What is Ameloblastoma?

Ameloblastoma

Ameloblastoma is one of the common benign odontogenic epithelial tumors. It grows slowly but has local invasiveness. If the resection is not complete, the recurrence rate is high, but there is basically no tendency to metastasize. The tumor originates from the residual epithelium of the enamel apparatus or dental plate, or the residual epithelium in the periodontal tissue. Ameloblastomas that occur outside the jawbone may develop due to ectopic basal cells or epithelium of the oral cavity. Others can occur in the tibia or pituitary.

Western Medicine Name: Ameloblastoma
English name: ameloblastoma

Affiliated Department: Department of Physiology-Stomatology
Disease site: The gums of the jaw, edentulous area, or alveolar mucosa of the edentulous jaw
Multiple groups: Male and female incidence rates are similar, with a wide range of ages

Introduction to Ameloblastoma Disease

Ameloblastoma is one of the common benign odontogenic epithelial tumors. It grows slowly but is locally invasive. If the resection is incomplete, the recurrence rate is high, but there is basically no tendency to metastasize.

Disease classification of ameloblastoma

WHO classified ameloblastoma into four types according to different clinical and pathological manifestations

(A) solid / multicystic ameloblastoma (AS / M)

(B) extraosseous / peripheral ameloblastoma (AE / P), accounting for 1.3% to 10% of all ameloblastomas

(Three) ameloblastoma-desmoplastic type (AD)

(IV) Unicystic ameloblastoma (AU), accounting for 5% to 15% of all ameloblastomas

Causes of Ameloblastoma Disease

do not know yet. Some genetic abnormalities associated with normal tooth development may play a role in their histological development. It may originate from odontogenic epithelium or odontogenic epithelium remnants, including enamel formation, Malassez epithelium remnants, Serres epithelium remnants, residual enamel epithelium, and lining epithelium of odontogenic cysts. Others believe that this tumor can occur in the oral mucosa epithelium.

Clinical manifestations of ameloblastoma

The incidence of men and women is similar, and the age range of onset is very wide. Most cases are diagnosed at the age of 30-60 years, and it is rare for patients under 20 years of age.

AS / M, which is specific to the jawbone, rarely occurs in the nasal cavity and maxillary sinus, and about 80% occurs in the mandible. The mandibular molar area and the ascending branch of the mandible are the most common disease sites.

Tumors grow slowly, with an average course of about 6 years. There is no conscious symptoms in the early stage, and the jaw is swollen in the later stage, which develops to the lip and buccal side. Compression growth can cause facial deformity and dysfunction. When the ameloblastoma of the maxilla is enlarged, it can affect the nasal cavity and cause nasal congestion. When it invades the maxillary sinus and spreads to the orbit and nasolacrimal duct, it can cause eyeball displacement, tearing, and diplopia. When the ameloblastoma of the mandible grows, the bone becomes thinner under pressure and absorbs it. When the tumor presses the inferior alveolar nerve, the affected lower lip and cheeks may feel numb and uncomfortable. During puncture, yellow and yellow-brown liquids can be drawn, and cholesterol crystals can be contained. The mucosa covered by the mass is generally smooth without special changes. Occasionally, bite marks on the jaw teeth may cause loosening, displacement or loss of teeth in the tumor area. In a few cases, secondary infections can occur, with tumors growing locally from the ulcer and pain.

AE / P, which occurs in the gingival or alveolar mucosa of the edentulous area, is a painless, solid, exogenous mass with a smooth or uneven surface, or a papillary shape. Except for the superficial absorption of alveolar ridges caused by tumor compression, significant bone involvement is rare.

AD, there are currently no reports of extraskeletal AD, the main clinical complaint is painless swelling of the jaw. On X-ray films, about 50% of AD manifests as mottled transmission / blocking artifacts, with unclear borders, suggesting fibro-osseous lesions; root absorption and osteogenesis may also occur.

AU, more common in young people, aged between 10 and 29 years old, with an average age of about 25 years old, occurs in the mandibular molar area. Nearly 80% of the cases are associated with the third mandibular molar. X-rays are clearly defined single-room transmissions, often located in the crown, and root resorption may occur.

Ameloblastoma of right mandible body

Histopathology of ameloblastoma

(I) AS / M

a, follicular type. It consists of odontogenic epithelial islands in the fibrous interstitium. It is characterized by basal cells of the epithelial islands that are highly columnar, deep-stained with nuclei, and arranged in a polar arrangement. Their nuclei are far from the basement membrane, and the cytoplasm is often vacuolated. The cells in the center of the epithelial island are loosely arranged, similar to the stellate network. This area often undergoes cystic changes and sometimes merges with each other.

b. Plexiform type. It is composed of basal cells arranged in strands and intertwined into a reticular pattern. The reticular layer is not obvious. The stroma is usually very slender and often cystic.

c. Acanthoma type. Extensive squamous metaplasia appeared in tumor epithelial islands, and sometimes keratinized beads were formed.

d. Granular cell type. Tumor epithelial cells can sometimes undergo granular-like degeneration, and granular cells can partially or completely replace tumor stellate cells.

e. Basal cell type. Tumor epithelium is densely packed or dendritic, with small and consistent cells and lack of stellate cell differentiation. It is rare and needs to be distinguished from basal cell carcinoma and intra-jaw adenoid cystic carcinoma.

f. Keratosis into ameloblastoma. It is a rare tissue subtype with extensive keratosis in the tumor. Microscopic tumors consist of multiple tiny cysts filled with keratin. The lining epithelium is mainly incomplete keratosis and accompanied by papillary hyperplasia, so it is also called papillary keratinoma to ameloblastoma.

