Periapical cyst On imaging, they generally appear as a round- or pear-shaped, unilocular, lucent lesion in the periapical region, measuring <1 cm. Epidemiology Periapical cysts are typically seen in middle to older age (3rd to 6th decades) 2. Pathology 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 centred on the apex of the tooth and tend to be small, most <1 cm. There is also unsurprisingly usually overt evidence of caries. Radiographic features 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 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. Differential diagnosis periapical abscess inflammation involves tooth root apex periapical granuloma dentigerous cyst lesion around the crown of an unerupted/impacted tooth keratocystic odontogenic tumor Lucent lesions of the jaw floating teeth odontogenic tumors (classification) Pathology odontogenic dentigerous cyst keratocystic odontic tumor (odontogenic keratocyst) ameloblastoma ameloblastic fibroma ameloblastic fibro-odontoma primordial cyst of the jaw periapical cyst residual cyst of the jaw traumatic bone cyst of jaw Stafne cyst cystic odontoma non-odontogenic fibrous dysplasia (cherubism) mandibular metastases squamous cell carcinoma invading mandible multiple myeloma periapical abscess giant cell granuloma aneurysmal bone cyst peripheal nerve sheath tumor of mandible Imaging differential diagnosis Nasopalatine duct cyst Periapical abscess
