Paul M. Speight - Shear's Cysts of the Oral and Maxillofacial Regions

Molecular studies have provided much useful and interesting information relating to the pathogenesis of odontogenic lesions, especially with regard to the role of the PTCH gene in the odontogenic keratocyst and to the role of the SHH (hedgehog), WNT, and MAPK signalling pathways in a variety of cysts and tumours (Diniz et al. 2017 ; Bilodeau and Seethala 2019 ). Molecular tests, however, have not yet proven to be useful in routine diagnosis of cysts. The main exception to this is the identification of MAML2 rearrangements that can be helpful in differentiating between the glandular odontogenic cyst and intraosseous mucoepidermoid carcinoma (discussed in Chapter 10). Table 2.4summarises a number of molecular techniques that may show some value as diagnostic markers.

Table 2.4 Immunohistochemical and molecular markers that might have diagnostic utility in the differential diagnosis of cysts.

Clinical Features Frequency Age Sex Site Clinical PresentationRadicular Cyst Residual Cyst

Radiological Features

Pathogenesis Pathology of Periapical Periodontitis Phase of Initiation Phase of Cyst Formation Growth and Enlargement of the Radicular CystRole of Hydrostatic Pressure Epithelial Proliferation Degradation of the Connective Tissues and Bone Resorption

Histopathology Cellular and Metaplastic Changes Hyaline Bodies Accumulation of Cholesterol Residual Cyst Pocket Cyst (Bay Cyst)

Malignant Change in Radicular Cysts

Treatment

The inflammatory odontogenic cysts arise as a result of epithelial proliferation within an inflammatory focus due to a number of causes. Radicular cyst is the most common inflammatory cyst and arises due to proliferation of epithelial remnants in the periodontal ligament as a result of periapical periodontitis following death and necrosis of the pulp. Radicular cysts are most commonly found at the apex of the involved tooth, but may arise on the lateral aspect of the root in relation to a lateral root canal. Quite often a radicular cyst remains behind in the jaws after removal of the offending tooth and this is referred to as a residual cyst (Speight and Soluk‐Tekkeşin 2022a ).

Inflammatory cysts may also occur on the lateral aspect of a tooth as a consequence of an inflammatory process in pericoronal tissues. This lesion has been referred to as a paradental or inflammatory collateral cyst (Main 1970 ; Craig 1976 ; Speight and Soluk‐Tekkeşin 2022b ). Radicular and residual cysts are considered in this chapter. The inflammatory collateral cysts are considered in Chapter 4.

Radicular and residual cysts are by far the most common cystic lesions of the jaw bones, probably accounting for more than half of all cystic lesions and about 60% of odontogenic cysts. In an analysis of nearly 10 000 radiolucent jaw lesions, Koivisto et al. (2012 ) found that 73% were periapical granulomas or cysts. Of these, 40.4% were granulomas and 33.0% were cysts.