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Home , Ameloblastic fibroma, Ameloblastoma, Cementoblastoma, Cementoma, Dental lamina, Enamel organ

ODONTOGENIC TUMORS: THE SHORT VERSION

UMORS IN THE JAWS THAT ARISE FROM ODONTO- tumors in adults. There is a third source, the reduced genic ( forming) tissues are referred to as enamel that envelopes the of Todontogenic tumors. But what are “odontogenic unerupted teeth. Now the tumors. tissues” and how do you get tumors from them in adults long after odontogenesis has ceased? If you remember the embryology and of tooth for- Ameloblastoma is a tumor in which the tumor cells mation, you may skip the next three paragraphs and form caricatures of the and some of go directly to the tumors starting with “ameloblas- them resemble . However, they are inca- toma”. pable of making enamel matrix. This tumor occurs Recall that two types of embryonic tissues con- chiefly in middle age people long after odontogenesis tribute to the formation of a tooth. Early in embryoge- has ceased. Presumably a carcinogen converts a cell in nesis, future dental cells (primitive ectomes- one of the epithelial rests to become a tumor cell. As enchyme) migrate from the neural crest to the jaws such, it starts to divide endlessly to form a tumor. and settle out in areas where teeth are to be formed. Remember the axiom, tumor cells tend to resemble They signal the overlying ectoderm (epithelium) to the tissues from which they arise. Since cells in rests send down a cord of cells (the ) which of Serres and Malassez were at one time capable of will become the enamel organ. It is the inner layer of becoming ameloblasts, it should not come as a sur- the enamel organ that will become ameloblasts that prise that tumor cells resemble ameloblasts. secrete enamel matrix. ( is the main pro- What are the main points about this tumor? It is tein found in enamel matrix. The gene that encodes unencapsulated and infiltrates surrounding bone mar- this protein is on the X chromosome.) row. Even though they are locally infiltrative, they do After the arrival of the enamel organ, the awaiting not metastasize. They may occur in any part of both ectomesenchymal cells turn into dental pulp cells. The jaws but most are in the middle and posterior regions outer cells of the pulp that are adjacent to the of the . are always purely ameloblasts differentiate into and make radiolucent and may be unilocular but frequently matrix whereupon the ameloblasts make enam- become multilocular as they increase in size. el matrix. After the crown forms, the inner and outer If not found and treated early, they will expand the layers of the enamel organ squeeze out the two middle jaw. layers ( and ) and grow downward as a cylinder shaped structure (Hertwig’s root sheath) that outlines the root. So remember, a tooth is formed from two types of embry- onic tissues, ectoderm and . It is one of the many wonders of embryogenesis that these tis- sues are genetically programmed so that they form a FIG. 1 Ameloblastoma: a multilocular radiolucent single rooted tooth in the front, a double rooted tooth lesion in the body and ramus of the mandible in a in the midjaw, and double and triple rooted teeth in 29 year old female. the posterior jaws. How do they know? Histologically, the tumor cells appear as islands of The point in telling you this is to refresh your odontogenic epithelium in a stroma of fibrous connec- memory about terminology and to tell you that all of tive tissue. these tissues do not undergo apoptosis when the job is done. Remnants of odontogenic epithelium remain in FIG. 2 Ameloblastoma, the periodontal ligament and gingiva forever. In the medium power gingiva, they are called epithelial rests of Serres and microscopy. Islands of in the periodontal ligament they are known as the rests odontogenic epithelium of Malassez. It is not known if remnants of ectomes- in a stroma of fibrous enchyme remain because it is indistinguishable from connective tissue. surrounding mesodermal tissues. It is from the epithe- The cells in the center of the islands resemble stel- lial rests (Serres and Malassez) that arise odontogenic late reticulum but may undergo squamous metaplasia

ODONTOGENIC TUMORS -1- to become keratinizing squamous epithelium. The cells at the periphery of the epithelial islands are tall columnar cells that rest on a basement membrane sep- arating them from the surrounding stroma.

