Epithelial plaques are seen in all cases of lateral periodontal cyst and are diagnostic if the cyst is unilocular and no other features are noted If the cyst is multilocular, then diagnostic for botryoid odontogenic cyst Gingival cyst shows similar features but is extraosseous Glandular odontogenic cyst may show plaques in about 65% of cases, but must be accompanied by other features (see Table 10.3)
Cuboidal or columnar cells at the luminal aspect of the cyst lining
Glandular odontogenic cyst
Typical feature and seen in up to 100% of glandular odontogenic cysts. Diagnostic when accompanied by other features (see Table 10.3). Similar cells are occasionally seen in other cyst types, including dentigerous cyst, but these lack other features
Figures 10.7 and 10.8
A simple cyst with ghost cells in the wall
Calcifying odontogenic cyst
This feature is diagnostic of calcifying odontogenic cyst. Note that the lining is ameloblastomatous and if ghost cells are not seen, a diagnosis of cystic ameloblastoma must be considered. Ensure the whole lining is examined (see discussion in Chapter 11). If the lesion is solid, then consider dentinogenic ghost cell tumour. Ghost cells may be seen in odontomas and rarely in ameloblastomas
Figures 11.8–11.10
Hyaline bodies
Various odontogenic cyst types
Hyaline (Rushton) bodies are often stated as being typical of radicular cyst. They are seen in about 10% of radicular cysts, but also in up to 10% of odontogenic keratocysts and dentigerous cysts (see discussion in Chapter 3). However, hyaline bodies are specific and diagnostic of odontogenic cysts
Cholesterol clefts result from an accumulation of cholesterol crystals as a results of long‐standing inflammations. They are therefore typical of radicular cyst and are seen in 30% or more of cases (Table 3.3) But they are not specific and may be seen in any cyst that has become chronically inflamed, in particular in inflamed dentigerous cysts or keratocysts
Mucous cells have been described in most types of odontogenic cyst and are not diagnostic. They are a result of metaplastic change and are seen in about 20% of radicular cysts, 25% of dentigerous cysts, and 2% of odontogenic keratocysts Note that mucous cells are not a diagnostic requirement for glandular odontogenic cyst and are seen in only about 70% of cases (Table 10.3). Mucous cells are seen in surgical ciliated cysts and in about 50% of nasopalatine duct cysts and nasolabial cysts
Sebaceous glands are rare in jaw cysts and when seen a diagnosis of dermoid cyst should be considered. If sweat glands and hair follicles are also present, then this is diagnostic for dermoid cyst. Sebaceous glands have rarely been reported in odontogenic keratocyst and orthokeratinised odontogenic cyst
Figures 18.2 and 18.3 (dermoid cyst)
Respiratory epithelium
Nasopalatine duct cyst Various cyst types
Among cysts in the jaws, respiratory epithelium is a typical feature of nasopalatine duct cyst and is seen in about 50% of cases However, this is not specific. Surgical ciliated cyst is lined by respiratory epithelium and metaplastic respiratory epithelium has been described in radicular cysts Among soft tissue cysts, nasolabial cyst, bronchogenic cyst, and thyroglossal duct cyst are lined by respiratory epithelium, and respiratory epithelium may be seen in cysts of foregut or branchial cleft origin (Boxes 18.2–18.4)
Despite these limitations, there are a few instances where immunohistochemistry can help establish a diagnosis and differentiate between lesions with similar histological features. A number of diagnostically useful applications are summarised in Table 2.4.
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 2.4 summarises 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.
Immunohistochemistry
Antibody
Target
Diagnostic utility
CK10
Type I keratin, found mainly in cornified epithelia
CK10 stains keratinising epithelium and is positive in the superficial layers of odontogenic keratocyst and orthokeratinised odontogenic cyst. Of little value in histological sections, but has some utility in cytological smears from aspiration biopsies. Cells from keratocyst and orthokeratinised odontogenic cyst are positive, but dentigerous cysts and ameloblastomas are negative (August et al. 2000 ). Pan‐cytokeratin antibodies (AE1/AE3) may also stain keratin in smears from inflamed cysts (Vargas et al. 2007 ) (Figure 7.22)
CK18 and CK19
Keratin intermediate filaments. Both are widely expressed, but CK19 is seen typically in odontogenic epithelium
Use of both antibodies together has been shown to be useful to distinguish a glandular odontogenic cyst from central mucoepidermoid carcinoma (Pires et al. 2004 ; discussed in Chapter 10). Glandular odontogenic cyst is CK19+/CK18‐. Mucoepidermoid carcinoma is CK19‐/CK18+
