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.

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.

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.

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.