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

2 General Considerations

      CHAPTER MENU

      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.

Pathogenesis of Cysts

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 3 and 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 2.1 shows 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 ).

Box 2.1 Pathogenesis: The Phases of Cyst Formation

      Three elements are needed:

      The cyst develops in three phases:

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

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