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

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features often leads to diagnostic errors and incorrect management (Barrett et al. 2017 ). In each chapter of this book we present all the features of each cyst type in context and discuss the differential diagnoses and potential errors that might occur if only small biopsies are examined. Throughout we advise on the importance of correlating clinical, radiological, and histological features and suggest that a diagnosis of an intraosseous lesion should never be made without considering the radiology. We also recommend that a diagnosis should never be made on a small biopsy if there is any uncertainty – when in doubt, the pathologist should request a further biopsy. In this chapter, we briefly discuss an approach to making a correct diagnosis and summarise the key features that can assist in making a diagnosis of cysts of the maxillofacial regions (Tables 2.2–2.4). With regard to the odontogenic cysts, an accurate diagnosis is facilitated by an understanding of tooth development and the pathogenesis of each cyst type (see ‘Pathogenesis of Cysts’ and Table 2.1)

      In most cases, the clinical features of cysts are not specific, since the most common presenting feature is a swelling with few other symptoms. The surgeon therefore must rely on additional features to assist in making a provisional diagnosis. For example, a swelling associated with an absent tooth may suggest a dentigerous cyst, and a small, bluish‐coloured swelling on the lower lip of a child is almost certainly a mucocele. Ultimately, however, a final diagnosis is usually made on histological examination, but before this both the clinician and the pathologist should examine the radiographs or imaging.

      The characteristic radiological feature of all cysts of the jaws is a well‐demarcated radiolucency with a well‐defined and often corticated margin. Further features that assist in diagnosis include the shape and size of the lesion and the site, but in most cases it is the relationship to the teeth that provides the best indication of the type of cyst. A conventional plane radiograph is usually sufficient to determine the extent and relationships of jaw cysts, but computed tomography (CT) and magnetic resonance imaging (MRI) are often useful and may be essential for planning surgery of larger lesions. These relationships are discussed and illustrated in each chapter, but here we present an overview of characteristic radiological signs and the basic principles of an approach to interpreting the radiology. Table 2.2 shows the cyst types that have characteristic radiological features, provides a cross reference to the figures in each chapter, and summarises the diagnostic utility of each feature.

Cyst type Radiological sign Diagnostic utility Figure references
Radicular cyst A radiolucency at the apex of a tooth All radicular cysts are located at the opening of the root canal, almost always at the apex. This feature can be considered diagnostic of radicular cyst if the tooth is also non‐vital. The radicular cyst also lies within the lamina dura. If the tooth is vital then other lesions must be considered, but are rare. This may include cemental lesions (cementoblastoma, cemento‐osseus dysplasia) or, in the anterior maxilla, nasopalatine duct cyst
Paradental cyst A radiolucency superimposed over the distobuccal aspect of an impacted third molar. The distal follicular space and lamina dura are intact This feature is diagnostic of paradental cyst. If an intact follicular space cannot be seen, then the radiolucency may be due to a hyperplastic follicle or pericoronitis Figures 4.2 and 4.5
Dentigerous cyst Radiolucency surrounds the crown of an unerupted tooth All dentigerous cysts show this feature. However, it is not specific, since it may be seen in about 30% of keratocysts, up to 50% of orthokeratinised odontogenic cysts, and occasionally in calcifying odontogenic cysts Figures 5.5–5.12, 5.14 (dentigerous cyst), 7.7 (odontogenic keratocyst), 12.3 (orthokeratinised odontogenic cyst)
Odontogenic keratocyst Mesiodistal extension with minimal buccolingual expansion This appearance is almost pathognomonic for keratocysts in the mandible. Note however that glandular odontogenic cyst may also show this growth pattern (see below). Other cyst types and ameloblastomas show ballooning expansion. The feature is best visualised on computed tomography (CT) scans Figures 7.6 (odontogenic keratocyst), 10.4, 10.5 (glandular odontogenic cyst, ameloblastoma)
A well‐demarcated unilocular radiolucency in the ascending ramus not associated with a tooth Such a radiolucency is most likely to be an odontogenic keratocyst. If the cyst is associated with an unerupted tooth a dentigerous cyst cannot be excluded, and if it is multilocular an ameloblastoma must be considered. A keratocyst is even more likely if there is little buccolingual expansion (see above) Figure 7.11
Lateral periodontal cyst Well‐defined, round corticated radiolucency lateral to the tooth root. Periodontal space and lamina dura are intact This feature is characteristic of lateral periodontal cyst. Lesions are rarely greater than 10 mm in diameter. If the lamina dura surrounds the cyst, or cannot be seen, a lateral radicular cyst must be considered. If the radiolucency is larger than 10 mm or is multilocular, an alternative diagnosis must be considered: possibly botryoid odontogenic cyst, keratocyst, or glandular odontogenic cyst Figure 8.2
Glandular odontogenic cyst Large multilocular radiolucency crosses the midline of the mandible in a symmetrical pattern This is not diagnostic, but is typical of the glandular odontogenic cyst. In some reports up to 85% of cases are located in the anterior mandible. Keratocysts and ameloblastoma may be multilocular, but are more often located in the posterior mandible Figures 10.3 and 10.4
Calcifying odontogenic cyst A cystic radiolucency associated with irregular calcifications About 25% of calcifying odontogenic cysts are associated with an odontoma and show irregular radiopacities either in or adjacent to the cyst. Note that simple bone cyst is occasionally associated with calcifications, but these are usually multiple and represent florid cemento‐osseous dysplasia (Chapter 17) Figures 11.4 and 11.5
A cystic radiolucency with a peripheral band of calcifications About 50% of calcifying odontogenic cysts contain dentinoid in the wall or show dystrophic calcification in the lining. A peripheral band of calcification is characteristic

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