FIG. 5 A cystic ameloblastoma associated with an unerupted and displaced molar tooth in a child. Note the hint at compartmental- FIG. 3 Ameloblastoma, high power micro- ization (multilocularity). It resembles an ordi- scopy. The center and left are odontogenic nary dentigerous except that dentiger- epithelium. The fibrous connective tissue stro- ous are ordinarily unilocular. ma is right and bottom. Notice the loose stel- late reticulum-like appearance in the middle of ADENOMATOID the epithelial island and the tall columnar cells (AOT) with reverse nuclear polarity at the outer edge of the epithelium (see arrow). This is a tumor mostly of teenagers. It occurs in the middle and anterior portions of the jaws in contrast to The nuclei of the tall columnar cells (ameloblasts) ameloblastoma which is found mostly in the posterior are typically found at the end of the cell most distant segment. Two-thirds occur in the and it is from the basement membrane, a feature referred to as more common in females. This tumor is encapsulated “reverse nuclear polarity”. and is treated by curettage with a recurrence rate The treatment of ameloblastoma is surgical exci- approaching zero. sion. This may require removal of a large segment of The radiographic appearance is a unilocular radi- the jaw. Simple curettage is usually met with recur- olucency, often around the crown of an unerupted rence. tooth in which case they resemble a dentigeous cyst Ameloblastomas that arise from rests of Malassez (Figure 6). occur as intrabony tumors. Rarely, ameloblastoma FIG. 6 Adenomatoid arises from rests of Serres. Here they grow as extra- odontogenic tumor (AOT) bony soft tissue tumors in the gingiva (Figure 4). associated with an unerupted tooth #11. It FIG. 4 A peripheral resembles a dentigerous ameloblastoma. This tu- cyst. Some AOTs pro- mor arises from rests of duce calcifications that Serres or alternately from may appear as “snow- basal epithelial cells in flake” densities. the gingiva in a manner analagous to cutaneous Histologic examination reveals a thick capsule of basal cell carcinoma. fibrous connective tissue. The tumor fills the central Additionally, the reduced enamel epithelium cavity, there is little stroma. Tumor cells frequently around the crown of unerupted teeth may turn into form ball-like structures referred to as “rosettes” ameloblastoma in which case it radiographically mim- (Figure 7). ics a (Figure 5). FIG. 7 Adenomatoid This type of tumor has been referred to as unicystic odontogenic tumor, medi- ameloblastoma or simply as cystic ameloblastoma and um power. Note how the has a much better prognosis. tumor cells form balls of cells that are called rosettes.

ODONTOGENIC TUMORS -2- Another identifying feature is the presence of duct- FIG. 10 CEOT, high like structures (Figure 8). power view. The tumor cells resemble squamous epithelium more than odontogenic epithelium. FIG. 8 Adenomatoid There is some variation odontogenic tumor. Note in nuclear size and the duct-like structures shape, but this is not a (see arrow) malignant tumor. Small calcifications may be found in the tumor. If FIG. 11 Calcifications they are present in sufficient size and number, they (extreme left) in a CEOT may show on the radiograph as a “snow-flake” pat- account for the density tern. A homogeneous, eosinophilic and amorphous noted on radiographs. material may occasionally be found in AOT. Its identi- These are thought to be ty is disputed. Some consider it a peculiar form of calcified amyloid or enamel matrix, others claim that it is a dentin-like amyloid-like material, material. This is of no clinical importance but does some of which can be raise questions if this is a pure epithelial tumor (enam- seen right of center as a pale eosinophilic globule el matrix) or has an ectomesenchymal component (arrow). (dentin matrix). NOTE: We have skipped malignant ameloblas- CALCIFYING EPITHELIAL ODONTOGENIC toma, ameloblastic carcinoma, clear cell odontogenic TUMOR (CEOT, Pindborg tumor) carcinoma and odontoameloblastoma and squamous This tumor is so rare that it deserves little discus- odontogenic tumors because they are too rare. They sion. In 1958, Dr. J.J. Pindborg of Denmark described are covered in your text. four cases of an unusual odontogenic tumor that still bears his name. This is the most “unodontogenic” tumor of the group, the tumor cells do not resemble This is a tumor of childhood, the typical patient is odontogenic tissue. Tumor cells are squamous-like, about 12 –14 years old, seldom is it seen beyond age they even have desmosomal attachments. There often 20. The posterior segment of the mandible is the most is variation in nuclear size, shape and staining intensi- common location. Local swelling or failure of teeth to ty—features that are often associated with erupt on time or in proper alignment may call atten- (Figure 10). This tumor forms an amorphous material tion to the tumor. Ameloblastic fibromas are purely that is said to be amyloid or amyloid-like (Figure 11). radiolucent. Whatever it is, it calcifies in a concentrically lamellat- FIG. 12 Ameloblastic ed “tree-ring” pattern known as Liesegang calcifica- fibroma in and around tions. This explains the name of calcifying epithelial the crowns of lower odontogenic tumor. molar teeth. It is subtle, CEOT lacks a capsule but apparently does not infil- the second deciduous trate as deeply into surrounding tissues as does molar tooth has been tilt- ameloblastoma. Excision with a small margin of sur- ed downward by the rounding bone is usually curative. tumor. Patient was a 5 year old boy. Radiographically, this tumor may appear as a radi- olucent tumor but if sufficient calcifications are pres- ent, it becomes dense (Figure 9).

