I. NORMAL ANATOMY. Of all the bones of the skeleton, the jaws are uniquely distinguished by harboring the odontogenic apparatus of the deciduous and permanent dentitions. The teeth germs are composed of three main components: the enamel organ, the dental papilla, and the tooth follicle. The enamel organ is composed of ectodermally derived epithelial cells, the ameloblasts, and is responsible for enamel formation. The dental papilla is of ectomesenchymal origin and produces the dentine. The tooth follicle is also ectomesenchymal; it surrounds the developing tooth and provides the supporting structures of the formed teeth, the periodontium. The odontogenic tissues may also be a source of a bewildering array of odontogenic cysts and tumors. Nonodontogenic cysts and tumors of the jaws will also be discussed in this chapter.
II. ODONTOGENIC AND NONODONTOGENIC CYSTS. Odontogenic cysts of the mandible and the maxilla are relatively common and can present over a large age range. Accurate diagnosis is simplified by location, radiographic correlation, and microscopic examination (e-Fig. 4.1).* Odontogenic tumors by contrast are uncommon. They may be epithelial, mesenchymal, or mixed; may be noncalcifying; or they may contain hard structures that mimic enamel, dentine, cementum, or bone. Although malignant odontogenic tumors are extremely rare, odontogenic carcinoma, sarcoma, and carcinosarcoma do occur.
A. Odontogenic cysts. With the exception of a few cysts that may develop along embryonic lines of fusion (known as “nonodontogenic cysts”), most jaw cysts are lined with epithelium that is derived from the odontogenic epithelium. Odontogenic cysts are classified as either developmental or inflammatory. Various types of odontogenic cysts are listed in Table 4.1.
1. Developmental odontogenic cysts
a. Dentigerous cyst (follicular cyst) is a unilocular cyst that forms in association with the crown of an impacted tooth and is usually associated with a molar or canine. Patients usually present with an asymptomatic, well-defined, expansive, radiolucent lesion. Microscopic examination shows a thin layer of cuboidal to slightly flattened epithelial cells. Focal keratinization, mucous cells, inflammation, and dystrophic calcification are possible. Enucleation and excision of the associated tooth are the treatment of choice. Eruption cyst is a subclass of dentigerous cysts associated with the erupting primary or permanent tooth.
b. Keratocystic odontogenic tumor (odontogenic keratocyst) usually presents as an asymptomatic unilocular cyst in the mandible or the maxilla. While more frequent in the second to fourth decades of life, they may be seen at any age. Their incidence is higher in Caucasians, especially in and men, and roughly 5% of patients with odontogenic keratocysts have nevoid basal cell carcinoma (Gorlin) syndrome. Gross examination typically yields a cyst containing keratinous debris. Microscopic examination shows palisading basal cells covered by a few layers of squamous cells under a
corrugated parakeratotic surface (e-Fig. 4.2). A key diagnostic feature is the lack of rete pegs. Satellite cysts and intramural epithelial cell proliferation are more commonly found in the syndrome-associated cases. Exceptionally, dysphasia and carcinoma develop in the cyst. Treatment is surgical excision, and recurrence is common.
TABLE 4.1 Odontogenic Cysts
Dentigerous cyst and eruption cyst
Keratocystic odontogenic tumor (odontogenic keratocyst)
Lateral periodontal cyst
Gingival cyst of the adult
Calcifying cystic odontogenic tumor (calcifying odontogenic cyst, Gorlin cyst)
Glandular odontogenic cyst
Periapical (radicular) cyst
Residual periapical (radicular) cyst
c. Lateral periodontal cyst generally presents as a well-demarcated radiolucent lesion in asymptomatic patients in their fifth to seventh decades of life. The typical locations are the lateral surface of the roots of the mandibular premolar teeth, although rare presentations in the maxilla may be encountered. Microscopic examination shows a thin layer of nonkeratinized epithelium with focal thickening and possible clear cells (e-Fig. 4.3). The adjacent soft tissue is not inflamed. A rare polycystic variant (botryoid odontogenic cyst) is characterized by rapid growth and an elevated probability of recurrence. Simple excision is typically curative.
