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

N, total number of odontogenic cysts – frequencies are proportions of odontogenic cysts only; NI, not included – proportions only given for the three main cyst types; NR, not reported.

aData for radicular cyst includes residual cysts.

bData for dentigerous cyst includes eruption cysts.

Among other cyst types, Jones and Franklin (2006a ) found that the most common were mucoceles (3.9%; n = 1720), while all other cysts were rare (less than 1.0%).

These data show that cysts are relatively common and that the most commonly encountered are the radicular cyst, dentigerous cyst, and mucoceles. They also suggest that when a periapical radiolucency is seen, about 50% will be a radicular cyst and 50% will be a periapical granuloma. Details of the frequency and incidence of each cyst type are illustrated and discussed in the following chapters.

Pathogenesis of Cysts

The Cyst–Tumour Interface

An Approach to the Diagnosis of Cysts of the Jaws Radiology of Cysts of the Jaws Histopathological Examination of Cysts Immunohistochemistry and Molecular Pathology

Cysts of the oral and maxillofacial regions are common and represent about 20% of all lesions encountered in an oral and maxillofacial pathology department (Jones and Franklin 2006a ,b ; discussed in Chapter 1). Clinicians are often therefore called upon to make an informed diagnosis and implement correct management. Of all the cysts discussed, those within the jaw bones are the most challenging to diagnose. Overall the most common jaw cyst is the radicular cyst, which presents as a periapical radiolucency and is probably the most common cause of a bony swelling in the tooth‐bearing areas of the jaws. The challenge is to accurately make a diagnosis and exclude other possible causes of a swelling or of a radiolucency. In most cases, a final diagnosis usually requires histological examination of the cyst, and it is the histopathologist who often takes responsibility for bringing together the clinical, radiological, and histological features and reporting the final diagnosis to the surgeon. Each cyst type has characteristic features and these are discussed and illustrated in each chapter of this book. In this chapter we consider general issues that help inform a careful and accurate approach to the diagnosis of cysts, and we summarise specific radiological and histological features that have diagnostic utility in the diagnosis of different cyst types.

The formation of a cyst requires three elements and can be considered to develop in three phases: a phase of initiation, a phase of cyst formation and a phase of growth and enlargement ( Box 2.1). For the inflammatory odontogenic cysts, the processes of cyst formation and expansion are well understood and are considered in detail in Chapters 3and 4, but for the developmental cysts the mechanisms are not so clear and many theories have been suggested, including aberrant developmental processes, underlying genetic abnormalities, and neoplasia. These are discussed in detail for each cyst type in the following chapters. For most cysts, the lining is derived from epithelial remnants or inclusions that remain in the tissues after developmental processes are complete. Table 2.1shows the source of epithelium for each cyst type and summarises the developmental origin. To fully understand the pathogenesis of cysts, it is therefore essential to have an understanding of the embryology and development of the head and neck. With regard to the odontogenic cysts (and odontogenic tumours), a thorough knowledge of tooth development is also needed to understand the pathogenesis, since the complex interactions between epithelium and mesenchyme that underpin normal morphogenesis and tooth eruption provide good models for the processes that drive cyst formation and growth. In addition, the histology of many lesions may recapitulate the features of the developing tooth and knowledge of these features facilitates the ability to reach an accurate diagnosis. A detailed consideration of embryology and development is beyond the scope of this book, but factors relevant to each cyst type are summarised in each chapter. For up‐to‐date and expert knowledge relating to development, readers should consult expert texts or reviews (Wise et al. 2002 ; Nel et al. 2015 ; Nanci 2017 ; Seppala et al. 2017 ; Diniz et al. 2017 ; Hovorakova et al. 2018 ; Bastos et al. 2021 ).

Three elements are needed:

A source of epithelium

A stimulus for epithelial proliferation

A mechanism of growth and bone resorption

The cyst develops in three phases:

Phase of initiation – a source of epithelium and stimulus for proliferation

Phase of cyst formation – a cyst cavity develops and becomes lined by epithelium

Phase of growth and enlargement – the cyst enlarges, and growth is accompanied by tissue remodelling and bone resorption

Table 2.1 Sources of the epithelial lining of cysts of the head and neck.

In the majority of odontogenic cysts, the epithelial lining is derived from epithelial remnants of the dental lamina ( Table 2.1). Early in the development of the jaws, the surface epithelium thickens and grows downwards into the mesenchyme of the future dental arches to form the dental lamina. This extends around the arch as a band that maps the future sites of tooth bud formation for both primary and secondary dentitions. The teeth develop as a result of complex epithelial–mesenchymal interactions that result in epithelial thickenings or placodes, which then form the enamel organs that pass through the well‐described bud, cap, and bell stages during formation of the fully developed tooth (Nanci 2017 ). The dental lamina remains as a thin band that joins the surface oral epithelium to the enamel organ and only disintegrates at the late bell stage of tooth development. Disintegration of the dental lamina results in the formation of small epithelial islands that lie over unerupted teeth, but also remain in the tissues adjacent to the teeth after eruption. The disintegrating vdental lamina is illustrated in Figure 9.9. The epithelial cell rests of the dental lamina give rise to most of the odontogenic cysts ( Table 2.1) as well as to most odontogenic tumours. Dental lamina rests are particularly numerous at the posterior aspect of the dental arches and in the tissues overlying unerupted teeth and in the dental follicle. This accounts for the fact that the angle of the mandible is a common site for many cyst types, and that many cysts (and tumours) may arise in the dental follicle and embrace or surround an unerupted tooth and lie in a dentigerous relationship. This especially affects the mandibular third molars, since these are the most commonly impacted teeth (Brown et al. 1982 ).