Effectiveness of MR imaging in characterizing small hepatic lesions: Routine versus expert interpretation

OBJECTIVE. The aim of our study was to compare the effectiveness of MR imaging characterization of small (less than or equal to2 cm) hepatic lesions made in a routine clinical setting with the effectiveness of such characterization made under standardized conditions by radiologists who are expert interpreters of MR imaging. MATERIALS AND METHODS. Forty-eight patients with 69 small (less than or equal to2 cm) hepatic lesions considered indeterminate on a prior routine CT scan were included in the study. The diagnosis for all lesions had been verified by histology (n = 10), surgery and intraoperative sonography (n = 5), imaging follow-up (n = 35), or clinical follow-up (n = 19). Using the initial radiology reports, the diagnoses based on MR imaging were rated on a 5-point confidence scale. In addition, two radiologists experienced in MR imaging who were unaware of the initial interpretations of the images or the clinical histories of the patients independently analyzed the MR imaging studies and characterized the lesions using the same 5-point scale. The observer performance for the initial MR imaging interpretations and the expert interpretations were measured using receiver operating characteristic analysis. Interobserver agreement was determined with weighted kappa statistics. RESULTS. Fifty-eight lesions were benign (six cysts, 22 hemangiomas, four regenerating nodules, two steatohepatitic lesions, one atypical blood vessel, three focal fat and five focal fat-sparing lesions, 13 flow-related pseudolesions, one diaphragmatic insertion, and one unspecified lesion), and 11 lesions were malignant (nine metastases and two hepatocellular carcinoma). The areas under the curve were 0.94 (initial reports), 0.88 (observer 1), and 0.84 (observer 2). Substantial agreement was found between the expert interpreters (kappa = 0.74), and moderate agreement, between the expert interpreters and initial interpreters (kappa = 0.44 each). CONCLUSION. MR imaging is an effective method of characterizing small (less than or equal to2 cm) hepatic lesions in routine clinical practice.