d. Gingival cyst of the adult is an infrequent lesion appearing on the buccal gingiva of the mandible near the premolars and canines. It represents the soft tissue counterpart of the lateral periodontal cyst. The typical age of patients is the fifth to sixth decades of life and they present with a <1-cm gingival cyst that has a normal to bluish overlying mucosal surface. While usually unicystic, rare multicystic gingival cysts (gingival botryoid odontogenic cyst) may be seen. Microscopic examination shows a cyst lined by a thin layer of epithelium with rare focal thickening; the adjacent soft tissue is fibrotic and does not show inflammation. Treatment is simple excision.
e. Calcifying cystic odontogenic tumor (calcifying odontogenic cyst, Gorlin cyst) presents as a radiolucent asymptomatic lesion of the maxilla or the mandible. The tumor can be unicystic, multicystic, and occasionally solid. Focal radio-opaque areas may be identified. The incidence peaks in the second and third decades, although cases occur in all age groups. Microscopic examination shows a proliferating layer of columnar palisaded basal cells similar to ameloblasts. The superficial layers frequently have larger ghost cells characterized by eosinophilic cytoplasm without nuclei (e-Fig. 4.4). Calcification of the tumor and adjacent soft tissue can be identified in some cases. Treatment is surgical excision and recurrence is uncommon.
f. Glandular odontogenic cyst is a recently defined lesion that has also been referred to as sialo-odontogenic cyst. The majority occur as a radiolucent cyst in the anterior mandible or the anterior maxilla. Patients typically present with pain and swelling, but some cases are asymptomatic. Microscopic examination demonstrates a unilocular/multilocular cyst with nonkeratinized epithelium, mucous producing cells, and focal
solid areas (e-Fig. 4.5A and B). Hyaline bodies, ghost cells, and ciliated cuboidal eosinophilic cells may be present. Care should be taken to differentiate between a glandular odontogenic cyst and a central mucoepidermoid carcinoma. Surgical excision is the treatment of choice.
2. Inflammatory odontogenic cysts. Radicular (periapical) cysts are associated with a nonviable carious teeth. The usual location is the apical third of the tooth root, with occasional cases involving the lateral root surface. The cyst is more common in the mandible. The typical age of patients is the third to sixth decades of life. The most common presentation is pain and swelling, but presentation as an incidental finding on routine radiographic examination is not unusual. Microscopic examination reveals an inflamed, nonkeratinizing, stratified epithelium. Cholesterol crystals, foamy macrophages, dystrophic calcifications, and intraepithelial hyaline bodies (Rushton bodies) may be identified (e-Fig. 4.6A and B). The residual cyst is a variant of radicular cyst that is seen at the site of an extracted tooth.
B. Nonodontogenic cysts. This class of lesions includes a group of epithelium-lined cysts as well as non-epithelium-lined bone cysts. The epithelial-lined cysts are believed to arise from epithelial remnants entrapped along embryonic lines of fusion and are referred to as fissural cysts (e-Fig. 4.7).
1. Epithelial-lined nonodontogenic cysts (fissural cysts)
a. Nasopalatine duct cyst (incisive canal cyst) is the most common of the fissural cysts. It is believed to arise from remnants of the nasopalatine duct. The cyst can develop almost at any age, but it is most common in the fourth to sixth decades of life. Most studies show a slight male predilection. The most common presenting symptoms include swelling of the anterior palate, drainage, and pain.
Radiographs usually demonstrate a well-circumscribed radiolucency, in or near the midline of the anterior maxilla, between and apical to the central incisor teeth. The lesion most often is round oval or pearshaped. Microscopically, the epithelial lining of the cyst may be stratified squamous, pseudostratified columnar, simple columnar, or cuboidal. Commonly, more than one epithelial type is present. Because the cyst arises within the incisive canal, moderate-sized nerves and small muscular arteries and veins are usually found in the cyst wall (e-Fig. 4.8). Surgical enucleation is the treatment of choice.
b. Globulomaxillary cyst is believed to develop from epithelium entrapped during fusion of the globular portion of the medial nasal process with the maxillary process, although its origin continues to be a subject of debate.
The cyst classically develops between the lateral incisor and cuspid teeth, although occasionally it has been reported between the central and lateral incisors. Radiographically, the cyst presents as well-circumscribed unilocular radiolucency between and apical to the teeth. The radiolucency is often pear-shaped. As the cyst expands, tilting of the adjacent teeth may occur. Microscopically, many of the cysts are lined with stratified squamous epithelium. Occasionally, however, the lining epithelium is of pseudostratified columnar ciliated type. Enucleation is the treatment of choice.
c. Median palatal cysts (median palatine cysts) are rare fissural cysts. They are believed to develop from epithelium entrapped along the embryonic line of fusion of the lateral palatal shelves of the maxilla. The cyst may be difficult to distinguish from the nasopalatine duct cysts, and some cases may actually represent a posteriorly placed nasopalatine duct cyst.
