Odontogenic Tumors: the Short Version
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ODONTOGENIC TUMORS: THE SHORT VERSION UMORS IN THE JAWS THAT ARISE FROM ODONTO- tumors in adults. There is a third source, the reduced genic (tooth forming) tissues are referred to as enamel epithelium that envelopes the crown 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 AMELOBLASTOMA remember the embryology and histology 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 enamel organ and some of go directly to the tumors starting with “ameloblas- them resemble ameloblasts. 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 pulp 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 dental lamina) 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. (Amelogenin 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 mandible. Ameloblastomas are always purely ameloblasts differentiate into odontoblasts and make radiolucent and may be unilocular but frequently dentin 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 (stratum intermedium and stellate reticulum) 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 ectomesenchyme. 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 cyst except that dentiger- epithelium. The fibrous connective tissue stro- ous cysts are ordinarily unilocular. ma is right and bottom. Notice the loose stel- late reticulum-like appearance in the middle of ADENOMATOID ODONTOGENIC TUMOR 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 maxilla 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 dentigerous cyst (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” AMELOBLASTIC FIBROMA 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 malignancy 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.