such as acanthomatous occur in older patients. In one center, desmoplastic ameloblastomas represented about 9% of all ameloblastomas encountered.
Treatment
While chemotherapyChemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
, radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
, curettage and liquid nitrogen have been effective in some cases of ameloblastoma, surgical resection or enucleation remains the most definitive treatment for this condition. In a detailed study of 345 patients, chemotherapy
Chemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
and radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
seemed to be contraindicated for the treatment of ameloblastomas. Thus, surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
is the most common treatment of this tumor. Because of the invasive nature of the growth, excision of normal tissue near the tumor margin is often required. Some have likened the disease to basal cell carcinoma (a skin cancer) in its tendency to spread to adjacent bony and sometimes soft tissues without metastasizing. While not a cancer that actually invades adjacent tissues, ameloblastoma is suspected to spread to adjacent areas of the jaw bone via marrow space. Thus, wide surgical margins that are clear of disease are required for a good prognosis. This is very much like surgical treatment of cancer. Often, treatment requires excision of entire portions of the jaw.
Radiation is ineffective in many cases of ameloblastoma. There have also been reports of sarcoma being induced as the result of using radiation to treat ameloblastoma. Chemotherapy is also often ineffective. However, there is some controversy regarding this and some indication that some ameloblastomas might be more responsive to radiation that previously thought.
While the Mayo Clinic
Mayo Clinic
Mayo Clinic is a not-for-profit medical practice and medical research group specializing in treating difficult patients . Patients are referred to Mayo Clinic from across the U.S. and the world, and it is known for innovative and effective treatments. Mayo Clinic is known for being at the top of...
recommends surgery for almost all ameloblastomas, there are situations in which a Mayo Clinic physician might recommend radiation therapy. These include malignancy, inability to completely remove the ameloblastoma, recurrence, unacceptable loss of function, and unacceptable cosmetic damage. In the case of radiotherapy, oncologists at the Mayo Clinic would use intensity-modulated radiotherapy.
Molecular biology
There is evidence that suppression of matrix metalloproteinase-2MMP2
72 kDa type IV collagenase also known as matrix metalloproteinase-2 and gelatinase A is an enzyme that in humans is encoded by the MMP2 gene....
may inhibit the local invasiveness of ameloblastoma, however, this was only demonstrated in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
. There is also some research suggesting that α5β1 integrin
Alpha-5 beta-1
α5β1 is an integrin that binds to matrix macromolecules and proteinases and thereby stimulates angiogenesis. It is composed of α5 and β1 subunits. It is the primary receptor for fibronectin...
may participate in the local invasiveness of ameloblastomas.
Recurrence
Recurrence is common, although the recurrence rates for block resection followed by bone graft are lower than those of enucleationEnucleation (surgery)
As a general surgical technique, enucleation refers to the surgical removal of a mass without cutting into or dissecting it.-Removal of the eye:Enucleation refers to removal of the eyeball itself, while leaving surrounding tissues intact....
and curettage
Curettage
Curettage, in medical procedures, is the use of a curette to remove tissue by scraping or scooping.Curettages are also a declining method of abortion. It has been replaced by vacuum aspiration over the last decade....
. Follicular variants appear to recur more than plexiform variants. Unicystic tumors recur less frequently than "non-unicystic" tumors. Persistent follow-up examination is essential for managing ameloblastoma. Follow up should occur at regular intervals for at least 10 years. Follow up is important, because 50% of all recurrences occur within 5 years postoperatively. Recurrence within a bone graft (following resection of the original tumor) does occur, but is less common. Seeding to the bone graft is suspected as a cause of recurrence. The recurrences in these cases seem to stem from the soft tissues, especially the adjacent periosteum
Periosteum
Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones....
. Recurrence has been reported to occur as many as 36 years after treatment.
To reduce the likelihood of recurrence within grafted bone, meticulous surgery with attention to the adjacent soft tissues is required.
Epidemiology
The annual incidence rates per million for ameloblastomas are 1.96, 1.20, 0.18 and 0.44 for black males, black females, white males and white females respectively. Ameloblastomas account for about one percent of all oral tumors and about 18% of odontogenic tumors. Men and women tend to be equally affected, although women tend to be 4 years younger than men when tumors first occur and tumors appear to be larger in females.See also
- Bone graftingBone graftingBone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures that are extremely complex, pose a significant health risk to the patient, or fail to heal properly....
- Epithelial cell rests of MalassezEpithelial cell rests of MalassezIn dentistry, the epithelial cell rests of Malassez or epithelial rests of Malassez are part of the periodontal ligament cells around a tooth. They are discrete clusters of residual cells from Hertwig's epithelial root sheath that didn't completely disappear...
- List of cutaneous conditions
- Matrix Metalloproteinase-2MMP272 kDa type IV collagenase also known as matrix metalloproteinase-2 and gelatinase A is an enzyme that in humans is encoded by the MMP2 gene....
- Tooth developmentTooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
and Odontogenesis