Clinically, the cyst presents as a firm or fluctuant swelling in the midline of the hard palate, posterior to the incisive papilla. It is more frequent in
young adults and is often asymptomatic. The average size is 2 × 2 cm, but these cysts may become quite large. Radiographs demonstrate a well-circumscribed lucency in the midline of the hard palate. Microscopically, the cyst is commonly lined by stratified squamous epithelium, but areas of pseudostratified columnar epithelium may be seen. Surgical removal is the treatment of choice.
2. Non-epithelial-lined nonodontogenic bone cysts of the jaws
a. Simple bone cysts are known by multiple names including unicameral bone cyst, solitary bone cyst, progressive bony cavity, hemorrhagic cyst, and traumatic bone cyst. The typical patient is younger than 20 years of age and has a well-demarcated osteolytic solitary lesion in the posterior mandible. Unusual cases have been seen in the maxilla. The cyst cavity is lined by fibrovascular tissue with hemosiderin-laden macrophages. Reactive bone and osteoclasts may be identified.
b. Aneurysmal bone cyst is a rapidly enlarging blood-filled cystic lesion usually identified in the first three decades of life. The majority are well-demarcated, unilateral pseudocysts located in the mandible (60%) and the maxilla (40%). Aneurysmal bone cyst may be identified alone or in conjunction with another lesion (e.g., chondroblastoma, osteoblastoma.) CT and MRI studies show characteristic layering of blood cells and serum. Microscopic examination shows a fibrotic stroma with giant cells, macrophages, and hemosiderin granules (e-Fig. 4.9A and B). Areas of ossification may be present. Treatment is curettage and enucleation, and about 25% of the lesions recur.
III. ODONTOGENIC TUMORS. Odontogenic tumors are classified according to their composition into epithelial, mesenchymal, or mixed. Epithelial odontogenic tumors are composed of only odontogenic epithelium, whereas mesenchymal odontogenic tumors are composed principally of ectomesenchymal elements. Mixed odontogenic tumors contain epithelial and ectomesenchymal tissues. Inductive interactive action between the epithelial and ectomesenchymal elements may mimic normal odontogenesis and thus dental hard tissues may, on occasions, be found in these tumors. As stated above, malignant odontogenic tumors are rare, but carcinomas, sarcomas, and carcinosarcomas do occur.
Odontogenic tumors are listed in Table 4.2.
A. Epithelial odontogenic tumors
1. Ameloblastoma is the most common clinically significant odontogenic tumor. Its relative frequency equals the combined frequency of all other odontogenic tumors, excluding odontoma. Ameloblastoma is slow-growing, locally invasive neoplasm. The tumor is encountered over a wide age range; it is rare in children and is most prevalent in the third to seventh decades of life. There is no gender predilection. Some studies show an increased frequency in blacks.
About 85% of ameloblastomas occur in the mandible, most often in the molar-ascending ramus area. About 15% of ameloblastomas occur in the maxilla, usually in the posterior region. Painless swelling or expansion of the jaw is the usual clinical presentation. If untreated, the lesion may grow slowly to massive or grotesque proportions. Pain and paresthesia are uncommon, even in large tumors. Radiographically, the most typical feature is that of a multilocular radiolucent lesion. Cortical expansion is frequently present. Microscopically, the lesion may present several patterns; these microscopic patterns have no bearing on the behavior of the tumor, and large tumors often show a combination of patterns.
The follicular pattern is the most common and recognizable. It is composed of nests of epithelium that resemble the enamel organ of the developing teeth, dispersed in a mature fibrous connective tissue stroma. The core of the nests is composed of loosely arranged angular cells that resemble the stellate
reticulum of the enamel organ. A single layer of tall columnar ameloblastlike cells surrounds the central core. The nuclei of these cells are placed away from the basement membrane (so-called reversed polarity) (e-Fig. 4.10). Cyst formation is common and may vary from microcysts forming within the follicles to large macroscopic cysts that may be several centimeters in diameter.
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