The radiolucent periapical jaw lesions of 34 patients, which were surgically enucleated, were investigated by two radiologists using MRI, based on the same six criteria, to categorize the lesions as granulomas or radicular cysts. After apicoectomies, two oral pathologists (blinded to the radiologist's diagnoses) analyzed all specimens by referring to seven specific parameters and diagnosed the specimens as granulomas or radicular cysts. The inter-rater agreements between the radiologists and pathologists in terms of MRI and histological diagnoses, respectively, along with the discriminant power of the adopted criteria and the accuracy of the MRI assessments compared with the histopathologic results, were calculated.

A strong inter-rater reliability was observed between the two radiologists (k-statistic = 0.86, p = 0.0001) and the two pathologists (k-statistic = 0.88, p = 0.0001). Reliability was higher for the radiological (Guttmann's lambda lower bound > 0.6) than histopathological criteria. The accuracy (true positives plus true negatives) of the radiologists was higher than that of the pathologists based on receiver operator characteristic analysis (area under the curve = 0.87 and 0.91, respectively). MRI reliability and accuracy were high and comparable to histopathological reliability, highlighting the usefulness of this non-invasive exam as a pre-treatment diagnostic method for periapical endodontic lesions.

Inclusion Criteria:

• patient age ≥ 18 years
• the diameter of the lesion ≥ 5 mm, assessed based on periapical x-ray,
• an acceptable endodontic treatment for the involved tooth.

Exclusion Criteria:

• general medical contraindications for classification of the patient as level III or higher according to the American Society of Anesthesiologists,
• teeth involved in the lesion, the function of which could not be salvaged after enucleation of the lesion and apicoectomy. The radiological exclusion criteria were
• contraindication undergoing magnetic resonance: presence of a pacemaker or any metallic devices that could interfere with the magnetic field;
• severe claustrophobia,
• weight ≥ 130 kg
• intolerance to gadolinium-DTPA as a contrast agent;

34 patients (17 males and 17 females; mean age 41.9 (range 21-76) years) with periapical endodontic lesions diagnosed by clinical and radiological examination using 2D standard x-rays (periapical and panoramic x-rays) or multislice CT/CBCT in the Oral and Maxillofacial Unit of the University of Bologna between January 2011 and December 2015, and treated with enucleation of the lesion and apicoectomy after a pre-operative MRI exam were retrospectively enrolled in this study. The chart of these patients, that underwent a traditional and standard therapeutic protocol, the radiological imaging and the histopathological data, were analysed after the treatment by a team of two radiologists and two pathologists.