Most radicular cysts are asymptomatic and are discovered incidentally during routine radiographic evaluation (Fig. 132.1). Radicular cysts rarely exceed 1 cm in diameter except when several adjacent teeth become devitalized as a result of trauma. Radiographically, the radicular cyst is round to ovoid, well circumscribed, and contiguous with the apex of the involved tooth.

The cyst is lined by stratified squamous epithelium of varying thickness. The cyst wall typically supports a variable inflammatory cell infiltrate, including lymphocytes and neutrophils. The cystic lumen will frequently contain necrotic cellular debris. A small percentage of radicular cysts have crescent-shaped hyaline (Rushton) bodies within the epithelial lining. Although unique to odontogenic cysts, the biologic significance of Rushton bodies is unknown. Multinucleated foreign body giant cells, cholesterol crystal clefts, and hemosiderin may be seen throughout the connective tissue of the cyst wall.

These cysts are treated by extraction of the infected tooth followed by enucleation of the cyst. Extraction of the tooth without removing the cyst may allow for persistent growth of the cyst. If the cyst is incompletely removed, a residual cyst may develop. Complete bony healing is typically seen within 6 months if the radicular cyst has been thoroughly removed.

Dentigerous cysts usually occur in the second and third decades with a slight male predilection. Because they are associated with an impacted tooth, the arch will appear to be missing a tooth. The cysts usually do not produce symptoms and can achieve significant size, causing bony expansion (Fig. 132.2A and B). The dentigerous cyst is usually a well-circumscribed, unilocular, radiolucency surrounding the crown of an unerupted tooth (Fig. 132.2C). Mandibular cysts can displace the tooth into the ramus or the inferior border of the mandible, while maxillary cysts can displace the tooth into the maxillary sinus toward the orbital floor. It is important to understand that the above-stated clinical and radiographic features are not specifically diagnostic
for a dentigerous cyst, although highly consistent (4). The differential diagnosis for similar-appearing radiographic lesions should include an ameloblastoma, keratocystic odontogenic tumor (KCOT), and adenomatoid odontogenic tumor (AOT).

The cystic lumen is lined by nonkeratinized, stratified squamous epithelium that is anywhere from 2 to 10 cell layers thick. It is common for the lining to be inflamed. The dentigerous cyst can share several microscopic features with the radicular cyst, such as Rushton bodies, cholesterol crystal clefts, and hemosiderin deposits. Chronic dentigerous cysts may exhibit areas of keratinized epithelium, which require the lesion to be differentiated from the KCOT (5). The epithelial lining of the dentigerous cyst is capable of ameloblastoma expression (3). Thus, timely diagnosis and treatment is critical.

Removal of the impacted tooth along with thorough enucleation of the cyst is usually definitive therapy. When a mandibular dentigerous cyst reaches considerable size, the cyst can be marsupialized to allow for decompression and shrinkage of the cyst with compensatory bone fill prior to definitive removal of the lesion.

The COC behaves like most other odontogenic cysts, and it has little recurrence potential. The COC has a wide age range, but the peak incidence occurs in the second decade. The lesion has a predilection for females, and most are located in the anterior portion of either jaw. The extraosseous lesion may present with painless gingival expansion. These cysts are often discovered as incidental findings on routine radiographic evaluation. They initially appear lucent. As the cyst develops, calcifications may develop causing a well-circumscribed mixed radiolucent/radiopaque appearance. However, these opacities are only seen in approximately one-third to one-half of all cases.

These usually unilocular cysts are lined by odontogenic epithelium. The basal layer is distinct with its columnar to cuboidal cells with hyperchromatic nuclei that are polarized away from the basement membrane (Fig. 132.3). Another characteristic histologic feature of the COC is the ghost cell—an altered epithelial cell with loss of the nucleus and bright eosinophilic cytoplasm—that represents abnormal keratinization. With time, these ghost cells tend to become calcified, sometimes even forming calcified masses. When these cells contact the connective tissue, a foreign body reaction occurs due to the release of keratin.

Surgical enucleation usually results in complete resolution. The extraosseous lesions are often associated with other odontogenic tumors and due to their low recurrence potential are managed conservatively with lesion removal only.

This lesion occurs most commonly in middle-aged adults. The majority of glandular odontogenic cysts have been reported in the mandible especially in the anterior region. They appear as multilocular radiolucencies and may cross the midline.

This lesion has several unique microscopic features: (a) an epithelial lining of variable thickness and a flat epithelial-connective tissue junction; (b) small microcysts and glandlike structures within the epithelial lining; and (c) a single layer of cuboidal or columnar cells lining the gland-like structures (Fig. 132.4).

Most glandular odontogenic cysts are amenable to enucleation and curettage. However, due to its recurrence potential, some advocate marginal resection (8). Regardless, long-term follow-up is advisable.

