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Periapical cysts, also known as radicular cysts, are the most frequent cystic lesion related to teeth (see mandibular lesions) and result from infection of the tooth. On imaging, they generally appear as a round- or pear-shaped, unilocular, lucent lesion in the periapical region, usually measuring <1 cm.
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Periapical cysts are typically seen in middle to older age (3rd to 6th decades) 2.
Periapical cysts result from infection of the tooth, which spreads to the apex and into the adjacent bone. This leads to apical periodontitis, granuloma formation and eventual cyst formation. These cysts are therefore centered on the apex of the tooth and tend to be small, most <1 cm. There is also unsurprisingly usually overt evidence of caries.
Plain radiograph and CT
Most radicular cysts appear as round- or pear-shaped, unilocular, lucent lesions in the periapical region 3. They are usually <1 cm in diameter and are bordered by a thin rim of cortical bone. The associated tooth usually has a deep restoration or large carious lesion. Caries will appear as erosion of the enamel/crown of the associated tooth.
MRI is not the first-line imaging modality but periapical cysts appear as a non-enhancing lesion at the apex of a tooth. These cysts typically return low T1 signal and high T2 signal.
periapical abscess: inflammation involves tooth root apex
dentigerous cyst: lesion around the crown of an unerupted/impacted tooth
lateral radicular cyst: considered a variant of a true peri-apical cyst
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