FIG. 9 Calcifying epithe- lial odontogenic tumor in the body of the mandible. It appears as a radiolucent lesion with smokey dense areas.

ODONTOGENIC TUMORS -3- Small lesions may be unilocular but larger lesions are ordinarily multilocular. Both odontogenic epitheli- um and odontogenic ectomesenchyme contribute to this tumor (an odontogenic mixed tumor not to be con- fused with the mixed tumor of salivary gland). The epithelium grows in small islands and cords (Figures 13 and 14).

IG FIG. 13 Ameloblastic F . 15 Compound , fibroma, medium power. the “bag of marbles” appearance. Islands of odontogenic epithelium exhibit peripheral columnar cells. The stroma is cellular ectomesenchyme that FIG. 16 Compound resembles the dental odontoma in the body of papilla, the forerunner of the mandible of a 17 the dental pulp. year old boy. In the larger islands, peripheral palisading of columnar cells with reverse nuclear polarity may be FIG. 17 Compound seen but seldom do the islands and cords open up large odontoma of tumor in enough to form central stellate reticulum. The tissue Figure 16, the small, surrounding the epithelium is cellular connective tis- closely spaced white sue that bears some resemblance to dental pulp. This is bodies are individual the ectomesenchymal component. malformed tooth-like structures.

FIG. 14 Ameloblastic fibroma, high power. Cords of epithelium lie in an ectomesenchyme stroma. E This tumor is clearly benign and is ordinarily treat- D ed by vigorous curettement. The recurrence rate is placed at about 15 %. Even though this tumor is com- P prised of both odontogenic epithelium and odonto- genic ectomesenchyme, it does not secrete either enamel matrix or dentin. The reason for making this point will become apparent later. FIG. 18 Compound odontoma, photomicrograph of decalcifed specimen. Note the structure that ODONTOMA: COMPOUND AND COMPLEX resembles a tooth with a pulp (P), a surrounding TYPES mantle of dentin (D) capped by enamel (E), center The tumors in which odontogenic differentiation is and left of center. fully expressed are the . In these tumors, the In the complex odontoma, there is little or no ten- epithelium and ectomesenchyme realize their potential dency to form tooth-like structures. The dentin and and make enamel and dentin respectively. As a result, enamel are entwined in a mass that bears no resem- these tumors are mostly radiodense. In the compound blance to teeth. The result is a solid, dense mass of odontoma, multiple small and malformed tooth-like hard tissue as seen in Figures 19, 20 and 21. structures are formed creating a “bag of marbles” radi- ographic appearance (Figure 15).

FIG. 19 Complex odontoma, posterior maxilla of a child.