(Two) AE / P

Histological manifestations are the same as those of the intraosseous type. Some lesions are located entirely within the connective tissue of the gums and have no connection with the surface epithelium; some lesions appear to fuse with or originate from the mucosal epithelium. Squamous cells in the echinoderma-like area of AE / P can form solid clusters of shadow cells or clear cells. Tumor stroma is mature fibrous connective tissue.

(Three) AD

Mainly interstitial components, squeezing odontogenic components. Epithelial islands are extremely irregular in shape, with a pointed, star-shaped appearance. Peripheral cells of epithelial islands are cubic, sometimes with deep nuclear staining. Apparently tall, columnar cells with polar nuclei are extremely rare. The center of the epithelial island is swirling, and the cells are abundant, which are spindle-shaped or squamous epithelial cells. Microcapsule formation can be seen in the center of the epithelial island. Mucous-like degeneration often occurs in the stroma adjacent to the epithelium, and sometimes metaplastic osteoid trabeculae can be seen.

(Four) AU

a. Simple cystic type. Presented as a cystic lesion with only epithelial lining in the cyst wall, showing the typical morphological characteristics of ameloblastoma, including columnar basal cells arranged in a fence-like pattern (nuclei are deeply stained and far from the basement membrane) with loosely arranged basal cells on the nucleus. In addition, tumor nodules protruding into the cystic cavity were seen, and the epithelial arrangement of plexiform ameloblastoma was characteristic. The tumor did not infiltrate the wall of the fibrous capsule.

b. Infiltration of the capsule wall. Follicular or plexiform ameloblastoma-like epithelium infiltrates into the cyst wall.

Diagnosis of ameloblastoma disease

A preliminary diagnosis can be made based on medical history, clinical manifestations, and X-ray characteristics.

Typical X-ray manifestations: a honeycomb-like shape in the early stage, multi-room cyst-like shadows formed later, and less single rooms. The edges of the surrounding capsule wall are often irregular, with a half-moon shape with notches and increased density of bone white lines. Tumor growth can lead to tooth displacement, and the roots of the capsule are indented or truncated, and those with ambush teeth can behave similarly. X features of dental cysts.

The same X-ray characteristics of various types of ameloblastoma are summarized as the following six points

1) Bone bulge, which is lateral to the cheeks;

2) The bone density disappears, and the alveolar bone disappears more often;

3) The tumor contains teeth or does not contain teeth. The teeth can be impacted teeth, impacted teeth or multiple teeth at various stages of development; the teeth in the mouth are pushed, loosened or shed by the tumor;

4) The tooth root is indented, and bone hyperplasia and sclerosis of the tumor edge

5) The tumor can infiltrate between the roots;

6) No calcification of the tumor.

Differential diagnosis of ameloblastoma

Odontogenetic keratocystic tumor: AS / M and multi-room type odontogenic keratocystic tumor are not easy to distinguish on X-ray manifestations. If cystic fluid is extracted before surgery, it is generally yellow-brown, without shed epithelial cells and yellow White flaky keratin, which can be distinguished from keratotic cysts, odontogenic keratocystic cystoma fluid can be white or yellow oil-like, cyst fluid smears can find keratinized epithelial cells.

Ossifying fibroma: It is more common in children and young people, and it is common in women. According to the degree of ossification, its X-ray performance varies. The jawbone is locally swollen, the densification is thin, the perimeter is clear, and the density is reduced. The light-transmitting area can be single-room or multi-room, with or without dense calcification.

Other odontogenic tumors: If the X-ray manifestations are similar to ameloblastoma with calcification, other odontogenic tumors should also be considered, such as odontogenic fibroma, odontogenic calcified epithelioma, and odontogenic Calcified cysts, etc., the final diagnosis depends on pathological examination.

Ameloblastoma Disease Treatment

Mainly surgical treatment. The traditional view is that ameloblastoma has the characteristic of locally infiltrating the surrounding bone. Therefore, curettage should not be performed. The bone surrounding the tumor must be removed at least 12.5px, otherwise incomplete treatment will cause recurrence. This year, some people also advocate curettage. Although this method has the advantages of preservation function and appearance, it has a high recurrence rate and should be used with caution. AE / P treatment is conservative resection. The recurrence rate of AU after curettage is low (about 10%)

1) Marginal alveolar resection is feasible for smaller tumors to preserve the continuity of the mandible.

2) For larger tumors, segmental jaw removal should be performed to ensure that no recurrence occurs after surgery. Immediate bone grafting can be used after mandibular resection; if oral challenge infection or soft tissue is not enough, vascularized osteomuscular flap can be used for reconstruction and repair, or Kirschner wire and other biological materials such as titanium plates are used to fix the stump to maintain the defect. The stump of the stump will undergo bone grafting at a later stage.

3) For cystic (mural) ameloblastoma, decompression angioplasty can be used and followed up regularly.

4) If it cannot be distinguished from jaw cysts or other dental tumors before surgery, a frozen section can be performed during the operation to confirm the diagnosis. If malignant changes, it should be treated according to the principle of malignant tumor surgery.

Prognosis of ameloblastoma disease

Long-term follow-up is recommended

1. AS / M has long been regarded as a "critical tumor" prone to recurrence and malignancy, and the cumulative prognosis of the posterior maxillary bone is poor. Current information shows that AD is similar.

2. AE / P is not invasive due to its growth confined to the gums, and it is easy to detect and remove surgically, so there is no recurrence after surgery. Very few cases of malignant AE / P (ameloblastoma) have been reported.

3. The recurrence rate of AU after curettage is low (about 10%). ^[1-4]