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

cyst is simply an inflammatory type of dentigerous cyst that arises as a result of inflammation of the pericoronal tissues surrounding the partially embedded crown of an impacted or erupting tooth. This would be a perfectly acceptable proposal, but for the fact that an inflamed and expanded pericoronal follicle would be indistinguishable from pericoronitis associated with inflammatory osteolysis. Yet paradental cysts show a very distinctive radiology with a buccally orientated radiolucency that is quite distinct from an expanded dental follicle (see ‘Radiological Differential Diagnosis’ and Figures 4.2 and 4.5). For these reasons, we believe that inflammatory collateral cysts and dentigerous cysts show distinctive diagnostic features and should be designated as separate entities (Box 4.2).

Histopathology

      Paradental cysts associated with third molars are removed by enucleation of the cyst along with extraction of the associated tooth. Occasionally, the whole specimen is received intact (Figure 4.6) and will show that the cyst is a sac‐like mass attached at the cementoenamel junction and located on the buccal aspect of the tooth roots. This is in contrast to a dentigerous cyst, which is also attached to the cementoenamel junction, but surrounds the crown of the tooth (see Figures 5.18 and 5.19). Careful examination with a probe will show that the lumen of the cyst is continuous with the periodontal or pericoronal pocket (Figure 4.6b). This appearance is virtually diagnostic of an inflammatory collateral cyst.

      Mandibular buccal bifurcation cysts are usually removed by enucleation or curettage and the tooth is left in situ. In this case the pathologist will often receive fragments of soft tissue that in places may resemble a cyst wall.

      Histological examination shows non‐specific features that are indistinguishable from radicular cyst and it will be impossible to make a diagnosis without consideration of the clinical findings and review of the radiology. The cysts are lined by a hyperplastic, non‐keratinised, stratified squamous epithelium, which may be spongiotic and of varying thickness. There is an intense chronic or mixed inflammatory cell infiltrate associated with the hyperplastic epithelium and in the adjacent fibrous capsule (Figure 4.7). As in radicular cysts, haemosiderin deposits, hyaline bodies, or accumulations of cholesterol crystals may be seen. An opening into the cyst lumen may also be seen and the epithelial lining may be continuous with sulcular or gingival epithelium at the periphery. Occasional cases may show focal accumulations of foreign body–type giant cells, consistent with impaction of food particles (Fowler and Brannon 1989 ; Colgan et al. 2002 ).

Treatment

      Inflammatory collateral cysts are simple cysts and there is no evidence to suggest that recurrence is a problem. Paradental cysts associated with third molars are usually enucleated along with the offending tooth. However, if the tooth is not impacted or angulated and appears to be erupting, it may be preserved and should continue to erupt into a normal occlusion.

      Mandibular buccal bifurcation cysts are often enucleated without removal of the associated tooth, which then erupts normally. Nevertheless, removal of the cyst may not be necessary, since there is good evidence that it may resolve after more conservative treatment. Marsupialisation of the cyst has been found to be effective and has resulted in compete regression, with normal eruption of the associated tooth and restoration of a normal gingival profile (Lizio et al. 2011 ). Cysts have also been shown to resolve after simple probing and irrigation, or even to heal spontaneously as the tooth erupts (David et al. 1998 ; Gomez et al. 2001 ; Zadik et al. 2011 ). That these cysts are self‐limiting and may resolve spontaneously is supported by the fact that they rarely reach a large size and they do not occur in adults.

Figure 4.7 Paradental cyst adjacent to the root of an impacted mandibular third molar. The cyst is lined by non‐keratinised stratified squamous epithelium of variable thickness and showing areas of proliferation and inflammation in the wall.

      Source: Courtesy of Prof G.T. Craig.