Gingival Cyst

Gingival cysts are divided in those occurring in adults and those in infants. They are located in the gingival tissues. Gingival cysts of adults are rarely larger than 1 cm and may be multiple. They are lined by either thin epithelium of one to three cell layers or thicker and exhibit keratinisation. Plaques similar to those occurring in the lateral periodontal cyst (see Sect. 4.3.2.2) may be seen [107].

Gingival cysts of infants occur either singularly or multiply on the edentulous alveolar ridge of the newborn infant. When occurring at the midline of the palate, they are known as palatal cysts of infants. These tiny lesions, usually not larger than 3 mm, disappear spontaneously within a short time. Histologically, they resemble epidermoid cysts [24, 94]. Historically, Epstein's pearls and Bohn's nodules are terms that have been used for these lesions.

4.3.3 Non-Odontogenic Cysts

4.3.3.1 Nasopalatine Duct Cyst

Nasopalatine duct cysts arise within the nasopalatine canal from epithelial remnants of the nasopalatine duct. Radiologically, they present as radiolucent lesions situated between the roots of both maxillary central incisor teeth. The cyst lining may be pseudostratified columnar ciliated epithelium, stratified squamous epithelium, columnar or cuboidal epithelium and combinations of these. As surgical treatment comprises emptying the nasopalatine canal, the specimen always includes the artery and nerve that run in this anatomic structure. These are seen within the fibrous cyst wall and form the most convincing diagnostic feature, as the specific epithelial structures may be obscured by inflammatory changes. Recurrences are rarely seen, and are probably due to incomplete removal [168].

4.3.3.2 Nasolabial Cyst

Nasolabial cysts are located in the soft tissue just lateral to the nose at the buccal aspect of the maxillary alveolar process and are thought to arise from the nasolacrimal duct. Non-ciliated pseudostratified columnar epithelium interspersed with mucous cells form the epithelial lining. These features may be lost through squamous metaplasia [180]. Apocrine metaplasia of the cyst lining has also been reported [83]. Treatment consists of enucleation.

4.3.3.3 Surgical Ciliated Cyst

Surgical ciliated cysts arise from detached portions of the mucosa that line the maxillary antrum and are buried within the maxillary bone. This may occur after trauma or surgical intervention in this area [93]. Mostly, the cyst is an incidental radiographic finding, observed as a well-defined unilocular radiolucency adjacent to the maxillary antrum.

The cyst lining is similar to the normal mucosal surface of the paranasal cavities: pseudostratified ciliated columnar epithelium with interspersed mucous cells. Treatment consists of simple enucleation.

4.3.4 Pseudocysts

4.3.4.1 Solitary Bone Cyst

The solitary bone cyst, also known as traumatic bone cyst or simple bone cyst is confined to the mandibular body. Its pathogenesis is ill-understood; a remnant of intraos-seous haemorrhage is the most favoured hypothesis. Radiographs show a cavity that varies from less than 1 cm in diameter to one that occupies the entire mandibular body and ramus. At surgical exploration, one encounters a fluid-filled cavity. Material for histologic examination may be difficult to obtain as a soft tissue lining of the bony cavity may be entirely absent or very thin. If present, it usually consists only of loose fibrovascular tissue, although it may also contain granulation tissue with signs of previous haemorrhage such as cholesterol clefts and macrophages loaded with iron pigment [136]. Sometimes, this cyst develops simultaneously with a variety of fibro-osseous cemental lesions [62].

4.3.4.2 Focal Bone Marrow Defect

The focal bone marrow defect represents an asymptomatic radiolucent lesion of the jaws that contains normal hematopoietic and fatty bone marrow. It is also called osteoporotic bone marrow defect. This condition is mostly seen at the angle of the mandible where it reveals its presence as a radiolucency with more or less well-defined borders. Due to the lack of radiographic specificity, the lesion is usually biopsied. Then, histo-logic examination will reveal the presence of normal hematopoietic marrow [141]. Of course, further treatment is superfluous.

4.4 Odontogenic Tumours

Odontogenic tumours comprise a group of lesions that have in common that they arise from the odontogenic tissue. They develop from the epithelial part of the tooth germ, the ectomesenchymal part or from both. Their behaviour varies from frankly neoplastic, including metastatic potential, to non-neoplastic hamartomatous. Some of them may recapitulate normal tooth development including the formation of dental hard tissues such as enamel, dentin and cementum [129]. Table 4.2 gives

Table 4.2. Odontogenic tumours [73, 181]

Epithelial

Mesenchymal

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