Men are affected twice as often as females, and this cyst occurs most frequently in the fourth to sixth decades. The nasopalatine duct cyst is either asymptomatic or presents as a soft tissue swelling in the midline of the anterior hard palate once the lesion has perforated the bone. The lesion is typically a well-circumscribed, oval-pear or heart-shaped, unilocular radiolucency in the midline of the anterior palate. If the cyst reaches large proportions, it can resorb the roots of the adjacent teeth. Some normal incisive canals are radiographically wide, which may make diagnosis of this lesion less precise. It is generally accepted that any radiographic lesion greater than 6 mm should be considered a cyst and not an enlarged incisive foramen. If no soft tissue or bony swellings are present and the patient is asymptomatic, then a diagnosis of nasopalatine duct cyst becomes unlikely.

The lining of this lesion can be either stratified squamous epithelium, ciliated columnar or cuboidal epithelium, or a combination of the two. This variable lining reflects whether the cyst has arrived from epithelium closer to the palate (stratified squamous) or more closely associated with the nasal cavity (ciliated columnar). The fibrous tissue contains elements of nerve and vascular tissue consistent with the surrounding incisive canal contents. Mucus glands are occasionally seen within the wall of the cyst as these glands are native to the adjacent nasal cavity.

Surgical enucleation is usually curative, but may result in sacrificing the nasopalatine nerve and vessel, resulting in denervation of the mucosa of the anterior palate and maxillary incisors. Recurrence is rare.

The odontoma is the most common odontogenic “tumor.” The lesion is typically asymptomatic and is discovered in the first two decades on radiographic examination, often initiated to evaluate lack of expected eruption of a permanent tooth. Radiographically, both the compound and complex odontomas are radiopaque masses and have a well-demarcated border. The compound odontoma resembles multiple tiny tooth structures, while the complex odontoma appears as a dense irregular mass.

Although reduced enamel epithelium may be present, odontomas are essentially composed of enamel, dentin, cementum, and pulp tissue. Fibrous tissue is sparse.

Removal of the lesion may be necessary to rule out other lesions or if the mass is impeding the eruption of a tooth. Enucleation and curettage is considered curative, and the lesion is not known to recur.

The KCOT differs from other odontogenic lesions with regard to its growth potential and recurrence rate. It can display aggressive growth, causing bony expansion and destruction, and reports have shown recurrence rates from 5% to 60% (16,17). The KCOT occurs over a wide age range; however, its peak incidence is within the second and third decades. When multiple KCOTs occur in a patient, the nevoid basal cell carcinoma syndrome (NBCCS) must be considered. The mean age of patients with multiple KCOTs, with or without NBCCS, is lower than those with single, nonrecurrent KCOTs. Radiographically, the KCOT appears as a well-circumscribed radiolucency with a distinct border, and many cause bony expansion or erosion of either cortex. Involved teeth may become displaced, but root resorption rarely occurs.

The KCOT has the following distinct microscopic appearance: its lining is parakeratinized, stratified squamous epithelium, which is six to eight cell layers thick; the luminal surface is covered by a corrugated layer of parakeratin; the basal layer is palisaded and cuboidal, with prominent, intensely stained hyperchromatic nuclei; and a lack of rete pegs. This flat epithelial-connective tissue interface results in a separation of the epithelium on histopathologic processing. Exfoliated parakeratin often fills the cyst lumen and presents during surgery as a creamy, white material. Daughter (satellite) epithelial islands and cysts may be seen in the surrounding connective tissue and may be indicative of the NBCCS.

The KCOT requires surgical enucleation and osseous curettage, and every attempt should be made to remove it in one piece (18). Modified Carnoy solution is a tissue fixative that can aid in a more complete lesion removal. Treatment of the residual bony cavity may devitalize microscopic remnants, thus decreasing the chance of recurrence (19,20). Some clinicians have advocated marginal resection to avoid recurrence (21). When large lesions are present, marsupialization may be performed to decompress the KCOT to allow for easier removal of the cyst at a later surgery (22,23). Secondary infection, need for high patient compliance, and variable results limit the use of marsupialization techniques. Most recurrences occur within 5 years, but reports of recurrence as long as 10 years later have been documented. Thus, close follow-up is mandatory. Recurrence of KCOT has been speculated based on several theories: incomplete removal of the cyst due to its thin friable membrane and adherence to adjacent tissues, residual satellite cysts following enucleation, and remnants of dental lamina not associated with the KCOT in question causing de novo cyst formation. The orthokeratinized odontogenic cyst is considered by some to be a unique cyst, and by others to be a variant of the KCOT. It is much less common than the KCOT and has a much lower recurrence rate (24). Unlike the KCOT, the orthokeratinized odontogenic cyst is lined by orthokeratinized stratified squamous epithelium. There is a prominent granular layer below a noncorrugated surface, and the basal layer is less prominent.