ODONTOGENIC TUMORS -4- there was dentin and enamel. What’s going on? The correct diagnosis would be ameloblastic fibro-odon- toma. The question is: Is ameloblastic fibroma just the immature stage of odontoma? Or to turn that around, is an odontoma the end-stage of an amelo- blastic fibroma? The compound and complex tumors are probably different tumors, not just different ver- sions of the same tumor. The compound odontoma is FIG. 20 Complex odontoma in anterior maxilla. Deciduous tooth probably a local form of hyperdontia, a . It is retained. is not the end stage of something else. On the other hand, the complex odontoma is thought to be the end- stage of a tumor that began as an ameloblastic fibroma FIG. 21 Complex odon- that progressed along the ameloblastic fibro-dentino- toma, histopathology of ma — ameloblastic fibro-odontoma, mature complex D decalcified specimen. The odontoma pathway. The histologic diagnosis would dentin (D) appears as thin depend on the stage during the tumor progression E strands of eosinophilic when it was biopsied. But there is a problem. Some material and the enamel people who have an ameloblastic fibroma have a (E) is more purple. recurrence years later and there is no evidence that it Both types of odontoma are found in the early has progressed; there is no dentin or enamel forma- years, usually in the teens or early twenties. Com- tion. So the theory is that that there are two varieties pound odontoma is more common in the anterior jaw of ameloblastic fibroma, (1) a truly neoplastic variant segment whereas the complex type is found more that does not progress and (2) a harmatomatous vari- commonly in the posterior jaws. Many are associated ent (malformation) that left untreated will become a with an unerupted tooth. Odontomas behave more like complex odontoma. In the early stage, it is not possi- developmental abnormalities () than true ble to tell them apart so they are all treated as if they . Although they may reach a large size, they are the neoplastic type. do eventually cease growing in contrast to true neo- ANOTHER NOTE: We skipped ameloblastic plasms which show continuous growth. fibrosarcoma, granular cell ameloblastic fibro- Treatment is elective . They have a limited ma, and odontogenic fibroma because this doc- growth potential and cause no pain or cosmetic defor- ument is the short version. mity. Note: Now a brief, arcane discussion about the MYXOMA () relationship of ameloblastic fibroma to odon- Tissue that is cell-poor and rich in mucopolysac- tomas. What would happen if you left an charide ground substance such as hyaluronic acid and ameloblastic fibroma untreated? Would it even- chondroitin sulfate is said to be myxoid tissue. tually make dentin (the first hard tissue formed Tumors that have the same histologic quality are in odontogenesis) and become an ameloblastic called myxoma (mix-oma). They are uncommon. fibro-dentinoma? And if still untreated, would it Within the skeleton, they occur almost exclusively in eventually make enamel (the other and always the jaws. Extragnathic skeletal lesions are a rarity. second hard tissue formed during odontogene- Those that occur in the jaws are said to be of odonto- sis) and become an ameloblastic fibro-odon- genic origin but there is no hard evidence that it is so. toma? Examine Figure 22. Myxoma is a tumor that occurs over a wide age range but most occur in the second and third decades. It is an unencapsulated, locally infiltrating tumor. If allowed to reach a large size, it takes a big operation FIG. 22 Ameloblastic to remove it. Like many odontogenic tumors, when fibro-odontoma, see text small it is ordinarily unilocular but becomes multiloc- for comments about this ular as it enlarges. Since it does not produce a calci- tumor. fied matrix material, it is purely radiolucent. Figures Microscopic examination of the radiolucent portion 23 and 24 are examples of myxoma. of this tumor revealed ameloblastic fibroma, there was no dentin or enamel. But within the radiodense areas,

ODONTOGENIC TUMORS -5- FIG. 26 Cementoblas- toma, typical radiograph- FIG. 23 Myxoma ic appearance of a ball of appearing as a unilocular clinging to the maxillary lesion. root.

FIG. 24 Myxoma, radi- ograph of a resected specimen. Note the “wispy” trabeculations, a feature said to be char- FIG. 27 , acteristic of this tumor gross specimen. Figure 24 is a radiograph of a myxoma of the max- This dense material is presumed to be cementum illa that has been surgically removed. Notice that it is and the tumor cell line that secretes it is cemento- a destructive, lucent lesion but extending into the radi- blasts, hence the name. So why the other name “true olucent area from the perimeter are whispy trabeculae ”? Recall that the lesion we know as of bone. This is said to be a characteristic feature of cementoma is a self-limiting lesion ordinarily found in myxomas. and around the apices of the lower incisor teeth. But FIG. 25 Myxoma, high the cementoblastoma is not self-limiting, it continues power histopathology. to grow until it is removed, hence it is a “true” tumor, Tumor cells lie randomly a true cementoma. Maybe we should call the self-lim- in a clear background of iting cementoma by its other name, periapical cemen- non-staining mucopoly- tal dysplasia. Histologically the mass of cementum is saccharide ground attached to the tooth root. As it expands, the cemento- substance. blasts at the periphery add new cementum. Notice that the tumor cells are round to angular to stellate and some resemble tadpoles. These are “myxoblasts” which in reality probably are fibroblasts that are secreting a large amount of ground substance rather than collagen. The reason the background is clear is that hyaluronic acid and chrondroitin sulfate do not stain with usual hematoxylin and eosin stain so it looks like the cells are floating in air. C CEMENTOBLASTOMA (TRUE CEMENTOMA) FIG. 28 Cementoblastoma, medium power As a group, odontogenic tumors are not common. histopathology of the decalcified specimen. Cementoblastoma is among the rarest of the rare. This The field is dominated by sheets of cementum tumor typically occurs around the roots of the lower with a rim of (C) with an outer rim posterior teeth. Like virtually all odontogenic tumors, of normal bone. it is benign but it expands the jaw, causes pain and requires surgical removal. Radiographically it appears The layer of cementoblasts appear on the radi- as a ball of dense material attached to the end of the ograph as a thin radiolucent line that abuts on sur- root (Figure 26). rounding bone. So the cementoblastoma appears as a ball of dense material with a thin halo of radiolucenty (Figure 26). Charles Dunlap, DDS UMKC School of August 2001

ODONTOGENIC TUMORS -6-