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

time to time, the frequency of neoplastic change is exceptionally rare in relation to the large numbers of cysts that are seen. There is no evidence, however, that cyst epithelium is at particular risk and there is therefore no justification for regarding cysts as pre‐cancerous lesions. The pathogenesis of malignant change is not known, but some have speculated that it is induced by the long‐standing chronic inflammation (Bodner et al. 2011 ; Jain et al. 2013 ). This would explain the higher frequency of malignant change in radicular cysts, and is in keeping with the now well‐established association between carcinogenesis and inflammation (Crusz and Balkwill 2015 ).

Treatment

      Radicular cysts may be removed by conservative surgery involving simple curettage of the lesion. Often this is carried out by an apicectomy procedure involving removal of the cyst and the root apex and sealing of the apical portion of the root canal. Occasionally the offending tooth may be removed, but if the cyst is not curetted, then a residual cyst may arise.

      Many periapical radiolucencies are treated non‐surgically by endodontic procedures that remove the necrotic pulp and disinfect and seal the root canal. In this way, about 95% or more of apical lesions heal or do not progress. In this case, however, the lesion is not removed for histological examination and, as discussed above, the majority will be periapical granulomas. In this respect, the lesion heals because the causative root canal infection has been removed and it is not necessary to make any distinction between periapical granulomas and cysts, nor between true cysts and pocket cysts (Ricucci et al. 2020 ).

      Useful analyses or reviews on the non‐surgical treatment of periapical lesions have been presented by Natkin et al. (1984 ), Nair (2003 , 2004 , 2006 ), Santos‐Junior et al. (2019 ), and Ricucci et al. (2020 ), and in systematic reviews by Sathorn et al. (2005 ), Torabinejad et al. (2005 ), and Glynis et al. (2021 ).

4 Inflammatory Collateral Cysts

      CHAPTER MENU

        Classification and Terminology of Inflammatory Collateral Cysts

        Clinical Features Frequency Age Sex Site Clinical Presentation

        Radiological Features Radiological Differential Diagnosis

        Pathogenesis Relationship of the Paradental Cyst to the Dentigerous Cyst

        Histopathology

        Treatment

      Inflammatory collateral cysts are cysts of inflammatory origin that are found towards the buccal aspect of the roots of partially or recently erupted teeth. They arise as a result of inflammation in the pericoronal tissues, but the pathogenesis and the epithelium of origin remain uncertain. Although it is possible for a collateral cyst to arise on any erupting tooth, the vast majority are associated with mandibular molars, with about 60% on third molars and most of the remainder seen on the buccal aspect of first or second molars. Thus, two main types of inflammatory collateral cyst are recognised: the paradental cyst, found predominantly on mandibular third molars, and the mandibular buccal bifurcation cyst, found on first or second molars (Speight and Soluk Tekkeşin 2022b ). In some respects the collateral cysts remain controversial, since it is clear that in some quarters their very existence is questioned. There are a number of papers reporting lesions associated with impacted third molars that do not include a single case of paradental cyst (Curran et al. 2002 ; Stathopoulos et al. 2011 ), while other series of pericoronal lesions on mandibular third molars have suggested that more than 50% may be paradental cysts (Costa et al. 2014 ). One reason for these discrepancies may be the very nature of the cyst itself. The lesion presents as a ballooning of the pericoronal tissues to form a pocket (Ackermann et al. 1987 ; Slater 2003 ) that some may not regard as a true cyst, while others regard it as a simple variant of a dentigerous cyst. Nevertheless, the clinical and radiological features are those of a cystic lesion and the inflammatory collateral cysts are widely accepted as an entity and are included in the World Health Organization (WHO) classification of jaw cysts (WHO 2022a ; Speight and Soluk Tekkeşin 2022b ).

Classification and Terminology of Inflammatory Collateral Cysts

In 1970 Main proposed a classification of jaw cysts based on a review and analysis of 274 odontogenic cysts. He found eight cysts (2.9%) that arose ‘alongside a vital tooth involved in pericoronitis’, which he called an inflammatory collateral cyst, in recognition of their association with chronic inflammation and a location on the lateral aspect of a tooth. This term also distinguishes it from a radicular cyst associated with a lateral accessory root canal of a non‐vital tooth, and from a developmental lateral periodontal cyst. Seven of his eight cases arose on mandibular third molars, and one on an impacted upper canine (Main 1970 ). Main's 1970 paper is often cited as the first report of this cyst, but Philipsen et al. (2004 ) found that Hofrath in 1930 had reported several jaw cysts on mandibular third molars affected by pericoronitis. Hofrath called these cysts ‘marginal wisdom tooth cyst’, but all the features were consistent with the inflammatory collateral cyst described by Main (1970 ) and the paradental cyst as currently defined.

      The first detailed account of inflammatory collateral cysts was by Craig (1976 ), who described a cyst of inflammatory origin that occurred on the lateral aspect of the roots of partially erupted mandibular third molars where there was an associated history of pericoronitis. He recognised that these cysts were the same clinicopathological entity as the inflammatory collateral cyst described by Main (1970 ), but he was the first to suggest the term paradental cyst. He felt this was more appropriate for this lesion because it emphasised the odontogenic associations of the cyst and its location adjacent to a tooth.

      Craig's series consisted of 49 cysts in 48 patients, which represented about 5% of odontogenic cysts seen in his department over a 21‐year period. In all cases the involved tooth was partially erupted and was associated with a history of pericoronitis. In terms of location, 26 cysts were on the buccal aspect of the roots, 19 were distal, and 4 were mesial, but Craig was of the opinion that there was some buccal involvement even in those cysts designated clinically as of mesial or distal location. Macroscopically, the cysts were firmly attached to the bifurcation area on the buccal aspects of the roots, and extended up to the cementoenamel junction. Craig's description of the paradental cyst associated with third molar teeth has become the defining feature of this lesion.

      Craig's paper on the paradental cyst was, for a number of years, the only detailed account of the entity. Subsequently, however, Ackermann et al. (1987 ) described 50 cases, all of which arose on impacted third molars and had similar features to those described by Craig. This was soon followed by a report of 6 cases by Fowler and Brannon (1989 ) and 15 cases by Vedtofte and Praetorius (1989 ), and then by numerous case reports and a number of case series or reviews (de Sousa et al. 2001 ; Colgan et al. 2002 ; Philipsen et al. 2004 ; Mohammed et al. 2019 ).

      In 1983, Stoneman and Worth described 17 cases of a lesion that